Ignition Criterion Studies on Lean and Diluted Mixtures for Clean Combustion in Automotive Engines

世界范围内使用尖端技术的努力正在取得重大进展，以提高人们对清洁内燃机的认识，从而提高对清洁内燃机的设计和控制。稀薄和稀释的混合燃料对提高火花点火(SI)发动机的效率和排放是有效的，但比化学计量和均匀的混合气更难点燃。传统上，汽油是在进气冲程期间喷射的，要么是在进气口，要么是直接进入气缸。在气缸压缩结束时，气缸充气通常达到完全均匀。在这种情况下，只要空气/燃料比(AFR)是化学计量比，即使火花能量和持续时间有限，火花点火也不会有什么困难。然而，化学计量比气缸装药的燃烧效率不足，通常有6%~8%的喷射燃料跳跃燃烧。整体稀薄混合气可以提高燃烧效率，减少部分负荷下对进气节流的依赖。废气再循环(EGR)的使用也减少了泵浦损失，同时降低了火焰温度和氮氧化物(NOx)的生成。当在稀薄和稀释的混合气中工作时，发动机需要增加进气以保持最大功率。在汽车小型化和混合动力的协同作用下，进气助推器也是小型发动机以更高的效率产生更多动力的必要条件。光学接近的燃烧室将被用来研究预混混合物的点火标准，精确控制AFR、温度、压力和稀释度。单缸研究发动机将用于研究缸内流动和均匀性的影响，在独立控制燃油喷射、进气增压和废气再循环的情况下。包括汽油、乙醇、甲烷和丙烷在内的挥发性燃料将在进气口或在单次或多次喷射中直接喷射到气缸中。对火花点火和电晕点火在点火能量、点火持续时间、点火事件、点火地点和点火体积等方面的控制进行了研究，为提高发动机清洁燃烧的燃油效率提供了指导，特别是在火花塞间隙的瞬变过程中形成了可局部点燃的混合气，从而完成了火核的形成和燃烧。本研究为HQP的培训提供了一个理想的场景。

Worldwide efforts with cutting-edge technologies are making significant progresses to improve the understanding, therefore the design and control of clean combustion engines. The lean and diluted fuel-air mixtures are effective to improve the efficiency and emissions of spark ignition (SI) engines, but are more difficult to ignite than a stoichiometric and homogeneous mixture. Traditionally, gasoline is injected during intake stroke, either at an intake port or directly into a cylinder. The cylinder charge usually reaches full homogeneity at the end of cylinder compression. Thereon, providing the air/fuel ratio (AFR) is stoichiometric, spark ignition succeeds with little difficulty, even with limited spark energy and duration. However, the burning efficiency of a stoichiometric cylinder charge is insufficient, and usually 6~8% of injected fuel skips combustion. An overall lean mixture can improve the burning efficiency, and reduces the reliance on intake throttling under partial loads. The use of exhaust gas recirculation (EGR) also reduces the pumping loss, while lowing the flame temperature and the nitrogen oxides (NOx) formation. When operating with lean and diluted mixtures, an engine needs to boost the intake air to retain full power. In synergy with automotive downsize and hybridization, the intake boost is also necessary for a small engine to produce more power at a higher efficiency.The proposed research establishes a strategy to study the criteria of ignition. Optically-accessible combustion cells will be used to study the ignition criteria of premixed mixtures, with precisely-controlled AFR, temperature, pressure, and dilution. Single cylinder research engines will be used to study the impact of in-cylinder flow and homogeneity, under independently-controlled fuel injection, intake boost, and EGR. Volatile fuels, including gasoline, ethanol, methane, and propane, will be injected at the intake port or directly into the cylinder, in single or multiple injection events. The spark and corona ignition with controls on the ignition energy, duration, events, sites, and volume will be investigated.The results of this research will provide guidelines for improving the fuel efficiency of SI engine clean combustion, specifically to the forming of a locally-ignitable mixture that encapsulates the gap of a sparkplug in transience to succeed the flame kernel formation and combustion. This research provides an ideal scenario for training HQP.