Egzoz sistemlerinde sıcaklık sensörü ölçüm doğruluğunun ve katalist sıcaklığının incelenmesi
Temperature sensor measurement accuracy and catalyst temperature investigation for automotive exhaust systems
Yazar: MUSTAFA BAHADIR HERGENÇ
Danışman: YRD. DOÇ. DR. MURAT ÇAKAN
İstanbul Teknik Üniversitesi / Enerji Enstitüsü / Enerji Bilim ve Teknoloji Ana Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Tez çalısması kapsamında, egzoz sistemlerinde kullanılan sıcaklık sensörünün prob
uzunluğunun, belirlenen bir sistem için ölçülen ortalama egzoz boru sıcaklığına etkisi
ve motor ile dizel oksidasyon katalisti arasındaki bağlantı borusunun uzunluğunun
oksidasyon katalisti giris ve çıkıs sıcaklıklarına olan etkisi irdelenmis, söz konusu
etki yakıt tüketimi ve egzoz zararlı gaz emisyonları ile birlikte değerlendirilmistir.
Tez çalısmasının birinci bölümünde, otomotiv egzoz sistemlerinde kullanılan
emisyon indirgeme ekipmanları ve bu ekipmanların kontrolü amacıyla kullanılan
sensörlerin literatür incelemesine, endüstride yaygın olarak kullanılan
uygulamalarına ve bu sistemlerde gerçeklesen kimyasal tepkimelere yer verilmistir.
Đkinci bölümde, egzoz sistemlerinde bulunan emisyon indirgeme cihazlarının çalısma
verimlerinin egzoz boru içerisindeki sıcaklık ve akıs özelliklerine bağlı olarak
değisimini inceleyen çalısmalara yer verilmistir.
Üçüncü bölümde, testler sırasında kullanılacak olan test düzeneği ve düzenek
içerisinde bulunan ekipmanların teknik ve fiziksel özelliklerine yer verilmistir. Aynı
zamanda test düzeneğinde incelenen parametreler açıklanmıs ve ölçüm belirsizliği
hesaplamaları yapılmıstır.
Dördüncü bölümde, birinci grup testler kapsamında, egzoz sistemlerinde katalist giris
ve çıkıs noktalarında bulunan sıcaklık sensörlerinin prob uzunluklarına bağlı olarak
alınan ölçüm ile aynı noktanın ortalama egzoz gaz sıcaklığı kıyaslanmıstır. Buna
bağlı olarak verilen sistem için incelenen farklı prob uzunluğuna sahip sıcaklık
sensörlerinin ortalama egzoz gaz sıcaklığından hangi oranda saptığı hesaplanmıs ve
verilen sistem için en uygun prob uzunluğu belirlenmistir. Deneysel çalısmalara ek
olarak yapılan sayısal analizler ile ölçüm sonuçları desteklenmistir. Đkinci grup testler
kapsamında, motor ile dizel oksidasyon katalisti arasındaki bağlantı borusu boyunun
kısaltılması neticesinde ısı kayıplarının düsürülerek katalist giris sıcaklığının
yükseltilmesi hedeflenmis ve bunun sonucunda katalistte istenilen sıcaklığa ulasmak
için post enjeksiyon sırasında püskürtülen yakıt miktarındaki değisim hesaplanmıstır.
Aynı sekilde farklı sürüs karakteristikleri için önerilen değisiklik sonucunda elde
edilecek toplam yakıt tasarrufu belirlenmistir.
Besinci ve son bölümde yapılan testler ve sayısal analizlerin sonuçları detaylı bir
sekilde ortaya konmus ve gelecek çalısmalar için önerilerde bulunulmustur.

Abstract:
In this thesis, for a defined system, temperature sensor tip length effect on
temperature measurement results of the average exhaust gas temperature has been
evaluated. Also effect of pipe length between engine out and diesel oxidation catalyst
on the catalyst temperature as well as resultant fuel consumption and emission
effects.
In parallel with increase on population and level of income, exhaust gases output
from motor vehicles would become an important factor on air pollution after air
pollution caused by industrial effects. This situation makes control of exhaust gas
emissions obligatory. Based on the fact that diesel engines has high efficiency, low
fuel costs, high robustness and high reliability diesel engines becomes leader on
commercial vehicle segment. Recently due to high fares on fuel, diesel engines
become important on passenger vehicle segment as well. It is expected that
proportion of the diesel engines will become higher in the next years. This growth
trend on diesel engine usage creates a need for investigating the effects of exhaust
gases and developing new technologies to increas efficiency of diesel combustion.
As part of this thesis, as a result of defining measurement reliability of the
temperature sensors based on its tip length, efficiency of diesel oxidation catalyst and
diesel particulate filter tried to be increased. Besides based on shortening the
connection pipe between engine and exhaust emission reduction components,
working efficiency of the emission reduction components tried to be increased and
the total exhaust emission tried to be reduced.
First section of thesis includes literature research of emission reduction equipments
being used on automotive exhaust system and the sensors being used to control those
equipments as well as industrial applications of those components with the chemical
reactions takes place in those equipments. All the emission reduction equipments
including several catalyst systems and the filter equipment defined, their application
on several positions explained. Comparably working principle and fields of
application for the sensors defined in the first section.
