Traffic & Transport
Anna van Buerenplein 1
2595 DA Den Haag
P.O. Box 96800
2509 JE The Hague
The Netherlands

TNO report
TNO 2020 R11883 | Final report

www.tno.nl

On road emissions of 38 petrol vehicles with
high mileages

T +31 88 866 00 00

Date

17 December 2020

Author(s)

Gerrit Kadijk
Mitch Elstgeest
Quinn Vroom
Mieke Paalvast
Norbert Ligterink
Peter van der Mark

Copy no
Number of pages
Number of
appendices
Sponsor

2020-STL-REP-100336164
88 (incl. appendices)
8

Project name
Project number

Dutch Ministry of Infrastructure and Water Management
PO Box 20901
2500 EX THE HAGUE
The Netherlands
In Use Compliance petrol vehicles with high mileages
060.37991

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© 2020 TNO

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Samenvatting
Grotere steekproef na eerder uitgevoerd onderzoek
Dit onderzoek is een vervolg op het door TNO in 2018 gerapporteerde onderzoek
waarin twaalf oudere benzinevoertuigen op een rollenbank zijn getest op hun
NOx emissie. Twee van de twaalf geteste voertuigen werden toen aangemerkt als
‘high- emitter’ (zij lieten een zeer hoog NOx emissieniveau zien) en enkele andere
voertuigen vertoonden ‘enigszins verhoogde’ NOx emissies. Op basis van deze
steekproef was echter onduidelijk in hoeverre verhoogde NOx emissies voor zouden
komen in de gehele Nederlandse vloot van oudere benzinevoertuigen met
driewegkatalysator. In opdracht van het Ministerie van Infrastructuur en Waterstaat
heeft TNO nu ter aanvulling uitlaatemissies gemeten van 38 oudere
benzinevoertuigen.
Primaire onderzoeksvraag was of benzinevoertuigen bij een toenemende leeftijd en
kilometerstand nog dezelfde emissieniveaus laten zien als bij hun typegoedkeuring,
of dat deze door verouderingseffecten oplopen. Om deze vraag te kunnen
beantwoorden zijn emissiemetingen uitgevoerd op de openbare weg waarbij ieder
van de te testen voertuigen was uitgerust met een mobiel emissiemeetsysteem.
De metingen zijn verricht aan voertuigen met een driewegkatalysator en bouwjaren
van 1998 tot 2017. Het betrof acht Euro 2, negen Euro 3, zestien Euro 4,
vier Euro 5 personenauto’s en één Euro 6 personenauto. De voertuigen hadden
een gemiddelde kilometerstand van ruim 220.000 km en een gemiddelde leeftijd
van ca. 16 jaar.
Naast beantwoording van de primaire onderzoeksvraag is gevraagd ook suggesties
te gegeven voor meettechnieken die kansrijk zijn voor een periodieke test op
NOx -emissies bij benzinevoertuigen.
Om een typegoedkeuring te verkrijgen moesten deze voertuigen voldoen aan
gestelde emissielimieten tijdens een ‘NEDC rollenbanktest’ in het laboratorium.
Echter, bij een kilometerstand hoger dan 100.000 km hoeven deze voertuigen niet
meer te voldoen aan een duurzaamheidseis die gecontroleerd wordt in ‘In-Service
Conformity’. Voor uitlaatgasnabehandelingssystemen geldt verder een effectieve
duurzaamheideis voor een kilometerstand tot aan 160.000 km.
Resultaten en conclusies
In dit vervolgonderzoek, met 38 voertuigen, is een lager aandeel auto’s met een
sterk verhoogde NOx-uitstoot gevonden dan bij het eerste onderzoek met twaalf
auto’s. Anderzijds was het aandeel voertuigen met verhoogde emissies (met
emissies tot een factor 2 tot 4 boven de oorspronkelijke waarde), wel groter dan
eerder gedacht. Aangezien het rollenbank testprogramma dat door TNO in 2018 is
uitgevoerd soortgelijk onderzoek betrof, zijn resultaten van beide programma’s
samengevoegd. De resultaten van de in totaal 50 geteste voertuigen leiden tot de
volgende conclusies:
Gemiddelde NOx emissies van oudere benzinevoertuigen zijn hoog:
Van de in totaal vijftig geteste voertuigen is de gemiddelde NOx emissie
200 mg/km. De limietwaarden verschillen per euroklasse en liggen tussen de 60
en 150 mg/km.

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De gewogen limietwaarde over de euroklassen van de geteste voertuigen is
115 mg/km. De gemiddelde conformiteitsfactor (CF) is daarmee 1,74. Dit betekent
dat de gemeten gemiddelde NOx emissie 74% hoger is dan de gewogen
limietwaarden van de typegoedkeuringstest op de rollenbank. Ter vergelijking:
emissies van 200 mg/km zijn hoger dan die van een gemiddelde moderne
dieselauto (Euro 6D Temp).
Oudere benzinevoertuigen stoten gemiddeld meer NOx uit dan vergelijkbare
jongere benzinevoertuigen:
De gemiddelde NOx emissie van de geteste oudere benzinevoertuigen van
200 mg/km is gemiddeld ca. twee keer hoger dan die van benzinevoertuigen die
eerder zijn getest toen deze nog nieuw waren en nog maar lage kilometerstanden
hadden. Deze voertuigen (die door TNO tot 2008 jaarlijks werden getest, en na die
tijd met tussenpozen) lieten toen maar beperkte afwijkingen zien tussen de
resultaten van typekeuringstesten en die van praktijkemissies.
Defecte voertuigen hebben grote impact op de gemiddelde NOx emissie:
Veertig voertuigen hadden een normale (CF < 1) of iets verhoogde NOx emissie
(CF < 2) en zeven voertuigen een verhoogde NOx emissie (CF = 2 – 4).
Drie voertuigen hadden een sterk verhoogde NOx emissie. Twee van deze drie
voertuigen waren afkomstig van het onderzoek uit 2018 en slechts één voertuig
uit het nu afgeronde grotere vervolgonderzoek. Gezamenlijk hadden deze drie
voertuigen een gemiddelde NOx emissie van 1197 mg/km. De bijdrage van deze
drie voertuigen (6% van het aantal geteste voertuigen) op de totale NOx emissie
van de vijftig geteste voertuigen is 36%.
Geen aanwijsbaar verband tussen hoge NOx emissies en voertuigparameters:
Uit de meetdata van de individuele voertuigen blijkt dat de gemeten NOx emissies
van de geteste voertuigen niet afhankelijk zijn van kilometrage (vanaf 160.000 km),
voertuigleeftijd, Euroklasse, voertuigmerk of voertuigmodel. Omdat bij een groot
aandeel van de geteste voertuigen ook de onderhoudshistorie niet of slechts deels
aanwezig was, kon ook geen verband worden gelegd tussen onderhoudshistorie en
verhoogde emissies.
Huidige duurzaamheidseisen voor emissies dekken de gemiddelde levensduur
van een voertuig niet af:
In Figuur 1-1 zijn (met driehoekjes) de gemiddelde gemeten NOx emissies per
Euroklasse weergegeven in relatie tot de gemiddelde kilometerstand van de geteste
voertuigen uit die klasse. Tevens zijn (met rondjes) de NOx limietwaarden
weergegeven, de oorspronkelijke waarden bij 0 gereden km’s en de waarden met
toegestane verouderingseffecten bij 80.000, 100.000 of 160.000 gereden km’s
(deze laatste afhankelijk van de betreffende Euroklasse).
De gemiddelde kilometerstanden van de geteste voertuigen uit de verschillende
Euroklassen was 1,2 tot 3,5 keer hoger dan de kilometerstanden gespecificeerd
voor de geldende duurzaamheidseisen. In de Nederlandse vloot van
benzinevoertuigen vormen de geteste voertuigen qua kilometerstand geen
uitzondering.
Vanuit de typekeuring is er dus geen referentiekader voor de beoordeling van de
emissieprestaties van voertuigen met kilometerstanden hoger dan die van de
duurzaamheidseisen.

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Voor personen- en bestelwagens gelden deze slechts tot kilometerstanden van
80.000 tot 160.000 km (afhankelijk van de Euroklasse van het voertuig). Er zijn wel
eisen vanuit het kader van periodieke controle maar die zien niet specifiek toe op
sterk verhoogde NOx-emissies. Verderop in de samenvatting wordt verdere
aandacht besteed aan de eisen vanuit de periodieke controle (APK).
Een sportieve rijstijl resulteert in substantieel hogere emissies:
Vier voertuigen zijn getest met een normale en sportieve rijstijl. Een sportieve
rijstijl resulteerde voor deze vier voertuigen in een toename van de emissies.
Deze toename bedroeg gemiddeld voor CO2: +13%, voor NOx: +96% en voor
NH3 +39%. Hieruit blijkt dat een sportieve rijstijl tot (substantiële) toenames van
de gemeten CO2, NOx en NH3 emissies leidt ten opzichte van die bij een normale
rijstijl.

Figuur 1-1: NOx limietwaarden per Euroklasse (rondjes), zonder en met toegestane veroudering in
relatie tot de kilometerstand. Ook is aangegeven, per Euroklasse, de gemiddelde
gemeten NOx emissie (driehoekjes) in relatie tot de gemiddelde kilometerstand van de
geteste voertuigen uit die klasse. De NOx limietwaarde van Euro 2 voertuigen is
geschat omdat wettelijk de HC+NOx limietwaarde is vastgelegd.

Repareren loont:
Reparatie van voertuigen met zeer hoge NOx emissies bleek een sterk positief
effect te hebben. Bij drie van de vier gerepareerde voertuigen resulteerde reparatie
in een gemiddelde daling van de NOx emissie met 37, 92 en 93%. Bij één voertuig
lag de nadruk op reparatie van het EGR (Exhaust Gas Recirculation) systeem en bij
twee voertuigen is de driewegkatalysator vervangen. De gemiddelde NOx emissie
van de vijftig geteste voertuigen daalde na de reparaties van 200 naar ongeveer
130 mg/km. De bijbehorende gemiddelde conformiteitsfactor (CF) is dan 1,15.
De tijdens het onderzoek uitgevoerde reparatie van een vierde voertuig bleek niet
effectief. Vermoedelijk had, naast de uitgevoerde reparaties aan lambda sensoren,
ook de driewegkatalysator een verminderd omzettingsrendement. Deze kon binnen
het project helaas niet meer worden vervangen.

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Uitlezen OBD systemen niet bruikbaar als indicatie voor verhoogde NOx emissies:
Er zijn Europese eisen ten aanzien van de periodiek controle (APK) van de
voertuigemissies. Voor benzineauto’s vanaf 1993 moet hiervoor de zogeheten
viergastest worden uitgevoerd. Voor auto’s vanaf 2006 wordt in plaats van de
viergastest bij de APK het EOBD-systeem (European On-Board Diagnostics
systeem, kortweg OBD) uitgelezen. Indien uitlezen van de EOBD niet goed kan
worden doorlopen of als emissie-gerelateerde foutcodes worden gevonden, dan
wordt alsnog de viergastest uitgevoerd.
Uit het onderzoek blijkt dat On Board Diagnose (OBD) systemen niet in staat zijn
om aan te geven dat een voertuig verhoogde NOx emissies vertoont. Twee van de
drie geteste voertuigen met zeer hoge NOx emissies hadden geen actieve OBD
codes. Ook bij de meeste geteste voertuigen met sterk verhoogde NOx emissie gaf
het betreffende OBD systeem geen meldingen.
Huidige APK viergastest niet geschikt voor detectie van verhoogde NOx emissies:
De huidige viergastest kan voertuigen met verhoogde NOx emissies nauwelijks
detecteren. Slechts één van de 50 geteste voertuigen, namelijk het voertuig met
een NOx emissie op de weg van 1267 mg/km, werd in de APK emissietest
afgekeurd. Dit voertuig was vier maanden eerder met een geforceerde
preconditionering (het voertuig was voor de test extreem opgewarmd) in de
reguliere APK test goedgekeurd. Ook de in 2018 geteste voertuigen met zeer hoge
NOx emissies waren in de APK goedgekeurd.
In de huidige APK viergastest wordt door middel van een CO-meting het oxiderend
vermogen van een katalysator gecontroleerd. Gemeten CO concentraties in een
viergastest bleken niet te correleren met gemeten NOx concentraties. Anders
gezegd: de CO-meting is niet bruikbaar om verhoogde NOx emissies te detecteren.
De huidige lambda APK limietwaarden zijn niet passend:
Het momenteel in de APK emissietest toegestane venster voor de lambda-waarde
bij verhoogd stationair toerental loopt van 0.965 tot 1.039. Het is de verwachting dat
aanscherping van deze APK lambda limietwaarden, in de vorm van een verkleining
van dit interval, kan bijdragen aan detectie van een groter aandeel voertuigen met
hoge NOx emissies.
Verbetering van de APK emissietestprocedure is naar verwachting effectief voor
betere detectie van benzinevoertuigen met een NOx emissieprobleem:
De huidige testprocedure van de APK viergastest leidt in de praktijk tot niet
éénduidige testresultaten.
Onder andere de volgende aspecten zijn denkbaar ter verbetering van de
procedure:
 Het hanteren van een minimale stabilisatie- en meettijd.
 Het voorschrijven van de meetfrequentie.
 Het definiëren van de volgorde en de tijdsduur van de testen bij hoog en laag
stationair toerental.
 Het stellen van eisen aan de preconditionering van de katalysator (in de huidige
testprocedure worden minimumeisen gesteld waardoor niet realistische
(excessieve) preconditionering is toegestaan.

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Stationaire testen met koude start zijn mogelijk toepasbaar als screeningstest:
Bij stationaire testen die aanvangen met een koude motor waarbij ongeveer
20 minuten lang, bij stationair toerental, opwarming van de drieweg katalysator
plaatsvindt, was de afname van de CO, THC en NOx concentraties bij de meeste
geteste voertuigen hoger dan 80%. Voor enkele voertuigen waren deze afnames 50
tot 80%. Slechts één voertuig had zeer lage afnames van minder dan 20%.
Deze opwarmtest is mogelijk een optie voor screening van voertuigemissies.
NH3 emissies zijn relatief hoog in stadsverkeer en variëren sterk per type voertuig:
In het kader van stikstofdepositie is het interessant om te weten welke NH3 emissies
vanuit diverse bronnen optreden. Om die reden zijn in dit project eveneens NH3
emissies gemeten. De gemiddelde NH3 emissie van de 38 op de weg geteste
voertuigen is 32.1 mg/km en per voertuig varieert deze van 1 tot 99 mg/km. In
stadsverkeer was de gemeten gemiddelde NH3 emissie 49 mg/km, op de buitenweg
22 mg/km en op de snelweg 21 mg/km.
Emissiefactoren beschrijven per component (bijvoorbeeld NOx, NH3) een
gemiddelde uitstoot per type voertuig en type weg en worden gebruikt voor
berekeningen ten behoeve van stikstofdepositie en luchtkwaliteit. De nu gemeten
gemiddelde NH3 emissies wijken af van de actuele waarden van NH3
emissiefactoren, deze zijn momenteel voor verkeer in stad/buitenweg/snelweg 18.8,
19.6 en 35.8 mg/km. De nu gemeten waarden worden meegenomen als input voor
de jaarlijkse bijstellingen van de emissiefactoren voor wegverkeer.
Verder blijken de NH3 emissie van vier geteste voertuigen na een koude start
relatief hoog te zijn. In de eerste 7.2 kilometer zijn deze gemiddeld ruim vier keer
hoger dan bij eenzelfde test met warme start.
Aanbevelingen:
 Aangezien voertuigen met ernstige defecte emissiecontrolesystemen een grote
invloed lijken te hebben op de totale emissie van benzinevoertuigen is het
wenselijk meer informatie te verkrijgen over het aandeel van deze voertuigen in
het Nederlandse wagenpark. Mogelijk bieden andere bronnen (zoals sluitende
APK-databases) verder inzicht in het minimum aandeel voertuigen dat een
defect emissiecontrolesysteem heeft.


Om een betere detectie mogelijk te maken, in de APK, van voertuigen met een
hoge NOx emissie, wordt terugkeer naar uitvoering van de viergastest (in plaats
van uitlezen van OBD) aanbevolen. Dit echter wel in combinatie met een
verbeterde testprocedure. Het advies is om nader te onderzoeken hoe de
huidige APK testprocedure voor de viergastest precies kan worden verbeterd.
Meerdere aspecten om daarbij te betrekken zijn in dit rapport benoemd. Is
detectie van voertuigen met een te hoge NOx emissie beter mogelijk geworden,
dan kunnen deze voertuigen daarna worden gerepareerd of, bij een niet
oplosbare bron van hoge emissie, mogelijk uit het wagenpark verdwijnen.

Afsluitende informatie
Inzicht in emissiefactoren bij hogere kilometerstanden
Gemeten voertuigemissieniveaus worden gebruikt voor het opstellen van
emissiefactoren. Emissies van benzinevoertuigen zijn in het verleden gemeten,
deze voertuigen waren destijds slechts een paar jaar oud en hadden nog een lage
kilometerstand.

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Op basis van deze gegevens zijn toen emissiefactoren opgesteld voor de
verschillende praktijksituaties op de weg. Het nu verkregen inzicht in de emissies
van de geteste voertuigen bij hogere kilometerstanden is waardevolle informatie
voor een bijstelling van de emissiefactoren ten gevolge van verouderingseffecten.
Waarmee zijn de emissies gemeten?
De voertuigen hebben een praktijkritcyclus op de openbare weg ondergaan.
Ook zijn APK emissietesten uitgevoerd. Bij de praktijktest op de openbare weg is
gebruik gemaakt van een aangepaste versie van het ‘Smart Emissions
Measurement System (SEMS) van TNO waarmee goede indicaties van NOx, NH3
en CO2-emissies worden verkregen. Uit validatiemetingen met testapparatuur van
een rollenbank is gebleken dat met het aangepaste meetsysteem beperkte
afwijkingen in gemeten CO2 emissies optraden van +6% tot +8% en voor NOx
emissies afwijkingen van -10% tot -14%.

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Summary
Larger sample after previous survey
This study is a follow-up to the study reported by TNO in 2018 in which twelve older
petrol vehicles were tested for their NOx emissions on a roller dynamometer. Two of
the twelve vehicles tested were then classified as 'high emitters' (they showed a
very high level of NOx emissions) and some other vehicles showed 'slightly
increased' NOx emissions. However, on the basis of this sample it was unclear to
what extent increased NOx emissions would occur in the entire Dutch fleet of older
gasoline vehicles equipped with three-way catalytic converters. Commissioned by
the Ministry of Infrastructure and Public Works, TNO has now additionally measured
exhaust emissions from 38 older petrol vehicles.
The primary research question was whether petrol vehicles with increasing age and
mileage, still show the same emission levels as at their type approval, or whether
these increase due to ageing effects. In order to answer this question, emission
measurements were carried out on public roads where each of the vehicles to be
tested was equipped with a mobile emission measurement system. The
measurements were carried out on vehicles equipped with three-way catalytic
converters and years of construction from 1998 to 2017. Tested were eight Euros 2,
nine Euros 3, sixteen Euros 4, four Euro 5 passenger cars and one Euro 6
passenger car. The vehicles had an average mileage of over 220,000 km and an
average age of around 16 years. In addition to answering the primary research
question, suggestions were also made for measurement techniques that may be
suitable for periodic testing for NOx emissions from petrol vehicles.
In order to be type-approved, these vehicles had to comply with set emission limits
during an 'NEDC chassis dynamometer test' in the laboratory. However, at a
mileage of more than 100,000 km, these vehicles no longer have to meet a
durability requirement that is checked in 'In-Service Conformity'. Exhaust
aftertreatment systems are also subject to an effective durability requirement for
mileage up to 160,000 km.
Results and conclusions
In this follow-up study with 38 vehicles, a lower proportion of cars with greatly
increased NOx emissions was found than in the first study with 12 cars. On the
other hand, the proportion of vehicles with increased emissions (with emissions up
to a factor of 2 to 4 above the original value) was higher than previously thought.
As the chassis dynamometer test programme carried out by TNO in 2018 involved
similar research, results from both programmes have been combined. The results of
a total of 50 vehicles tested lead to the following conclusions:
Average NOx emissions from older petrol vehicles are high:
Out of a total of fifty vehicles tested, the average NOx emissions are
200 mg/km. Limit values vary between Euro classes and are between 60 and
150 mg/km. The weighted limit value over the euro classes of the vehicles tested is
115 mg/km. The average compliance factor (CF) is therefore 1.74. This means that
the measured average NOx emission is 74% higher than the weighted limit values
of the type approval test on the chassis dynamometer. In comparison, emissions of
200 mg/km are higher than those of an average modern diesel car (Euro 6D Temp).

