基于脉冲喷射汽油的稀燃汽油机后处理技术研究

Research on Aftertreatment Technology of Lean-burn Gasoline Engine Based on Pulse Jet Gasoline

稀燃汽油机能够大幅提高燃料转化效率,从而降低油耗,但同时NO_(x)排放升高。传统的三元催化转化器(TWC)在稀燃模式下只能有效控制HCs和CO排放,无法有效控制NO_(x)排放。对于稀燃汽油机的NO_(x)去除,目前主要是通过NSR催化剂来实现。但在温度高于450℃时,NSR催化剂的NO_(x)吸附率会降低,从而导致NO_(x)转化率降低。针对这一问题,通过试验研究,提出了一种基于脉冲喷射汽油的稀燃汽油机后处理技术,其原理是耦合TWC和NSR催化器,并在NSR催化剂前端以一定的频率喷射汽油,形成具有还原性的活性中间物种-CN和-NCO来转化NO_(x)。采用该技术,汽油机可一直运行在稀燃模式,避免切换至浓混合气燃烧模式。该技术控制简单,成本较低。研究结果表明,该技术可以在较宽的空燃比范围内有效去除稀燃汽油机尾气中的有害气体,尤其是NO_(x)。在不同工况下,NO_(x)均能保持85%以上的转化率,大大提高了稀燃汽油机的可应用性。另外,对该技术的关键影响因素,包括汽油喷射频率、汽油喷射压力以及工况进行了探究和分析。

Lean-burn gasoline engines can greatly improve fuel conversion efficiency,thereby reducing fuel consumption,but at the same time,its NO_(x) emissions will increase.The traditional TWC can only effectively control HCs and CO emissions under lean burn conditions,but cannot effectively control NOx emissions.For lean-burn gasoline engines,NO_(x) removal is currently mainly achieved through NSR catalysts.However,when the temperature is higher than 450°C,the NO_(x) adsorption rate of the NSR catalyst will decrease,resulting in a decrease in the NO_(x) conversion rate.In response to this problem,through experimental research,a lean-burn gasoline engine aftertreatment technology based on pulseinjected gasoline is proposed.The principle is to couple TWC and NSR catalyst,and inject gasoline at a certain frequency at the front end of the NSR catalyst,which forms the reductive active intermediate species-CN and-NCO to convert NO_(x).By adopting this technology,the gasoline engine can be operated in lean-burn conditions,which means that it is not necessary to switch to rich-burn conditions.In addition,this technology has the advantages of simple control and lower cost.The research results show that this technology can effectively remove harmful gases in the exhaust gas of lean-burn gasoline engines in a wide range of air-fuel ratio.In particular,NO_(x) can maintain a conversion rate of more than 85%under different working conditions,which greatly improves the applicability of lean-burn gasoline engines.In addition,the key influencing factors of this technology,including gasoline injection frequency,gasoline injection pressure and working conditions,have been explored and analyzed in detail.