Modeling of Spark Ignition and Aftertreatment Systems for SI Combustion Engines

开发燃油经济性更好的发动机已成为汽车行业应对全球变暖和满足政府法规的主要焦点。稀薄/稀释火花点火发动机已被证明可以提高燃油经济性并减少污染物排放，但不利的空气/燃料化学计量导致更突出的循环变化，这限制了稀薄燃烧和egr稀释高效运行的扩展。对稀/稀汽油机进行优化的关键是改进火花点火和火焰核发展过程，特别是对利用强气缸流加速燃烧以提高效率的汽油机而言。火花引发的火焰传播涉及等离子体通道拉伸以及在强交叉流场中的多次重击等复杂现象。从火花等离子体到可燃气体的能量传递是实现稳定火焰核形成的关键因素，从而减少高效稀释汽油机的循环变化。目前，由于在强湍流条件下火花拉伸和重击的复杂现象，在燃烧模型中对火花等离子体通道的预测仍然缺乏准确性。对于稀/稀汽油机来说，由于排气温度较低，废气中氧含量较高，氮氧化物后处理具有挑战性。因此，三元催化剂（TWC）的低温熄火特性和储氧能力对于工业需要的精益/稀释SI发动机的TWC建模至关重要。本文的研究重点是：1)建立能较好地预测火花拉伸和重击现象的经验火花点火模型；2)定量确定火花通道的能量分布和火花到气体的能量传递；3)研究稀薄/稀释SI发动机TWC的低温熄火。该研究将利用由郑博士领导的清洁内燃机实验室（CCEL）在测量和控制资源方面的专业知识和优势，并得到FCA的支持。

Developing engines with better fuel economy has become the main focus for the automotive industry to counter global warming and meet government regulations. Lean/diluted spark ignition engines have been proven to improve fuel economy and reduce pollutant emissions, but the unfavorable air/fuel stoichiometry results in more prominent cycle-to-cycle variation which limits the extension of lean-burn and EGR-diluted high efficiency operations. A critical part to optimize the lean/diluted gasoline engines is to improve the spark ignition and flame kernel development processes, especially for the engines that utilize strong cylinder flow to accelerate the combustion for better efficiency. Spark initiated flame propagation involves complex phenomena such as plasma channel stretching as well as multiple restrikes in a strong cross flow field. Energy transfer from the spark plasma to the combustible gas is a key factor to enable stable flame kernel formation thereby reducing the cycle-to-cycle variation of high efficiency diluted gasoline engines. Currently, there is still a lack of accuracy in combustion modeling to predict the spark plasma channel because of the complex phenomenon of spark stretching and restrike under strong turbulent flow. As for the lean/diluted operation of gasoline engines, the nitrogen oxides aftertreatment is challenging due to the lower exhaust temperature and the oxygen abundance in the exhaust stream. Thus, the low temperature light-off characteristics and oxygen storage capability of the three-way-catalyst (TWC) are of critical importance in TWC modeling for lean/diluted SI engines for industrial needs. The proposed research will focus on: 1) building an empirical spark ignition model which can better predict the spark stretching and the restrike phenomenon; 2) quantitatively determining the energy distribution of the spark channel and the spark-to-gas energy transfer; 3) investigating the low temperature light-off of TWC for lean/diluted SI engines. The proposed research will utilize the established expertise and advantages in measurement and control resources at the Clean Combustion Engine Laboratory (CCEL), directed by Dr. Zheng with supports from FCA.