| Currently, the development direction of diesel engine is high efficiency and lowemissions. Optimization in-cylinder combustion process is potentially effective way toreduce original emission from engines. In this paper, experiment study was conducted on a6-cylinder, turbocharged, common-rail diesel engine, the effect of multiple injectionstrategies coupling of EGR on combustion process, characteristic parameters, emission andeconomy of diesel engine is studied. The technical measures to achieved China Phase4emission standard are analyzed by the way.In the1stpart, the influence of each single boundary condition on combustion processand characteristic parameters of diesel engine are investigated. Then the effect of typicalparameters as CA50and combustion duration (CD) on emissions and economy are analyzed.The test was performed at50%load and1650rpm. The conclusions are as follows:1. Injection pressure has a significant influence on the CA50and CD, with the increaseof injection pressure, CA50is advanced and CD is shortened; with the injection timingadvanced, CA50moves forward and showed a nearly linear relationship, but injectiontiming shows little effect on CD. With CA50forward, fuel consumption is lower andthermal efficiency is increased. However, the thermal efficiency increases no more to acertain extent CA50(10°CA ATDC), meanwhile, too early injection timing may cause thecombustion process rude.2. Results show that using post injection accompanied with main injection has asignificant beneficial effect on combustion process so that it could reduce the maximumcombustion temperature, furthermore, NOxemission decrease. However, there is anoptimized dwell, and too much post-injection fuel cause fuel consumption and smoke rise.The main-post injection shows little influence on CA50, but CD prolongs as the increase ofpost injection fuel and injection dwell.3. EGR rate can be used as the primary means of controlling the rate of heat release,with the increases of EGR rate slightly, CA50retards slightly and CD prolongs significantly.EGR is an effective way to reduce NOxemission. However, too much EGR rate can lead tofuel consumption and smoke emission deterioration.In the2ndpart, design of experiment (DoE) is applied to investigate the influence ofinjection parameters coupled with EGR on diesel engine performance and emissions. Thetest condition is1650r/min and50%load. The results show that: 1. The response surface methodology model is made of five factors and three responsesby central composite design. These factors are injection pressure, injection timing of maininjection, fuel mass of post injection, dwell between main and post injection and EGR rate.Three models show to be all significant effective, then desirability function are applied tofind the optimization point. The restrictive objectives are China Phase4emission and anincrement of5%of BSFC. Model predicted values coincide highly with verification results.This illustrate the model within the test conditions can predict the response precisely.2. Then the EGR rate, injection pressure and fuel mass of post injection are fixed at agood level, CA50and CD are researched by changing the injection timing and postinjection dwell to analysis their impacts on engine performance and emissions. The resultsshows that an optimized split can minimize smoke emission, with the ahead of CA50andshorten of CD, fuel consumption decreases, but NOxemission increases.3. The optimized strategy of multiple injections coupled with EGR achieves NOxandPM as3.3g (kWh)-1and0.019g (kWh)-1, the NOxemission reduces by65%compared withthe prototype. The engine achieves China Phase4emission standard without the help ofafter-treatment system. However, fuel consumption increased by5.1%. In addition, if theBSFC equals to the level of prototype, NOxemission reduces by40%by means of multipleinjections coupled with EGR. It may sacrifice more fuel to cut down NOxemissionsubstantially. Under the studied conditions in this paper, it’s hard to solve the contradictionbetween NOxand BSFC. |
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