汽油压燃（GCI）燃烧方式低负荷燃烧稳定性机理研究

Considering the ultra-low NOx and soot emissions along with relatively high thermal efficiency, gasoline compression ignition (GCI) is turned out to be a research focus in engine combustion field. However, due to the poor auto-ignition quality of gasoline, how to extend the lowest load limit becomes an urgent issue to be solved. Thus, the investigation on combustion stability mechanism of GCI combustion concept at low-load conditions will be performed systematically in this project by applying the combination of optical diagnosis, numerical simulation and engine bench test. This research includes the following aspects: The mixture formation process and concentration distribution of gasoline under high injection pressure will be studied. The formation and evolvement processes of the important intermediates and free radicals, as well as their effects on auto-ignition will be studied, and the reduced chemical kinetic mechanism of multi-component gasoline surrogates with highly EGR dilution will be developed. The effects of in-cylinder thermal condition through coupling control of internal and external EGR, and also mixing characteristic on auto-ignition, combustion process and combustion stability at low-load conditions will be studied, and the combustion control strategy of GCI combustion concept at low-load conditions based on coupling control of internal and external EGR and fuel injection strategy will be proposed consequently. This research has important theoretical significance on deep understanding the combustion theory of GCI combustion concept, and has great guiding value in exploring the pathway to realize high-efficiency and clean combustion with high-octane fuels in a boarder operating range.

汽油压燃（GCI）燃烧方式由于能够在实现超低氮氧化物和碳烟排放的同时获得较高热效率而成为内燃机燃烧领域的研究热点，但汽油自燃性较差，如何拓展低负荷工况极限成为亟待解决的问题。本项目拟综合运用光学诊断、数值模拟和台架试验技术手段，系统开展GCI燃烧方式低负荷工况燃烧稳定性机理研究。主要内容包括：研究高喷射压力下汽油燃料的混合气形成过程和浓度分布特性；研究重要燃烧中间产物和自由基的生成、演化历程及其对自燃着火反应的影响机理，构建高EGR稀释下的多组分汽油替代混合物简化化学动力学机理；研究内/外部EGR耦合控制的缸内热力学状态及混合气分布特性对低负荷工况自燃着火、燃烧过程和燃烧稳定性的影响机理，探索基于内/外部EGR耦合和燃油喷射控制的GCI燃烧方式低负荷工况燃烧控制策略。本研究对深入认识GCI燃烧方式的燃烧反应机理具有重要理论意义，对寻求高辛烷值燃料宽广工况范围的高效清洁燃烧具有较高指导价值。

汽油压燃（GCI）燃烧方式由于能够在实现超低氮氧化物（NOX）和碳烟（soot）排放的同时获得较高热效率而成为内燃机燃烧领域的研究热点，但汽油自燃性较差，如何拓展低负荷工况极限成为亟待解决的问题。本项目系统开展了GCI燃烧方式低负荷工况燃烧稳定性机理研究，主要内容包括：研究了可变气门策略和多次喷射策略对缸内初始热力学状态和混合气浓度分布的影响，进气掺混汽油重整产物对燃烧效率和反应过程的影响，燃烧控制参数和含氧燃料特性对颗粒物粒径分布特性的影响，并提出了基于碳平衡和摩尔数平衡的新型燃油消耗率计算方法。.研究结果表明，低内部EGR率结合靠近上止点的CA50可获得较高的热效率，并使CO/HC和NOX排放获得较好的折中关系。随预喷比例升高，混合气当量比离散度下降，而随内部EGR率提高，离散度升高；高预喷比例和高内部EGR率下混合气浓区和高温区重合度较高，这是提升GCI燃烧方式低负荷工况着火性能的关键。汽油低温重整的产物主要有CO、H2和CH4，高温和高氧浓度环境有利于提高产出率。内部EGR率为20~50%时，随H2掺混摩尔分数升高，燃烧效率先降低再升高；较低内部EGR率下，燃烧效率随CO掺混摩尔分数升高而持续提升。掺混H2时，对燃烧初期燃料转化起主要作用的自由基是H；而掺混CO时，起主要促进作用的自由基是OH。颗粒物粒径分布均以核态为主，且与颗粒数峰数对应粒径约为20nm。有无EGR参与时，颗粒物均呈现单峰分布，而随着喷油时刻提前，颗粒数峰值逐渐降低且对应粒径也逐渐增大。与无EGR情况相比，采用EGR后颗粒粒径分布区间也随喷油时刻提前向粒径增大方向移动，但颗粒数明显升高。汽油中掺混PODE可使颗粒数峰值和颗粒数浓度下降超过两个数量级，但继续提高掺混比对颗粒数的影响大幅降低。相比于传统的碳平衡方法，本项目提出的新型燃油消耗率计算方法充分考虑了低温燃烧中EGR成分以及碳烟排放量的影响，具有较高的计算精度，适用于高挥发性燃料的燃油消耗率检测。本研究对深入认识GCI燃烧方式的燃烧反应机理具有重要理论意义，对寻求高辛烷值燃料宽广工况范围的高效清洁燃烧具有较高指导价值。