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This document is meant purely as a documentation tool and the institutions do not assume any liability for its contents
►B COUNCIL DIRECTIVE
of 2 August 1972
on the approximation of the laws of the Member States relating to the measures to be taken
against the emission of pollutants from diesel engines for use in vehicles
(72/306/EEC)
(OJ L 190, 20.8.1972, p. 1)
Corrected by:
►C1Corrigendum, OJ L 215, 6.8.1974, p. 20 (72/306)
►C2Corrigendum, OJ L 299, 23.11.1977, p. 27 (72/306)
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COUNCIL DIRECTIVE
of 2 August 1972
on the approximation of the laws of the Member States relating to
the measures to be taken against the emission of pollutants from
diesel engines for use in vehicles
(72/306/EEC)
THE COUNCIL OF THE EUROPEAN COMMUNITIES,
Having regard to the Treaty establishing the European Economic
Community, and in particular Article 100 thereof;
Having regard to the proposal from the Commission;Having regard to the Opinion of the European Parliament;Having regard to the Opinion of the Economic and Social Committee;Whereas the technical requirements which motor vehicles must satisfy
pursuant to national laws relate, interalia , to the emission of pollutants
from diesel engines for use in vehicles;
Whereas those requirements differ from one Member State to another;
whereas it is therefore necessary that all the Member States adopt thesame requirements either in addition to or in place of their existingrules, in order, in particular, to allow the EEC type approval procedurewhich was the subject of the Council Directive(
1) of 6 February 1970
on the approximation of the laws of the Member States relating to thetype approval of motor vehicles and their trailers to be applied inrespect of each type of vehicle;
Whereas, it is desirable to follow the technical requirements adopted by
the UN Economic Commission for Europe in its Regulation No 24(Uniform provisions concerning the approval of vehicles equipped withdiesel engines with regard to the emission of pollutants by the engine),which is annexed to the Agreement of 20 March 1958 concerning theadoption of uniform conditions of approval and reciprocal recognitionof approval for motor vehicle equipment and parts(
2);
HAS ADOPTED THIS DIRECTIVE:
Article 1
For the purposes of this Directive, ‘vehicle'means any vehicle with a
diesel engine, intended for use on the road, with or without bodywork,having at least four wheels and a maximum design speed exceeding 25km/h, with the exception of vehicles which run on rails, agriculturaltractors and machines and public works vehicles.
Article 2
No Member State may refuse to grant a vehicle EEC type approval or
national type approval on the ground that pollutants are emitted by thediesel engine which drives the vehicle, if the engine complies withAnnexes I, II, III, IV and VI.
Article 3
The Member State which has granted type approval shall take the
necessary measures to ensure that it is informed of any modification ofa part or characteristic referred to in item 2.2 of Annex I. Thecompetent authorities of that Member State shall decide whether freshtests should be carried out on the ►
C1modified vehicle type ◄and a
(1) OJ No L 42, 23.2.1970, p. 1.
(2) Doc. E/EEC/324 — E/EEC/TRANS/505, Rev 1/add 23,23.8.1971.
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fresh report drawn up. Where the tests reveal failure to comply with thisDirective, the modification shall not be approved.
Article 4
The amendments necessary for adjusting the Annexes so as to take
account of technical progress shall be adopted in accordance with theprocedure laid down in Article 13 of the Council Directive of 6February 1970 on the approximation of the laws of the Member Statesrelating to the type approval of motor vehicles and their trailers.
Article 5
1. Member States shall put into force the provisions needed in order
to comply with this Directive within eighteen months of its notificationand shall forthwith inform the Commission thereof.
2. Furthermore, once notification of this directive has been effected
the Member States shall ensure that the Commission is informed, intime for it to submit its comments, of the most important laws, regula-tions and administrative provisions which they envisage adopting in thefield covered by this Directive.
Article 6
This Directive is addressed to the Member States.
