The Investigation On Combustion Process Of Diesel Engine Based On The Concept Of EGR And LTC

With the increasingly stringent exhaust emission standards of the diesel engine, it is very imperative for China to develope diesel emission control technology to meet low emissions regulations. EGR is one of the most effective methods for reducing the emissions of NOx of diesel engines. In a turbocharged engine, however it is difficult to introduce EGR at the high load because of the high boost pressure in the intake port. Consequently, a new type Venturi EGR mixer and a reed-valve EGR system were developed in this dissertation. Based on the concept of LTC, the control strategy was investigated to obtain low temperature combustion using high levels of EGR in a two-valve diesel engine in order to reduce NOx and soot emissions simultaneously. With mechanical fuel injection pump and EGR system, the two-valve diesel engine has been developed to meet low emissions regulations.The low temperature combustion process was studied by CFD numerical simulations and engine experiments. At different loads and EGR rates, in-cylinder conditions of combustion were predicted by CFD numerical simulations to supplemente theΦ(equivalence ratio)-T(temperature)map. The results showed that the decrease in soot emissions is an effect of low temperature combustion resulted in low soot emissions because of low oxygen availability , when the EGR rate exceeds approximately 61% at 10% load and 1800 rpm. At 25% load, the combustion process moved to the low combustion region by reducing the EGR temperature, which is far away the soot region.A new idea was presented in this paper that the design of the combustion chamber should be suited to EGR technology. In order to use large amounts of cooled EGR , the combustion chamber has been optimized. The simulation result indicates that a small portion of the air-fuel mixture is released from the bowl when impinging on the piston bowl wall. In the new combustion chamber the air-fuel mixture distribution inside and outside the bowl is deemed to be the most appropriate to adopt a larger EGR ratio, thereby resulting in a lower NOx emission.A new type Venturi EGR mixer was designed to introduce large amounts of EGR in a turbocharged engine, and to get uniform mixing of EGR/air. Using mechanical fuel injection pump and EGR system, the two-valve non-road diesel engines can meet the US Tier 3 off highway emission regulation with the results of NOx = 3.258g/kW.h(reduced 45%),PM=0.0265g/kW.hThe reed-valve EGR system was used to meet EUROⅢEmission Standards and the EGR rate is up to 14% at 100% load and 1740rpm. It was shown that a method for expanding the EGR-feasible load range to high-load operation is essential and the reed-valve EGR system achieves this objective more effectively than the conventional exhaust choke system without any kind of additional flow restriction within the intake system. The results showed that the vehicle diesel engine can meet the EUROⅢemission regulation with the results of NOx = 4.77g/kW.h, PM=0.067g/kW.h.