Numerical Study On The Mechanism Of Fuel Injection Strategy Coupled With EGR For Diesel Engine

In the context of low consumption and low emissions engines development, the clean and high-efficiency combustion theory and technology of diesel engine has been widely researched. Fuel injection strategy and EGR are the important measures for combustion control in diesel engine. This paper mainly studied all spatial and temporal characteristics as well as local properties of LTC by applying the available diesel combustion model (ECFM-3Z) implemented in a commercial AVL-FIRE code and considered how LTC reduced NOx and soot simultaneously, and then studied the combustion controlling mechanism of single injection timing coupled with EGR.A single fuel injection strategy has been deployed to push the diesel cycle into low temperature combustion with EGR. When increasing EGR from low levels to a level that corresponds to low temperature combustion, soot emissions initially increase due to soot oxidation lower than formation before decreasing to almost zero due to very low soot formation. When the oxygen concentration dropped to some threshold, longer ignition delay madeФ-T avoid the soot formation region. The flame temperature considerably decreased with decreasing oxygen concentration in the ambient gas. NOx level was decreased greatly by the low flame temperature.In other words, it decreased NOx and soot simultaneously.The simulation results indicated that a higher injection pressure can increase air entrainment, improve the mixing between the fuel and air and then reduce the combustion duration. Soot emissions lower due to more oxidation while NOx increasing due to higher temperature.With the increase of intake pressure at low oxygen concentration, the ignition delay shortened, the combustion heat release accelerated, the temperature in the post-combustion was lower, the combustion efficiency and NOx emissions increased because the local temperature in more area was larger than 1900K and oxygen absolute content increased; soot emissions decreases, more oxygen content increased the soot oxidation.The last part mainly studied that the injection timing coupled with EGR had effects on the combustion and emissions, the simulation and experiment results both showed advanced SOI coupled with large EGR(CaseA) can reach CA50 at the same time as delayed SOI with small EGR(CaseB),the heat release rate of the former increased rapidly and its peak was higher, thermal efficiency of CaseA is more than of CaseB. But for the former, the top pressure, pressure rise rate and NOx are higher, soot increases firstly then decreases. As CA50 delayed, the local and mean combustion temperature both decrease, the combustion efficiency reduced, NOx emissions decrease, while soot emission increases firstly and then decreases.