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ANNEX 1(a)
DEFINITIONS,APPLICATIONFOREECTYPEAPPROVAL,SYMBOL
OF THE CORRECTED ABSORPTION COEFFICIENT, SPECIFICA-
TIONS AND TESTS AND CONFORMITY OF PRODUCTION
(1.)2. DEFINITIONS
For the purposes of this Directive:
(2.1.)2.2. ‘Vehicle type as regards the limitation of the emission of pollutants from
the engine'means motor vehicles which do not differ in such essentialrespects as the vehicle and engine characteristics defined in Annex II;
2.3. ‘Diesel engine'means an engine which works on the compression-igni-
tion principle;
2.4. ‘Cold-start device' means a device which by its operation temporarily
increases the amount of fuel supplied to the engine and is intended fofacilitate the starting of the engine;
2.5. ‘Opacimeter' means an instrument for continuous measurement of the
absorption coefficients of the light by the exhaust gases emitted byvehicles.
3. APPLICATION FOR EEC TYPE APPROVAL
3.1. The application for approval must be submitted by the vehicle manufac-
turer or by his duly accredited representative.
3.2. It must be accompanied by the undermentioned documents in triplicate
and the following particulars:
3.2.1. A description of the engine type including all the particulars referred to
in Annex II:
3.2.2. Drawings of the combustion chamber and of the upper face of the
piston.
3.3. An engine and the equipment prescribed in Annex II to the Regulation
for fitting to the vehicle to be approved shall be submitted to thetechnical service conducting the approval tests defined in item 5.However, if the manufacturer so requests and the technical serviceconducting the approval tests agrees, a test may be carried out on avehicle representative of the vehicle type to be approved.
3a EEC TYPE APPROVAL
A certificate conforming to that shown in Annex X shall be attached to
the EEC type approval certificate.
4. SYMBOL OF THE CORRECTED ABSORPTION COEFFICIENT
(4.1.)(4.2.)(4.3.)4.4. To every vehicle conforming to a vehicle type approved under this
Regulation there shall be affixed, conspicuously and in a readily acces-sible place specified in the Annex to the type approval certificate shownin Annex X, a symbol being a rectangle surrounding a figure expressingin m
−1the corrected absorption coefficient obtained, at the time of
approval, during the test under free acceleration, and determined at thetime of approval by the method described in item 3.2 of Annex IV.
(a) The text of the Annexes is similar to that of Regulation No 24 of the UN Economic
Commission for Europe; in particular the breakdown into items is the same. For thisreason, where an item of Regulation No 24 has no counterpart in this Directive, itsnumber is given in brackets as a token entry.
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4.5. The symbol must be clearly legible and indelible.
4.6. Annex IX gives an example of the symbol.
5. SPECIFICATIONS AND TESTS5.1.General
The components liable to affect the emission of pollutants shall be so
designed, constructed and assembled as to enable the vehicle, in normaluse, despite the vibration to which it may be subjected, to comply withthe provisions of this Directive.
5.2.Specifications concerning cold-start devices
5.2.1. The cold-start device shall be so designed and constructed that it cannot
be brought into or kept in action when the engine is running normally.
5.2.2. The provisions of item 5.2.1 above shall not apply if at least one of the
following conditions is met:
5.2.2.1. The light absorption coefficient of the gases emitted by the engine at
steady speeds when measured by the method described in Annex IIIwith the cold-start device operating is within the limits prescribed inAnnex VI.
5.2.2.2. Keeping the cold-start device in operation causes the engine to stop
within a reasonable time.
5.3.Specifications concerning the emission of pollutants
5.3.1. The emission of pollutants by the vehicle type submitted for approval
shall be measured by the two methods described in Annexes III and IV,relating respectively to tests at steady speeds and to tests under freeacceleration. (
b)
5.3.2. The emission of pollutants, as measured by the method described in
Annex III, shall not exceed the limits prescribed in Annex VI.