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Older petrol vehicles emit on average more NOx than comparable younger petrol
vehicles:
The average NOx emission of 200 mg/km is on average about twice as high as that
of petrol vehicles that were tested earlier when they were new and only had low
mileages. Petrol vehicles tested annually by TNO until 2008, and intermittently after
that time, showed only limited deviations between the results of type approval tests
and those of real world emissions.
Defective vehicles have a major impact on average NOx emissions:
Forty vehicles had normal (CF < 1) or slightly increased NOx emissions (CF < 2)
and seven vehicles had increased NOx emissions (CF = 2 - 4).
Three vehicles had greatly increased NOx emissions. Two of these three vehicles
were from the 2018 study and only one vehicle from the now completed larger
follow-up study. Together, these three vehicles had an average NOx emission of
1197 mg/km. The contribution of these three vehicles (6% of the number of vehicles
tested) to the total NOx emissions of the 50 vehicles tested is 36%.
No demonstrable correlation between high NOx emissions and vehicle parameters:
The measurement data of the individual vehicles show that the measured NOx
emissions of the tested vehicles do not depend on mileage (from 160,000 km),
vehicle age, Euro class, vehicle make or vehicle model. Since maintenance history
was not present or only partially present for a large proportion of the vehicles
tested, it was also not possible to establish a link between maintenance history and
increased emissions.
Current durability requirements for emissions do not cover the average service life
from a vehicle:
Figure 1.1 shows (with triangles) the average measured NOx emissions per Euroclass in relation to the average odometer value of the tested vehicles of that class.
It also shows (with small circles) the NOx limit values, the initial values at 0 km
driven and the values with permissible aging effects at 80,000, 100,000 or
60,000 km driven (the latter depending on the Euro class concerned).
The average mileages of the tested vehicles of the different Euro-classes were
1.2 to 3.5 times higher than the mileages specified for the durability requirements in
force. In the Dutch fleet of petrol vehicles, the tested vehicles are no exception in
terms of mileage.
From the type approval point of view, therefore, there is no reference framework for
the assessment of the emission performance of vehicles with odometer readings
higher than those specified for the durability requirements. For passenger cars and
vans, these only apply up to 80 000 to 160 000 km (depending on the Euro class of
the vehicle). There are periodic inspection requirements but they do not specifically
address significantly increased NOx emissions. Further on in the summary, further
attention is paid to the requirements from the periodic inspection (PTI).
A sporty driving style results in substantially higher emissions:
Four vehicles have been tested with a normal and sporty driving style. A sporty
driving style resulted in an increase in emissions for these four vehicles. The
average increase for CO2 was +13%, for NOx +96% and for NH3 +39%.

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This shows that a sporty driving style leads to (substantial) increases of the
measured CO2, NOx and NH3 emissions compared to a normal driving style.

Figure 1-1: NOx limit values (small circles) per Euro-class without and with permitted aging
in relation to mileage. The average measured NOx emissions per Euro-class
(triangles) in relation to the average odometer value of the vehicles tested in that
class are also indicated. The NOx limit value of Euro 2 vehicles is estimated
because the HC+NOx limit value is laid down by law.

Repair pays off:
Repairing vehicles with very high NOx emissions proved to have a strong positive
effect. Three out of four vehicles repaired resulted in an average reduction in NOx
emissions of 37, 92 and 93%. In one vehicle the emphasis was on repairing the
EGR (Exhaust Gas Recirculation) system and in two vehicles the three-way
catalytic converter was replaced. The average NOx emission of the 50 vehicles
tested decreased from 200 to about 130 mg/km after the repairs. The
corresponding average compliance factor (CF) is then 1.15.
The repair carried out during the study on a fourth vehicle proved to be ineffective.
In addition to the repairs carried out on lambda sensors, the three-way catalytic
converter probably also had a reduced conversion efficiency. Unfortunately, it could
not be replaced within the project.
Read-out of OBD systems could not be used as an indication for increased NOx
emissions:
There are European requirements with regard to the periodic inspection (PTI) of
vehicle emissions. For petrol cars from 1993 onwards, the so-called four-gas test
has to be carried out. For cars from 2006 onwards, instead of the four-gas test at
the PTI, the European On-Board Diagnostics system (EOBD or OBD) will be read
out. If it is not possible to read out the OBD properly or if emission-related error
codes are found, the four-gas test will still be carried out.
The investigation shows that On Board Diagnostics (OBD) systems are not able to
indicate that a vehicle exhibits elevated NOx emissions. Two of the three vehicles
tested with very high NOx emissions had no active OBD codes.

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Also for most of the vehicles tested with very high NOx emissions, the OBD system
in question did not give any reports.
Current PTI four-gas test is not suitable for detection of elevated NOx emissions:
The current four gas test can hardly detect vehicles with elevated NOx emissions.
Only one of the 50 vehicles tested, namely the vehicle with a NOx emission on the
road of 1267 mg/km, was rejected in the PTI emission test. This vehicle had been
approved four months earlier with forced preconditioning (the vehicle was extremely
warmed up prior to the test) in the regular PTI test. The vehicles tested in 2018 with
very high NOx emissions were also approved in the PTI.
In the current PTI four-gas test, the oxidising capacity of a catalytic converter is
checked by means of a CO measurement. Measured CO concentrations in a fourgas test were found not to correlate with measured NOx concentrations. In other
words, the CO measurement cannot be used to detect increased NOx emissions.
The current PTI limit values for lambda are not appropriate:
The window currently permitted in the PTI emission test for the lambda value at
increased idling speed ranges from 0.965 to 1.039. It is expected that a tightening
of these PTI lambda limit values, in the form of a reduction of this interval, can
contribute to the detection of a larger proportion of vehicles with high NOx
emissions.
Improvement of the PTI emission test procedure is expected to be effective for
better detection of petrol vehicles with a NOx emission problem:
The current test procedure of the PTI four-gas test leads in practice to non-uniform
test results.
The following aspects, among others, are conceivable to improve the procedure:
 The use of a minimum stabilisation and measurement time.
 The prescription of the measurement frequency.
 Defining the sequence and duration of the tests at high and low idle speeds.
 Setting requirements for the preconditioning of the catalyst (in the current test
procedure, minimum requirements are set which do allow non-realistic
(excessive) preconditioning.
Cold start stationary tests may be applicable as a screening test:
In idling tests starting with a cold engine and warming up of the three-way catalyst
for about 20 minutes at idling speed, the CO, THC and NOx concentrations
decreased by more than 80% in most of the vehicles tested. For some vehicles
these reductions were 50 to 80%. Only one vehicle had very low reductions of less
than 20%. This warm-up test may be an option for screening of vehicle emissions.
NH3 emissions are relatively high in urban traffic and vary greatly depending on the
type of vehicle:
In the context of nitrogen deposition, it is interesting to know which NH3 emissions
occur from various sources. For this reason, NH3 emissions have also been
measured in this project. The average NH3 emission of the 38 vehicles tested on the
road is 32.1 mg/km and varies from 1 to 99 mg/km per vehicle. In urban traffic the
measured average NH3 emission was 49 mg/km, on rural roads 22 mg/km and on
highways 21 mg/km.

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Emission factors describe per component (e.g. NOx, NH3) an average emission per
type of vehicle and type of road and are used for nitrogen deposition and air quality
calculations. The currently measured average NH3 emissions differ from the actual
values of NH3 emission factors which are for urban/off-road/highway 18.8, 19.6 and
35.8 mg/km. The currently measured values are used as input for the annual
update of the emission factors for road traffic.
Furthermore, the NH3 emission of four tested vehicles, after a cold start, appears to
be relatively high. In the first 7.2 km these are on average more than four times
higher than in the same test with a warm start.
Recommendations:
 Since vehicles with severely defective emission control systems seem to have a
major influence on the total emissions of petrol vehicles, it is desirable to obtain
more information about the share of these vehicles in the Dutch fleet. Other
sources (such as conclusive PTI databases) may provide further insight into the
minimum proportion of vehicles with defective emission control systems.


To allow better detection, in the PTI, of vehicles with high NOx emissions, a
return to the four-gas test (instead of read out of the OBD) is recommended.
However, this in combination with an improved test procedure. The advice is to
investigate further how exactly the current PTI procedure for the four-gas test
can be improved. Several aspects to be taken into account have been identified
in this report. Once the detection of vehicles with excessive NOx emissions has
become more feasible, these vehicles can then be repaired or, in the case of an
insoluble source of high emissions, possibly disappear from the vehicle fleet.

Closing information
Insight into emission factors at higher mileages
Measured vehicle emission levels are used to establish emission factors. Emissions
from petrol vehicles have been measured in the past, these vehicles were only a
few years old at the time and still had low mileage. On the basis of these data,
emission factors were then drawn up for the various practical situations on the road.
The insight now obtained into the emissions of the vehicles tested at higher
mileages is valuable information for adjusting the emission factors due to ageing
effects.
What were the emissions measured with?
The vehicles have undergone a practical driving cycle on public roads.
PTI emission tests were also carried. The practical test on public roads used a
modified version of the Smart Emissions Measurement System (SEMS) from TNO,
which provides good indications of NOx, NH3 and CO2 emissions. Validation
measurements with test equipment of a roller dynamometer showed that with the
adapted measuring system limited deviations in measured CO2 emissions occurred
from +6% to +8% and for NOx emissions deviations from -10% to -14%.

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Contents
Samenvatting ........................................................................................................... 2
Summary .................................................................................................................. 8
1
1.1
1.2
1.3
1.4

Introduction ............................................................................................................ 15
Context .................................................................................................................... 15
Aim and approach.................................................................................................... 18
TNO policy with respect to publication of data ........................................................ 18
Structure of the report .............................................................................................. 19

2
2.1
2.2
2.3
2.4

Test program .......................................................................................................... 20
Selection, origin and mileage validity of the tested vehicles ................................... 20
Emission limit values ............................................................................................... 21
Test equipment ........................................................................................................ 23
Test procedure......................................................................................................... 24

3
3.1
3.2
3.3
3.4
3.5
3.6

Test results............................................................................................................. 26
Summary on road emission test results .................................................................. 26
PTI emission test results ......................................................................................... 30
State of maintenance of the tested vehicles ............................................................ 33
On Board Diagnostic data ....................................................................................... 33
Three-way catalyst performances in cold and warm condition ............................... 34
Effects of vehicle repairs on emission levels ........................................................... 38

4
4.1
4.2
4.3
4.4
4.5
4.6
4.7

Analyses of test results ........................................................................................ 45
NOx emissions ......................................................................................................... 45
Periodic Technical inspections ................................................................................ 50
Vehicle repairs ......................................................................................................... 50
Emissions with cold and warm engine starts ........................................................... 51
Performance PTI emission test ............................................................................... 51
Quality of the measured NOx concentrations .......................................................... 54
NH3 emissions ......................................................................................................... 56

5
5.1
5.2

Discussion.............................................................................................................. 60
Emissions ................................................................................................................ 60
Investigations for an improved PTI emission test procedure .................................. 61

6

Conclusions ........................................................................................................... 65

7

Recommendations................................................................................................. 69

8

Abbreviations ......................................................................................................... 70

9

Acknowledgements ............................................................................................... 71

10

References ............................................................................................................. 72

11

Signature ................................................................................................................ 73

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

Appendices
A Specifications of the Mobile Emission Measurement System (MEMS)
B Validation of the Mobile Emission Measurement System
C Tested vehicles
D On road emission test results
E Technical comments of the tested vehicles
F PTI emission test results
G Backgrounds of NOx emission control strategies
H Backgrounds of NH3 emissions

14 / 73

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1

15 / 73

Introduction
This report presents detailed results of on road emission tests carried out by TNO
in the period autumn 2019 - summer 2020. The tests focussed on emissions of
in-use, older, petrol vehicles with three-way catalyst and high mileages.
This vehicle group has a significant impact on the total emissions of passenger
vehicles after 2020, mainly due to the fact that it concerns still several millions of
vehicles in the Netherlands. The emission tests were carried out for the Dutch
Ministry of Infrastructure and Water Management.
With this report TNO intends to provide clarity and understanding on the measured
data and what the results do and do not imply. TNO and the Dutch Ministry of
Infrastructure and Water Management aspire to provide maximum transparency on
the information that feeds into policy decisions regarding air quality and emission
legislation. Results of the chassis dynamometer measurements with twelve other
passenger vehicles were published in an earlier stage [TNO 2018]. However, it was
decided to test a larger set of vehicles, on the road. The current report presents the
measurement results of this larger set of vehicles.

1.1

Context
Euro emission standards
To minimize air pollutant emissions of light-duty vehicles, in 1992 the European
Commission introduced the Euro emission standards. In the course of time, these
standards have become more stringent. Currently produced light duty vehicles
of categories M and N must comply with the Euro 6b standard. The Euro 6c and
6d-Temp standards, that further limit the emissions, will become mandatory in the
period of 2018 - 2020.
The standards apply to vehicles with spark ignition engines and to vehicles with
compression ignition engines and cover the following gaseous and particulate
emissions:
 CO (carbon monoxide);
 THC (total hydrocarbons);
 NOx (nitrogen oxides);
 PM (particulate mass),
 PN (particulate number, for direct injection only).
As a result of the Euro emission standards, the pollutant emissions of light-duty
vehicles, passenger cars and vans, as observed in type approval tests have
reduced significantly over the past decade. However, under real driving conditions
some emissions substantially deviate from their type approval values.
The real driving emissions of nitrogen oxides, or NOx, from diesel vehicles are
currently the most important issue with regard to pollutant emissions, as many
cities fail to satisfy the NO2 air-quality standards mainly through the poor real-world
performance of diesel cars.1

http://www.platformparticipatie.nl/projecten/alle-projecten/projectenlijst/aanpassing-nationaalsamenwerkingsprogramma-luchtkwaliteit-2018/index.aspx
1

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As NOx represents the sum of NO and NO2 emitted, and much of the NO is
converted to NO2 in ambient conditions, reducing NOx emissions of vehicles is
important for bringing down the ambient air NO2 concentration in cities.
In the Netherlands, the ambient NO2 concentration still exceeds European limits
at numerous urban road-side locations2.
For petrol vehicles, tested by TNO annually till 2008 and more intermittently after
that time, limited deviations between the type-approval tests and the real-world
tests were observed. The NEDC type-approval test definitions, with the low test
velocity, short distance, and the cold start, formed stringent requirements for petrol
vehicle technology which ensured in real-world circumstances the emissions were
typically lower than the emission limits in the type-approval test.
Moreover, from monitoring programs, such as remote sensing studies, there was
little concern on the real-world performance of petrol vehicles. However, given the
size of the fleet and, for example, the impact on the total emissions after 2020,
there are risks that minor deviations in the estimates will have considerable
consequences for the total real-world emissions.
Commissioned by the Dutch Ministry of Infrastructure and Water Management,
TNO regularly performs emission measurements within the “in-use compliance
programme for light-duty vehicles”. In the early years, i.e., in 1987 to 2000, the
focus was on performing a number of standard type approval tests on a large
number of vehicles in the lab. In recent years, however, the emphasis has shifted
towards gathering emission data under conditions that are more representative for
real-world driving, by using various non-standard, i.e., real-world, driving cycles in
the lab and by increasingly testing cars on the road with mobile emission
measurement equipment.
Emission factors
The emission factors, or average emissions, for pollutant tailpipe emissions of this
group of vehicles are typically below the type-approval limit. The 2017 emission
factors are given in Table 1-1.
The urban emissions are substantially higher than rural and motorway emissions.
This is the result of the cold start contribution. In the total emissions, the start of the
cold engine typically dominates the emissions. In the first 300 metres of driving the
same emissions are produced as in the next twenty or more kilometres. For urban
driving it is estimated that for every 7 kilometres of driving one cold start occurs.3
TNO is one of the few institutes in Europe that perform independent emission tests.
Based on the results of performed emission tests, TNO develops, and annually
updates, Dutch vehicle emission factors that represent the average real-world
emissions data for specific various vehicle types categories under different
driving and traffic conditions.

2
3

http://www.atlasleefomgeving.nl/en/meer-weten/lucht/stikstofdioxide
See report: CBS Methods for calculating emissions of transport in the Netherlands, 2017.

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Table 1-1: Emission factors for Euro-2 to Euro-5 petrol vehicles for the Dutch air-quality
assessments of 2017.

road type
urban

rural

motorway

g/km
NOx
HC
PM
CO
Elemental Carbon
real‐world CO2
NOx
HC
PM
CO
Elemental Carbon
real‐world CO2
NOx
HC
PM
CO
Elemental Carbon
real‐world CO2

Euro‐2
0.4684
0.5132
0.0046
10.6833
0.0012
284.7
0.2130
0.2334
0.0023
4.3987
0.0006
143.3
0.1984
0.0654
0.0050
3.4073
0.0013
203.0

Euro‐3
0.1480
0.4374
0.0023
6.6475
0.0004
254.6
0.0594
0.2153
0.0012
3.2906
0.0002
152.6
0.0360
0.0216
0.0025
1.8849
0.0004
203.6

Euro‐4
0.0539
0.4197
0.0023
5.6150
0.0004
235.9
0.0248
0.2118
0.0012
2.8732
0.0002
149.2
0.0147
0.0189
0.0025
1.6523
0.0004
194.8

Euro‐5
0.0431
0.3357
0.0019
4.4920
0.0003
213.2
0.0199
0.1694
0.0009
2.2985
0.0001
134.9
0.0117
0.0151
0.0025
1.3218
0.0004
176.1

Vehicle emission factors are used for emission inventories and air quality
monitoring. The emission factors, and the underlying test results, are one of the
few independent sources of evidence for the growing difference between legislative
emission limits and real-world emission performance of cars. Furthermore, the
insights obtained in emission measurement programs serve as input for the
activities of the Dutch government and the RDW in the context of regulation and
legislative processes in Brussels (European Commission) and Geneva (GRPE )
to improve emission legislation and the associated test procedures for light duty
vehicles, all with the aim to reduce real-world emissions and improve air quality.
Lack of data of older petrol vehicles
With the focus in recent years on diesel vehicles and NOx emissions, the test
programmes for petrol vehicles were limited. With Euro-5 a few incidental and
specialized test programmes for petrol vehicles were executed. The test
programme in 2016, was intended to determine PM and EC emissions of the
emerging GDI technology vehicles. The test program of 2018-2019 was intended
to investigate emissions of petrol vehicles with high mileages.
A lack of emission data of older petrol vehicles was identified: Petrol passenger
cars have been measured in the past when these vehicles were only a few years
old and had limited odometer readings. With the prevalence of petrol cars on the
Dutch roads of all ages, they are a major contributor to the emission totals.
Even a minor underestimation of petrol vehicle NOx or NH3 emission may have
significant environmental impact. On the basis of this data, emission factors have
been determined for the different practical situations on the road. With increasing
age and mileages, the question is whether these vehicles still have the same
emission levels.

