Temperature sensor measurement accuracy and catalyst temperature investigation for automotive exhaust systems

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.