5.3.3. In the case of engines with an exhaust-driven supercharger the absorp-
tion coefficient measured under free acceleration shall not exceed thelimit prescribed in Annex VI for the nominal flow value correspondingto the maximum absorption coefficient measured during the tests atsteady speeds, plus 0 ·5m
−1.
5.4. Equivalent measuring instruments shall be allowed. If an instrument
other than those described in Annex VII is used, proof of its equivalencefor the engine considered shall be required.
(6.)7. CONFORMITY OF PRODUCTION
7.1. Every vehicle in the series must conform, with regard to components
affecting the emission of pollutants by the engine, to the vehicle typeapproved.
(7.2.)7.3. As a general rule conformity of the vehicle with the approved type as
regards the emission of pollutants from diesel motors shall be verifiedon the basis of the description given in the Annex to the EEC approvalcertificate shown in Annex X. In addition:
7.3.1. Where a check is carried out on a vehicle taken from the series, the tests
shall be carried out as follows:
7.3.1.1. A vehicle which has not been run in shall be subjected to the test under
free acceleration described in Annex IV. The vehicle shall be deemed toconform to the approved type if the absorption coefficient determineddoes not exceed by more than 0 ·5m
−1the figure shown in the approval
mark.
7.3.1.2. If the figure determined in the test referred to in item 7.3.1 above
exceeds by more than 0 ·5m−1the figure shown in the approval mark, a
vehicle of the type considered or its engine shall be subjected to the test
(b) A test under free acceleration shall be carried out, especially in order to provide a
reference figure for administrations which use this method to check vehicles in use.
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at steady speeds over the full-load curve, as described in Annex III. The
emission levels shall not exceed the limits prescribed in Annex VI.
(8.)(9.)
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ANNEX II

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ANNEX III
TEST AT STEADY SPEEDS OVER THE FULL-LOAD CURVE
1. INTRODUCTION
1.1. This annex describes the method of determining emissions of pollutants at
different steady speeds over the full-load curve.
1.2. The test may be carried out either on an engine or on a vehicle.
2. MEASUREMENT PRINCIPLE
2.1. The opacity of the exhaust gases produced by the engine shall be meas-
ured with the engine running under full load and at steady speed. Sixmeasurements shall be made at engine speeds spaced out uniformlybetween that corresponding to maximum power and the higher of thefollowing two engine speeds:
— 45 per cent of the engine speed corresponding to maximum power;
and
— 1 000 rpm.
The extreme points of measurement shall be situated at the limits of the
interval defined above.
2.2. In the case of diesel engines which are fitted with an air supercharger
which can be engaged at will, and in which engines the entry intooperation of the air supercharger automatically brings about an increase inthe quantity of fuel injected, the measurements shall be made both withand without the supercharger working.
For each engine speed, the result of the measurement shall be the higher
of the two figures obtained.
3. TEST CONDITIONS3.1.Vehicle or engine
3.1.1. The engine or the vehicle shall be submitted in good mechanical condi-
tion. The engine shall have been run in.
3.1.2. The engine shall be tested with the equipment described in Annex II.3.1.3. The settings of the engine shall be those described by the manufacturer
and by Annex II.
3.1.4. The exhaust device shall not have any orifice through which the gases
emitted by the engine might be diluted.
3.1.5. The engine shall be in the normal working condition prescribed by the
manufacturer. In particular, the cooling water and the oil shall each be atthe normal temperature indicated by the manufacturer.
3.2.Fuel
The fuel shall be the reference fuel whose specifications are given in
Annex V.
3.3.Test laboratory
3.3.1. The absolute temperature T of the laboratory, expressed in degrees Kelvin,
and the atmospheric pressure H, expressed in torr, shall be measured, andthe factor F shall be determined by the formula
F=
(750
H)0·65
×(T
298)0·5
3.3.2. For a test to be recognized as valid, the factor F shall be such that 0 ·98≤
F≤1·02.
3.4.Sampling and measuring apparatus
The light-absorption coefficient of the exhaust gases shall be measured
with an opacimeter satisfying the conditions laid down in Annex VII andinstalled in conformity with Annex VIII.
