Influence Of Gas Supply Strategy On Diesel Engine Transient Pefrormance

Diesel engine with good performance、fuel economy and high reliability has beenconcerned. But face with the situation that energy and environment are growing deteriorationand haze arose, we have to improve the performance of diesel engine. Diesel engine work attransient condition in lots of time, and performance get worsen. In many technologies, twostage turbocharging system has huge potential to improve diesel engine’s transientperformance with higher intake air pressure and faster responsiveness.Base on high pressure common rail–turbocharged diesel engine, to research theinfluence of gas supply strategy on diesel engine transient performance. The study includestwo parts. The first part, through the transient experiment on diesel engine, to find out thereason why performance of diesel engine get worse under the transient operating condition.Test point selection for constant engine speed and increasing torque process. The specificresearch results as follows:1) Through the test comparison of steady-state and transient operating condition, resultsshow that combustion process of diesel engine get worse at transient operating condition,smoke opacity increase and NOx emission decrease.2) Compared with steady-state condition, the influence of inherent turbo lag characteristic ofturbocharged engine on diesel engine transient performance more important than differentinitial load under constant engine speed and increasing torque process.The second part, study the effect of two stage turbocharging system on diesel engineperformance. Including the selection of important component of two stage turbochargingsystem、system validity verification and influence on diesel engine transient performance.The specific research results as follows:1) Through the test of diesel engine work at full-load operating condition, compared withoriginal engine, air-fuel ratio has obvious increase within the range of condition, thebiggest increase is about31percent; when diesel engine work at low speed condition, theperformance has obvious improvement, such as fuel economy、smoke opacity. BSFC decreased12percent, smoke opacity decrease from9.96to1.19; work at high speed, dueto increased exhaust back pressure, the performance of diesel engine with two stageturbocharging system is deteriorated.2) Through the test of load characteristic, the performance of diesel engine with two stageturbocharging system is worse than original engine when load is low. With the increaseof load, BSFC and smoke opacity are improved, reaching full-load condition, it betterthan original engine. Increasing engine speed, the advantage will be weakened.3) Study about different valve opening of turbo bypass valve, different operating conditionhave different best opening, effective adjusting range, at the same time, is0-40percentopening.4) Compared with original engine transient performance, two stage turbocharging systemcan enhance diesel engine transient performance obvious.5) Study about different turbo bypass valve opening at constant speed and increasingoperation condition, the results show that BSFC is improved, compared with originalengine, but the emission of soot is increased, when turbo bypass valve opening at10percent. Increasing to20percent, both BSFC and smoke opacity get worse than10percent opening.6) Study about different loading time at constant speed and increasing operation condition,the results show that diesel engine transient performance is deteriorative with loadingtime shortening.