Second section of thesis includes, studies related with the effects of the exhaust gas
flow and temperature properties on working efficiencies of emission reduction
components on the exhaust system. Several similar studies including changing the
shape and lentgth of selective catalytic reduction inlet pipe and investigating effect of
these two cases based on selective catalytic reduction conversion efficiency and the
temperature requirement for the diesel particulate filter regeneration process and
controlling the diesel oxidation catalyst NO/NO2 conversion rate based on the fuel amount injected on post injection process has been summarised and results given as
it is defined in the original article.
Third section of thesis includes testing equipments and techincal and physical
properties of those equipments being used during tests. Thermocouples and the
temperature sensors as well as the burner and the compressor defined. System inputs
and outputs which are reflecting the real life condition defined. Parameter selection
and the range for the selected parameters during testing decided. Uncertainity
calculation for each parameter given based on the values given by the manufacturer.
Fourth section of thesis includes, first group of tests completed on the test bench.
First group of test aims to investigate coherence between temperature sensor
measurements and average temperature value on exhaust cross section area based on
tip length. Based on this deviation from the average exhaust gas temperature has
been calculated based on tip length and optimum tip length for the given system
specified by assuming that the thermocouples are measuring the avarage exhaust
temperature correctly. Addition to those testings, numerical analysis completed with
computational fluid dynamics method to support the measurement results.
Temperature distribution on the cross section exhaust pipe for the exhaust gas
temperature sensor position at the diesel oxidation catalyst inlet is calculated through
the computational fluid dynamics program. Results investigated and given for each
50 °C with colour codes. Avarage velocity value for the whole exhaust inlet pipe is
given also. Input values for the numerical analysis taken as average of the
temperature measurements of each thermocouples being used on the first group of
tests.
As part of second group tests, it has been aimed to reduce heat loss and increase
catalyst inlet temperature based on reduction of length of exhaust pipe between
engine outlet and diesel oxidation catalyst. Two different connection pipe length
between the engine outlet and diesel oxidation catalyst has been used during tests to
measure temperature differences and calculate the saving from the heat losses.
Second group tests completed on a vehicle which is equipped with an engine and
modeling the conditions such as in the real life for an avarage customer. As a result
of this increase on the catalyst inlet temperature, savings of the post injection fuel
amount has been calculated and total fuel saving amount calculated during lifetime
of a vehicle. Lifetime period of a vehicle has been defined based on assumption of
the warranty period given by the car manufacturer companies. Avarage fules saving
amount calculated for three different usage style including city usage, subway usage
and rural usage.
In the final section, summary of results and suggestions are obtained. It is necessary
that results sum up;
-Based on recurrent tests for the sensors using 30mm,50mm and 70mm tip length,
temperature measurements taken by first exhaust gas temperature sensor and second
exhaust gas temperature sensor is proportional to the measurements taken with the
first thermocouple and second thermocouple.
-Temperature measurements taken with thermocouple 2 has shown close figures with
the temperature measured with the exhaust gas temperature sensor 1 however this is
not calid for the temperature measured with the second exhaust gas temperature
sensor.
-Based on selecting temperature measurements done by second thermocouple as
reference, margin of error has been calculated for the three different sensors using
different tip length.
-Based on calculations, margin of error has been calculated as %2.52,%5.52 and
%9.85 for the 70 mm,50 mm and 30 mm in the same order.
-At the same time a numerical analysis has been completed to compare the test
results and the velocity and temperature distribution of the cross section pipe area
defined.
-On the numerical analysis, it has been calculated that the gas velocity mean value is
between 5 m/s and 15 m/s for the concave edge. This value increasing by progressing
to the convex edge of the pipe and reaching up to 29 m/s.
-After investigating the numerical analysis results, margin of error has been
calculated as %5 and %10 for the sensor with 50 mm and 30 mm tip length in the
same order based on the assumption that sensor with the 70 mm tip length measuring
the avarage exhaust gas temperature correctly.
-For the given system, sensor having 30 mm probe length will not represent the
physical conditions. This situation prevent to reach aimed emission levels. Likewise
deviations which will occur on the temperature measured by the second exhaust gas
temperature sensor will effect the regeneration period of the vehicle.
-Change on the regeneration period will increase the amount of fuel consumed and
negatively effect the comfort of the driver.
-Effect of the connection pipe between the engine and the emission control
equipments has been investigated by conducting group of test on the vehicle.
-In regards to the test results, reducing the length of the connection pipe between the
engine and emission control equipments results to decrease on the heat loss and
increase on the diesel oxidation catalyst temperature. This condition will have a
positive effect on the fuel amount to be consumed during post injection process
which aims to maintain required temperature limit for the diesel particulate filter
regeneration process.
-Within the test completed on the vehicle, based on reducing the length of the
connection pipe between the engine and emission control equipments fuel saving
amount has been calculated per every stroke of the engine for three different driving
operation mode.
-On the basis of those calculations, fuel saving amount for lifetime of a vehicle is
found as 0.2304 kg for the city cycle, 0.1536 kg for the rural cycle and 0.1024 for the
subway cycle.
-In consequence of the test done during this thesis, along with having quite a little
effect on the fuel consumption of a vehicle considering lifetime fuel consumption of
a vehicle by reducing the connection pipe length between the engine and the
emission reduction components, considering to have positive effect on the exhaust
gas emissions, suggested improvement can be implemented by considering the
packaging constraints.
For future studies, some suggestions are given below:
-Diesel oxidation catalyst length can be optimized by measuring and analysing the
chemical reaction speed taking place inside the catalyst.
-Temperature of the diesel oxidation catalyst can be controlled by adding a heater
before the catalyst and the effect of this action to the complete system cost can be
investigated.