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4. LIMIT VALUES
4.1. For each of the six engine speeds at which the absorption coefficient is
measured pursuant to paragraph 2.1 above, the nominal gas flow G,expressed in litres per second, shall be calculated by means of thefollowing formulae:
— for two-stroke engines G=Vn
60
— for four-stroke engines G=Vn
120
where:
V is the cylinder capacity of the engine expressed in litres; andn is the engine speed in revolutions per minute.
4.2. For each engine speed the absorption coefficient of the exhaust gases shall
not exceed the limit value given in the table in Annex VI. Where the valueof the nominal flow is not one of those given in that table, the limit valueapplicable shall be obtained by interpolation on the principle of propor-tional parts.
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ANNEX IV
TEST UNDER FREE ACCELERATION
1. TEST CONDITIONS
1.1. The test shall be carried out on the vehicle or engine which has undergone
the test at steady speeds described in Annex III.
1.1.1. If the engine is tested on a bench the test shall be carried out as soon as
possible after the test for measurement of opacity under full load at steadyspeed. In particular, the cooling water and the oil shall be at the normaltemperatures indicated by the manufacturer.
1.1.2. If the test is carried out on a stationary vehicle, the engine shall first be
brought to normal operating condition by a road run. The test shall becarried out as soon as possible after completion of the road run.
1.2. The combustion chamber shall not have been cooled or fouled by a
prolonged period of idling preceding the test.
1.3. The test conditions described in Annex III, items 3.1, 3.2 and 3.3, shall
apply.
1.4. The conditions described in Annex III, item 3.4, with regard to the
sampling and measuring apparatus shall apply.
2. TEST METHODS
2.1. If the test is a bench test, the engine shall be disconnected from the brake,
the latter being replaced either by the rotating parts driven when no gear isengaged or by an inertia substantially equivalent to that of the rotatingparts.
2.2. If the test is carried out on a vehicle, the gear-change control shall be set
in the neutral position and the engine in gear.
2.3. With the engine idling, the accelerator control shall be operated quickly,
but not violently, so as to obtain maximum delivery from the injectionpump. This position shall be maintained until maximum engine speed isreached and the governor comes into action. As soon as this speed isreached the accelerator shall be released until the engine resumes its idlingspeed and the opacimeter reverts to the corresponding conditions.
2.4. The operation described in item 2.3 above shall be repeated not less than
six times in order to clear the exhaust system and to allow for anynecessary adjustment of the apparatus. The maximum opacity values readat each successive acceleration shall be noted until stabilized values areobtained. No account shall be taken of the values read while the engine isidling after each acceleration. The values read shall be regarded as stabi-lized when four consecutive readings are situated within a band width of0·25 m
−1and do not form a decreasing sequence. The absorption coeffi-
cient XMto be recorded shall be the arithmetic mean of these four values.
2.5. Engines fitted with an air supercharger shall be subject, where appropriate,
to the following special requirements:
2.5.1. In the case of engines with an air supercharger which is coupled with or
driven mechanically by the engine and is capable of being disengaged,two complete measurement cycles with preliminary accelerations shall becarried out, the air supercharger being engaged in one case and disen-gaged in the other. The measurement result recorded shall be the higher ofthe two results obtained;
2.5.2. In the case of engines with an air supercharger which can be cut out by
means of a driver-operated bypass, the test shall be carried out with andwithout the bypass. The measurement result recorded shall be the higherof the results obtained.
3. DETERMINATION OF THE CORRECTED VALUE OF THE ABSORP-
TION COEFFICIENT
3.1.Notation
X
M=value of the absorption coefficient under free acceleration measured
as described in item 2.4 of this Annex;
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XL=corrected value of the absorption coefficient under free acceleration;
SM=value of the absorption coefficient measured at steady speed (Annex
III, item 2.1.) which is closest to the prescribed limit value corre-sponding to the same nominal flow;
S
L=value of the absorption coefficient (Annex III, item 4.2.) for the
nominal flow corresponding to the point of measurement which gavethe value S
M;
L =effective length of the light path in the opacimeter.
