直喷式火花塞点火透明发动机中氮氧化物形成过程的激光光谱学研究

Growing environmental concerns, such as global warming due to the emission of the greenhouse gas CO2 by automotive power plants, lead to the need for cleaner and fuel saving combustion systems. Direct injection combustion systems applied to the spark ignited engine might be a way to improve the efficiency particularly by reducing pumping and heat losses during part load while maintaining the advantages of high power density and engine speeds during high loads [Zhao, Lai et al., 1999]. Initially, wall guided combustion systems were pursued, but high hydrocarbon and soot emissions led to the investigation of spray guided systems. Here a higher degree of stratification is possible, which yields improved emissions [Drake, Fansler et al., 2004; Honda, Kawamoto et al., 2004]. Nonetheless, due to high oxygen availability and locally rich mixture, the nitric oxide formation is comparably high. This is detrimental as the widely employed exhaust aftertreatment by a three way catalytic converter is inefficient for overall lean mixtures. NO storage catalytic converters are widely employed, but require rich exhaust gas to reduce the stored NO. This is generated by operating the engine homogeneous-rich for a brief period of time, which of course comes with a fuel consumption penalty [Tamura, Kikuchi et al., 2001; Krebs, Pott et al., 2002]. A reduction of in-cylinder nitric oxide is desirable to minimize the number of regeneration cycles. Hence the understanding of in-cylinder NO formation is important, so that the necessary scientific background for improvement of the combustion system is provided. An assessment of the NO formation process inside the engine exclusively by drawing conclusions from engine out emissions is difficult, because of the highly inhomogeneous nature of the stratified charge combustion process. Also, due to high cyclic variability cycle resolved measurements are desirable, which conventional emissions analyzers are not capable of.