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The NO distribution in a directly-injected Diesel engine with realistic combustion chamber geometry was investigated with laser-induced fluorescence (LIF) imaging with KrF excimer laser excitation. The highest possible level of selectivity has been ensured using spectrally resolved LIF investigations inside the Diesel engine. To minimize interference from both, oxygen and polycyclic aromatic hydrocarbon (PAH) LIF the NO signal was detected around 237 nm, blue-shifted compared to the excitation wavelength resulting in a background contribution below 10% at the earliest detection timing possible in the engine under study (20°ca after top dead center, TDC). The in-cylinder NO LIF intensities were compared for different injection systems and operating conditions and correlated to variations in pressure traces and soot temperature measurements.

The formation of nitric oxide in a transparent direct injection gasoline engine was studied experimentally using two different schemes of laser-induced fluorescence (LIF) with KrF excimer (248 nm) excitation. With detection of the fluorescence shifted towards the red, strong interference from fluorescence of partially burned fuel was found. With blue-shifted fluorescence, interference was minimized allowing selective detection of NO. Possibilities of quantifying NO fluorescence intensities in inhomogeneous combustion are discussed.