3.2. When the absorption coefficients are expressed in m−1and the effective
length of the light path in metres, the corrected value XLis given by the
smaller of the following two expressions:
X/prime1L=SL
SM·XMouXL=XM+ 0,5
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ANNEX V
SPECIFICATIONS OF REFERENCE FUEL PRESCRIBED FOR APPROVAL TESTS AND
TO VERIFY CONFORMITY OF PRODUCTION
Limits and units Method
Density 15/4 °C 0·8 3 0±0 ·005 ASTM D 1298-67
Distillation ASTM D 86-67
50 % min. 245 °C
90 % 3 3 0±1 0 °C
Final boiling point max. 370 °C
Cetane index 5 4±3 ASTM D 976-66
Kinematic viscosity at 100 F 3±0 ·5 est ASTM D 445-65
Sulphur content 0·4·0·1 % by weight ASTM D 129-64
Flash-point min. 55 °C ASTM D 93-71
Cloud point max. −7 °C ASTM D 2500-66
Aniline point 6 9±5 °C ASTM D 611-64
Carbon residue on 10 % bottoms max. 0 ·2 % by weight ASTM D 524-64
Ash content max. 0 ·01 % by weight ASTM D 482-63
Water content max. 0 ·05 % by weight ASTM D 95-70
Copper — corrosion test at 100 °C max. 1 ASTM D 130-68
Net calorific value
ASTM D 2-68
(Ap. VI)
Strong acid number nil mg KoH/g ASTM D 974-64
Note:The fuel must be based only on straight-run distillates, hydrodesulphurized or not, and must
contain no additives.
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ANNEX VI
LIMIT VALUES APPLICABLE IN THE TEST AT STEADY SPEEDS
NominalflowG
litres/secondAbsorptioncoefficientK
m−1
≤42 2 ·26
45 2 ·19
50 2·08
55 1 ·985
60 1 ·90
65 1 ·84
70 1·775
75 1 ·72
80 1 ·665
85 1·62
90 1 ·575
95 1 ·535
100 1·495
105 1 ·465
110 1 ·425
115 1·395
120 1 ·37
125 1 ·345
130 1·32
135 1 ·30
140 1 ·27
145 1·25
150 1 ·225
155 1 ·205
160 1·19
165 1 ·17
170 1 ·155
175 1·14
180 1 ·125
185 1 ·11
190 1·095
195 1 ·08
≤200 1·065
Note:Although the above values are rounded to the nearest 0 ·01 or 0 ·005, this does not mean that the
measurements need to be made to this degree of accuracy.
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ANNEX VII
CHARACTERISTICS OF OPACIMETERS
1. SCOPE
This annex defines the conditions to be met by opacimeters used in the
tests described in Annexes III and IV.
2. BASIC SPECIFICATION FOR OPACIMETERS
2.1. The gas to be measured shall be confined in an enclosure having a
non-reflecting internal surface.
2.2. In determining the effective length of the light path through the gas,
account shall be taken of the possible influence of devices protecting thelight source and the photoelectric cell. This effective length shall beindicated on the instrument.
2.3. The indicating dial of the opacimeter shall have two measuring scales,
one in absolute units of light absorption from 0 to (m
−1) and the other
linear from 0 to 100; both scales shall range from 0 at total light flux tofull scale at complete obscuration.
3. CONSTRUCTION SPECIFICATIONS3.1.General
The design shall be such that under steady-speed operating conditions
the smoke chamber is filled with smoke of uniform opacity.
3.2.Smoke chamber and opacimeter casing
3.2.1. The impingement on the photoelectric cell of stray light due to internal
reflections or diffusion effects shall be reduced to a minimum (e.g. byfinishing internal surfaces in matt black and by a suitable generallayout).
