基于汽油醇类双燃料复合喷射技术的高增压汽油机爆震机理的研究

Recently, alcohol-gasoline dual-injection technology has received wide attention. By directly injecting alcohols into cylinder, it can effective suppress engine knock and allow engines to use higher compress ratio to reach higher efficiency. However, the antiknock mechanism of this technology and interaction between various influencing factors are still not clear. This project focuses on auto-ignition characteristic and knocking propensity in a supercharged spark-ignition engine with alcohol-gasoline dual-injection. Three scientific problems will be solved in this study:influence of in-cylinder flow on alcohol fuel spray and mixture distribution process, mechanism of alcohol-gasoline auto-ignition under high pressure and temperature and contribution of different factors on knock suppressing. Optical engine, constant volume bomber, single cylinder engine and numerical simulation are adopted to investigate these three aspects. In this research, the influence of in-cylinder flow, mixture formation and mixture physicochemical property on auto-ignition and corresponding control mechanism will be revealed and proposed. The mechanisms of pre-ignition and knock origination will be clarified, the conditions required for pre-ignition origination, knock and detonation initiation will be detailed. The effectiveness of different factors on knock suppressing will be quantitative analyzed. This research has important scientific significance on developing multiphase flow theory and combustion science. It also has great realistic significance to the industrialization application of alcohol-gasoline dual-njection technology.

近来汽油醇双燃料复合喷射技术受到广泛关注，该技术通过缸内直接喷醇，取得了明显抑制汽油机爆震倾向的效果，从而允许使用更高的压缩比达到较高的热效率。但该技术抗爆震机理和各影响因素间相互作用还不清晰。本课题围绕醇汽油双燃料复合喷射技术，拟解决缸内流动对醇燃料临界喷雾特性及混合气浓度分布演化过程的影响规律；高温高压条件下汽油醇可燃混合气起爆机制；爆震抑制作用各因素贡献度三个关键科学问题。研究利用光学发动机、定容燃烧弹、单缸机和数值模拟相结合的方式开展与汽油醇复合喷射技术爆震机理相关，上述三方面有机结合的研究。以期揭示复合喷射条件下缸内流动、混合气形成以及混合气理化特性对早燃和爆震的影响及其调控机制；获得双喷射早燃、爆震发生机理；早燃-爆震-爆轰发生临界条件以及量化的爆震抑制作用贡献度。项目研究结果将丰富多相流和燃烧学的理论，对高增压复合喷射发动机的产业化应用具有重要的实际意义。

本项目开展了汽油进气道喷射+乙醇缸内直喷技术对内燃机爆震抑制作用的基础性研究。项目通过定容燃烧弹，发动机台架以及数值模拟相结合的方式，系统的研究了乙醇喷雾，雾化、蒸发以及喷射控制参数（压力、温度、正时），对乙醇油雾在缸内混合、蒸发、碰壁的影响因素，以及这些因素对缸内降温、火焰传播、浓度场分布等对爆震产生关键因素的影响。同时，利用模拟获得的结果，优化了发动机台架试验的控制条件和实验参数，在此技术上通过发动机台架试验，获得了乙醇不同掺混条件下，混合气理化特性的改变对爆震诱导因素的影响，以及各个因素对内燃机抗爆震能力贡献度的数据。并分析了，不同掺混比条件下内燃机燃烧和排放特性。同时，进一步的模拟研究了乙醇直喷蒸发吸热、自燃温度、火焰传播速度变化、混合气浓度、密度、温度分布等因素对早燃的抑制影响关系。这些数据的获得对进一步优化乙醇/汽油双喷射系统控制方式，理解乙醇直喷对爆震抑制作用规律和抑制机理，进一步探索利用该双喷射方式提高汽油机功率密度具有指导性作用。