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

Abstract

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. We present quantitative in-cylinder imaging measurements of NO mole fractions in a gasoline engine with spray-guided direct injection using laser-induced fluorescence (LIF). The optical engine design was kept close to that of a serial four-cylinder engine. Optical access was achieved via sapphire windows, requiring only minor modifications to the engine block. The engine was operated with commercial gasoline and fired continuously. The data interpretation applies the spectral simulation tool LIFSim to calculate pressure, temperature, and gas-composition dependencies of the LIF signal. Temperature-dependent CO 2 absorption cross-sections are used to correct for laser and signal attenuation. A sensitivity analysis of the quantitative NO concentrations on the different parameters entering the evaluation is presented. The LIF measurements are compared to results from in-cylinder fast gas sampling through a modified spark plug. The two techniques show good quantitative agreement. The LIF measurements are also compared to charge-averaged working-cycle-resolved NO chemiluminescence measurements in the exhaust port. NO-LIF imaging results are presented for stratified engine operation with different levels of exhaust gas recirculation (EGR), showing the large impact of EGR on in-cylinder NO formation.