3.2.2. The optical characteristics shall be such that the combined effect of
diffusion and reflection does not exceed one unit on the linear scalewhen the smoke chamber is filled with smoke having an absorptioncoefficient near 1 ·7m
−1.
3.3.Light source
The light source shall be an incandescent lamp with a colour tempera-
ture in the range 2 800 to 3 250 °K.
3.4.Receiver
3.4.1. The receiver shall consist of a photoelectric cell with a spectral response
curve similar to the photopic curve of the human eye (maximumresponse in the range 550/570 nm; less than 4 per cent of that maximumresponse below 430 nm and above 680 nm).
3.4.2. The construction of the electrical circuit, including the indicating dial,
shall be such that the current output from the photoelectric cell is alinear function of the intensity of the light received over the operating-temperature range of the photoelectric cell.
3.5.Measuring scales
3.5.1. The light-absorption coefficient k shall be calculated by the formula Φ=
Φ
o·e−kL, where L is the effective length of the light path through the gas
to be measured, Φothe incident flux and Φthe emergent flux. When the
effective length L of a type of opacimeter cannot be assessed directlyfrom its geometry, the effective length L shall be determined
— either by the method described in item 4 of this Annex; or
— through correlation with another type of opacimeter for which the
effective length is known.
3.5.2. The relationship between the 0-100 linear scale and the light absorption
coefficient k is given by the formula
k=−1
Lloge(1−N
100)
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where N is a reading on the linear scale and k the corresponding value
of the absorption coefficient.
3.5.3. The indicating dial of the opacimeter shall enable an absorption coeffi-
cient of 1 ·7m−1to be read with an accuracy of 0 ·025 m−1.
3.6.Setting and testing of the measuring apparatus
3.6.1. The electrical circuit of the photoelectric cell and of the indicating dial
shall be adjustable so that the pointer can be reset at zero when the lightflux passes through the smoke chamber filled with clean air or through achamber having identical characteristics.
3.6.2. With the lamp switched off and the electrical measuring circuit open or
short-circuited, the reading on the absorption-coefficient scale shall be ,and it shall remain at with the measuring circuit reconnected.
3.6.3. An intermediate check shall be carried out by placing in the smoke
chamber a screen representing a gas whose known light-absorptioncoefficient k, measured as described in item 3.5.1. is between 1 ·6m
−1
and 1 ·8m−1. The value of k must be known to within 0 ·025 m−1. The
check consists in verifying that this value does not differ by more than0·05 m
−1from that read on the opacimeter indicating dial when the
screen is introduced between the source of light and the photoelectriccell.
3.7.Opacimeter response
3.7.1. The response time of the electrical measuring circuit, being the time
necessary for the indicating dial to reach 90 per cent of full-scaledeflection ►
C2on insertion ◄of a screen fully obscuring the photo-
electric cell, shall be 0 ·9t o1 ·1 second.
3.7.2. The damping of the electrical measuring circuit shall be such that the
initial overswing beyond the final steady reading after any momentaryvariation in input (e.g. the calibration screen) does not exceed 4 per centof that reading in linear scale units.
3.7.3. The response time of the opacimeter which is due to physical
phenomena in the smoke chamber is the time between the entry of thegas into the measuring apparatus and the complete filling of the smokechamber; it shall not exceed 0 ·4 second.
3.7.4. These provisions shall apply solely to opacimeters used to measure
opacity under free acceleration.
3.8.Pressure of the gas to be measured and of scavenging air
3.8.1. The pressure of the exhaust gas in the smoke chamber shall not differ by
more than 75 mm (water gauge) from the atmospheric pressure.
3.8.2. The variations in the pressure of the gas to be measured and of the
scavenging air shall not cause the absorption coefficient to vary by morethan 0 ·05 m
−1in the case of a gas having an absorption coefficient of 1 ·7
m−1.
3.8.3. The opacimeter shall be equipped with appropriate devices for meas-
uring the pressure in the smoke chamber.
3.8.4. The limits of pressure variation of gas and scavenging air in the smoke
chamber shall be indicated by the manufacturer of the apparatus.
