| The technologies to save energy and reduce emission haves been urged by increasingly severe standards of fuel consumption and emission.Compared with steady state,the in-cylinder combustion and emission are worse during transient condition.As the proportion of transient condition is high in the whole operating condition,it's significant for meeting emission regulations to reduce the emission during transient condition.The current key points of energy conservation and emission reduction are mainly on the fuel injection and air intake technology.Multiple injection and EGR are regarded as important technical methods for cleaning burning.The lower air inflow is an important reason for performance deterioration and emission increase during transient condition,so it's important to increase air inflow to alleviate performance deterioration.Therefore,aimed at the typical transient condition which is at the constant speed and increasing torque,the simulation platform which is based on the CA6 DL diesel engine is set up to study the effect of air inflow and fuel injection on transient performance.Results show that:(1)With the increase of EGR rate,the reduced density of oxygen inlet will result in poor effect on the mixing of fuel and air,lower value on in-cylinder temperature and total driving energy of the mixing of fuel and air,higher internal remaining fuel rate and aggrandized combustion duration.The NO emission has reduced a lot for the reduced density of oxygen inlet.But the Soot generation peak value become higher and peak's phase is advanced as the increase of EGR rate,and the peak value of Soot generation become lower and peak's phase is lagged when the EGR rate is more than 10%.The Soot emission value is only 25% of the original machine transient-state condition and the NO emission close to zero when the EGR rate is 40%.(2)With the 20% EGR rate,increasing load stagnation time can cause not only higher air inlet quantity and optimize the mixing of fuel and air,but also prominent added in-cylinder pressure and the advanced phase of the first heat release rate peak.Increased load stagnation time lead to shorter combustion duration,higher temperature of in-cylinder during ignition delay period,increased thermal efficiency and reduced fuel consumption rate.Besides,the NO emission is maximally increased by 34.9% and the soot emission has little change.But the Soot emission has increased 45.4% compared to the transient B50 load of the original machine.The combustion reaction trend in the Soot formation region is similar with rich mixture region(2<?),but it has big difference from high temperature region.It is shown that the Soot formation mainly depends on the proportion of rich mixture,but it also influenced a lot on soot formation when the deterioration of in-cylinder temperature is heavy.Similarly,the NO formation mainly depends on the high temperature zone(T>2200K)volume ratio.(3)When the EGR rate is 20%,the load stagnation time is 0.8s and the interval between main injection and post injection is fixed at 8°CA,the increase of post injection amount can reduce the Soot formation peak and soot emission,at the same time,the phase of peak is advanced and the second peak is appeared.The Soot emission is decreased 82.52% compared to the post injection is 5% when the post injection amount is 30%.Besides,the NO emission is influenced little by post injection amount,but it changes as first climb up and then decline,the highest and lowest value is 0.816 mg and 0.749 mg respectively.Post injection strategy can effectively promote the in-cylinder flow.Since there is a lot of oxygen which cannot mix with fuel by entrainment effect,the oxygen which is add to the injection direction area in the interval between main injection and post injection can facilitate the mixture of air and post injection fuel and provide a favorable environment conditions for the combustion of post injection fuel.Compared to the transient B50 load of the original machine,the coordinated control strategy of multiply parameters not only has higher in-cylinder pressure and advanced phase of heat release rate peak,CA10 and CA50,but also prolongs combustion duration and reduces the remaining fuel rate,Soot emission and NO emission.In view of the combined consideration of thermal efficiency,fuel consumption rate,combustion duration and emissions,the use of 20% EGR rate,0.8s load stagnation,8°CA between the main and post injection and amount of the 20% post injection has a best effect at 50% load and under transient condition.Compared with the transient B50 load of the original machine,not only the thermal efficiency has increased 1.5% and the fuel consumption rate has decreased 1.5%,but also the emission of Soot and NO are reduced by 72.5% and 60.4% respectively. |
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