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Because petrol cars are their entire lifespan on the Dutch roads (they are hardly
exported, but imported in significant numbers), and because, as they get older,
they become a growing share of the total amount of vehicles within cities, they
are relevant for urban air quality. It is also the largest group of cars: they constitute
more than 70% of all urban traffic. Modern petrol cars reach on average 100,000
kilometres after 7 years [TNO 2015].
A vehicle from 1990 and before had an average lifespan of 18 years or less and
150,000 kilometres. Vehicles from 2005 and earlier reach the 150,000 at 10 years,
and likely drive more than 200,000 kilometres in total. Furthermore, a lack of
emission data of older vehicles is still the case. Therefore, it was decided to perform
an exploratory emission measurement program with petrol passenger cars with high
mileages. Also the fact that the Dutch petrol fleet has an increasing age possibly
showing deterioration effects of after treatment system parts, is another point of
concern and underlines the importance of this study.
1.2

Aim and approach
The aim of the project was to assess the real-world NOx emission performance of
petrol passenger cars with three way catalyst and higher mileages, and to provide
suggestions for promising measurement techniques for a periodic test for NOx
emissions from petrol vehicles. This was done by performing emission
measurements on the road under real-world conditions and analysis of the collected
results. Measurement results are also input for an update of the emission factors for
this vehicle category.
This study involves on-road emission measurements on a total of 38 Euro 2,
Euro 3, Euro 4, Euro 5 and Euro 6 passenger vehicles. Together with the former
twelve petrol vehicles that were tested on the chassis dynamometer this number
of vehicles provides a basis to determine trends in their emission behaviour and
to indicate average deterioration factors for the different road types.

1.3

TNO policy with respect to publication of data
TNO takes the care in generating data and in communication on the findings of its
studies to the various stakeholders. It is beneficial to ensure no errors are made in
the testing and problems are addressed early.
In the evaluation and interpretation of test results on individual vehicles the
following considerations need to be taken into account:


The tests performed by TNO are intended to determine the levels and trends
of emissions of various categories of vehicles. The tests are not intended for
enforcement, and they are not suitable for identifying or claiming fraud or
other vehicle-related irregularities in a scientifically and legally watertight
way.



For each make or model, only a single vehicle or a small number of vehicles
is/are tested a limited number of times. This means that the results correlate
to the specific condition of the tested vehicles or to specific test conditions.
The latter is especially the case in real-world testing on the road in which a
large number of conditions, that have a strong influence on test results, vary
from trip to trip.

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In publications about the emission test results on light duty vehicles TNO has up to
March 2016, for reasons as indicated above, chosen to present test results in a way
that does not allow makes and models to be identified. In case results of individual
vehicles were reported, these were always anonymized.
As part of TNO’s constructive contribution to the on-going public debate about the
real-world NOx emissions of diesel cars, TNO has decided to present test results
with references to makes and models. This decision also meets a desire expressed
by the Dutch Ministry of Infrastructure and Water Management.
By presenting results from the complete sample of vehicle models tested, covering
a wide range of makes and models, and by providing the necessary background
information on test procedures and test conditions as well as caveats with respect
to what can be concluded from these data, the test results on individual vehicle
models are presented in a context that allows a well-balanced interpretation of
the meaning of the results.
Finally, we would like to emphasize that as an independent knowledge institute,
TNO is, has been, and will be open to constructive dialogue with industry and
governments. This is part of TNO’s efforts to work together with relevant
stakeholders in finding and supporting the implementation of effective solutions
to reduce real-world emissions of harmful substances from vehicles, as well to
determine and demonstrate the effects of implemented measures in an objective
way.
1.4

Structure of the report
Information regarding the selection and the basic specifications of the selected
vehicles can be found in Chapter 2. This chapter also provides detailed information
about emission limit values, the used test cycles and the test equipment.
Chapter 3 presents an overview of the test results for the tested vehicles, followed
by analyses in chapter 4 and discussions in chapter 5. Conclusions and
recommendations for further research are reported in the chapters 6 and 7.
Test results of the individual vehicles as well as the specification of the test
equipment as used during the tests are part of the appendices.

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2

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Test program
This chapter presents the most important characteristics of the on-road test
program as performed.

2.1

Selection, origin and mileage validity of the tested vehicles

2.1.1

Vehicle selection
Starting point for the selection of vehicles to be tested was the actual Dutch fleet
composition of September 2019. The number of vehicles to be tested within this
project was limited to 38. Selection was done in such a way that the test vehicles
represent the older vehicles. Most of the selected vehicles belong to the group of
highest sales vehicles, were kindly offered by private individuals and generally in
private use.

2.1.2

Vehicle properties
In Table 2-1 summarized data of the mileages and ages of the tested vehicles are
specified. All vehicles had a first date of registration between 1998 and 2017 and
mileages were between 156,663 and 550,384 km. Thirty-two vehicles were privately
owned and six vehicles were obtained from two car dealers. More details of the
tested vehicles are reported in Appendix B. Figure 2-1 shows the relationship of
vehicle age and mileage of the tested vehicles.
Table 2-1: Mileages of tested petrol passenger cars with a three-way catalyst.

Euro
class

Number of
tested
vehicles

Mileage
range
[km]

Average
Mileage
[km]

Average
Age
[year]

1

0

-

-

-

2
3

8
9

181,228 – 550,384
177,478 – 370,859

283,683
234,298

20.9
17.0

4

16

156,663 – 262,826

194,361

14.3

5

4

176,074 – 220,292

197,309

7.1

6
Total

1
38

175,728
156,663 – 550,384

175,728
222,444

3.0
15.8

All tested vehicles were equipped with a three-way catalyst. In 36 vehicles
stoichiometric air-fuel mixtures were applied in the full engine map and two vehicles
(Toyota Avensis and BMW 320i) were operating with a dual air-fuel strategy (lean
burn and stoichiometric). The BMW 320i was also equipped with a Lean NOx Trap.
Validity of vehicle mileages
The history of the vehicle mileages of the tested vehicles was checked in the Dutch
national database of vehicle registrations. Since 2011 all vehicle mileages of regular
maintenance activities and periodic technical inspections are stored in this database
(see https://ovi.rdw.nl/ or use the RDW vehicle app).

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Figure 2-1: Age and odometer readings of the tested vehicles (the 12 vehicles of the chassis
dynamometer test program of 2018 are included). Vehicles were selected on the
basis of odometer values, and therefore centre around 200,000 kilometres.

Table 2-2 shows the results of the validity checks of the vehicle mileages.
Thirty-one vehicles had a vehicle mileage with sense, their consecutive registered
mileages have a logic order. Three vehicles were imported and could not be
assessed because data were missing. Four vehicles had a vehicle mileage which
made no sense with the state of the vehicle. This might be caused in case of an
odometer change, incorrect registration or manipulation of the odometer. From the
individual mileage registration reports the correct vehicle mileages could be derived.
Table 2-2: Validity of vehicle mileages.

Status vehicle
mileage

Number of
vehicles

Comment

Plausible
Implausible

31
4

Toyota Starlet, Peugeot 206,
Renault Megane, Opel Zafira.

Imported vehicle

3

Opel Corsa, VW Golf, BMW 320i

Unknown
Total

38

-

2.2

Emission limit values

2.2.1

European type approval emission limit values
In Table 2-3 the European emission limit values of passenger vehicles and their
durability and In Service Conformity mileages are shown. The limit values are
based on a New European Driving Cycle (NEDC) with a cold start.

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Table 2-3: NEDC Emission limit values of petrol passenger vehicles.

Emission limit values of M1 Class 1 petrol vehicles
Emission

THC

NMHC

CO

-

-

2,720

Class

NOx

PM

HC+
NOx

-

-

970

[mg/km]

Euro 1

PN
[#/km]

Durability
limit
[km]

ISC
limit
[km]

-

80,000

-

Euro 2

-

-

2,200

-

-

500

-

80,000

-

Euro 3
Euro 4

200
100

-

2,300
1,000

150
80

-

-

-

80,000
100,000

tbr

Euro 5a

100

68

1,000

60

5.0

-

-

160,000

100,000

Euro 5b
Euro 6b

100
100

68
68

1,000
1,000

60
60

4.5
4.5

-

6.0E+12

160,000
160,000

100,000
100,000

Euro 6c

100

68

1,000

60

4.5

-

6.0E+11

160,000

100,000

For calculation of the conformity factors (CF) of Euro 2 vehicles, the informal NOx
limit value is set at 300 mg/km assuming an informal THC limit value of 200 mg/km.
In this project the definition of the NOx conformity factor (CF) formula is the NOx
emission of an on road test with warm start [mg/km] divided by the NOx limit value
[mg/km] of an NEDC type approval test with cold start.
2.2.2

NOx deterioration factors
The durability of the vehicle emission performance is characterised with
deterioration factors and a mileage. In Table 2-4 the NOx deterioration factors,
mileages and corrected NOx deterioration factors @ 160,000 km are reported
(with the assumption that deterioration is a linear mechanism).
Table 2-4: NOx limit values incl. durability factors and mileage corrections of positive ignition
engines (class M).

NOx limit value
w.o. / w
deterioration
[mg/km]
‘300’ – 450

Corrected NOx limit value
Incl. deterioration*

[km]
80,000

NOx
deterioration
factor
[-]
1.5

3

80,000

1.2

150 – 180

210

4
5

100,000
160,000

1.2
1.6

80 – 96
60 – 96

106
96

6

160,000

1.6

60 - 96

96

Euro
class

Durability
Mileage

2

[mg/km]
600

*Assumed linear deterioration
2.2.3

European emission limit values for the Periodic Technical Inspection
The European Directive 2014/45/EC and the Dutch vehicle regulation
(Wegenverkeerswet, Regeling Voertuigen) for periodic technical inspections
(PTI) describe a similar PTI emission test procedure. For petrol vehicles with a
three way catalyst the warmed up engine is tested at low- and high idle speed
and CO, CO2, THC and O2 concentrations are measured in the tailpipe and the
actual lambda value is calculated. In Table 2-5 the CO emission limit values and
the range of allowed lambda values for low and high idle speed tests are reported.

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Table 2-5: European PTI emission limit values for petrol vehicles (Source 2014/45/EU).
Registration date
From

To

1‐1‐1974
1‐10‐1986
1‐1‐1986
1‐7‐2002

30‐9‐1986
30‐6‐2002
30‐6‐2002
>

Registration date
From

To

1‐1‐1974
1‐10‐1986
1‐1‐1993
1‐7‐2002

30‐9‐1986
30‐6‐2002
30‐6‐2002
>

Low idle speed warm engine
Emission class

CO

15.03
15.04
Euro 1,2
Euro 3,4,5,6

[vol%]
4.5
3.5
0.5
0.3

Catalyst + lambda sensor

high idle speed 2000 ‐ 3200 rpm
Emission class

CO

15.03
15.04
Euro 1,2
Euro 3,4,5,6

[vol%]
‐
‐
0.3
0.2

Catalyst + lambda sensor

Lambda
min
[‐]
‐
‐
‐
‐

Lambda
max
[‐]
‐
‐
‐
‐

Lambda
min
[‐]
‐
‐
0.97
0.97

Lambda
max
[‐]
‐
‐
1.03
1.03

2.3

Test equipment

2.3.1

Mobile Emission Measurement System (MEMS)
In order to be able to screen vehicle emissions on the road with different vehicle
bodies a dedicated mobile emission measurement system (MEMS) was developed,
see Figure 2-2, Figure 2-3 and Figure 2-4. This test set up, an adapted version of
the SEMS measurement system, and the data processing steps are specified in
Appendix A. Emission test results are based on exhaust mass flow measurements
(pitot tube) and the signals of the GPS, lambda, NOx-O2 and NH3 sensors.
In addition, an automotive 5-gas tester, measuring CO, CO2, C6H14, NOx and O2
concentrations of undiluted exhaust gas, was installed in the trunk. Furthermore
OBD data were logged (if available). A bicycle carrier provided a practical approach
for quick assembly and disassembly suited for almost all vehicle makes and bodies.

Figure 2-2: Vehicle with test equipment.

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Figure 2-3: Flow measuring tube with dilution air pump and lambda, NOx-O2 and NH3 sensors.

Figure 2-4: Automotive 5-gas tester, 12V battery, 12/24 V DC-convertor, pressure sensor box for a
pitot tube and SEMS data logger in the trunk.

In Appendix B the results of the validation of MEMS are reported.
2.4

Test procedure
In this study the vehicles were subjected to a defined test procedure that contains
the next steps:
1. Vehicle registration.
2. Vehicle inspection and validation check of the mileage.
3. Vehicle preparation.
4. Installation and commissioning of test equipment.
5. Idle speed tests and warming up of the engine.
6. On road emission test of 50 km (see Figure 2-5).
7. Idle speed tests.
8. Data processing.
9. Determination of pass/fail.
10. In case of a pass the test procedure is terminated.
11. In case of a fail the vehicle may be repaired and the test procedure
repeated, starting at step 5.
Undiluted exhaust gas was sampled in PTI and on road tests with a 5-gas tester
(CO, CO2, C6H14, O2 and NOx) with a sample rate of 4 Hz.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

2.4.1

Vehicle inspection and preparation
After receival the vehicles were inspected and prepared as follows:
a.
b.
c.
d.
e.

2.4.2

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Registration of maintenance history (if available)
Leak check of the exhaust system.
Registration of active OBD fault codes, if any.
Installation of the Mobile Emission Measurement System (MEMS)
Commissioning of the test set up in a short road trip of 5 km.

Applied fuels:
In Table 2-6 the applied test fuels of the test program are specified.
Table 2-6: Applied EN 228 test fuels

Type
Quality
RON
Ethanol content

2.4.3

1

2

[-]

Trade E10
95

Trade E5
98

[vol%]

< 10

<5

Applied emission test procedure
All vehicles were tested in the technical condition ‘as received’ and subjected to
the next test emission test program:
1.
2.
3.
4.

Low idle speed test with cold engine start and warming up at low idle speed.
High and low idle speed test with a warm engine.
On road test of 48-51 km with a warm engine start (urban, rural, motorway).
High and low idle speed test with a warm engine.

In Figure 2-5 the speed profile of the on road test is shown. Due to actual traffic
conditions the profile may deviate slightly from test to test.

Figure 2-5: Example of an on-road test trip of 50.8 km with urban 19.4 km, rural 20.8 km and
motorway 10.6 km use. The average vehicle speed in this test is 38.6 km/h.

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3

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Test results
The emission tests were performed between December 2019 and September 2020.
In the following sections the validation of MEMS and the overall test results are
reported. Detailed test results are reported in appendices B, C and D.

3.1

Summary on road emission test results

3.1.1

Overview average emission test results of 38 tested vehicles.
After the warming up test at idle speed every vehicle was subjected to an on-road
emission test with a length of 48-50 km.
In Table 3-1 an overview of the average emission test results of the 38 tested petrol
vehicles is given.




The measured on road NOx emission of 38 tested vehicles is in the range of
17 to 1,267 mg/km and on average 166.4 mg/km. The conformity factors are
in the range of 0.2 to 4.7 and on average 1.21. The measured on road CO2
emission of 38 tested vehicles is in the range of 111 to 217 g/km and on
average 164.3 g/km. It must be noted that the emission limit is based on a cold
start NEDC test. Warm engine emissions, with functioning emission control are
expected to be less than half of the limit.
The measured NH3 emission of 38 tested vehicles is in the range of 1 to 99
mg/km and on average 32.1 mg/km.

Table 3-1: Overview average on road emission test results of 38 petrol vehicles with high mileages

Mileage
Range
Average
St. deviation

CO2

NOx

NH3

[km * 1,000]

[g/km]

[mg/km]

[mg/km]

157 - 550
222.4

111 - 217
164.3

17 - 1267
166.4

1 - 99
32.1

71.3

26.7

207.2

23.6

Detailed test results of individual vehicles are reported in Appendix A and sorted
results in the next sections.
In Table 3-2 the average on-road emission test results are sorted per Euro class.
For every Euro class the spread in NOx and NH3 emission is large.
Detailed test results of individual vehicles are reported in Appendix A and sorted
results in the next sections.

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Table 3-2: On-road average emission test results (NOx, NH3 and CO2) of 38 tested vehicles sorted
per Euro class.

No of vehicles
Av. age
Av. mileage
Av. empty mass

[-]
[year]

Euro 2

Euro 3

Euro 4

Euro 5

Euro 6

8
20.9

9
17.0

16
15.0

4
9.3

1
3.0

[km*1000]

284

234

194

197

176

[kg]

1159

1169

1172

1234

1011

[mg/km]
[mg/km]

300*
382

150
140

80
95

60
113

60
35

NOx
NEDC limit value
Average
St. deviation

[mg/km]

340

103

71

100

-

Minimum

[mg/km]

163

43

17

44

-

Maximum

[mg/km]

1267

352

264

284

-

Average
St. deviation

[mg/km]
[mg/km]

40
26

23
12

27
21

58
26

20
-

Minimum

[mg/km]

10

5

1

12

-

Maximum

[mg/km]

99

38

85

77

-

Average
St. deviation

[mg/km]
[mg/km]

166
24

166
18

170
29

145
14

111
-

Minimum

[mg/km]

135

141

121

125

-

Maximum

[mg/km]

209

198

217

160

-

NH3

CO2

*Derived from HC+NOx limit value of 500 mg/km.

3.1.2

NOx emissions
In Figure 3-1 the average on road NOx emissions of all tested vehicles and in
Figure 3-2 the NOx conformity factors are shown. One vehicle had a very high
NOx emission of 1267 mg/km.
The NOx conformity factors of the tested vehicles are in the range of 0.4 – 4.7
and on average 1,21. The NOx emissions as well as the NOx conformity factors
have a large spread and are not correlated with vehicle mileage (> 160.000 km).
In Figure 3-3 the average NOx emissions of the tested vehicles are sorted per
Euro class. The vehicle with a mileage of 550,000 km was a VW Passat (Euro 2)
with a second three-way catalyst which was mounted at a mileage of 359,975 km.
In every Euro class with multiple vehicles there is a large spread of NOx emission.
The NOx emissions of the tested vehicles are not correlated with Euro class.
In section 4.1 a detailed analysis of the NOx emissions of all vehicles and the
conclusions are reported.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

Figure 3-1: Average on road NOx emission as function of the mileage of 38 petrol vehicles.

Figure 3-2: NOx conformity factors as function of odometer readings of 38 petrol vehicles.

Figure 3-3: Average on road NOx emissions as function of Euro class of 38 petrol vehicles.

28 / 73

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3.1.3

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NH3 emissions
In Figure 3-4 the average on road NH3 emissions as a function of vehicle mileage of
the tested vehicles and in Figure 3-5 the NH3 emissions as a function of vehicle age
are shown. The measured on road average NH3 emission of 38 tested vehicles is in
the range of 1 to 99 mg/km and on average 32.1 mg/km.
The NH3 emissions of the tested vehicles are not correlated with vehicle age or
mileage.
In Figure 3-6 the average NH3 emissions of the tested vehicles are sorted per
emission class. For every Euro class with multiple tested vehicles there is a large
spread of NH3 emission and they are not correlated.
In section 4.7 a more detailed analysis of the NH3 emissions and conclusions are
reported.

Figure 3-4: Average NH3 emissions of road tests as function of the mileages of 38 petrol vehicles.

Figure 3-5: : Average on-road NH3 emissions as function of vehicle age of 38 petrol vehicles.

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Figure 3-6: Average on road NH3 emissions as function of Euro class of 38 petrol vehicles.