3.9.Temperature of the gas to be measured
3.9.1. At every point in the smoke chamber the gas temperature at the instant
of measurement shall be between 70 °C and a maximum temperature,
specified by the opacimeter manufacturer, such that the readings overthis temperature range do not vary by more than 0 ·1m
−1if the chamber
is filled with a gas having an absorption coefficient of 1 ·7m−1.
3.9.2. The opacimeter shall be equipped with appropriate devices for meas-
uring the temperature in the smoke chamber.
4. EFFECTIVE LENGTH ‘L' OF THE OPACIMETER4.1.General
4.1.1. In some types of opacimeter the gas between the light source and the
photoelectric cell, or between transparent parts protecting the source andthe photoelectric cell, is not of constant opacity. In such cases theeffective length L shall be that of a column of gas of uniform opacity
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which gives the same absorption of light as that obtained when the gas
is admitted in a normal way into the opacimeter.
4.1.2. The effective length of the light path is obtained by comparing the
reading N of the opacimeter operating normally with the reading Noobtained with the opacimeter modified so that the test gas fills a welldefined length L
o.
4.1.3. It will be necessary to take comparative readings in quick succession to
determine the correction to be made for shifts of zero.
4.2.Method of assessment of L
4.2.1. The test gas shall be exhaust gas of constant opacity or a light-absorp-
tive gas of a gravimetric density similar to that of the exhaust gas.
4.2.2. A column of length Loof the opacimeter, which can be filled uniformly
with the test gases, and the ends of which are substantially at rightangles to the light path, shall be accurately determined. This length L
oshall be close to the presumed effective length of the opacimeter.
4.2.3. The mean temperature of the test gas in the smoke chamber shall be
measured.
4.2.4. If necessary, an expansion tank of compact design and of sufficient
capacity to damp the pulsations may be incorporated in the samplingline as near to the probe as possible. A cooler may also be fitted. Theaddition of the expansion tank and of the cooler must not unduly disturbthe composition of the exhaust gas.
4.2.5. The test for determining the effective length shall consist of passing a
sample of test gas alternately through the opacimeter operating normallyand through the same apparatus modified as indicated in item 4.1.2.
4.2.5.1. The opacimeter readings shall be recorded continuously during the test
with a recorder whose response time is equal to or shorter than that ofthe opacimeter.
4.2.5.2. With the opacimeter operating normally, the reading on the linear scale
of opacity is N and that of the mean gas temperature expressed inKelvin degrees is T.
4.2.5.3. With the known length L
ofilled with the same test gas, the reading on
the linear scale of opacity is Noand that of the mean gas temperature
expressed in Kelvin degrees is To.
4.2.6. The effective length will be
4.2.7. The test shall be repeated with at least four test gases giving readings
evenly spaced between the 20 and 80 on the linear scale.
4.2.8. The effective length L of the opacimeter will be the arithmetic mean of
the effective lengths obtained as stated in item 4.6 with each of thegases.
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ANNEX VIII
INSTALLATION AND USE OF THE OPACIMETER
1. SCOPE
This annex specifies the installation and use of opacimeters for the tests
described in Annexes III and IV.
2. SAMPLING OPACIMETER2.1.Installation for steady-speed tests
2.1.1. The ratio of the cross-sectional area of the probe to that of the exhaust
pipe shall not be less than 0 ·05. The back pressure measured in the
exhaust pipe at the intake of the probe shall not exceed 75 mm (watergauge).
2.1.2. The probe shall be a tube with an open end facing forwards in the axis of
the exhaust pipe, or of the extension pipe if one is required. It shall hesituated in a section where the distribution of smoke is approximatelyuniform. To achieve this, the probe shall be placed as far downstream inthe exhaust pipe as possible, or, if necessary, in an extension pipe so that,if D is the diameter of the exhaust pipe at the outlet, the end of the probeis situated in a straight portion at least 6 D in length upstream of thesampling point and 3 D in length downstream. If an extension pipe isused, no air shall be allowed to enter the joint.
