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

世界范围内的尖端技术正在取得重大进展，以提高对清洁内燃机的理解，从而设计和控制。稀薄和稀释的燃料-空气混合物对于改善火花点火（SI）发动机的效率和排放是有效的，但是比化学计量和均质混合物更难点燃。传统上，汽油在进气冲程期间在进气口处或直接喷射到气缸中。气缸充气通常在气缸压缩结束时达到完全均匀。因此，只要空气/燃料比（AFR）是化学计量的，火花点火成功的困难不大，即使有限的火花能量和持续时间。然而，化学计量的气缸充气的燃烧效率是不足的，并且通常6~8%的喷射燃料跳过燃烧。全稀混合气可以提高燃烧效率，并减少在部分负荷下对进气节流的依赖。废气再循环（EGR）的使用也减少了泵送损失，同时降低了火焰温度和氮氧化物（NOx）的形成。当使用稀薄和稀释的混合物时，发动机需要增加进气以保持全功率。在与汽车缩小尺寸和混合动力的协同作用下，进气增压对于小型发动机以更高的效率产生更多的动力也是必要的。建议的研究建立了一个战略，研究点火标准。光学可访问的燃烧室将用于研究预混混合物的点火标准，精确控制AFR，温度，压力和稀释。单缸研究发动机将被用来研究缸内流动和均匀性的影响，在独立控制的燃料喷射，进气增压，和EGR。挥发性燃料，包括汽油、乙醇、甲烷和丙烷，将在进气口处以单次或多次喷射事件喷射或直接喷射到气缸中。将研究火花和电晕点火，控制点火能量、持续时间、事件、地点和体积。*研究结果将为提高火花塞发动机清洁燃烧的燃油效率提供指导，特别是在火花塞的差距中形成局部可燃混合气，以实现火焰核心的形成和燃烧。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.******