Quantitative in-cylinder NO-LIF imaging in a realistic gasoline engine with spray-guided direct injection

Limiting the in-cylinder nitric oxide (NO) formation is a crucial task in the development of engines with gasoline direct injection. Exhaust gas aftertreatment requires storage catalysts that tolerate a maximum NO flux only, and the frequency of energy consuming catalyst regeneration cycles is directly correlated with engine-out NO. Quantitative in-cylinder imaging measurements of NO mole fractions in a gasoline engine with spray-guided direct injection were presented. Laser-induced fluorescence of NO proved a viable technique for quantitative in-cylinder measurements of NO concentrations in a spray-guided DI engine with minimized optical accesses and operation with commercial gasoline. The major source of uncertainty arises from the unknown temperature and flame diameter that determine the correction for laser and signal attenuation. Comparison with in-cylinder sampling showed good agreement, and the comparison with exhaust port charge-averaged measurements confirmed the image of a spatially very inhomogeneous in-cylinder NO distribution. The influence of exhaust-gas recirculation on NO formation under stratified engine operation was examined. The peak NO concentrations decreased by a factor of 11 when increasing the exhaust gas recirculation ratio from 0 to 30%. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).