Egzoz sistemlerinde sıcaklık sensörü ölçüm doğruluğunun ve katalist sıcaklığının incelenmesi

Abstract

Tez çalısması kapsamında, egzoz sistemlerinde kullanılan sıcaklık sensörünün probuzunluğunun, belirlenen bir sistem için ölçülen ortalama egzoz boru sıcaklığına etkisive motor ile dizel oksidasyon katalisti arasındaki bağlantı borusunun uzunluğununoksidasyon katalisti giris ve çıkıs sıcaklıklarına olan etkisi irdelenmis, söz konusuetki yakıt tüketimi ve egzoz zararlı gaz emisyonları ile birlikte değerlendirilmistir.Tez çalısmasının birinci bölümünde, otomotiv egzoz sistemlerinde kullanılanemisyon indirgeme ekipmanları ve bu ekipmanların kontrolü amacıyla kullanılansensörlerin literatür incelemesine, endüstride yaygın olarak kullanılanuygulamalarına ve bu sistemlerde gerçeklesen kimyasal tepkimelere yer verilmistir.Đkinci bölümde, egzoz sistemlerinde bulunan emisyon indirgeme cihazlarının çalısmaverimlerinin egzoz boru içerisindeki sıcaklık ve akıs özelliklerine bağlı olarakdeğisimini inceleyen çalısmalara yer verilmistir.Üçüncü bölümde, testler sırasında kullanılacak olan test düzeneği ve düzenekiçerisinde bulunan ekipmanların teknik ve fiziksel özelliklerine yer verilmistir. Aynızamanda test düzeneğinde incelenen parametreler açıklanmıs ve ölçüm belirsizliğihesaplamaları yapılmıstır.Dördüncü bölümde, birinci grup testler kapsamında, egzoz sistemlerinde katalist girisve çıkıs noktalarında bulunan sıcaklık sensörlerinin prob uzunluklarına bağlı olarakalınan ölçüm ile aynı noktanın ortalama egzoz gaz sıcaklığı kıyaslanmıstır. Bunabağlı olarak verilen sistem için incelenen farklı prob uzunluğuna sahip sıcaklıksensörlerinin ortalama egzoz gaz sıcaklığından hangi oranda saptığı hesaplanmıs veverilen sistem için en uygun prob uzunluğu belirlenmistir. Deneysel çalısmalara ekolarak yapılan sayısal analizler ile ölçüm sonuçları desteklenmistir. Đkinci grup testlerkapsamında, motor ile dizel oksidasyon katalisti arasındaki bağlantı borusu boyununkısaltılması neticesinde ısı kayıplarının düsürülerek katalist giris sıcaklığınınyükseltilmesi hedeflenmis ve bunun sonucunda katalistte istenilen sıcaklığa ulasmakiçin post enjeksiyon sırasında püskürtülen yakıt miktarındaki değisim hesaplanmıstır.Aynı sekilde farklı sürüs karakteristikleri için önerilen değisiklik sonucunda eldeedilecek toplam yakıt tasarrufu belirlenmistir.Besinci ve son bölümde yapılan testler ve sayısal analizlerin sonuçları detaylı birsekilde ortaya konmus ve gelecek çalısmalar için önerilerde bulunulmustur.

