Investigation On EGR Technology Of An Automotive Turbo-charged And Inter-cooled Diesel Engine

With the fast development of the automotive industry, the population of the automobile expands sharply,and the pollutant emissions from the automobiles affect the atmospheric environment and human health, restrict the development of the economy, and have already caused great public concern. Especially in the past decade, human environmental consciousness was strengthened significantly, stricter and stricter emission regulations were issued for the internal combustion engines and engine powered vihicles in many countries successively. The NOX emission from the diesel engine is equivalent to the SI engine, while the emission of the particulate matter from the diesel is obviously higher than that from the SI engine, so emphasis on limiting these two kinds of pollutants from the diesel has been placed in emission regulations of various countries.In this thesis, the effects of EGR on the feul economy and emission behavior of the automotive turbocharged and intercooled diesel engineof the type YC4112ZLQ were studied. The formation mechanism of NOX was discused and the technical measures to reduce the NOX emission from the diesel engine were explained. It is concluded that high temperature, rich oxygen and retention time are three major factors to promote NOX formation and suppressing these promoting factors is the ultimate measure to control the formation of NOX, EGR is exactly has the effective measure for the NOX emission control.EGR or exhaust gas recirculation, is to recycle a certain portion of the exhaust gas into the inlet system to increase the mass fraction of inert gases (H2O vapor, N2 and CO2, etc.) in the intake charge. Because the inert gas does not participate the combustion, and is higher in thermal capacity to absorb more combustion heat, and thus depresses the engine's peak combustion temperature. Meanwhile, EGR reduces the oxygen mass fraction in the intake charge and depresses the formation of NOX. However, when EGR is introduced, the particulate matter, CO and HC emissions may increase, and the feul economy may deteriorate, too. Therefore, the trde-off between reduction of the NOX emission and increase of the other emissions or the deterioration of the feul economy must be considered when EGR is used to fight against the NOX pollution.According to the temperature of the recycled exhaust gas, the EGR technology can be divided into hot or uncooled EGR and cold or cooled EGR. The hot EGR leads a higher intake charge temperature, and consequently a higher combustion temprature, thus weakens it's effect of reducing NOX emission. Experiments have proved that, compared with cold EGR, the particulate matter, CO, CO2 and HC emission with hot EGR are higher. So, in this thesis, the cold EGR was adopted and an EGR cooler was incerted in the EGR passage, which limits EGR temperature to 120~160℃ under all tested operating conditions.In this thesis, the EGR system used a so-called High Pressure Route passage, i.e, recycled the exhaust gas from upstream of the turbine to downstream of the compressor to avoid malfunction of the compressor and the intercooler on the condition of Low Pressure Route. And an intake throttle was used to reduce the pressure at EGR inlet in cooperation with an EGR valve to control the EGR flow.Effects of different EGR ratio on the performance and emissions of the diesel engine were investigated experimentally in the whole operating condition range of the engine, the EGR ratios in all operating conditions were optimized according to the Trade-off relation of the NOX and particulate matter emissions and the requires of power and feul economy, and an optimized EGR ratio map wsa accomplished.The hardware was integered and the software was compiled for the EGR sys tem. An 80C196KC single chip processor was used as the control unit, the accelerator position and rotational speed of the engine were the input parameters. During the operation of the engine, the ECU is detecting the accelerator position signal and the rotational speed signal constantly, and through searching the...