3.2

PTI emission test results
After execution of the on road emission test, so with a warm motor, PTI emission
tests at low and high idle speed were performed. In Figure 3-7 the measured
CO emission at low idle speed of the tested vehicles is shown. Except for two
vehicles, all measured CO concentrations at low idle speed are less than 0.30 vol%.
Vehicles with deviating CO concentrations were retested and the CO concentration
in a second test was less than 0.30 vol%. These vehicles had an irregular emission
behaviour because the air-fuel control (lambda) of the engine was not stable.
The four vehicles with higher lambda values (1.01, 1.03 and 1.08) at low idle speed
had exhaust system leakages (flange not tight or muffler leakage), despite earlier
visual inspections. After repair the lambda values were 0.99 and 1.00.

Figure 3-7: CO concentrations as function of lambda of 38 gasoline vehicles at low idle speed.

The measured CO concentration at high idle speed of the tested vehicles is shown
in Figure 3-8. The CO concentration of all tested Euro 3, 4, 5 and 6 vehicles at high
idle speed is below the PTI limit value of 0.2 vol%.

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Two Euro 2 vehicles exceeded the CO limit value of 0.3 vol%. The Renault Clio
was retested and the CO emission was not stable and sometimes less than
0.30 vol%. For the Euro 2 Peugeot 206 the CO concentration stayed above the limit
value of 0.30 vol%.
All vehicles operated at high idle speed in the required lambda window of 0.97 to
1.03. Lambda at high idle speed of most vehicles is in the range of 0.99 to 1.00.
The three vehicles with higher lambda values at high idle speed had an exhaust
system leakage or worn three-way catalyst.

Figure 3-8: CO concentrations and lambda values of 38 gasoline vehicles at high idle speed.

In the executed PTI’s on top of the regular emission test, more data were
measured/determined. In Figure 3-9 the results of the executed PTI tests of all 38
tested vehicles and the on-road NOx classification (medium or high emitter) are
reported. When a colour pops up the specific test fails or specific criteria were met
and with a blank the specific test had a pass.
The specific PTI fail criteria were:
-

MIL is burning (yellow).
Engine and emission related OBD codes are active (grey).
CO concentration at low or high idle speed is too high (black).
Lambda at high idle speed is out of range (< 0.965 or > 1.039) (purple).
NOx concentration at low idle speed > 50 ppm (light blue).
NOx concentration at high idle speed > 150 ppm (dark blue).
Medium NOx emitter, CF > 2 and NOx < 750 mg/km (orange).
High NOx emitter, CF > 4 and NOx > 750 mg/km (red).

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Figure 3-9: PTI parameters and emission characteristics of the 38 tested vehicles (x-axis has no
meaning).

Ten vehicles had one or more failures or elevated emissions, these are:











Fiat Punto: NOx = 235 mg/km (CF = 2.9). Nothing was detected in PTI tests
Citroen C5: NOx = 352 mg/km (CF = 2.3). Nothing was detected in PTI tests.
Suzuki Wagon: NOx 296 mg/km (CF = 2.0). Active OBD codes P0130 and
P0400.
VW Golf: NOx 355 mg/km (CF = 1.2). Active OBD codes 17840 and 17538.
BMW 3: NOx 162 mg/km (CF = 2.0). Active OBD codes: 2854, 2783 and 2865.
Peugeot 206: NOx 1267 mg/km (‘CF = 4.2’). CO and NOx at idle speed >
150 ppm.
Toyota Aygo: NOx 264 mg/km (CF = 3.3). MIL on. OBD code P0420 active and
NOx at high idle speed > 150 ppm.
Ford Focus Euro 4: Active OBD code P000A active.
BMW 320i: NOx = 284 mg/km (CF = 4.7). Active OBD code 30EA.
Hyundai Tucson: NOx = 62 mg/km (CF = 0.8) Active OBD codes P0011 and
P0016.

High emitter:
The Euro 2 Peugeot 206 (without OBD system) with an average on-road NOx
emission of 1267 mg/km did not meet the Dutch PTI emission criteria because
the CO concentration at high idle speed was 0.41 – 0.88 vol% and higher than
the effective limit value of 0.39 vol%. An additional measurement of the NOx
concentration at idle speeds indicated high values (NOx @ low idle speed > 50 ppm
and at high idle speed > 150 ppm).
Medium emitters:
Six vehicles with an elevated NOx emission (CF = 2 – 4) passed the Dutch PTI.
From these vehicles the MIL of the Toyota Aygo (CF = 3.3) was on and this vehicle
had an active OBD emission code; the NOx concentration at high idle speed was
more than 150 ppm.

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The Suzuki Wagon (CF = 2.0) and the BMW 3 (CF = 2.0) had active OBD emission
codes. The residual three vehicles (Fiat Punto, Citroen C5 and BMW 320 i) with
elevated NOx emission passed the PTI without any reporting of the OBD system.
Low emitters: Three out of 28 vehicles with a regular NOx emission (CF < 2) had
active OBD emission codes.
3.3

State of maintenance of the tested vehicles
In The Netherlands the registration of the maintenance history of a vehicle is not
mandatory. From most tested vehicles the maintenance file (a booklet) was stored
in the vehicle and (partially) completed. In addition all vehicle owners were
requested to deliver maintenance data and information.
In Table 3-3 a summary of the documented state of maintenance of all vehicles is
shown. All tested vehicles passed the mandatory periodic technical inspection in
the last 12 months before emission testing. During the lifetime of 19 vehicles all
required maintenance activities were executed (documents were complete and
up to date). From 11 vehicles maintenance activities were partly registered and
8 vehicles had no maintenance file.
Table 3-3: Maintenance history of the tested vehicles.

Documented state of maintenance
No data

Number of
vehicles
8

Partly documented

11

Fully documented

19

The documentation of the maintenance history of 50% of the on-road tested
vehicles was complete, 29% of the vehicles had a partial documented maintenance
history and 21% of the vehicles had no maintenance history documentation
3.4

On Board Diagnostic data
As part of the vehicle inspection the vehicle OBD system was read out. The OBD
tests were performed before the execution of the on-road emission test programme
of the vehicles. In Table 3-4 the OBD and MIL status of the tested vehicles are
reported.
Table 3-4: Overview diagnostic test results of petrol vehicles as received and tested.

Total number of tested vehicles
Number of vehicles without OBD system

38
5

Number of vehicles without active emission OBD fault codes

27

Number of vehicles with active emission OBD fault codes

7

Number of vehicles with burning MIL

1

In Table 3-5 the registered OBD codes and MIL status of the individual vehicle are
reported.

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Table 3-5: OBD details of vehicles with active OBD codes and MIL status.

Vehicle

Emission related OBD fault code

Suzuki Wagon R+

P0400 EGR system, P0130 Lambda sensor

VW Golf

17840 Banks 1 & 2 too lean, 17835 Idle emission not stable
P0420, Catalyst system efficiency below threshold bank 1. MIL on.

Toyota Aygo
BMW 3

2854 variable valve gear, sensor plausibility.
2783 hot-film air mass flow sensor
2865 variable valve gear, power limitation in limp home operating mode

Ford Focus Euro 4
BMW 320i

P000A Position of camshaft slow reaction
P30EA, DeNox catalytic converter, sulphurised

Hyundai Tucson

P011, P016, Camshaft and crankshaft positions

3.5

Three-way catalyst performances in cold and warm condition

3.5.1

Emissions at idle speed during warming up
At the start of every test program the three-way catalyst emission performance was
investigated in a warming up test at idle speeds. After having reached the light off
temperature the CO, C6H14 or NOx conversion starts and can be flawless at higher
operating temperatures. Typically first the CO conversion is completed, sometime
later followed by NOx conversion and it ends with C6H14 conversion.
Catalyst deterioration typically shows longer warming up times and imperfect
conversions. Inactive or worn catalysts are not able to convert the three elements
CO, C6H14 or NOx.
In Figure 3-10, Figure 3-11 and Figure 3-12 examples of warming up tests of the
next three different vehicles are shown:
Figure 3-10 Mercedes C180 Euro 4 @ 193,458 km with well working catalyst.
Figure 3-11 Peugeot 206 Euro 3 @ 250,611 km with normal deteriorated catalyst.
Figure 3-12 Peugeot 206 Euro 2 @ 314,852 km with defective catalyst.

Figure 3-10: Warming up test of a Mercedes C180 (Euro 4) @ 193,458 km at low and high idle
speeds (after cold start). Within 100-120 seconds CO, NOx and C6H14 concentrations
reduce towards zero.

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Figure 3-11: Warming up test of a Peugeot 206 (Euro 3) @ 250,611 km at low and high idle
speeds (after cold start). CO and NOx concentrations reduce near zero within 240 and
300 s seconds and the C6H14 concentration is near zero at 1280 seconds after the
warming up at high idle speed.

Figure 3-12: Warming up test of a Peugeot 206 (Euro 2) @ 314,852 km with defective three-way
catalyst at low and high idle speeds (after cold start). CO and NOx concentrations at
low idle speed are 0.71 vol% and 82 ppm. The C6H14 concentration reduces during
the warming up from 350 to 170 ppm.

In Table 3-6 the rate of emission reduction (cold versus warmed up catalyst) and
the stabilization (or activating) times of the three vehicles are reported. Catalyst
deterioration is measured by lower reduction rates and longer stabilization times.

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Table 3-6: Rate of emission reduction cold versus warm engine at low idle speed.

Vehicle
Mercedes C180 Euro 4

Stabilization time [s]
CO
120

C6H14
120

Reduction rate [%]

NOx
100

CO
100

C6H14
100

NOx
100

Peugeot 206 Euro 3

240

1280

300

95

75

100

Peugeot 206 Euro 2

1200

1200

1200

0

19

11

In addition the emission reduction rates of the low idle speed tests were calculated
on the basis of the measured emission concentrations (Conc). The definition of the
emission reduction rate is:
Emission reduction rate = 1 - Conc @ warm engine / Conc @ cold engine
In Figure 3-13, Figure 3-14 and Figure 3-15 the CO, C6H14 and NOx reduction rates
of all tested vehicles measured during the warming up of the three-way catalysts
are shown. Except one vehicle the reduction rates are above 40% but most are
above 80%. The CO, C6H14 and NOx reduction rates of the three-way catalyst of the
Euro 2 Peugeot 206 were 0%, 20% and 10%.
Some vehicles had a decreased CO reduction rate at low idle speed.
This was mainly caused by relative rich air-fuel mixtures (lambda < 0.985).
In idle speed tests with a cold start followed by a warming up of approximately
20 minutes at low idle speed the CO, THC and NOx reduction rates (based on the
measured concentrations) of the majority of the tested vehicles is above 80%. For
some vehicles this reduction rate was 50 – 80%. Only one vehicle had a very low
emission reduction rate of 0-20%.

Figure 3-13: CO reduction rates at low idle speed during warming up.

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Figure 3-14: C6H14 reduction rates at low idle speed during warming up

Figure 3-15: NOx reduction rates at low idle speed during warming up.

3.5.2

On road tests with cold and warm start
In Table 3-7 the on road CO2, NOx and NH3 emission test results with cold and
warm start of four different vehicles are reported.
For three tested vehicles the CO2 emission in tests with cold start is 6 to 10% higher
than with warm start. For the Citroen C2 the CO2 emission of the test with warm
start was 11% higher than with cold start.
For the Volvo S60 the NOx emission of the tests with cold start is higher than with
warm start, for the Mazda 5 there is no difference and surprisingly the average cold
start NOx emission of the VW Polo and Citroen C2 is lower than with warm start.
Table 3-7: On road emission test results with cold and warm engine start (road trip of 48-50 km).

Vehicle

CO2

NOx

NH3

CO2

[g/km]

[mg/km]
Cold start

[mg/km]

[g/km]

NOx

NH3

[mg/km]
[mg/km]
Warm start

VW Polo

130.9

37.9

21.0

114.3

46.9

15.3

Volvo S60
Mazda 5

198.5
188.3

158.3
36.2

48.8
27.6

180.4
176.5

103.2
35.5

38.3
8.7

Citroen C2

148.4

86.3

10.4

155.3

134.0

7.9

Further analysis of NOx emissions with cold and warm start is executed in section
4.4.

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3.5.3

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Emissions with different driving styles
Four vehicles were tested with a regular and a sportive driving style; In Table 3-8
the average CO2, NOx and NH3 test results of two vehicles are reported.
With a sportive driving style the measured CO2 emissions were 6 to 18 % higher,
the NOx emission was 19 to 260 % higher and the NH3 emission was 2 to 88 %
higher than with a regular driving style.
Table 3-8: Average on road emission test results with regular and sportive driving styles.

Vehicle

3.6

CO2

NOx

NH3

CO2

NOx

NH3

[g/km]

[mg/km]
Regular

[mg/km]

[g/km]

[mg/km]
Sportive

[mg/km]

Ford Focus

143.1

241.9

20.3

168.9

313.1

24.5

Citroen C2
Opel Corsa

155.3
158.3

134.0
17.4

7.9
16.1

182.5
174.7

159.7
62.7

11.4
16.4

Hyundai Tucson

205.2

62.1

13.8

217.9

109.6

25.9

Effects of vehicle repairs on emission levels
In order to investigate the effect of vehicle repairs four tested vehicles with elevated
NOx emissions or active OBD failure codes were diagnosed by one of the
associated dealers. It was decided to carry out defined repairs and after repair the
vehicles were retested on the road. In this section detailed information and analysis
of the repairs and emission test results are presented and discussed.

3.6.1

Summary vehicle repairs
The NOx reductions of these repaired vehicles are summarized in Table 3-9. Three
repairs resulted in a substantial on-road NOx reduction of 37 – 93%. The exchange
of the lambda sensors of the fourth vehicle (Fiat Punto) didn’t reduce the on-road
NOx emission, probably the elevated NOx emission was caused by deterioration of
the catalyst (which was not exchanged).
With current Dutch PTI emission test procedures and criteria the Suzuki Wagon and
Toyota Aygo pass. With excessive preconditioning the Peugeot 206 with worn
catalyst probably also passes the PTI emission test. The elevated NOx emission of
the Fiat Punto (CF 3.0) cannot be detected with OBD information or the current PTI
emission test.
Table 3-9: NOx reduction of four repaired petrol vehicles.

Vehicle

NOx
as received

NOx
after repair

NOx
reduction

[mg/km]

[mg/km]

[%]

Suzuki Wagon R
Fiat Punto

297
256

187
250

37
2

Peugeot 206

1267

87

93

Toyota Aygo

264

20

92

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3.6.2

Details of the four repaired vehicles

3.6.2.1

Fiat Grande Punto Euro 4 @ 156,604 km.
At first the Fiat Grande Punto was tested in two on-road tests in the condition as
received. In a next stage, six months later, two new lambda sensors (pre and post
catalyst) were installed because the lambda values seemed to deviate slightly (too
lean mixture) and the vehicle was retested.
Results OBD diagnose and PTI emission tests:
Upon receipt of the vehicle no OBD codes were active and the PTO CO
concentrations were well below the limit vales at lambda 1.00.
Emission test results before and after repairs:
In Table 3-10 an overview of the executed on road test results is given.
In the received vehicle condition without OBD fault codes the measured emission
in the two on-road tests with an average ambient temperature of 6 and 8 ⁰C was:
CO2 145.7 and 151.3 g/km, NOx 277.8 and 234.5 mg/km and NH3 25.5 and 23.7
mg/km. The measured CO concentration al low idle speed was 0.18 vol% (@
lambda 1.00). At high idle speed the measured lambda was 1.00 and the CO
concentration was 0.12 vol%. With these PTI emissions the vehicle passes the
PTI test.
Results of the retest, after replacement of the lambda sensors: The measured
emission in the two on-road tests with an average ambient temperature of 6 and 8
⁰C was: CO2 143.4 and 145.3 g/km, NOx 229.4 and 270.7 mg/km and NH3 21.0 and
24.5 mg/km. The measured CO concentration al low idle speed was 0.33 vol% (@
lambda 1.01). At high idle speed the measured lambda was 1.00 and the CO
concentration was 0.15 vol%. With these PTI emissions the vehicle passes the PTI
test.
Table 3-10: On road test results of the Fiat Grande Punto (Euro 4 @ 156,604 – 163,798 km) with
old and new lambda sensors.

Vehicle condition
Used lambda sensors 1

Dist.

Tamb.

Av.
speed

CO2

NOx

NH3

[km]
48.4

[⁰C]
6.0

[km/h]
35.5

[g/km]
145.7

[mg/km]
277.8

[mg/km]
25.5

Used lambda sensors 2

48.4

7.8

32.9

151.3

234.5

23.7

New lambda sensors 1
New lambda sensors 2

49.5
49.3

22.0
18.0

39.1
41.7

143.4
145.3

229.4
270.7

21.0
24.5

Effect of repairs on the NOx emission of the Fiat Grande Punto:
The measured on-road NOx emission of the Fiat Grande Punto with used lambda
sensors was on average 256 mg/km and the NOx emission of the vehicle with new
lambda sensors was on average 250 mg/km. In the on road emission tests with
used and new lambda sensors the NOx emission was on a similar level.
In Table 3-11 the PTI 4-gas tests results of the Fiat Punto are reported.
The vehicle passed in all PTI tests the CO and lambda emission criteria. The NOx
concentrations at low and high idle speed were significantly lower with new lambda
sensors (at low idle speed 136 and 9 ppm versus 11 and 1 ppm and at high idle
speed 59 and 106 ppm versus 5 and 7 ppm).

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Table 3-11: PTI test results of the Fiat Grande Punto (Euro 4 @ 156,604 – 163,798 km) with old
and new lambda sensors.

Low idle speed
Vehicle condition
Used lambda sensors 1

High idle speed

CO

NOx

Lambda

CO

NOx

Lambda

[vol%]
0.21

[ppm]
136

[-]
0.993

[vol%]
0.04

[ppm]
59

[-]
0.993

Used lambda sensors 2

0.10

9

1.001

0.12

106

0.996

New lambda sensors 1
New lambda sensors 2

0.35
0.31

11
1

1.005
1.006

0.15
0.15

5
7

0.998
0.998

Conclusion of repairs of the Fiat Grande Punto:
The elevated NOx emission of the Fiat Grande Punto was investigated and the
vehicle was tested with old and new lambda sensors. With old and new lambda
sensors the on road NOx emission was on average similar (256 versus 250 mg/km).
From these results it can be concluded that the elevated NOx emission of the Fiat
Grande Punto was not caused by defective lambda sensors.
Furthermore, the measured NOx concentration at low and high idle speeds with new
lambda sensors was on average significantly lower than with old lambda sensors
(73 versus 6 ppm and 83 versus 6 ppm).
The fact that installation of two new lambda sensors resulted in unchanged on road
NOx emissions and lower NOx concentrations at idle speeds indicates that on road
NOx emissions of petrol vehicles are not related to the NOx concentrations at low
and high idle speed.
Additional analysis NOx emissions of the Fiat Grande Punto:
The Fiat Grande Punto is not equipped with an EGR-system so NOx control is
mainly done by the three-way catalyst. Because the elevated NOx emission is not
caused by a defective lambda sensor, degradation of the performance of the
three-way catalyst is likely the cause, however this was not further investigated.
3.6.2.2

Suzuki Wagon R+ Euro 3 @ 222,134 km
Upon receipt of the vehicle, OBD codes P0130 (lambda sensor) and P0400
(EGR-system) appeared to be active. At first the Suzuki Wagon R+ was tested
in this received condition. The measured lambda at low idle speed was 1.14.
After a cold start and with accelerations the vehicle smoked heavily, white and
blue plumes were emitted.
In order to understand the effect on emissions of the pending OBD codes, the
vehicle was offered to the Suzuki dealer and the EGR valve was repaired after
which the vehicle was retested. In a second repair round, the intake and exhaust
systems were repaired and in this condition the vehicle was tested on the road
again.
Emission test results before and after repairs:
In Table 3-12 and Table 3-13 an overview of the test results is given.
With the two active OBD fault codes the measured emission in the on-road test with
an average ambient temperature of 8.5 ⁰C was: CO2 140.7 g/km, NOx 296.2 mg/km
and NH3 32.8 mg/km. The measured lambda al low idle speed was 1.09. At high
idle speed the measured lambda was 1.01 and the CO concentration was 0.02 %.
With these PTI emissions the vehicle passed the PTI emission test.

