Luminosity and Laser-Induced Incandescence Investigations on a DI Gasoline Engine

The effectiveness of two optical measurement techniques better known from diesel engine investigations concerning soot investigations applied to a direct injection (DI) gasoline engine is demonstrated. The first technique records the luminosity emitted by the combustion flame via an optical probe and analyzes it with temporal and spectral resolution using an imaging spectrograph and an image intensifying streak CCD camera. Chemiluminescence of OH radicals can be detected simultaneously by selecting an according wavelength range. Most combustion cycles of the research engine under investigation are burning lean but a few combustions are rich. In those cycles time-resolved combustion temperatures are derived by an optimized multi-color method.

Laser-induced Incandescence (LII) needs larger optical access but has the advantage that the soot can be imaged in a light-sheet plane and the soot can be traced until outlet when there are no chemiluminescent emissions anymore. LII signals in the present approach are excited by a KrF excimer laser at 248 nm. Parameter studies show this to be possible. A suitable detection timing and optical filter can exclude interference of fluorescence signals. The great advantage of using a KrF laser is a complete hardware compatibility from LII to laser-induced fluorescence (LIF) experiments.

Luminosity measurements and LII together are complementary and well suitable to in-cylinder soot investigations on direct injection gasoline engines.