Effect Of Fuel Injection Parameters On Combustion Process Of Diesel Engine During Transient Operations

Auto works on transient operations in most of time, because it needs toconstantly adjust acceleration and brake pedal to meet different road conditions.Torque and speed change frequently which results to different combustion processbetween steady state conditions and transient operations. Especially for theturbocharged diesel engine, the emissions and economic performance deteriorateobviously during transient operations due to the lag of intake air compared to theother combustion boundary condition. Facing the increasingly serious environmentalproblems and stringent emission regulations, people who work in engine emissioncontrol technology nowadays make how to improve the transient performance ofdiesel engine and resolve emission problems the key research direction. Based on aturbocharged electronically controlled common rail diesel engine, this articleresearched on the effect of multiple injection strategy on the combustion process andemissions during constant speed and increasing torque operation. The concreteresearch content includes two parts: The first part is that the effect of multipleinjection strategy on fluctuation of rail pressure and stability of the fuel, andcorrection method for fluctuation of fuel. The second part is that the influence ofmultiple injection strategy on combustion process of diesel engine and theoptimization strategy during transient operations.To study the influence of fuel injection parameters on fluctuation of rail pressureand stability of fuel, the author did the test under steady state (the speed is1650r/minand the load is50%) by adjusting each single injection parameter. Based on theunderstanding of the influence of fuel injection parameters on stability of fuel, theauthor also put forward a correction method for fuel which is suitable for programcontrolling during transient operations. The results show that:1. There is obvious difference of the quantity of fuel between measurement value and controlling target value when using multiple injection strategy, themaximum deviation range is40.3%;2. Rail pressure, interval between main injection and post injection and fuelquantity of post injection have greater influence on fluctuation of railpressure and stability of fuel than main injection timing. As the rail pressuregets lower, and the interval between main injection and post injection getsshorter, the fluctuation of rail pressure becomes fiercer and the stability offuel becomes worse;3. Fluctuation of rail pressure is a principal main factor in volatility of the fuel.The key factor of effect of fluctuation of rail pressure is the interval betweenthe ending of main injection and the beginning of post injection;4. To deal with the fluctuation in fuel when using multiple injection strategy, theauthor constantly adjusted the charging time of post injection until thequantity of the fuel is the same with that of the original engine. Then theauthor carried out the validation test and the results show that the correctionstrategy is effective and feasible. Significantly, the correction strategy can becontrolled by program and applied to transient operations.To research the influence law of effect of multiple injection strategy on transientperformance of diesel engine during transient operations, the author selected constantspeed (1650r/min) and increasing load (load is increased from10%to90%with thesame acceleration in5seconds) as the transient test cycle. And the author raised anoptimization strategy to improve the economy efficiency of diesel engine which usesmultiple injection strategy. Then EGR was led in the test engine, and the influence ofEGR on transient performance of diesel engine during transient operations also bestudied. The experimental conclusions are showed below:1. Multiple injection strategy is helpful to reduce the smoke and NOxsimultaneously during transient operations, and the biggest decreasingamplitude of peak smoke was able to reach70%. However, the economyefficiency of diesel engine became worse. For example, when intervalbetween main injection and post injection is2800μs, and quantity of post injection is30%, bem(mean BSFC) increased by16.5%;2. Quantity of post injection and interval between main injection and postinjection have great effect on diesel transient performance during constantspeed increasing torque test. With increasing of quantity of post injection orprolonging the interval between main injection and post injection,Pmax(maximum explosion pressure) and IMEP(Indicated Mean EffectivePressure) reduces, CA50(crank angle of50%fuel combustion) lags, durationof combustion extends, NOx emission reduces, fuel economy deteriorates.Shorter interval between main injection and post injection helps to improvePmax and IMEP. Nevertheless, longer interval between main injection andpost injection plays an important part in reducing smoke;3. With improving rail pressure20MPa based on the original diesel engine,there is a reduction of5.93%of bem(mean BSFC) which reduced thedeterioration of bem from16.5%to10.6%. Meanwhile, it also helps tofurther reduce smoke emission;4. After introducing EGR into engine, smoke deteriorated sharply duringtransient operations. Peak smoke was able to attain51%which is2.63timeshigher than original engine. When we adopted multiple injection strategy(interval between main injection and post injection is2800μs, quantity ofpost injection is30%), peak smoke reduced51.8%. On the basis of themultiple injection strategy, the author improved rail pressure20MPa anddelayed injection timing4°CA, peak smoke got further reduction withdecline of78.9%. After optimizing by adjusting the fuel injection parameters,smoke peak is even lower than original engine.