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After repair of the blocked EGR valve actuator the measured emissions in the
on-road test with an average ambient temperature of 14 ⁰C were: CO2 126.7 g/km,
NOx 229.8 mg/km and NH3 34.1 mg/km. OBD code P0400 was not active anymore.
However, lambda at low idle speed was still too high (1.12). Again the vehicle was
offered to the Suzuki dealer and a second repair round was executed. After repair
of the leakages in the intake and exhaust system (new throttle valve body gasket,
new spark plugs and a new exhaust muffler) the OBD codes were not active
anymore and the measured lambda al low idle speed was 0.99.
The measured emissions in the on-road test with an average ambient temperature
of 15 ⁰C were: CO2 128.3 g/km, NOx 187.0 mg/km and NH3 63.3 mg/km.
Table 3-12: PTI test results of the Suzuki Wagon (Euro 3 @ 222,134 – 222,335 km)

Low idle speed

High idle speed

Vehicle condition

CO
[vol%]

NOx
[ppm]

Lambda
[-]

CO
[vol%]

NOx
[ppm]

Lambda
[-]

As received

0.15

12

EGR valve repaired
Repair intake manifold
and exhaust, new spark
plugs.

0.18

1

1.09

0.02

25

1.01

1.17

0.09

7

1.01

0.21

0

0.99

0.01

10

1.00

Table 3-13: On road test results of the Suzuki Wagon (Euro 3 @ 222,134 – 222,335 km)

Vehicle condition

Distance
[km]

Av. speed
[km/h]

CO2
[g/km]

NOx
[mg/km]

NH3
[mg/km]

As received

48.0

44.4

140.7

296.2

32.8

EGR valve repaired

48.4

44.8

126.7

229.8

34.1

Repair leakage intake
manifold and exhaust, new
spark plugs.

48.0

46.3

128.3

187.0

63.3

Effect of repairs on the NOx emission of the Suzuki Wagon:
The measured on-road NOx emission of the Suzuki Wagon R+ ‘as received’ was
58% higher than the NOx emission of the repaired vehicle (296.2 mg/km versus
187.0 mg/km). In both on road emission tests the NOx emissions was on a similar
or lower level as the type approval limit value. In all executed PTI 4-gas tests the
vehicle passed. If the OBD P-codes would be part of the pass/fail criteria of the PTI
this vehicle would have failed.
3.6.2.3

Peugeot 206 Euro 2 @ 251,836 km
At first the Peugeot 206 with an odometer reading of 251,836 km was tested in the
received condition. In addition the vehicle was repaired and the vehicle was
retested. “According to the RDW database, the indicated mileage of 251,836 km
was rated as ‘not logic’. By using the odometer report the corrected mileage
appeared to be 314,852 km.
Results intake, OBD diagnosis and PTI emission tests:
During the intake the vehicle seemed to run without major failures because the
engine was running smoothly in a 35 km trip to the test location performed by
TNO personnel.

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The OBD system of this Euro 2 vehicle was not available/accessible. During the
inspections at the intake of the vehicle no major failures were detected. Some small
leaks in the exhaust system were repaired with gum.
In the PTI emission test the CO concentration at low idle speed was 0.00 vol%
(@ lambda 1.03) and at high idle speed 0.78 vol% (@ lambda 1.02). The vehicle
failed in this PTI test.
Three months earlier the vehicle passed the PTI in a regular Dutch PTI station.
The person in charge of the PTI station was interviewed and explained that the
vehicle passed the PTI emission test because the vehicle was preconditioned in
a sportive road test followed by very high idle speed operation. Directly after this
preconditioning the CO emission at high idle speed was shortly less than 0.30 vol%
and as a result the vehicle passed the test.
Emission test results before and after repairs:
The unmodified vehicle was tested on the road and the measured emission, at an
average ambient temperature of 19 ⁰C was: CO2 134.8 g/km, NOx 1267 mg/km and
NH3 37.0 mg/km. The PTI test was repeated and the CO concentration at low idle
speed was 0.00 vol% (@ lambda 1.03). At high idle speed the measured lambda
was 1.01 and the CO concentration was 0.80 vol%. With these PTI emissions the
vehicle failed in the PTI.
A new three-way catalyst (replacement version) and exhaust system were installed
by a local Peugeot dealer and the vehicle was preconditioned over a distance of
70 km and retested. After installation of the new three-way catalyst and exhaust
system, the measured on road emission at an average ambient temperature of
21.0 ⁰C was: CO2 139.6 g/km, NOx 167.1 mg/km and NH3 29.9 mg/km. In this on
road test, at a speed of around 80 km/h, an unexpected high NOx emission was
measured. Furthermore, the lambda control seemed not very stable.
The PTI test was repeated and the CO concentration at low idle speed was
0.01 vol% (@ lambda 1.01). At high idle speed the measured lambda was 1.00
and the CO concentration was 0.01 vol%. With these PTI emissions the vehicle
passed the PTI criteria.
In addition to the first repair round, a new lambda sensor was installed and the
vehicle was tested again.
The measured on road emission with an average ambient temperature of 17 ⁰C
was: CO2 138.6 g/km, NOx 87.0 mg/km and NH3 28.3 mg/km.
The PTI test was repeated and the CO concentration at low idle speed was 0.00
vol% (@ lambda 1.00). At high idle speed the measured lambda was 1.00 and the
CO concentration was 0.00 vol%. With these PTI emissions the vehicle passed the
PTI test.
Table 3-14: PTI test results of the Peugeot 206 (Euro 2 @ 314,852 – 315,849 km).

Low idle speed

High idle speed

CO

NOx

Lambda

CO

NOx

Lambda

Vehicle condition
As received

[vol%]
0.00

[ppm]
101

[-]
1.029

[vol%]
0.78

[ppm]
275

[-]
1.016

New three-way catalyst

0.01

0

1.005

0.01

83

1.003

New lambda sensor

0.00

5

1.003

0.00

0

1.000

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Table 3-15: On road test results of the Peugeot 206 (Euro 2 @ 314,852 – 315,849 km)

Vehicle condition

Distance
[km]

Av. speed
[km/h]

CO2
[g/km]

NOx
[mg/km]

NH3
[mg/km]

As received

48.0

45.1

134.8

1266.5

37.0

New three-way catalyst
New lambda sensor

48.7
48.1

42.8
45.4

139.6
138.6

167.1
87.0

29.9
28.3

Analysis Peugeot 206:
The measured on-road NOx emission of the Peugeot 206 ‘as received’ was
14.6 times higher than the NOx emission of the repaired vehicle with new
three-way catalyst and new lambda sensor (1266.5 mg/km versus 87.0 mg/km).
In the initial PTI high idle speed test the CO emission exceeded the limit value of
0.3 vol% and consequently the vehicle failed in the PTI.
Installation of a new three-way catalyst resulted in a NOx reduction of 1099 mg/km
(-87%) and in a second repair round the installation of a new lambda sensor
resulted in a further NOx reduction of 80 mg/km (-6.3%). With the new catalyst the
vehicle had a PTI pass and the new NOx sensor improved the lambda control and
NOx emissions substantially.
The preconditioning as used during the regular PTI test heavily determined the
actual operating temperatures and CO conversion rates of the three-way catalyst
and the PTI emission test results.
Effect of repairs on the NOx emission of the Peugeot 206:
In the received condition (with a worn catalyst) the average on road NOx emission of
the Peugeot 206 was 1267 mg/km and in the PTI emission test the vehicle failed
because the measured CO concentration at high idle speed was 0.78 vol%.
Installation of a new three-way catalyst and lambda sensor resulted in an average
on road NOx emission of 87 mg/km (reduction of 93 %) and a PTI pass.
3.6.2.4

Toyota Aygo Euro 4 @ 206,334 km
At first the Toyota Aygo with 206,334 km was tested in the received condition.
In addition the vehicle was repaired and the vehicle was retested.
Results intake, OBD diagnosis and PTI emission tests:
During the intake the vehicle ran smoothly but the MIL was burning and
OBD code P0420 (Catalyst system efficiency below threshold bank 1) was active.
In the first PTI emission test the CO concentration at low idle speed was 0.04 vol%
(@ lambda 1.00) and at high idle speed 0.26 vol% (@ lambda 1.00). The vehicle
passed this PTI test.
Emission test results before and after repairs:
The unmodified vehicle was tested on the road and the measured emission at an
average ambient temperature of 19 ⁰C was: CO2 120.8 g/km, NOx 264.3 mg/km /
and NH3 9.5 mg/km.
The PTI test was repeated and the CO concentration at low idle speed was 0.14
vol% (@ lambda 1.00). At high idle speed the measured lambda was 1.00 and the
CO concentration was 0.49 vol%. With these PTI emissions the vehicle had a PTI
fail.
A new three-way catalyst (replacement version) was installed by a local Toyota
dealer and the vehicle was preconditioned over a distance of 120 km and retested.

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The vehicle ran without an active OBD code and the MIL was off. After installation
of the new three-way catalyst the measured on road emission at an average
ambient temperature of 22.0 ⁰C was: CO2 118.6 g/km, NOx 19.9 mg/km and NH3
21.0 mg/km.
Table 3-16: PTI test results of the Toyota Aygo (Euro 4 @ 206,334 – 209,373 km).

CO

Low idle speed
NOx
Lambda

CO

High idle speed
NOx
Lambda

Vehicle condition

[vol%]

[ppm]

[-]

[vol%]

[ppm]

[-]

As received 1
As received 2

0.04
0.14

0
0

1.00
1.00

0.26
0.49

184
381

1.00
1.02

New three-way catalyst 1

0.04

0

1.00

0.00

0

1.00

New three-way catalyst 2

0.03

0

1.00

0.00

0

1.00

Table 3-17: On road test results of the Toyota Aygo (Euro 4 @ 206,334 – 209,373km).

Vehicle condition

Distance

Av. speed

CO2

NOx

NH3

As received

[km]
48.2

[km/h]
45.0

[g/km]
120.8

[mg/km]
264.3

[mg/km]
9.5

New three-way catalyst

49.4

43.4

118.6

19.9

21.0

Analysis Toyota Aygo:
The measured on-road NOx emission of the Toyota Aygo ‘as received’ was
13.3 times higher than the NOx emission of the repaired vehicle with new three-way
catalyst and new lambda sensor (264 mg/km versus 20 mg/km).
In the initial PTI high idle speed test the CO emission was lower and higher than
the limit value of 0.3 vol% and consequently the vehicle failed in the PTI.
Installation of a new three-way catalyst resulted in a NOx reduction of 244 mg/km
(-92. With the new catalyst the vehicle had a PTI pass and the on-road NOx
emissions decreased from 264 to 20 mg/km.
Effect of repairs on the NOx emission of the Toyota Aygo:
In the received condition (with a worn catalyst) the average on road NOx emission
of the Toyota Aygo was 264.3 mg/km and in one PTI emission test the vehicle failed
because the measured CO concentration at high idle speed was 0.49 vol%.
Installation of a new three-way catalyst and lambda sensor resulted in an average
on road NOx emission of 20 mg/km (reduction of 92 %) and a PTI pass.

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Analyses of test results
In this chapter the test results of the chassis dynamometer program of 2018
[TNO 2018] and the on-road test program of 2020 are combined and analysed.

4.1

NOx emissions

4.1.1

Average NOx emissions of the (38 + 12) tested vehicles
In Table 4-1 the average NOx emissions of the chassis dynamometer test program
of 2018 and of the on road test program of 2020 and the total, urban, rural and
motorway average results of both test programs are reported.
The average NOx emission of the 50 tested vehicles is 200 mg/km (CF= 1.74).
The total average NOx emission of the chassis dynamometer program with two
Euro 4 high emitting vehicles is 305 mg/km (CF = 3.44) and substantial higher
than the total average NOx emission of 166 mg/km (CF = 1.21) of the on road test
program with one Euro 2 high emitting vehicle.
When the NOx emission of the three high emitting vehicles is assumed at an
average value (related to the Euro class) of 100 and 250 mg/km, the total average
NOx emissions of the 2018 and 2020 test programs are 130 and 144 mg/km.
This indicates that the average test results of the chassis dynamometer test
program and the on-road test program are similar.
Table 4-1: Overview of average NOx emission (total, urban, rural and motorway) of the tested
vehicles and the test results of the 2018 chassis dynamometer test program.

Number

Total

Total

Urban

Rural

Motorway

of

cold

warm

Warm

warm

warm

vehicles

[mg/km]

2018

12

299

305

383

177

379

2020

38

-

166

206

119

155

Total

50

-

200

248

133

209

In Table 4-2 an overview of the very low, low, medium and high NOx emitting
vehicles per test program is reported. In total 31 out of 50 vehicles have a
conformity factor below 1 and 9 vehicles have elevated emissions (CF = 1–2).
Seven vehicles have medium emissions (CF is 2-5 and NOx < 500 mg/km) and
3 vehicles are high emitters with an average NOx emission of 1191 mg/km.
In Table 4-3 an overview of shares of the very low, low, medium and high NOx
emitting vehicles per test program is reported. In the first test program of 2018
1 out of 6 vehicles (16.7 %) had a very high NOx emission and 50% were very low
emitters. In the second test program od 2020 1 out of 38 vehicles (2.6%) had a very
high NOx emission and 66% were very low emitters. The shares of vehicles with
elevated and medium NOx emissions were in both test programs nearly similar.

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Table 4-2: Overview of low, medium and high NOx emitting vehicles.

Category
Very low emitter
Elevated
Medium emitter
High emitter

CF range [-] and NOx

Number of vehicles

< 1.0

2018
6

2020
25

Total
31

1.0 - 2.0

2

7

9

2

5

7

2

1

3

12

38

50

2.0 – 5.0 and
NOx < 500 mg/km
> 5.0 or
NOx > 500 mg/km

Total

Table 4-3: Overview of relative shares of low, medium and high NOx emitting vehicles.

Category

CF range [-] and NOx

Share of vehicles [%]
2018

2020

Total

Very low emitter
Elevated

< 1.0
1.0 - 2.0

50
16.7

66
18

62
18

Medium emitter

2.0 – 5.0 and
NOx < 500 mg/km

16.7

13

14

High emitter

> 5.0 or
NOx > 500 mg/km

16.7

3

6

100

100

100

Total

Figure 4-1 shows the emission limit values incl. deterioration (lines) and average
test results per Euro class of 38 on road tested petrol vehicles with high mileages
(open triangles) and the total set of 50 (38 + 12) vehicles (filled up triangles).
The average NOx test results of the chassis dynamometer and on road test program
are similar for Euro 3 and 5 vehicles but deviate for Euro 2 and 4 vehicles because
2 Euro 4 vehicles (1103 and 1203 mg/km) were high emitters in the chassis
dynamometer test program and 1 Euro 2 vehicle (1,267 mg/km) in the on road test
program.

Figure 4-1: Emission limit values incl. deterioration and average test results per Euro class of
38 on road tested (open triangles) petrol vehicles with high mileages and the total set
of 38 + 12 vehicles (filled triangles).

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Analysis deterioration NOx emission of older petrol vehicles.
On the basis of current Dutch NOx emission factors (see section 1.1), the applied
road test of 50.8 km (see section 2.4.2) and the division of the 50 tested vehicles
over the Euro classes the average NOx emission of the 50 tested vehicles in relative
new condition (max. 50,000 km) would be 95 mg/km. In this test program the
average measured NOx emission of the 50 tested vehicles is 200 mg/km and this
is 2.1 times higher than vehicles with a low mileage.
Analysis relative cumulative NOx shares related to the total NOx emission.
In Figure 4-2 the cumulative NOx share of the 50 tested vehicles as function of
the vehicle share is reported. The NOx contribution of the three high emitting
vehicles (6.0 % of the tested fleet) to the total average NOx emission of the
50 tested vehicles is 35.8 %.

Figure 4-2: Cumulative NOx share as function of the share of 50 tested vehicles.

4.1.2 Detailed NOx emissions
 In Figure 4-3 the average on road NOx emissions of all tested vehicles are
reported, one could recognise two groups of vehicles: most vehicles have NOx
emissions below 400 mg/km. The NOx emission of the three high emitters is in
the range of 1,103 to 1,267 mg/km.
 In Figure 4-4 the relationship of vehicle age and the NOx conformity factors are
reported. The figure shows that there is no correlation between NOx emission
and vehicle age.
 In Figure 4-5 and Table 4-4, Table 4-5 and Table 4-6 the NOx emissions of the
tested vehicles per emission class are reported. The figure shows that there is
no correlation between NOx emission and emission class.
 In Figure 4-6 the NOx conformity factors per Euro class are reported. There is
no correlation between the NOx conformity factor and Euro class.

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Figure 4-3: Average NOx emissions of the 38 + 12 tested petrol vehicles with high mileages.

Figure 4-4: NOx conformity factors of 38 + 12 petrol vehicles with high mileages related to vehicle
age.

Figure 4-5: Average measured on road NOx emission per Euro class of 38 + 12 petrol vehicles
with high mileages.

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Figure 4-6: NOx conformity factors of 38 +12 petrol vehicles per Euro class with high mileages.
Table 4-4: Average on road NOx emission per emission class of 38 tested vehicles

Euro 1

Euro 2

Euro 3

Euro 4

Euro 5

Euro 6

No. of vehicles

-

8

9

16

4

1

Av. NOx [mg/km]

-

382

140

95

113

35

Table 4-5: Average chassis dynamometer NOx emission per emission class of 12 tested vehicles

Euro 1

Euro 2

Euro 3

Euro 4

Euro 5

Euro 6

No. of vehicles

-

1

3

7

1

-

Av. NOx [mg/km]

-

134

107

456

17

-

Table 4-6: Average NOx emission in mg/km per emission class of all 50 tested vehicles

Euro 1

Euro 2

Euro 3

Euro 4

Euro 5

Euro 6

No. of vehicles

-

9

12

23

5

1

Av. NOx [mg/km]

-

354

132

205

94

35

On the three high NOx emitting vehicles:
The Euro 2 Peugeot 206 had an average on road NOx emission of 1267 mg/km. As
reported in paragraph 3.7.2 after two repair rounds, the NOx emission decreased
further to 87 mg/km.
Both high emitting vehicles of the former TNO project (Fiat Punto and BMW 325
with NOx emission of 1103 and 1203 mg/km) mainly operated with a deviating
lambda control with an average lambda of 1.02. Under these conditions the CO
was very well oxidised in the PTI tests and the vehicles passed the PTI. However
the three-way catalyst didn’t reduce NOx with lean mixtures (lambda > 1). For a
proper NOx reduction in a three-way catalyst the average lambda must be around
0.99.

.

