Simulated Analysis Of The Spray And Premixed Combustion Process Of Diesel Engine

Using diesel fuel has been a trend of modern automobile engine. Because ofDiesel engine's advantages such as high thermal efficiency, easy to usingturbo-charge, low consumption of fuel, big torque, high reliability and long life-span,more and more auto-factories pay their attention to diesel engine. The more attentionwe pay to the crisis of energy and environment, the more economy and emission toautomobile should be considered. People think much of the emission of dieselengine because its fuel economy is better than gasoline engine's. Although dieselengine's emission rate of HC and CO is excelled gasoline engine, its' NOX emissionis worse than the latter. Further more, the PM emission of diesel is dozens times ofthat of gasoline engine. So, how to reduce the emission of NOX and PM of diesel is aproblem that we should urgently figure out.The combustion process and emission characteristics in diesel engine aremainly depended on the mixture formation in cylinder. It can make Homogeneouspremixed gas before ignition by increase the fuel injection advance angle. And theEGR gas is to control the ignition time and bate the burst combustion caused by the.Homogeneous premixed gas ignited at the same time. And the EGR gas can alsodecrease the NOX emissions because of its' high specific heat it can decreasecombustion temperature and dilute the oxygen concentration.The experiments are the main means of combustion research in a period of timebecause of the complicacy of combustion. Limited to the experiment condition,thedevelop level and precision of the testing technology and experiment instrument.This experiment research has a big limitation. Now, go with the computertechnology and computer science quickly developed, lots of researchers pay theirattention to the numerical simulation of the work process of engine. It includes thesimulation of gas inlet process,the simulation of spray process,the combustionsimulation and so on. It has many strongpoint to use CFD(computational fluiddynamic)software for simulation, such as low cost;high speed;can supply someinformation that experiment couldn't.The spray and combustion process of CA498 diesel engine was simulated withthe CFD software FIRE. The simulation of operating conditions were1400rpm,thesingle cylinder fuel supply quantity was 14mg. The result indicates that: thesimulation result and the experiment result inosculate basically. So the FIREsoftware can simulate the combustion process of diesel engine.The diesel engine's spray and combustion process on the condition of no EGRand the fuel injection advance angel changing was simulated. Analyzing the results,we find that: with the fuel injection advance angel increasing, the equality of themixed gas at the ignition time is first increase and then decrease, also the peak valueof the rate of heat release, but the position of the rate of heat release was pushedforward. When the fuel injection advance angle is large, the position will not pushedforward. with the fuel injection advance angel increasing, the peak of combustionpressure and the temperature are also first increasing and then decrease. Thetemperature of -30oCA fuel injection advance angel is the highest, and also the NOxemission is the highest.The diesel engine's spray and combustion process on the condition of fixed fuelinjection advance angle and the EGR rate changing was also simulated. We concludethat: with the EGR rate increasing, the ignition start time is deferred, the ignitiondelay period became longer, the mixed gas at the ignition time becamehomogeneous;with the EGR rate increasing, the combustion pressure decrease, thepeak of the rate of heat release didn't change, but it's position pushed backward, thehighest and the average temperature are decreased, as a result, the NOx emission isdecreased .