Quantitative Laser Diagnostic Studies of the NO Distribution in a DI Diesel Engine with PLN and CR Injection Systems 2001-01-3500

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.

Laser and signal attenuation were assessed in separate experiments 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 calculations shows that the main contribution to the observed 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.