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Periodic Technical inspections
All 38 vehicles were tested according the Dutch PTI emission test procedure.
Thirty one vehicles passed the PTI because they had no active OBD emission
codes. The residual seven vehicles had active emission related OBD code and six
of these vehicles passed the PTI emission test.
One vehicle (the Euro 2 Peugeot 206) did not pass the PTI CO emission criteria at
high idle speed (CO concentration was 0.78 vol%). On the road the measured NOx
emission of this vehicle was 1267 mg/km.
When the PTI test results of the 12 vehicles of the chassis dynamometer test
program are added, one out of 50 vehicles had a PTI fail. The two high emitting
vehicles of the chassis dynamometer test program were not determined as a PTI
fail.
Are medium and high NOx emitters detected in the periodic technical inspection?
In this test program and the former test program [TNO 2018] the three high emitting
vehicles had a NOx emission in the range of 1103 to 1267 mg/km. Two were Euro 4
vehicles and they passed the PTI OBD and emission tests, the Euro 2 vehicle failed
because the CO concentration at high idle speed was more than 0.39 vol%.
The two Euro 4 vehicles had no active OBD failures. So the OBD systems of the
Euro 4 vehicles were not able to detect high NOx emissions.
The failing Euro 2 vehicle with high a NOx emission was not equipped with OBD
and was detected as a vehicle with three-way catalyst with low CO oxidation
performance.
Furthermore, the NOx volumetric concentrations are not measured in the current
PTI emission test and consequently the NOx reduction performance of the threeway catalyst cannot be judged.
From all OBD systems the OBD system of the Toyota Aygo only reported a
decreased efficiency of the three-way catalyst. As a prime example this OBD failure
corresponded with the on-road NOx emission of 264 mg/km (CF = 3.3). The OBD
system of the Toyota Aygo was able to detect a decreased catalyst efficiency.
The OBD system of the BMW 320i mentioned a sulphured Lean NOx catalyst
(NOx was 284 mg/km and CF = 4.7) but met the CO criteria of the PTI emission
test. Normally the Lean NOx catalyst is automatically regenerated by the emission
control system of the vehicle when the right conditions (mostly at higher vehicle
speeds) are present. The OBD system of the BMW 320i only indicated a certain
status of the Lean NOx catalyst.
Suzuki Wagon
The OBD system of the Suzuki Wagon mentioned a defective EGR system and
lambda sensor. After repair of the EGR system it resulted in a decrease of the onroad NOx emission.

4.3

Vehicle repairs
The NOx emission of three out of four repaired vehicles reduced very strong
(37, 92 and 93%).

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However, the indication for the repair was based on the on-road measured NOx
emission with simultaneous active OBD code (Suzuki Wagon and Toyota Aygo)
or a failing 4-gas PTI emission test (Peugeot 206).
The repair of the Fiat Punto (new lambda sensors) had no significant effect on
the NOx emission. This is typically an example of a vehicle with an increased NOx
emission without having failures of the OBD system or too high CO emissions in
the PTI emission test.
4.4

Emissions with cold and warm engine starts
Four vehicles were tested in road trips (49 km) with cold and warm starts. In order
to investigate the possible cold start effects the mass emissions of the first 7.2 km
of these trips were calculated. In Table 4-7 the CO2, NOx and NH3 mass emissions
of the first 7.2 km of road tests with cold and warm start are reported.
For the Volvo and VW Polo the CO2 emission of the first 7.2 km with a cold start are
higher than with a warm start and for the Mazda and Citroen it was the other way
around. Only the Mazda 5 had a higher NOx emission with cold start than with a
warm start. Apparently, fixed single road trips that are executed by different drivers
with different ambient conditions resulted in a large spread in emission levels.
All tests with cold start had higher NH3 emission than with a warm start.
In order to have a more clear view on on-road emission tests with cold and warm
start a more dedicated test program with a higher number of tests is needed.
Table 4-7: Mass emissions of the first 7.2 km of a road trip

Cold start

Warm start

CO2

NOx

NH3

CO2

NOx

NH3

[g]

[mg]

[mg]

[g]

[mg]

[mg]

Volvo S60

2011

1200

656

1677

1355

488

VW Polo

1493

449

390

1135

673

340

Mazda 5

1732

868

471

1768

668

39

Citroen C2

1466

297

204

1513

609

75

4.5

Performance PTI emission test

4.5.1

Properties and analysis of the current PTI emission tests
The European Directive 2014/45/EC and the Dutch vehicle regulation
(Wegenverkeerswet, Regeling Voertuigen) for periodic technical inspections (PTI)
describe for positive ignited engines an emission test at low and high idle speed.
In this test the CO, THC, CO2 and O2 volumetric concentrations are measured and
lambda is calculated on the basis of these measured concentrations.
The applicable CO limit values are meant to check the oxidation performance of the
catalyst. There is no HC limit value, so the HC oxidation performance of the catalyst
is not checked. Furthermore the NOx concentration is not measured because it is
not prescribed. Consequently the NOx reduction performance of the three-way
catalyst cannot be checked.
By means of a lambda measurement at high idle speed the functionality of the
lambda control is checked. At high idle speed lambda must be in the band of
0.97-1.03.

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Analysis of the preconditioning of the engine and three-way catalyst in a current
4-gas test:
Execution of PTI tests are defined with warm engine and the criteria for a warm
engine are:
- Test trip with active cooling fan.
- Lubricant > 80 °C.
- 3 minutes with a minimum engine speed of 3000 rpm.
These three criteria of a warm engine will result in different conditions of the engine
and temperature of the three-way catalyst in the PTI emission test.
In Figure 4-7 an example of a low and high idle speed test is shown. The HC and
NOx concentrations vary in time because the temperature of the three-way catalyst
is, by nature, not stable and the conversion rate of the three-way catalyst is, among
others, temperature dependent.
In the current PTI test procedure the sequence of the low and high idle speed test,
durations of preconditioning, stabilisation and measuring times are not specified.
Consequently the PTI emission test is very undefined with a random character.
Furthermore this may result in a forced execution of the PTI test (with relatively high
catalyst temperatures) obtaining most favourite conditions of the engine and/or
catalyst.

Figure 4-7: Low and high idle speed tests with warm engine of a Fiat Punto (Euro 4). Emission
concentrations vary in time because the three-way catalyst cools down at low idle
speed and warms up at high idle speed.

The nature of the criteria for a warm engine are defined as minimum cases.
However the conversion rate of a catalyst increases with increasing temperatures
and with current test criteria one is allowed to precondition the catalyst to a
relatively high temperature (i.e. a test trip with high engine speeds or very high idle
speeds).

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In order to test with more realistic catalyst temperatures the preconditioning criteria
of the PTI test must be extended with:
-

A maximum vehicle speed (i.e. 80 km/h) with maximum engine speeds of
3200 rpm.
A maximum engine speed for warming up at high idle speed (i.e. 3200 rpm)

Analysis of the measuring time of a 4-gas test.
Due to a lack of a defined measuring time in the European Directive and national
PTI regulation the 4-gas test is practically a momentary check (or spot check).
Consequently the vehicle passes/fails on the basis of a momentary result.
Analysis of the test sequence of a 4-gas test.
The European Directive and national regulation doesn’t prescribe a test sequence
and consequently the low and high idle speed tests can be randomly executed with
a random preconditioning of both tests. In case of a prescribed sequence (i.e. 1.
preconditioning, 2, low idle speed test and 3. high idle speed test) PTI tests can be
executed with more defined and realistic test conditions.
Analysis of the CO limit values of a 4-gas test
From the measured CO concentrations at low and high idle speed (see Figure 3-7
and Figure 3-8) only one vehicle did not meet the CO emission PTI limit value of
0.30 vol% at high idle speed. This Peugeot 206 had an average on road NOx
emission of 1267 mg/km. In this specific case of the Peugeot 206 the CO oxidation
and NOx reduction performances of the three-way catalyst were near zero. On the
contrary the two high emitting vehicles (BMW and Fiat) of the former research
program [TNO 2018] passed the PTI (with sufficient CO oxidation performance but
had a similar NOx emission as the Peugeot 206. These results indicate that the CO
reduction performance of a three-way catalyst is not related to the NOx emission
reduction performance.
Analysis of the lambda limit values of a 4-gas test:
The current allowed lambda window in the high idle PTI test is 0.97 to 1.03. This
allowed lambda window is wider than the window of actual lambda values of the
tested vehicles in this test program. For all well operating three-way catalysts the
lambda values at high idle speed were in the range of 0.990 – 1.005. For the
Peugeot 206 and Toyota Aygo with worn and deteriorated three-way catalyst the
lambda values at high idle speed were 1.016 and 1.025.
If the PTI lambda limit value band will be tightened to 0.98 to 1.00 it is expected that
more vehicles with elevated emissions will not pass the PTI.
4.5.2

NOx concentrations in low and high idle speed tests
In this test program the NOx concentration at low and high idle speed of all tested
vehicles was measured. In Figure 4-8 the on-road NOx emission of the 38 road trips
as function of the measured NOx concentration at low idle speed is plotted and in
Figure 4-9 as function of the measured NOx concentration at high idle speed. Both
NOx concentrations have a very poor correlation with the on-road NOx emission.

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Figure 4-8: On-road NOx emission of 38 tested vehicles as function of the NOx concentration at low
idle speed.

Figure 4-9: On-road NOx emission of 38 tested vehicles as function of the NOx concentration at
high idle speed.

4.6

Quality of the measured NOx concentrations
The quality of the NOx concentrations measured with MEMS is validated from
comparisons to chassis dynamometer measurements of a Euro 6 Volkswagen
Polo petrol vehicle. This vehicle has an odometer reading of 175,000 km and
EN 228 trade fuel (E10 grade) was applied. Two CADC tests with cold start tests
and two CADC tests with warm start tests were performed, of which the details are
described in Appendix A and B.
In Figure 4-10 the cumulative NOx concentrations of these tests are shown.

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Figure 4-10: Cumulative NOx concentrations of the two cold start (top panels) and two warm start
(bottom panels) chassis dynamometer tests. The purple line indicates the chassis
dynamometer results. The NOx concentration MEMS measurements are performed in
undiluted and diluted gas. The dilution factor is derived from the O2 concentration of
the undiluted and diluted gas. NOx concentrations of undiluted gas is shown in dark
blue. This signal is corrected for NH3 interference by the diluted NH3 MEMS
measurement (light blue), which was first converted to undiluted NH3 concentrations.
NOx concentrations converted from the diluted gas and corrected for NH3 interference
are shown in green. The percentages show the deviation from the chassis
dynamometer NOx concentration.

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The NH3- and dilution-corrected NOx concentrations measured in diluted gas
deviate between -6.7% to 1.4% from the measured NOx concentrations in a
chemiluminescent NOx analyser. Undiluted and NH3-corrected NOx concentrations
deviate between 11.5% and 16.4% from these reference NOx concentrations.
The MEMS NOx sensor is strongly influenced by NH3 concentrations.
NH3 corrections are therefore necessary to correctly derive the NOx concentrations.
Since the MEMS NH3 sensor is expected to perform poorly in oxygen depleted gas,
NH3 needs to be measured from the diluted gas.
4.7

NH3 emissions
In this section the NH3 emission of the tested vehicles is analysed in more detail.
At first average test results of all tested vehicles are presented and in addition
detailed results per vehicle are investigated.

4.7.1

Average NH3 emissions
In Table 4-8 an overview of the average NH3 emissions (total and per road type) of
the 38 on road tested vehicles is reported (NH3 measurements were not executed
in the chassis dynamometer test program). The total average NH3 emission of the
38 on-road tested vehicles is 32.1 mg/km. On average the urban NH3 emission per
kilometre is 49.0 mg/km and more than two times higher than the NH3 emission on
rural roads and on the motorway.
Table 4-8: Overview of average NH3 emission (total, urban, rural and motorway) of the 38 on road
tested vehicles.

2020

Number

Total

Total

Urban

Rural

Motorway

of

cold

warm

warm

warm

warm

Vehicles

[mg/km]

[mg/km]

[mg/km]

[mg/km]

[mg/km]

38

-

32.1

49.0

22.2

20.6

The NH3 emissions of the 38 tested vehicle can be categorized as follows:
- Low emitters (< 10 mg/km), 6 vehicles
- Medium emitters (10-30 mg/km), 16 vehicles
- High emitters (> 30 mg/km), 16 vehicles
As shown in Figure 4-11 the NH3 emissions of the tested vehicles have no
correlation with vehicle age and Figure 4-12 indicates that NH3 emissions also have
no correlation with emission class.

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Figure 4-11: Average measured on road NH3 emission as function of mileage of petrol vehicles.

Figure 4-12: Average measured on road NH3 emission as function of Euro class of petrol vehicles.

In Figure 4-13 the NH3 mass emissions as function of their NOx emission of 38
petrol vehicles are plotted; There is no correlation between the NOx and NH3
emissions.

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Figure 4-13: Average measured on road NH3 emissions as function of average NOx emissions of
petrol vehicles.

NH3 analysis of single vehicles
In order to understand the root cause of the NH3 emission some measuring data of
two vehicles were analysed in detail.
The on road test of the Toyota Avensis offers some clarity about the conditions of
the NH3 emission production. This vehicle operates with three air-fuel strategies.
From 0 to 60 km/h the engine operates with stoichiometric air-fuel mixtures
(lambda = 1.00) and above 60 km/h the engine operates with a lean mixture
(lambda = 1.35). After cold start and during vehicle accelerations the air-fuel
mixtures are rich (lambda < 1). In Figure 4-1 the cumulative NH3 emission shows
that the NH3 emission is the very high at rich mixtures (lambda < 1), moderate at
lambda = 1 and the lowest at lean mixtures.

Figure 4-14: On road emission test of a Toyota Avensis.

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In Figure 4-15 during the idle speed test of the VW Golf the air-fuel strategy
changes (for unknown reasons) from stoichiometric to rich air-fuel mixtures
(lambda decreases from 1.00 to 0.92). At the same time the NH3 concentration
increases from 70 to 200 ppm.

Figure 4-15: Idle speed tests of the VW Golf.

The test results of the Toyota Avensis and VW Golf show the relationship of lambda
and NH3 emissions. NH3 emissions of petrol vehicles with a three-way catalyst are
mainly produced with rich air-fuel mixtures

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5

Discussion

5.1

Emissions

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NOx emissions and high emitters:
For 31 out of 50 tested vehicles the measured NOx emission is (CF < 1), 9 vehicles
have an elevated NOx emission (CF = 1-2), 7 vehicles have medium NOx emissions
and 3 vehicles are high emitters with an average NOx emission of 1191 mg/km.
The contribution to the total NOx emission of the three ‘high emitters’ out of 50
tested vehicles is 36%.
From repair actions it is clear there is a potential for improvement of the emissions
of a vehicle with high NOx emission. However the current in-field detection
possibilities in service and inspection programs are very poor.
Durability of vehicle emissions:
Legal durability criteria of exhaust emissions of light duty road vehicles are set with
mileage or time. Currently Euro 6 vehicles must comply 5 years or 100,000 km and
this is checked in In Service Conformity test programs. Extra durability requirements
are set for exhaust aftertreatment systems with deterioration factors up to a mileage
of 160,000 km.
In the Netherlands vehicles run on average approximately 18 years before
demolition and many vehicles run 250.000 km or more. From this perspective the
current durability criteria don’t cover the whole vehicle life cycle. Furthermore, there
is an insufficient systematics for determination of high emissions of defective
vehicles and consequently effective enforcement is not possible. A vehicle owner
may decide to skip repairs as long as the currently very poor PTI emission criteria
are met.
New technologies and new possibilities for emission monitoring;
Due to the presence of NOx emission sensors in new and future vehicles in
combination with an appropriate OBD system the vehicle life time emissions can be
monitored and guaranteed. Permanent information of vehicle emissions will
probably build the awareness of vehicle owners, drivers and maintenance
technicians. Due to the complexity of these monitoring systems vehicle
manufacturers are the appropriate stakeholder for creating the right conditions for
emission monitoring. The quality of such monitoring and OBD systems need to be
checked by independent testing.
NH3 emissions:
In this test program first attempts were made for measuring NH3 emissions with a
sensor in diluted exhaust gas. Measurements seemed reproducible in repetitive onroad tests.
The NH3 emission of petrol vehicles with a three-way catalyst is related to air-fuel
ratios of exhaust gas. Due to fuel abundancy at rich mixtures (lambda < 1) NH3 is
formed. With lean mixtures (lambda > 1) the NH3 emission is relatively low.
Practically the lambda control of an engine is mainly optimised reaching the lowest
CO, THC and NOx emissions with a certain three-way catalyst configuration.
This optimisation is done with the lambda controller.

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A certain lambda variation is programmed. The unregulated NH3 emission is not
taken into account and consequently it is not measured.
The configuration and calibration of the fuel control system determines the quality
of the lambda control (variations, average lambda values, minimum and maximum
values as well as the frequency of control). In most conditions the average lambda
is set around 0.990 to 0.995 because the optimum three-way catalyst performance
can be reached. However, lambda pre catalyst oscillates continuously and partly
the engine runs with richer air-fuel mixtures (i.e. lambda oscillates between
0.985 and 0.995). The amplitude and frequency of the lambda control determines
the NH3 emission.
The spread of NH3 emission is large because the average NH3 emission of
all on-road tested vehicles is 1 to 99 mg/km. For some vehicles (VW Golf, Nissan
Primera, Peugeot 308, Seat Cordoba, BMW 320i, Kia Rio) it seems that the
average lambda is set at richer mixtures because this results in maximum NOx
conversion in the three-way catalyst; The average NH3 emission of these vehicle
is relatively high (> 60 mg/km).
When NH3 emission limit values are added to current emission legislation vehicle
manufacturers have to optimize the trade of NOx and NH3 emissions applying a
proper lambda control and possibly an extra oxidation catalyst.
Consequences in case of regulated NH3 emissions:
When NH3 emissions are regulated the NH3 measuring technique must be defined
by legislators. Secondly, the NH3 limit values need to be developed and set.
In case of regulated NH3 emissions for petrol vehicles with three-way catalyst a
vehicle manufacturer must cope with the CO-NH3 / NOx trade of. This seems to
be feasible because many tested vehicles already have low NOx and NH3
emissions (< 30 mg/km).
5.2

Investigations for an improved PTI emission test procedure
In current PTI tests vehicles with high NOx emissions are not detected. The 4-gas
test has only CO and lambda criteria, lambda criteria at high idle speed are too
weak. Other weak points are the preconditioning of the vehicle and the very
undefined test procedure.
On Board Diagnosis:
Current OBD systems are useful and very helpful for vehicle repairs but are not
suitable for PTI purposes. This research proves that current OBD systems have
insufficient performance for detection of vehicles with a high NOx emission.
The OBD systems of the two Euro 4 vehicles with a very high NOx emission had
no active OBD codes. Furthermore, not all PTI stations have the state of the art
OBD readers and consequently they cannot read the OBD information. Finally OBD
systems can be manipulated.
In this emission test program different kinds of emission and PTI tests are executed,
investigated and assessed. With these test results and insights the current test
procedure might be improved to have a simple and low cost PTI emission test that
correlates with real world emissions of vehicles.

