乙醇/汽油双燃料双直喷模式下分层稀薄燃烧试验研究

针对乙醇与汽油固定掺混比例下使用不能充分发挥乙醇燃料优势的问题,开发出了乙醇汽油双燃料-双直喷系统,并在一台点燃式单缸试验机上进行试验,研究了稀薄燃烧下3种不同的喷射策略对发动机燃烧和性能的影响。研究发现:在稀薄燃烧的情况下,随喷射时刻的推迟,不同喷射策略下动力性呈现先增长后降低的趋势。在保证喷油量不变时,有效热效率随过量空气系数增大而明显提高,当量燃油消耗率逐渐降低。随喷射时刻的推迟,热效率呈现先升高后降低的趋势。在过量空气系数为1.2,汽油喷射时刻为上止点前180°,乙醇喷射时刻为上止点前300°时,有效热效率达到最高值40.5%。此外,相比于汽油,添加乙醇燃料使得稀薄燃烧更稳定,循环波动更小。

Experimental Study on Stratified Lean Combustion in an Ethanol/Gasoline Dual-Fuel Dual-Injection Spark Ignition Engine

The advantages of ethanol cannot be fully utilized when ethanol is mixed with gasoline in a fixed proportion. To solve this problem, a system which can inject both ethanol and gasoline directly into cylinder was developed. With this system, the effects of three different injection strategies on combustion characteristics and engine performance under lean-burn condition were experimentally conducted on a spark ignition gasoline engine. The three injection strategies were: injecting gasoline and ethanol at the same time; fixing gasoline injection timing and delaying ethanol injection timing gradually; fixing ethanol injection timing and delaying gasoline injection timing gradually. The results show that with the three injection strategies engine power output and thermal efficiency increase first and then decrease with the delay of the injection timings under lean-burn condition. When the amount of injected fuel is kept constant, the effective thermal efficiency increases remarkably with the excess air coefficient, while the equivalent fuel consumption decreases gradually. The optimal combustion is obtained at the excess air coefficient of 1.2 and with the gasoline injection timing of 180° in crank angle before the top dead center and ethanol injection timing of 300° in crank angle before the top dead center. In this case, the effective thermal efficiency peaks to 40.5%. Besides, adding ethanol into gasoline makes lean-burn combustion more stable with less cycle variation.