掺氢汽油转子机燃烧机理与排放特性的研究

The gasoline rotary enignes, with the advantages of small size, light weight and simple structure, always encounter problems including the increased fuel consumption and elevated exhaust emissions. Hydrogen prosesses many desirable phycochemical properties which avail improving the gasoline combustion in rotary enignes. This subject is carred out to investigatethe atomization, evaporation, diffusion, and fuel-air mixing characteristics in hydrogen-enriched gasoline rotary enignes, and to explore the influencing mechanism of hydrogen enrichment on promoting the mixing quality, improving the combustion, and restraining the emissions formation for gasoline rotary engines. Through establishing the computational model for in-cylinder flow in hydrogen-enriched gasoline rotary engines, the effects of hydrogen enrichment on in-cylinder flow and its spacial distribution in the gasoline rotary enignes are studied. By coupling the turbulence and chemical dynamics models of hydrogen-gasoline blends, the numerical simulations on the operating processes in hydrogen-enriched gasoline rotary enignes are performed to quantatively analyze and predict the effects of hydrogen enrichment on the ignition, combustion, and emissions formation in gasoline rotary enignes, and to reveal the influencing routine of hydrogen enrichment in these processes. Through developing the fuel supplement, combustion and emissions test systems for hydrogen-enriched gasoline rotary engines, the experimental tests are conducted under both steady and transiet operating conditions, to study the influences of hydrogen enrichment on the lean burn limit, thermal efficiency, cyclic variation, ignition delay time, combustion duration, and emissions level for the gasoline rotary engines. The system development and experimental test could provide fuel supplement and combustion controling strategies for realizing the high-efficiency, stable, and clean operation for hydrogen-enriched gasoline rotary engines, specify the degree of improvement in gasoline rotary engine performance with hydrogen enrichment, and obtain the combustion mechanism and emissions characteristics for hydrogen-enriched gasoline rotary engines. These observations and findings could benifit the commercialization of hydrogen-enriched gasoline rotary engines with fundamental data and theoretical models.

汽油转子机体积小、重量轻、结构简单，但其油耗和排放高，氢气独特的物化特性能够改善汽油在转子机内的燃烧。研究掺氢汽油燃料在转子机内的雾化、蒸发、扩散及混合特性，探索掺氢改善汽油转子机缸内混合气质量及燃烧和排放的机理。建立掺氢汽油转子机缸内流动模型，研究掺氢对汽油转子机缸内混合气流动及分布规律的影响。耦合掺氢汽油湍流和化学反应动力学模型，进行掺氢汽油转子机工作过程的数值模拟，定量分析和预测掺氢对汽油转子机混合气着火、燃烧和排放物生成的影响规律，揭示氢气的作用机理。开发掺氢汽油转子机燃料供给、燃烧和排放测试系统，在稳态和瞬态工况下，通过台架实验研究掺氢对汽油转子机稀燃界限、热效率、循环变动、滞燃期、燃烧持续期、排放等的影响，确定全工况下实现掺氢汽油转子机高效、稳定、清洁运行的燃料及燃烧控制策略，明确掺氢对汽油转子机性能的改善程度，获得掺氢汽油转子机的燃烧机理和排放特性，为其应用提供基础数据。

基于一台160cc点燃式转子发动机，完成了掺氢汽油转子机电控系统软、硬件设计、开发及调试，实现了氢气与汽油的电控独立喷射，所开发的电控系统能够对混合气过量空气系数、掺氢体积分数及点火提前角进行准确控制；完成了掺氢汽油转子机的实验系统搭建，实现了对掺氢汽油转子机缸压的采集及基于缸压数据的放热过程分析。完成了掺氢分数、点火角、当量比等对汽油转子机燃烧和排放特性影响的研究，明确了在不同转速及负荷下实现掺氢汽油转子机高效、稳定、清洁燃烧的掺氢策略及点火角控制规律。发现掺氢能够有效缩短汽油转子机的火焰发展期和快速燃烧持续期，在怠速及部分负荷条件下，掺混3%体积分数的氢气可以使汽油转子机的火焰发展期缩短4 oCA以上，快速燃烧持续期缩短2 oCA以上；发现掺氢可以有效减少汽油转子机的有害排放，HC降低40%以上、CO降低70%以上和CO2排放降低10%以上；虽然NOx排放有一定增加，但可以采用稀燃控制策略来抑制；在保证循环变动及有效热效率与原机相当的条件下，发现掺入6%体积分数的氢气即可将汽油在转子机内的稀燃极限对应的过量空气系数拓展到1.45。此外，构建了掺氢汽油转子机的CFD模型，揭示了转子机缸内流场特性，发现在压缩终了时刻转子机缸内会形成与转子运动方向一致的主流流场；在主流流场的影响下，与主流同向的火焰传播被促进，反向火焰则被抑制，并导致在排气门开启时刻，燃烧室尾端依然存在一定量的未燃混合气；提出了采用缸内氢气直喷改善掺氢汽油转子机缸内混合气浓度分布的控制方法，发现采用该策略可以使适当浓度的氢气分布在火花塞及燃烧室尾端区域，进而保证火焰可以快速传播到整个燃烧室，解决了尾端未燃混合气的问题；就直喷掺氢汽油转子机的结构对混合气燃烧特性的影响规律开展了详细研究，并针对氢气喷嘴的布置方式和喷射规律进行了优化，发现氢气喷射位置在火花塞与进气口之间，距离转子长轴50 mm的位置，且喷射时刻设为110 oCA BTDC，喷射脉宽为40 oCA，可以获得最佳的燃烧及排放效果。