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，但比化学计量和均质混合物更难点燃。传统上，汽油是在进气冲程中注入的，要么在进气口，要么直接注入气缸。气缸装药通常在气缸压缩结束时达到完全均匀性。因此，提供空气/燃料比（AFR）是化学计量的，火花点火成功几乎没有困难，即使在有限的火花能量和持续时间。然而，化学计量气缸装药的燃烧效率不足，通常有6~8%的喷射燃料跳过燃烧。整体稀混合气可以提高燃烧效率，并减少部分负载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。当使用稀混合气和稀混合气时，发动机需要增加进气以保持全部动力。在汽车小型化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大的动力也是必要的。本研究建立了一种研究点火判据的策略。光学可及的燃烧电池将用于研究预混混合物的点火标准，具有精确控制的AFR，温度，压力和稀释。单缸研究发动机将用于研究在独立控制燃油喷射、进气增压和EGR下缸内流量和均匀性的影响。挥发性燃料，包括汽油、乙醇、甲烷和丙烷，将在进气口或在单次或多次喷射事件中直接注入气缸。火花和电晕点火与控制点火能量，持续时间，事件，地点，和体积将进行调查。这项研究的结果将为提高SI发动机清洁燃烧的燃油效率提供指导，特别是形成局部可燃混合物，该混合物在瞬态中封装火花塞的间隙，以接替火焰核的形成和燃烧。本研究为HQP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.