Quantitative laser diagnostic studies of the NO distribution in a DI diesel engine with PLN and CR injection systems
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 arom. 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 Degca 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 temp. measurements. Laser and signal attenuation were assessed in sep. expts. using spectrally resolved O2 LIF detection with the same optical path as in the imaging measurements. Attenuation is then measured using the Franck-Condon pattern of the emission spectrum of excited oxygen. A comparison with model calcns. shows that the main contribution to the obsd. attenuation effects is absorption by hot, vibrationally excited CO2. Using these absorption data and an external calibration source the LIF intensities of a selected data series are quantified.
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