基于FIRE软件以某1.4T汽油缸内直喷(GDI)发动机为研究对象,对单侧进气道均质废气再循环(EGR)、下侧引入和侧面引入EGR回路3种方式进行模拟,并得到以下结论:3种方式在活塞经过下止点上行时会出现废气扩散加剧现象;单侧进气道均质EGR的模式获得的分层效果并不理想,在点火时刻火花塞附近区域的局部EGR率过高;降低EGR侧压力会对整体EGR率产生很大的影响,缸内大部分区域的局部EGR率趋于一致,火花塞附近区域局部EGR率相对较高.单侧进气道下侧引入EGR回路和均质EGR 2种分层方式的掺混趋势十分相似;进气道侧面引入EGR的分层方式对进气行程时的EGR分层有显著的改善,仅小部分废气从气缸中心一侧进入气缸,在175.曲轴转角(CA)时局部EGR率差达到80％,但是在点火时刻火花塞附近局部EGR率差仅能保持30％左右;增加了气流挡板之后,在点火时刻缸内仍可以保持接近30％的局部EGR率差,火花塞距离局部EGR率较高的区域也比较远;增加EGR回路直径后,点火时刻缸内EGR率差增加了 9％,总EGR率提高4.5％,火花塞附近区域局部EGR率在14％左右;转速升高后会使EGR分层效果变差,火花塞附近区域局部EGR率升高.

为了实现发动机高效清洁燃烧，本文利用自行开发的可变气门升程机构，在无节气门条件下研究了进气门调整策略（VIV）、排气门调整策略（VEV）和进排气门耦合调整策略（VICE）对发动机性能的影响。结果表明，与原发动机相比，三种气门控制策略都可以降低有效燃油消耗率（BSFC）并提高热效率（ITE）。其中VICE策略的效果最为突出，与原发动机相比BSFC和ITE最多可优化28%和6%。VIV策略和VICE策略都可以减小发动机泵气损失，尤其是VIV策略，与原发动机相比最多可以将泵气损失减少36%。三种策略都可以降低NO x 排放，其中VEV策略表现最优异。当NMEP超过3bar后，不同气门策略对THC排放的影响较小。

以某款四缸缸内直喷汽油发动机为研究对象,对停缸技术的节能机制进行了探讨,并分析了停止工作气缸气门的不同关闭时刻对发动机性能的影响.研究发现:当气门关闭时刻过早或过迟时,发动机的传热损失、泵气损失和摩擦损失均有所增加,压缩上止点前30°CA气门关闭时刻可使发动机获得较佳的燃油经济性改善效果,从而有效降低汽油机燃油消耗量;传热损失、泵气损失的降低分别是停缸技术节能的主、次要原因,但其会增加发动机摩擦损失和排气损失.

The experiment was conducted on a GDI turbocharged engine fueled with methanol gasoline blends with 0％,10％ and 20％ volume fraction methanol.The effects of blended fuel on particle size distribution,particle number concentration and mass concentration were studied under lean burn condition.Experimental results showed that the peak of particle number concentration gradually increased and the particle size showed a bimodal distribution with the increase of methanol proportion.Nuclear mode particle and accumulation mode particle gradually increased and those of M20 blends were the largest.The peak particle size also increased.The peak size of nuclear mode particle was 20.54-31.62 nm and that of accumulation mode particle was 56.23-100 nm.In addition,the mass concentration increased with the increase of methanol proportion.The accumulation mode particle with a size of 316-700 nm obviously increased,the mass concentration of accumulation mode particle obviously increased with the increase of particle size,and hence the mass concentration increased.However,the mass concentration of 56.23-316 nm particle decreased.

