【作者】 宋如钢；

【导师】 杨延相；

【作者基本信息】 天津大学 ， 动力机械及工程， 2009， 博士

【摘要】 缸内汽油直接喷射大大减少了二冲程汽油机扫气过程中的燃料流失,因此可以降低排放和油耗,是二冲程汽油机研究的重点。目前在小型二冲程直喷汽油机上使用的多为空气辅助喷射方案,单一液体喷射(如FAI直喷系统)应用很少。本文首次探讨了在50cm3这样小排量二冲程汽油机上采用FAI直喷技术的可行性、优点和问题,以及利用可变扫气道和分层燃烧、分层充气来分别降低中大负荷和小负荷排放和油耗的方法。试验证明FAI直喷系统在小排量二冲程汽油机上是可行的。在节气门全开时最低燃油消耗率为336 g/kW.h,碳氢排放为15.7g/kW.h,比原机(化油器)降低47%和88%,达到了同排量四冲程汽油机的水平。为进一步降低中大负荷碳氢排放和油耗,需改善燃烧室内混合气的分布。首次研究了扫气道对于二冲程直喷汽油机喷雾混合过程的影响,发现在中到大负荷,利用可变扫气道,即由三或五扫气道切换到双扫气道,可以促进燃油蒸发和均匀混合气的形成,并明显降低碳氢排放和油耗。通过推迟喷油,在小负荷实现了一定程度的分层燃烧。碳氢排放和油耗有所降低,但仍高出四冲程发动机很多。喷油方向、缸内流场和点火时刻对分层燃烧影响显著。缸内残余废气过多以及废气与新鲜空气的过度混合是小负荷时燃烧不稳定的一个主要原因。本文首次提出了一种使废气与新鲜空气在燃烧室内分层分布的方法——废气再循环分层充气。模拟结果表明,该方案分层效果明显且受转速和燃烧室形状影响较小,但受活塞顶形状和扫气口不对称的影响较大。更多还原

【Abstract】 Gasoline direct injection(GDI), which greatly reduces fuel short circuit out of exhaust port during scavenge process and decreases hydrocarbon emission and fuel consumption as a consequence, is a main research subject of two-stroke gasoline engine. Currently, most of small two-stroke GDI engine utilize air-assisted fuel injection technology, while single fluid fuel injection, such as FAI (Free Armature Injection) injection system, is seldom used. This paper explored the feasibility, advantage and problem of adopting FAI injection system on a small capacity, such as 50 cm3, two-stroke gasoline engine. Methods like variable transfer ports (VSP) and stratified combustion, stratified charging are also explored to reduce hydrocarbon emission and fuel consumption during middle to heavy load and low load respectively.Experiments certified the feasibility of FAI system. At full throttle, the minimum brake specific fuel consumption (BSFC) and brake specific hydrocarbon emission (BSHC) are 336 g/kW.h and 15.7g/kW.h, which are 47% and 88% lower than the base carbureted engine and comparable to those of four-stroke engines of the same capacity.In order to further reduce hydrocarbon emission and fuel consumption, mixture distribution in combustion chamber should be improved. Effects of scavenge ports on spray and mixture formation process in two-stroke GDI engine are studied for the first time. It is found that more rapid fuel evaporation and more homogenous mixture formation are achieved by shifting from three or five scavenge ports to dual scavenge port during middle to heavy load which results in obvious decrease of hydrocarbon emission and fuel consumption.Stratified combustion is achieved to certain degree by retarded injection. Hydrocarbon emission and fuel consumption are decreased to some extent, but the values are still high comparing to four-stroke engine. Injection timing, in-cylinder flow field and ignition timing are crucial factors that affect stratified combustion.The existence of overmuch residual exhaust gas together with its over mixing with fresh charge is one of the main causes of unstable combustion at low load. A new methods, EGR(exhaust gas recirculation) stratified charging, is proposed to form stratified distribution of exhaust gas and fresh charge in combustion. Simulation results show that this method gives clear stratification which is little affected by engine speed and combustion chamber shape, but obviously affected by piston shape and asymmetry of scavenge ports.更多还原