3-D Simulation Of Spray And Combustion For Multiple Injections In Common-Rail Diesel Engine

Engine combustion process optimization is of great necessity for the increasingly stringent emission regulations, and it can be realized by optimized control of injection rate and multiple injcetions. The TY3100CR non-road diesel engine is simulated on a software STAR-CD with moving mesh created in an expert tool for internal combustion engin called ES-ICE. Effects of multiple injections (pilot and post injections) on spray, combustion and emissions are studied.First, the TY3100CR engine with a single injection is studied. Macroscopic variables such as cylinder pressure, cylinder temperature, heat release rate, NOx and SOOT emission are predicted and analyzed. It was found that the heat release rate curve rises too fast in the beginning, which may bring high combustion noise. The production of NOx begins from the moderate burning period, reaches a peak quickly and keep constant. The production of SOOT is smainly in the late of fast burning period to the moderate burning period, and most of the SOOT is oxidized.Then a microscopic study of in-cylinder airflow movement, fuel distribution, temperature change and pollution production is conducted. It was found that NOx shows in the area with temperature over2000K and high concentration area corresponds with high temperature area. The concentration of SOOT corresponds with the concentration of fuel, the inner area of fuel vapor gives a higher concentration of SOOT because of high temperature and lack of oxygen.Finaly, different multiple injection schemes (pilot+main, main+post) are proposed. For the pilot+main cases, simulation is conducted for different injection intervals and different pilot amount; for the main+pilot cases, simulation is conducted for different injection intervals and different pilot amount. Results followed:1. For the pilot+main cases, small amount of pilot injection (5%) combined with relatively moderate interval (10℃A) could improve the flow movement well, better for the ignition of the main injection fuel. With emission, NOx and SOOT production increase a little for the combustion of the pilot fuel just before the main injection and the unretarded main injection. Therefore, the premixing fraction increased, temperature of premixed combustion increased and so the NOx emission increased. 2. For the main+post cases, small amount of post injection (5%) coupled with small interval (5℃A) are more conducive to spray and air-fuel mixing, bring about reduced peak value for NOx and SOOT production. However, for the SOOT curve, two peaks appear.