2.1.3. The pressure in the exhaust pipe and the characteristics of the pressure
drop in the sampling line shall be such that the probe collects a samplesubstantially equivalent to that which would be obtained by isokineticsampling.
2.1.4. If necessary, an expansion tank of compact design and of sufficient
capacity to damp the pulsations may be incorporated in the sampling lineas near to the probe as possible. A cooler may also be fitted.
The design of the expansion tank and cooler shall not unduly disturb the
composition of the exhaust gas.
2.1.5. A butterfly valve or other means of increasing the sampling pressure may
be placed in the exhaust pipe at least thre e 3 D downstream from the
sampling probe.
2.1.6. The connecting pipes between the probe, the cooling device, the expan-
sion tank (if required) and the opacimeter shall be as short as possiblewhile satisfying the pressure and temperature requirements described inAnnex VII, items 3.8 and 3.9. The pipe shall be inclined upwards from thesampling point to the opacimeter, and sharp bends where soot mightaccumulate shall be avoided. If not embodied in the opacimeter, a bypassvalve shall be provided upstream.
2.1.7. A check shall be carried out during the test to ensure that the requirements
of Annex VII, item 3.8, concerning pressure and those of Annex VII, item3.9, concerning the temperature in the measuring chamber are observed.
2.2.Installation for tests under free acceleration
2.2.1. The ratio of the cross-sectional area of the probe to that of the exhaust
pipe shall not be less thas 0 ·05. The back pressure measured in the
exhaust pipe at the intake of the probe shall not exceed 75 mm (watergauge).
2.2.2. The probe shall be a tube with an open end facing forwards in the axis of
the exhaust pipe, or of the extension pipe if one is required. It shall besituated in a section where the distribution of smoke is approximatelyuniform. To achieve this, the probe shall be placed as far downstream inthe exhaust pipe as possible or, if necessary, in an extension pipe so that,if D is the diameter of the exhaust pipe at the outlet, the end of the probeis situated in a straight portion at least 6 D in length upstream of thesampling point and 3 D in length downstream. If an extension pipe isused, no air shall be allowed to enter the joint.
2.2.3. The sampling system shall be such that at all engine speeds the pressure of
the sample at the opacimeter is within the limits specified in Annex VII,item 3.8.2. This may be checked by noting the sample pressure at engineidling and maximum no-load speeds. Depending on the characteristics ofthe opacimeter, control of sample pressure can be achieved by a fixedrestriction or a butterfly valve in the exhaust pipe or extension pipe.
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Whichever method is used, the back pressure measured in the exhaust
pipe at the intake of the probe shall not exceed 75 mm (water gauge).
2.2.4. The pipes connecting with the opacimeter shall be as short as possible.
The pipe shall be inclined upwards from the sampling point to the opaci-meter, and sharp bends where soot might accumulate shall be avoided. Abypass valve may be provided upstream of the opacimeter to isolate itfrom the exhaust-gas flow when no measurement is being made.
3. FULL-FLOW OPACIMETER
The only general precautions to be observed in steady-speed and free-
acceleration tests are the following:
3.1. Joints in the connecting pipes between the exhaust pipe and the opaci-
meter shall not allow air to enter from outside.
3.2. The pipes connecting with the opacimeter shall be as short as possible, as
in the case of sampling opacimeters. The pipe system shall be inclinedupwards from the exhaust pipe to the opacimeter, and sharp bends wheresoot might accumulate shall be avoided. A bypass valve may be providedupstream of the opacimeter to isolate it from the exhaust-gas flow whenno measurement is being made.
3.3. A cooling system may also he required upstream of the opacimeter.
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ANNEX IX
EXAMPLE OF THE SYMBOL OF THE CORRECTED ABSORPTION
COEFFICIENT
The above symbol shows that the corrected absorption coefficient is 1 ·30 m−1.
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ANNEX X

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