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One of the main findings of this research study is that the current PTI emission test
doesn’t detect vehicles with high NOx emissions. For potential next steps of the
improvement of the PTI test procedure the next options are pre-assessed:
Improved OBD:
Current OBD systems of petrol vehicles are mostly not able to detect high
emissions. The BMW 325 and Fiat Punto (both Euro 4 vehicles with OBD system)
of the former test program are good examples of vehicles with OBD-systems
without active emission codes and very high NOx emissions. Most tested vehicles
with moderate NOx emissions (CF = 2-4) also ran without active OBD codes.
If next generations of vehicles are equipped with suitable NOx sensors a permanent
emission monitoring is possible and even a continuous average emission can be
shown to the driver.
Warming up emission test is useful but not practical:
In this test program the three-way catalyst performance was assessed in idle tests
with a cold start, followed by a warming up and an idle test with warm engine.
During warming up the catalyst efficiency increases. The emission reduction rate
and the test time can be used to assess the catalyst performance. Sometimes the
three-way catalyst needs very long warming up times and/or running at high idle
speedto reach high conversions.
The main disadvantages of such a warming up test are the start with a cold engine
(not practical in PTI context) and the required test time of 10 – 20 minutes.
Furthermore the determination of the reduction rates is not easy because the
emission concentrations with cold start are not stable.
NOx emission test at idle speed seems not feasible:
In this test program the NOx concentrations at low and high idle speed were
measured. The NOx test results in section 4.5.2 show a poor correlation between
the NOx concentrations at idle speeds and the on-road NOx emission. Consequently
measuring NOx concentrations at idle speed is not option for a PTI emission test.
Potential for an improved PTI test procedure:
In section 4.2 the current PTI emission test procedure is investigated. Several weak
points are determined and investigated. Potential improvements which should be
further investigated and validated are: Revised criteria for preconditioning of the
engine/catalyst, a revised test procedure (fixed sequence and duration of low and
high idle speed test) and revised lambda limit values.
Some first ideas for a potential revised PTI emission test are given below:
Criteria for preconditioning:
In order to establish a realistic catalyst temperature the current three criteria for
preconditioning must be modified:
-

Test trip with active cooling fan and a maximum vehicle speed of 80 km/h
and a maximum engine speed of 3200 rpm.
Lubricant > 70 °C after 120 seconds low idle speed.
Coolant temperature > 70 °C and < 3 minutes high idle speed of maximum
3200 rpm.

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Test sequence:
A proposed mandatory test sequence is (see Figure 5-1):
1. Low idle speed
2. High idle speed.
Step and cycle times:
The minimum step times for low and high idle speed are 70 seconds (60 seconds
stabilisation time and 10 seconds measuring time). The minimum test cycle time is
160 seconds. In Table 5-1 and Figure 5-1 the total test procedure with a minimum
duration of 160 seconds is described.
Table 5-1: Option for a revised PTI emission test for petrol vehicles (engine is constantly running).

Activity

Warm up engine
Set low idle speed
Install probe in tail pipe

Minimum
time period
[s]
t.b.d.

Comment

Representative catalyst temperature

0
0

Stabilisation time

0 - 60

Measuring time
Set high idle speed

60 – 70
70 – 80

Stabilisation time

80 – 140

Measuring time
End of test

140 – 150
160

Average of 10 samples
Auxiliaries activated
Average of 10 samples

Figure 5-1: Option for a revised PTI test cycle.

Pass-Fail criteria:
The current CO criteria can stay unmodified.
The proposed revised lambda window at high idle speed is 0.98 to 1.00 and with a
two digit reading this effective lambda window is 0.975 to 1.005 because this
lambda window corresponds with the lambda window of the three-way catalyst,
see Figure 5-2.

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Figure 5-2: The typical emissions of a petrol engine and (revised) PTI lambda limit values. Within
the current PTI lambda band when lambda is 1.01 to 1.03 the NOx emissions are very
high. In rich operation (lambda < 0.97) on the left hydrocarbon and CO emissions are
high. Around lambda 0.995 HC, CO, and NOx are produced in the right balance to be
converted in a three-way catalyst into harmless products. The revised PTI lambda limit
values (blue dotted vertical lines) correspond better with the lambda window of the
three-way catalyst.

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Conclusions
With the introduction of the three-way catalyst in 1992, petrol cars have become
much cleaner than the older petrol- and diesel cars. Euro-3 petrol vehicles, which
have to satisfy a more stringent test, reduce the NOx emissions by a factor 20,
compared to vehicles without a three-way catalyst. In the meantime many vehicles
with high mileages run on European roads and there is a lack of emission data of
these vehicles.
In this study, with real-world emission tests on the road and PTI emission tests at
idle speeds, 38 vehicles with high mileages were tested. The results of an earlier
similar TNO study of 12 vehicles, that was based on a chassis dynamometer test
program, were integrated. The sorted conclusions are:
NOx emissions:
The average warm NOx emission of the 50 tested vehicles with an average mileage
of 222,444 km is 200 mg/km and 74% higher than their type approval limit values,
this can be marked as a very substantial deterioration.
The NOx contribution of three (6%) high emitting vehicles to the total NOx emission
is 35.8%. If the technical failures of these vehicles would be detected and repaired
the total average estimated NOx emission of the 50 tested vehicles drops to 130
mg/km. This shows that detection of high NOx emitters and subsequently repair of
these vehicles has a strong positive effect on the average NOx emission of this
group of vehicles.
The analysed NOx emission data of all 50 tested vehicles clearly show that the NOx
emissions of petrol vehicles with high mileages are not related to vehicle mileage
(> 160,000 km), vehicle age, emission class, vehicle trade mark, type or model.
When the NOx emission of the three high emitting vehicles is assumed at an
average value (related to the Euro class) of 100 and 250 mg/km, the total average
NOx emissions of the 2018 and 2020 test programs are 130 and 144 mg/km.
This indicates that the average test results of the chassis dynamometer test
program and the on-road test program are similar.
Vehicles with a high mileage emit on average substantial more NOx than new
vehicles. The average measured NOx emission of the 50 tested vehicles with an
average mileage of 222,444 km is 200 mg/km and is on average 2.1 times higher
than from these type of vehicles in new condition.
Current durability requirements don’t correspond with the average life-time mileage
of the tested vehicles:
Per Euro class the average mileage of the tested vehicles is 1.2 to 3.5 times higher
than the applicable durability mileage ( i.e. 80,000 or 160,000 km). Consequently
there is no reference for judgement of the emission performance of vehicles with a
high mileage.

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NH3 emissions:
In this on-road test program the average measured NH3 emission of 38 vehicles is
32 mg/km. Per vehicle it varies from 1 to 99 mg/km and this variation seem to be
dependent on the air-fuel control strategies of the engines. The NH3 emissions are
not related to vehicle mileage (> 160.000 km), vehicle age or Euro class.
With cold engine conditions the NH3 emission is relatively high. In the first 7.2 km of
road tests with a cold start the measured NH3 emission is 15 to 1208 % higher than
in tests with a warm start.
Emissions with different driving styles:
The sportive driving style resulted in an increase of CO2, NOx and NH3 emissions,
these are: CO2 13%, NOx 96% and NH3 39%.
Emission tests with cold and warm start:
Single on-road emission tests with cold and warm start of four tested vehicles
showed inconsistent CO2 and NOx results. Multiple emission tests are needed for a
solid assessment.
In idle speed tests with a cold start followed by a warming up of approximately
20 minutes at low idle speed the CO, THC and NOx reduction rates (based on the
measured concentrations) of the majority of the tested vehicles is above 80%.
For some vehicles this reduction rate was 50 – 80%. Only one vehicle had a very
low emission reduction rate of 0-20%.
This warming up test may not be suitable for the PTI because the required test time
is too long and the requirements for the start condition of the test are very strict.
This warming up test might be a screening option for (In Service Conformity)
emission test programs.
OBD systems:
OBD systems are not able to detect vehicles with a medium or high NOx emission.
The OBD systems of two Euro 4 vehicles with a high NOx emission which were
tested on the chassis dynamometer had no active OBD codes. Furthermore active
emission related OBD codes of the tested vehicles were not correlated with NOx
emissions and most vehicles with medium NOx emissions (CF = 2 – 4) had no
active OBD codes. Other vehicles with active OBD codes had a regular NOx
emission (CF < 2).
Periodic Technical Inspections:
The current PTI 4-gas test procedure is poor defined because mandatory
instructions for the stabilisation and measuring times and the sequence of the low
and high idle speed tests are not prescribed.
The current PTI CO emission test checks the CO oxidation performance of the
three-way catalyst and the CO limit values seem to be not very stringent. Only one
vehicle exceeded the CO limit value with normal preconditioning. The PTI CO test
results are not correlated with the PTI NOx concentrations.
The current PTI emission test has a very poor detection performance for high
emitting vehicles, 37 out of 38 tested vehicles passed the PTI emission test. Only
one vehicle with a high on-road NOx emission of 1,267 mg/km didn’t pass.

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However, this vehicle passed the regular PTI test with an excessive preconditioning
which was executed a few months earlier. Six tested vehicles with a medium NOx
emission (CF = 2-4) also passed the PTI emission test. Furthermore, the two
vehicles with a high NOx emission of the chassis dynamometer test program of
2018 passed the PTI emission test as well.
NOx measurements in the PTI:
For petrol vehicles with a three-way catalyst NOx concentrations in idle tests have a
very poor correlation with the on-road NOx emission. Therefore an extension of the
current PTI emission test procedure with a NOx measurement at idle speeds is not
suitable. Adding a NOx measurement at idle speed would result in false positive and
false negative PTI test results.
Vehicle repairs are effective:
Repairs of four tested vehicles with a high NOx emission are effective.
From 3 out of 4 vehicles with a medium or high average on-road NOx emission the
vehicle repairs resulted in an average reduction of the on-road NOx emission of
37 – 93%. From 2 vehicles the three-way catalyst was replaced and the
EGR-system of the third vehicle was repaired. The repair of the fourth vehicle was
not effective. Presumably this three-way catalyst has also a reduced conversion
efficiency.
Potential improvements of the current PTI emission test procedure:
The current PTI emission test procedure for petrol vehicles which is described in EC
Regulation 2014/45 is not suitable for detection of high emitting vehicles. Especially
vehicles with high NOx emissions are not detected. An additional NOx measurement
at idle speeds is not a solution for the PTI but a better defined emission test
procedure with revised lambda criteria seems feasible and more effective for
detection of vehicles with a high NOx emission.
Potential improvements are:
 Better criteria for preconditioning of the three-way catalyst:
Catalyst efficiencies mostly increase with increasing operating temperatures.
The current criteria for preconditioning of the vehicle in a PTI emission test are
defined with minimum requirements, the catalyst should reach a certain operating
temperature. Excessive preconditioning of the catalyst which result in a higher
operating temperature is allowed In order to avoid unrealistic test conditions (too
high catalyst temperature) the preconditioning of the vehicle must be defined with
requirements that limit the temperature of the catalyst.
 Defined test cycle:
In order to improve the quality of the PTI emission test result, a minimum
stabilisation time, measuring time, a measuring frequency and the standard
deviation of the test result should be prescribed.
 Defined test procedure:
In order to improve the reproducibility and repeatability of the PTI emission test
result a defined test sequence of the current low and high idle speeds should be
prescribed.

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 Improved lambda limit values:
The current lambda limit values (0.97 to 1.03) of the PTI emission test doesn’t
correspond with the lambda window of three-way catalysts. In order to avoid
passing vehicles with high NOx emissions it is advised to limit the range of lambda
values to 0.98 to 1.00.
Emission tests with different driving styles:
Four vehicles were tested with a regular and sportive driving style. The sportive
driving style resulted in an increase of CO2, NOx and NH3 emissions, these are on
average CO2 13%, NOx 96% and NH3 39%.
Validation mobile emission measurement system:
On the basis of chassis dynamometer tests and the flow validation of the exhaust
flow meter of the Mobile Emission Measurement System (MEMS) it is estimated
that the average on road measured CO2 emission of MEMS is 6 to 8% higher than
the CO2 emissions of the chassis dynamometer (CVS-bag). The average estimated
NOx emission of MEMS is 10 to 14 % lower than the measured NOx emissions of
the chassis dynamometer. From these validation results it is concluded that MEMS
is suitable for screening of average CO2 and NOx emissions of petrol vehicles.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

7

69 / 73

Recommendations
The European Directive 2014/45/EC and the Dutch vehicle regulation
(Wegenverkeerswet, Regeling Voertuigen) for periodic technical inspections (PTI)
describe a similar PTI emission test procedure for petrol vehicles. At low and high
idle speed the tail pipe emission concentrations have to be measured.
Several weak points in this test procedure result in false positive test results, these
are:
- The three described preconditioning options in combination with the
description of the low and high idle speed tests may lead to unrealistic (too
high) operating temperatures in the PTI emission tests.
- No described sequence and duration of low idle and high idle speed tests.
- No defined stabilisation time of the engine and three-way catalyst,
- The test result is a momentary value and not an average value over a certain
measuring time.
In order to improve the current PTI emission test procedure for positive ignited
engines with three-way catalyst the development of a more defined emission test
procedure is recommended which defines maximum values of certain criteria.
It is expected that the revised PTI emission test procedure will result in a higher and
more realistic PTI failure rate of defective vehicles with high a NOx emission.
In order to get a better view on the share of vehicles of the total Dutch fleet with
high emissions it is recommended to study statistical data from PTI data bases.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

8

Abbreviations
AAT
CADC
CF
CO
CO2
ECT
EMF
EGR
EOBD
GPS
LFE
MAF
MEMS
MIL
NEDC
NH3
NOx
O2
OBD
PTI
RON
SEMS
THC

Ambient Air Temperature
Common Artemis Driving Cycle
Conformity Factor
Carbon monoxide
Carbon dioxide
Engine Coolant Temperature
Exhaust Mass Flow
Exhaust Gas Recirculation
European On Board Diagnostics
Global Position Sensor
Liquid Fuel Economy
Mass Air Flow
Mobile Emission Measurement System
Malfunction Indication Light
New European Driving Cycle
Ammonia
Nitrogen Oxides (NO + NO2)
Oxygen
On Board Diagnostics
Periodic Technical Inspection
Research Octane Number
Smart Emission Measurement System
Total Hydro Carbons

70 / 73

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

9

71 / 73

Acknowledgements
Acknowledgments go to 32 private vehicle owners and the automotive companies
Select Car Lease in Woerden and Wittebrug in The Haque because they supplied
the vehicles that were tested.
Further acknowledgements go to RDW (the Dutch type approval authority and
responsible for periodic technical inspections in The Netherlands) for their input
and discussion on PTI related subjects of this study.
Finally acknowledgements go to the Ministry of Infrastructure and Water
Management for funding this test program.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

10

72 / 73

References
[TNO 2016A]

Heijne et al., Assessment of road vehicle emissions:
methodology of the Dutch in-service testing programme, TNO
report 2016 R11178.

[TNO 2016b]

Ligterink, N.E., Emissions of three common GDI vehicles, TNO
report 2016, R11247.

[PBL 2017]

Kleijn et al., Methods for calculating the emissions of transport
in the Netherlands, Task Force on Transportation of the Dutch
Pollutant Release and Transfer Register, 2017.

[TNO 2018]

Kadijk et al., Emissions of twelve petrol vehicles with high
mileages, TNO report 2018 R11114.

[Adams 2014]

Adams et al., Ammonia formation over supported platinum and
palladium catalysts, Elsevier Applied Catalysis B
Environmental 165 (2015), 10-19.

[Oh 2013]

Se H. Oh and Ty Triplett, Reaction pathways and mechanism
for ammonia formation and removal over palladium-based
three-way catalyst: Multiple roles of CO, Elsevier Catalysis
Today 231 (2014) 22-32

[Brinkmeier 2006]

Brinkmeier C., Automotive Three-Way Exhaust Aftertreatment
under Transient Conditions – Measurements, Modeling and
Simulation, Dissertation 23-02-2006, Faculty of mechanical
engineering of the university of Stuttgart.

[TNO 2015]

van Zyl S. et al., In-use compliance and deterioration of vehicle
emissions, TNO report TNO 2015 R11043.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

11

Signature
The Hague, 17 December 2020

TNO

Chantal Stroek
Research Manager STL

Peter van der Mark
Author

73 / 73

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

A

Appendix A | 1/3

Specifications of the Mobile Emission Measurement
System (MEMS)
MEMS contains the next modules:
1.
2.
3.

A modified bicycle carrier.
Stainless steel tubing (internal diameter 38.3 mm @ length of 240 cm)
An automotive Exhaust Mass Flowmeter (EFM) (Horiba B-type, 0 – 4.5 m3/min)
which consists of a pitot tube, a pressure sensor box and a thermocouple.
4. An Automotive Exhaust Gas Tester (TEN Innova) with CO, CO2, C6H8, O2 and NOx
analysers and on-line lambda calculation. Measuring frequency is 4 Hz. This unit
sampled undiluted exhaust gas and powered with a 12/230 V DC convertor.
5. A dilution air pump that has a fairly constant mass flow of 5 g/s.
6. 2 Continental NOx – O2 , 1 Delphi NH3 and 2 lambda automotive sensors and
2 thermocouples. Undiluted and diluted gas was measured.
7. A GPS sensor.
8. A SEMS data logger that is connected to the OBD-system (if present) and sensors.
Measuring frequency 10 Hz.
9. Electrical power (12V battery) for the MEMS.
10. Central database and postprocessing of emission mass flow rates.
11. Access to processed data via internet.

Schematic overview of the Mobile Emission Measurement System.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

Specification sensors;
NOx - O2:

Continental.

SNS 155A , 5WK96755A

NH3:

Delphi.

Part Number 5801627706

Lambda:

Bosch.

LSU 4.9

Appendix A | 2/3

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

Appendix A | 3/3

Data processing architecture:
Note: For diesel vehicles the sample rate of data acquisition is 1 Hz and exhaust
gas dilution is NOT applied.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

Appendix B | 1/5

B

Validation of the Mobile Emission Measurement
System

B.1.1

Validation on the chassis dynamometer.
In section 2.3 and Appendix B the configuration of the Mobile Emission
Measurement System is described. MEMS was validated using Common Artemis
Driving Cycles on a chassis dynamometer because the configuration was new and
the MEMS performance was unknown.
All emission tests were carried out on a Euro 6 VW Polo petrol vehicle with an
odometer reading of 175,000 km, EN 228 trade fuel (E10 grade) was applied. In
Table 11-1 the activities of the chassis dynamometer test program are specified and
in Table 11-2 the applied road load settings. Soaking of the vehicle and emission
testing were carried out with an ambient temperature of 23 ⁰C.

Figure 11-1: Validation of MEMS on the chassis dynamometer.
Table 11-1: Chassis dynamometer test program of the VW Polo Euro 6 petrol.

Day

Emission test

0

Soak

1
1

CADC cold start
CADC warm start

1/2

Soak

2

CADC cold start

2

CADC warm start

Table 11-2: Road load settings on the chassis dynamometer.

Parameter
Inertia

Unit
[kg]

Value
1550

F0

[N]

130

F1
F2

[N/(km/h)]
[N/(km2/h2)]

0.00
0.040

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

Appendix B | 2/5

Mass Air Flow (MAF) and Liquid Fuel Economy (LFE) data were available on the
OBD port and they were logged. The exhaust mass flow (EMF) was determined
with a Horiba pitot flow meter. Due to initial technical imperfections of the pitot flow
meter the validation was split into two parts:
Step 1: Chassis Dynamometer emission validation on the basis of MAF + LFE
Step 2: Exhaust flow validation on the road (EMF versus MAF + LFE).
Results chassis dynamometer emission validation:
In CADC tests with cold start the average CO2 emission of the chassis
dynamometer was 152.4 g/km and MEMS measured on average 156.0 g/km
(difference is + 2.4%), see Figure 11-2. In CADC tests with warm start the average
measured CO2 emission of the chassis dynamometer was 151.7 g/km and MEMS
measured on average 153.8 g/km (difference is +1.4%).
The average NOx emission in the CADC tests with cold start of the chassis
dynamometer was 55.6 mg/km and MEMS measured on average 45.7 mg/km
(difference -18%), see Figure 11-3. In the CADC tests with warm start the NOx
emission of the chassis dynamometer was on average 66.2 mg/km and MEMS
measured on average 56.6 mg/km (difference -15.5 %).

Figure 11-2: CO2 CADC test results with cold and warm starts of the VW Polo Euro 6 petrol
measured on the chassis dynamometer (CVS-bag) and with MEMS (MAF + LFE
based).

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

Appendix B | 3/5

Figure 11-3: NOx CADC test results with cold and warm starts of the VW Polo Euro 6 petrol
measured on the chassis dynamometer (CVS-bag) and with MEMS (MAF + LFE
based).