Separate introduction of the recycling exhaust and fresh charge of a spark ignition methanol engine was realized by installing an EGR tube in the helical intake port .The effects of different EGR access times and different combustion chamber pit shapes on EGR stratification were simulated with the CFD FIRE software .The results show that the addition of EGR tube can realize the EGR stratification and the EGR access time and the combustion chamber pit shape have significant effect on EGR stratification .The stratification of low EGR concentration around the spark plug and higher EGR concentration far from com-bustion chamber top is formed when the combustion chamber pit shows shallow cylinder shape ,the pressures of fresh charge and EGR are 100 kPa and 160 kPa respectively and the recirculation finished at 300° BTDC .The influence of stratified EGR and homogeneous EGR on in-cylinder combustion of methanol engine is analyzed based on the same EGR ratio and fuel consump-tion .The stratified EGR can improve the peak cylinder pressure ,shorten the combustion delay period and advance the combus-tion starting point effectively and is useful to improve the in-cylinder combustion of methanol engine .

通过一台柴油机改装的高压缩比(17.5)进气道喷射点燃式甲醇发动机,研究了废气再循环(EGR)和过量空气系数协同控制对甲醇发动机部分负荷经济性和排放性能的影响.结果表明:负荷越小,协同调节范围越宽,节油潜能越大,在1 400 r/min、50％负荷时,甲醇消耗率降低幅值最大可达13.1％,25％负荷时甲醇消耗率最大可降低26.6％;EGR率小于20％或过量空气系数小于1.4时,协同控制对缸压峰值的影响较明显;当过量空气系数大于1.4后,甲醇发动机燃烧持续期急剧增加,循环变动迅速变大;与无外部EGR、过量空气系数为1相比较,合理利用EGR和过量空气系数协同控制,可以保证HC、CO排放值增幅不大且能有效降低NOx,甚至实现NOx的“零”排放.

On a retrofitted methanol engine with 17 .5 compression ratio ,intake throttle ,intake port injection and spark igni-tion ,the influences of ignition timing on combustion and emission characteristics in 1 400 r/min were investigated .The results show that the methanol engine can run stably at the ignition advance angle of 18°BTDC ,15°BTDC and 12°BTDC .However , the maximum ignition timing delays with the load increase due to the limit of engine knock .With the increase of load ,the igni-tion delay period shortens and the maximum in-cylinder pressure and heat release rate increase obviously .With the advance of ignition timing ,the combustion process advances ,the maximum in-cylinder pressure and heat release rate increase ,and the combustion duration decreases .Therefore ,the optimized ignition timing can bring about a good compromise of economy and emission especially in low and medium load .

Numerical simulation of thermodynamic cycle and combustion of a turbocharged vehicle diesel engine with closed post injections under high load operations was carried out by means of a CFD tri-dimensional numerical analy-sis software FIRE.In this paper,the effects of closed post injection fuel quantity and interval between post and main injection on combustion process were discussed.The computed results indicated that with the increasing interval and post injection fuel quantity,the generation of NOx was evidently reduced,while the fuel economy had worsened.At the same time,the post injection technology is a very effective means to reduce soot emissions.The appropriate post injection parameters could,on the one hand,reinforce the disturbance effect of in-cylinder flow field;on the other hand,post injection fuel could form fuel vapor mainly in the oxygen-enriched region,thus obviously reducing the generation of soot.Better compromise performance of the indicated mean pressure,NOx and soot could be achieved by using post injection than by the original machine.Even better performance could be achieved when post injection mass is 10%—21% and the main and post injection interval is 10°—18° CA.

In the test, the engine run at a specific speed when fuel consumption (Be) and torque remained constant. An ETAS calibration system is used to control the Maps for adjusting the rail pressure and injection timing. Experimental data show that when fuel injection is delayed, fuel consumption, CO and HC increase while formation of NOx reduces. The formation rate of pre-mixed gas is proportional to the rail pressure. When the rail pressure increases, more pre-mixed gas forms which will reduce the fuel consumption, improve CO and HC emissions but increase NOx. The data that is before and after optimization indicates that: in the selected test conditions, fuel consumption and torque are slightly lower on the optimized engine while values of NOx and smoke respectively reduce by 20% and 23%.