In this thesis, for a defined system, temperature sensor tip length effect ontemperature measurement results of the average exhaust gas temperature has beenevaluated. Also effect of pipe length between engine out and diesel oxidation catalyston the catalyst temperature as well as resultant fuel consumption and emissioneffects.In parallel with increase on population and level of income, exhaust gases outputfrom motor vehicles would become an important factor on air pollution after airpollution caused by industrial effects. This situation makes control of exhaust gasemissions obligatory. Based on the fact that diesel engines has high efficiency, lowfuel costs, high robustness and high reliability diesel engines becomes leader oncommercial vehicle segment. Recently due to high fares on fuel, diesel enginesbecome important on passenger vehicle segment as well. It is expected thatproportion of the diesel engines will become higher in the next years. This growthtrend on diesel engine usage creates a need for investigating the effects of exhaustgases and developing new technologies to increas efficiency of diesel combustion.As part of this thesis, as a result of defining measurement reliability of thetemperature sensors based on its tip length, efficiency of diesel oxidation catalyst anddiesel particulate filter tried to be increased. Besides based on shortening theconnection pipe between engine and exhaust emission reduction components,working efficiency of the emission reduction components tried to be increased andthe total exhaust emission tried to be reduced.First section of thesis includes literature research of emission reduction equipmentsbeing used on automotive exhaust system and the sensors being used to control thoseequipments as well as industrial applications of those components with the chemicalreactions takes place in those equipments. All the emission reduction equipmentsincluding several catalyst systems and the filter equipment defined, their applicationon several positions explained. Comparably working principle and fields ofapplication for the sensors defined in the first section.Second section of thesis includes, studies related with the effects of the exhaust gasflow and temperature properties on working efficiencies of emission reductioncomponents on the exhaust system. Several similar studies including changing theshape and lentgth of selective catalytic reduction inlet pipe and investigating effect ofthese two cases based on selective catalytic reduction conversion efficiency and thetemperature requirement for the diesel particulate filter regeneration process andcontrolling the diesel oxidation catalyst NO/NO2 conversion rate based on the fuel amount injected on post injection process has been summarised and results given asit is defined in the original article.Third section of thesis includes testing equipments and techincal and physicalproperties of those equipments being used during tests. Thermocouples and thetemperature sensors as well as the burner and the compressor defined. System inputsand outputs which are reflecting the real life condition defined. Parameter selectionand the range for the selected parameters during testing decided. Uncertainitycalculation 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 sensormeasurements and average temperature value on exhaust cross section area based ontip length. Based on this deviation from the average exhaust gas temperature hasbeen calculated based on tip length and optimum tip length for the given systemspecified by assuming that the thermocouples are measuring the avarage exhausttemperature correctly. Addition to those testings, numerical analysis completed withcomputational fluid dynamics method to support the measurement results.Temperature distribution on the cross section exhaust pipe for the exhaust gastemperature sensor position at the diesel oxidation catalyst inlet is calculated throughthe computational fluid dynamics program. Results investigated and given for each50 °C with colour codes. Avarage velocity value for the whole exhaust inlet pipe isgiven also. Input values for the numerical analysis taken as average of thetemperature measurements of each thermocouples being used on the first group oftests.As part of second group tests, it has been aimed to reduce heat loss and increasecatalyst inlet temperature based on reduction of length of exhaust pipe betweenengine outlet and diesel oxidation catalyst. Two different connection pipe lengthbetween the engine outlet and diesel oxidation catalyst has been used during tests tomeasure temperature differences and calculate the saving from the heat losses.Second group tests completed on a vehicle which is equipped with an engine andmodeling the conditions such as in the real life for an avarage customer. As a resultof this increase on the catalyst inlet temperature, savings of the post injection fuelamount has been calculated and total fuel saving amount calculated during lifetimeof a vehicle. Lifetime period of a vehicle has been defined based on assumption ofthe warranty period given by the car manufacturer companies. Avarage fules savingamount calculated for three different usage style including city usage, subway usageand rural usage.In the final section, summary of results and suggestions are obtained. It is necessarythat 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 secondexhaust gas temperature sensor is proportional to the measurements taken with thefirst thermocouple and second thermocouple.-Temperature measurements taken with thermocouple 2 has shown close figures withthe temperature measured with the exhaust gas temperature sensor 1 however this isnot calid for the temperature measured with the second exhaust gas temperaturesensor.-Based on selecting temperature measurements done by second thermocouple asreference, margin of error has been calculated for the three different sensors usingdifferent 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 testresults and the velocity and temperature distribution of the cross section pipe areadefined.-On the numerical analysis, it has been calculated that the gas velocity mean value isbetween 5 m/s and 15 m/s for the concave edge. This value increasing by progressingto the convex edge of the pipe and reaching up to 29 m/s.-After investigating the numerical analysis results, margin of error has beencalculated as %5 and %10 for the sensor with 50 mm and 30 mm tip length in thesame order based on the assumption that sensor with the 70 mm tip length measuringthe avarage exhaust gas temperature correctly.-For the given system, sensor having 30 mm probe length will not represent thephysical conditions. This situation prevent to reach aimed emission levels. Likewisedeviations which will occur on the temperature measured by the second exhaust gastemperature sensor will effect the regeneration period of the vehicle.-Change on the regeneration period will increase the amount of fuel consumed andnegatively effect the comfort of the driver.-Effect of the connection pipe between the engine and the emission controlequipments 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 theengine and emission control equipments results to decrease on the heat loss andincrease on the diesel oxidation catalyst temperature. This condition will have apositive effect on the fuel amount to be consumed during post injection processwhich aims to maintain required temperature limit for the diesel particulate filterregeneration process.-Within the test completed on the vehicle, based on reducing the length of theconnection pipe between the engine and emission control equipments fuel savingamount has been calculated per every stroke of the engine for three different drivingoperation mode.-On the basis of those calculations, fuel saving amount for lifetime of a vehicle isfound as 0.2304 kg for the city cycle, 0.1536 kg for the rural cycle and 0.1024 for thesubway cycle.-In consequence of the test done during this thesis, along with having quite a littleeffect on the fuel consumption of a vehicle considering lifetime fuel consumption ofa vehicle by reducing the connection pipe length between the engine and theemission reduction components, considering to have positive effect on the exhaustgas emissions, suggested improvement can be implemented by considering thepackaging constraints.For future studies, some suggestions are given below:-Diesel oxidation catalyst length can be optimized by measuring and analysing thechemical reaction speed taking place inside the catalyst.-Temperature of the diesel oxidation catalyst can be controlled by adding a heaterbefore the catalyst and the effect of this action to the complete system cost can beinvestigated.