The measured NH3 emissions (MAF + LFE based) in CADC tests with cold start
are 10.9 and 10.0 mg/km and with hot start they are 9.7 and 8.2 mg/km, see
Figure 11-4. These results are not validated.

Figure 11-4: NH3 CADC test results with cold and warm starts of the VW Polo Euro 6 petrol
measured with MEMS (MAF + LFE based).

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

B.1.2

Appendix B | 4/5

Exhaust mass flow validation on the road.
In a second step the flow characteristics of the pitot tube were validated with the
MAF and LFE of the VW Polo in on road tests with a length of 48 km. In order to
check the repeatability the test was repeated three times. The total measured
exhaust masses of the pitot tube in the three executed on road tests were
3.8 to 6.4 % higher than the MAF + LFE based exhaust masses and the
repeatability of this measurement is good, see Table 11-3. An example of
cumulative exhaust masses of one on road test is given in Figure 11-5.
Table 11-3: Mass flow results of the pitot tube and vehicle sensors (MAF + LFE)

Distance

Duration

EMF pitot

MAF +
LFE

[km]

[s]

Test 1

48.29

Test 2
Test 3

Delta flow
(EMF
versus
MAF+LFE)

cum.

cum.

[g]

[g]

[%]

4130

29497

27717

6.4%

48.26

3918

28566

27491

3.9%

48.29

4419

29599

28526

3.8%

Figure 11-5: Cumulative exhaust mass flows of an on road test of 49 km of the VW Polo Euro 6
petrol measured with the pitot tube (EMF) and the vehicle sensors (MAF + LFE).

B.1.3

On road repeatability check of the test procedure with MEMS.
The repeatability of the on road test was checked with the Euro 6 VW Polo in three
equal on road tests. The tests with a length of 48.3 km were started with a warm
engine and executed on one day and the start-stop system was activated.
In Table 11-4 the test results of the three on road tests are reported. Average
ambient temperatures in the three tests were 12.8, 15.9 and 16.4 ⁰C. Due to traffic
conditions the duration of the three tests varied from 3918 to 4419 seconds.
Exhaust mass flows were measured in two ways.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

Appendix B | 5/5

The cumulative pitot tube mass flows were on average 3.8 to 6.4% higher than the
cumulative exhaust mass flows based on MAF and LFE readings from the vehicle.
The average measured CO2 emissions of the three tests were 111.4, 109.8 to 114.3
g/km, the NOx emission was 34.7, 108.8 and 46.9 mg/km and the NH3 emission
was 20.4, 12.2 and 15.3 mg/km.
The deviating NOx emission in the second test of 108.8 mg/km was caused by
extremely high measured NOx concentrations of the automotive NOx sensor in the
latest 600 seconds of the test. This NOx sensor measures also O2 concentrations
and these measuring signals were also disturbed. As a fall back option the NOx
concentrations were always simultaneously measured with an automotive 5-gas
analyser and these NOx measurements didn’t have deviating high numbers. In the
third on road test and in the residual test program such NOx deviations were not
measured. For the time being the deviating NOx results in the second test are
stated as a single failure.
Table 11-4: Test results of three repetitive on road tests of the VW Polo with MEMS.

Test

Dist.
[km]

Dur.
[s]

AAT
[⁰C]

EMF
pitot

MAF +
LFE

Delta

cum.

cum.

Mass

[g]

[g]

[%]

CO2

NOx

NH3

[g/km] [mg/km] [mg/km]

1

48.29

4130

12.8

29497

27717

6.4%

111.4

34.7

20.4

2

48.26

3918

15.9

28566

27491

3.9%

109.8

108.8

12.2

3

48.29

4419

16.4

29599

28526

3.8%

114.3

46.9

15.3

A detailed analysis of the measured NOx concentrations of the applied NOx-O2
sensors is reported in section 4.6.
B.1.4

Conclusions of the validation of MEMS:
On the basis of chassis dynamometer tests and the flow validation of the exhaust
flow meter of the Mobile Emission Measurement System (MEMS) it is estimated
that the average on road measured CO2 emission of MEMS is 6 to 8% higher than
the CO2 emission measured with the chassis dynamometer (CVS-bag).
The average estimated NOx emission of MEMS is 10 to 14 % lower than the NOx
emissions measured with the chassis dynamometer.
On the basis of the validation results of MEMS it is concluded that MEMS is suitable
for screening of average CO2 and NOx emissions of petrol vehicles.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

C

Appendix C | 1/1

Tested vehicles
No

Brand

Model

Euro
Class

Power
[kW]

Year of first
Registratio
n

Odometer
[km]

Empty
Mass [kg]

1

VW

Polo

6

70

2017

175,728

1,011

2

Fiat

Punto

4

48

2010

156,604

1,005

3

Citroen

C5

3

100

2002

177,478

1,342

4
5

Toyota
Suzuki

Starlet
Wagon R

2
3

55
56

1998
2001

257,829
222,134

905
885

6

Opel

Corsa

4

43

2001

223,735

880

7
8

Suzuki
Toyota

Swift
Yaris

4
4

75
64

2005
2003

166,851
182,411

975
870

9

Toyota

Avensis

2

81

1999

323,151

1,315

10
11

Peugeot
VW

406
Golf

2
2

81
150

2000
1999

203,034
250,090

1,385
1,415

12

BMW

3

4

105

2002

262,826

1,295

13
14

Ford
Peugeot

Focus
206

2
2

74
55

2000
2000

181,228
251,836

1,093
925

15

Volvo

S60

3

147

2002

307,843

1,570

16
17

Renault
Mazda

Clio
5

3
4

72
85

2003
2006

192,048
159,708

975
1,370

18

Toyota

Aygo

4

50

2006

206,334

795

19

Nissan

Primera

4

85

2004

172,273

1,318

20
21

Citroen
VW

C2
Passat

3
4

54
96

2004
2003

213,774
243,970

966
1,376

22

VW

Passat

2

110

1998

550,384

1,295

23
24

Volvo
Mercedes

V40
C180K

3
4

90
105

2002
2006

193,920
193,458

1,255
1,435

25

Renault

Laguna

4

125

2008

200,949

1,463

26
27

Renault
Citroen

Clio
Berlingo

2
3

55
80

1999
2004

188,895
211,780

935
1226

28

Renault

Megane Sc

3

83

2004

276,102

1,420

29
30

Peugeot
Opel

206
Zafira

3
4

44
77

2004
2002

250,611
202,250

885
1,293

31

Peugeot

308 SW

5

88

2011

200,690

1,381

32
33

Seat
Ford

Cordoba
Focus

4
4

74
85

2006
2006

168,964
200,121

1,041
1,139

34

BMW

320i

5

125

2011

220,292

1,345

35

Skoda

Octavia

5

77

2010

192,181

1,205

36
37

Opel
Hyundai

Corsa
Tucson

4
4

66
104

2008
2010

169,682
199,577

1,063
1,437

38

Kia

Rio

5

63

2011

176,074

1,004

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

D

Appendix D | 1/1

On road emission test results
No

Trade mark model

Euro
Class

CO2

NH3

1

NOx

[mg/km]

[mg/km]

[mg/km]

CF

VW Polo

6

111.4

20.4

34.7

0.3

2

Fiat Punto

4

151.3

23.7

237.1

3.0

3

Citroen C5

3

180,0

12.1

351.6

2.3

4

Toyota Starlet

2

160,5

45.2

196.7

0.7

5

Suzuki Wagon R+

3

140.7

32.8

296.2

2.0

6

Opel Corsa

4

124.0

11.5

69.0

0.9

7

Suzuki Swift

4

145.0

14.2

101.0

1.3

8

Toyota Yaris
Toyota Avensis

4

132.5

27.9

23.8

0.3

9

2

150.8

25.1

353.7

1.2

10

Peugeot 406

2

178.1

30.0

162.8

0.5

11

VW Golf

2

209.3

99.0

355.2

1.2

12

BMW 3

4

192.7

0.8

161.7

2.0

13

Ford Focus

2

143.1

20.3

241.9

0.8

14

Peugeot 206

2

134.8

37.0

1266.5

4.2

15

Volvo S60

3

180.4

38.3

103.2

0.7

16

Renault Clio

3

148.1

5.3

49.8

0.3

17

Mazda 5

4

176.5

8.7

35.5

0.4

18

Toyota Aygo

4

120.8

9.5

264.3

3.3

19

Nissan Primera

4

193.0

61.4

133.0

1.7

20

Citroen C2

3

155.3

7.9

134.0

0.9

21

VW Passat

4

212.6

41.6

56.8

0.7

22

VW Passat

2

192.9

54.6

212.5

0.7

23

Volvo V40

3

173.0

28.1

67.3

0.4

24

Mercedes C180K

4

183.2

22.0

54.2

0.7

25

Renault Laguna

4

216.6

21.3

52.9

0.7

26

Renault Clio

2

150.6

10.3

257.2

0.9

27

Citroen Berlingo

3

173.6

22.7

43.4

0.3

28

Renault Megane Sc

3

197.9

36.5

104.8

0.7

29

Peugeot 206

3

148.7

27.4

113.3

0.8

30

Opel Zafira

4

158.1

30.8

136.6

1.7

31

Peugeot 308 SW

5

154.9

70.9

79.5

1.3

32

Seat Cordoba

4

171.5

85.2

61.6

0.8

33

Ford Focus

4

182.5

49.0

52.1

0.7

34

BMW 320i

5

124.6

76.8

284.2

4.7

35

Skoda Octavia

5

160.3

12.4

44.3

0.7

36

Opel Corsa

4

158.3

16.1

17.4

0.2

37

Hyundai Tucson

4

205.2

13.8

62.1

0.8

38

Kia Rio

5

141.5

70.6

43.8

0.7

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

E

Appendix E | 1/1

Technical comments of the tested vehicles
No.
1

Make - model
VW Polo

Technical comments
-

2

Fiat Punto

-

3
4

Citroen C5
Toyota Starlet

No OBD available.

5

Suzuki Wagon R+

EGR system defective, intake air leakage. OBD codes: P0400
and P0130. CO emission @ low idle speed not stable.

6

Opel Corsa

-

7
8

Suzuki Swift
Toyota Yaris

CO emission @ low idle speed not stable.

9

Toyota Avensis

No OBD available. Lean burn engine > 60 km/h.

10

Peugeot 406

11

VW Golf

No OBD available.
OBD codes 17840 and 17538.
CO emission @ low idle speed not stable.

12

BMW 3

-

13

Ford Focus

-

14
15

Peugeot 206
Volvo S60

No OBD available. Three-way catalyst defective.
-

16

Renault Clio

-

17
18

Mazda 5
Toyota Aygo

OBD code P0420. Three-way catalyst reduced performance.

19

Nissan Primera

-

20
21

Citroen C2
VW Passat

Low idle speed variation +/- 50 rpm.
Coolant high at low speeds. Cooling fan defective.

22

VW Passat

Actual three-way catalyst age is 190,000 km.

23
24

Volvo V40
Mercedes C180K

Coolant 70 to 100 ⁰C (thermostat defective).
Coolant 47 to 80 ⁰C (thermostat defective).

25

Renault Laguna

-

26
27

Renault Clio
Citroen Berlingo

CO emission @ low idle speed not stable.
-

28

Renault Megane Sc

-

29

Peugeot 206

-

30
31

Opel Zafira
Peugeot 308

CO emission @ low idle speed not stable.

32

Seat Cordoba

Static friction brakes.

33

Ford Focus

34

BMW 320i

35

Skoda Octavia

-

36

Opel Corsa

-

37
38

Hyundai Tucson
Kia Rio

OBD codes P011 and P016.
New engine @ 105,000 km.

OBD code P000A: Position of camshaft slow reaction
Coolant 57 to 77 ⁰C (thermostat defective).
Shared lean burn and stoichiometric concept.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

F

Appendix F | 1/1

PTI emission test results
Table 11-5: PTI test results of idle tests of tested petrol vehicles with warm engines (average of 15
seconds after stabilisation). The vehicles were tested ‘as received’.
Low

High idle speed

idle
speed
Vehicle

Euro

MIL

CO

CO

Lambda

PTI Result

Class

On/Off

[vol%]

[vol%]

[-]

Pass / Fail

1

VW Polo

6

Off

0.00

0.00

1.000

Pass

2

Fiat Punto

4

Off

0.10

0.12

0.996

Pass

3

Citroen C5

3

Off

0.00

0.00

1.000

Pass

4

Toyota Starlet

2

Off

0.00

0.01

0.998

Pass

5

Suzuki Wagon**

3

Off

0.15

0.02

1.009

Pass

6

Opel Corsa

4

Off

0.02

0.02

1.000

Pass

7

Suzuki Swift

4

Off

0.02

0.00

1.000

Pass

8

Toyota Yaris**

4

Off

0.00

0.11

0.997

Pass

9

Toyota Avensis

2

Off

0.00

0.08

0.997

Pass

10

Peugeot 406

2

Off

0.14

0.00

1.012

Pass

11

VW Golf**

2

Off

0.28

0.30

0.991

Pass*

12

BMW 3

4

On

0.00

0.00

1.000

Pass

13

Ford Focus

2

Off

0.00

0.00

1.000

Pass

14

Peugeot 206

2

Off

0.00

0.78

1.015

Fail

15

Volvo S60

3

Off

0.02

0.02

0.999

Pass

16

Renault Clio

3

Off

0.01

0.01

1.000

Pass

17

Mazda 5

4

Off

0.03

0.08

0.998

Pass

18

Toyota Aygo

4

On

0.08

0.17

0.999

Pass*

19

Nissan Primera

4

Off

0.00

0.01

1.000

Pass

20

Citroen C2

3

Off

0.00

0.00

1.000

Pass

21

VW Passat

4

Off

0.00

0.00

1.000

Pass

22

VW Passat

2

Off

0.10

0.04

0.999

Pass

23

Volvo V40

3

Off

0.00

0.00

1.001

Pass

24

Mercedes C180K

4

Off

0.00

0.00

1.000

Pass

25

Renault Laguna

4

Off

0.00

0.00

1.000

Pass

26

Renault Clio**

2

Off

0.01

0.29

0.992

Pass

27

Citroen Berlingo

3

Off

0.02

0.00

1.001

Pass

28

Renault Megane Sc

3

Off

0.00

0.00

1.000

Pass
Pass

29

Peugeot 206

3

Off

0.12

0.00

1.000

30

Opel Zafira

4

Off

0.18

0.00

1.000

Pass

31

Peugeot 308**

5

Off

0.18

0.23

0.990

Pass

32

Seat Cordoba

4

Off

0.32

0.00

0.999

Pass

33

Ford Focus

4

Off

0.00

0.10

0.995

Pass

34

BMW 320i

5

Off

0.00

0.00

2.477

Pass

35

Skoda Octavia

5

Off

0.00

0.00

1.000

Pass

36

Opel Corsa

4

Off

0.01

0.00

0.999

Pass

37

Hyundai Tucson

4

Off

0.00

0.00

1.000

Pass

38

Kia Rio

5

Off

0.24

0.17

0.995

Pass

*After on road preconditioning, **Emissions are not stable.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

G

Appendix G | 1/2

Backgrounds of NOx emission control strategies
In order to understand the measured emission behaviour of all tested vehicles first
some background knowledge of EGR-systems, three-way catalyst and the lambda
control strategy is given.
EGR systems
Exhaust gas recirculation (EGR) systems are mainly applied to reduce NOx and
CO2 emissions at low engine loads. The share of inert exhaust gas reduces the
operating temperature of the combustion chamber which results in lower NOx
production. Furthermore EGR reduces pumping losses of the engine which results
in a lower CO2 emission.
Three-way catalysts
Three-way catalysts convert CO and HC to CO2 and H2O when the catalyst runs in
its temperature window and sufficient O2 is available for oxidation. These lean
mixture conditions are available when the so-called lambda value exceeds 0.995.
However NOx is reduced in the warm catalyst when sufficient CO is available with
rich mixtures at lambda values lower than 0.995. In the left part of Figure 11-6 the
relationship of lambda and conversion of emissions in a three way catalyst is
shown. Optimal conversion of CO THC and NOx emissions can be realised in a very
narrow lambda window which can be established with a so-called lambda controller
which contains a lambda sensor.

Figure 11-6: The typical emissions of a petrol engine. In lean operation, on the right, NOx
emissions are high. In rich operation on the left hydrocarbon and CO emissions are
high. In between, at the dashed line, HC, CO, and NOx are produced in the right
balance to be converted in a three-way catalyst into harmless products.

Both conditions, rich and lean, are realised with the lambda controller which
oscillates between a rich and lean mixture. The normal lambda operating window of
lambda controlled engine with a three-way catalyst is in the range of 0.99 to 1.00.
At higher engine loads mixture enrichment is applied, lambda can be around 0.80.
The determination of the mixture quality around a lambda value of 1.00 is measured
by the lambda sensor which is basically an oxygen sensor. The output signal of the
lambda sensor is 50 to 950 mV and a very steep switch of the sensor output signal
occurs at lambda 1.00.

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

Appendix G | 2/2

A small shift of this sensor measuring signal, which can be caused by deterioration,
may lead to an effective average leaner mixture and a decreased conversion of the
three way catalyst.
Requirements of lambda control
When lambda is below 0.99 CO is not oxidised and NOx can be reduced. In vehicle
applications lambda pre catalyst oscillates between i.e. 0.985 and 0.995
(see example in Figure 11-7). This very subtle lambda variation in the required
lambda window with a frequency of appr. 1 Hz enables a three-way catalyst to
oxidise CO and HC and to reduce NOx. In case of a lambda deviation the
performance of a three way catalyst is immediately changed.
In order to have a maximum conversion rate of the three-way catalyst the lambda
must be set in the required lambda window. Very small deviations (when the air-fuel
mixture is too lean, i.e. 1.00 instead of 0.99) can lead to substantial higher NOx
emissions, see Figure 11-6.

Figure 11-7: Exhaust air to fuel ratio upstream of the catalyst during rich bias conversion
experiments (∆λ =±0.01, f =1 Hz) Reference [Brinkmeier 2006]

The four potential main causes for increased NOx emissions are:
 A failing EGR system
 A failing lambda sensor
 A failing air-fuel control system
 Catalyst deterioration

TNO report | TNO 2020 R11883 | Final report | 17 December 2020

H

Appendix H | 1/1

Backgrounds of NH3 emissions
The applied test set up contained an ammonia sensor to measure the ammonia
emission of all vehicles under test. As an unregulated emission component for light
duty vehicles, ammonia (NH3) is not very often measured in emission tests. So first
a short literature study of ammonia emissions of three-way catalysts was executed.
Adams et al. [Adams 2014] tested different types of catalysts in a steady state gas
bench with various lambda values.
From the results, see Figure 11-8, the relationship of lambda and the formation of
ammonia can be split in three sections:




With lean mixtures (lambda > 1) the formation of ammonia is negligible.
With rich mixtures (lambda < 1), the formation of ammonia is related to lambda.
For some catalyst types the operating temperature and water-gas-shift have an
effect on the ammonia formation but all catalysts produced ammonia with rich
mixtures.

The formation of ammonia in three way catalysts seem to depend on the actual
lambda value and is similar to the formation of CO (see Figure 11-6).

Figure 11-8: Steady-state formation of NH3 versus oxygen concentration at 250, 350 and 450 ◦C
(left figure non Water Gas Shift (WGS) assisted and right figure WGS assisted). The
gas feed contained 500 ppm NO and 1500 ppm H2 while the O2 concentration was
varied between 0 and 1050 ppm (S = 0.33–1.73) in steps of 150 ppm. Air was used
as balance and space velocity was 40,000 h−1 [Adams 2014] .

A second study [Oh 2013] confirmed the formation of ammonia in different types of
three-way catalysts with rich mixtures (lambda < 1).