NO laser-induced fluorescence imaging in the combustion chamber of a spray-guided direct-injection gasoline engine
In direct-injection gasoline (GDI) engines with charge stratification, minimizing engine-out nitrogen oxide (NOx) emission is crucial since exhaust-gas aftertreatment tolerates only limited amts. of NOx. Reduced NOx prodn. directly lowers the frequency of energy-inefficient catalyst regeneration cycles. In this paper we investigate NO formation in a realistic GDI engine. Quant. in-cylinder measurements of NO concns. are carried out via laser-induced fluorescence imaging with excitation of NO (A-X(0,2) band at 248 nm), and subsequent fluorescence detection at 220-240 nm. Engine modifications were kept to a min. in order to provide results that are representative of practical operating conditions. Optical access via a sapphire ring enabled identical engine geometry as a prodn. line engine. The engine is operated with com. gasoline ("Super-Plus", RON 98). Recent high-pressure spectroscopic studies of NO, O2 and CO2 are utilized to select an appropriate detection scheme for quant. NO measurements under realistic conditions. CO2 UV light absorption data is used to correct for laser and signal attenuation. NO-LIF concns. are compared to extractive measurements using a fast gas sampling valve (GSV). NO formation is investigated at different operating conditions such as variable exhaust gas recirculation (egr).
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