Optical Detection of the Combustion Produced by the Pre-Injected Fuel in a DI Diesel Engine 2002-01-2667
In this paper it is set down how the luminosity of the pre-combustion inside an optically accessible direct injection common rail diesel engine is directly detected by super-sensitive detection technique consisting of an image intensified UV and VIS CCD camera with on-chip integration. During pre-combustion first a weak chemi-luminescence of hydrocarbon is observed which is followed in some cases by bright light emissions from soot. This investigation focuses on chemiluminescence. Due to the extremely weak light emissions the image intensifier was switched to maximum, the light emissions of usually 100 single engine cycles were summed up on the CCD chip at an exposure duration of two degrees crank angle for each cycle. Stoichiometric or lean pre-combustion can clearly be detected with this highly sensitive setup. The application of a transparent engine with a window in the piston bowl enables two-dimensional images of the pre-combustion showing the shape of seven separate vaporized and burning fuel jets according to the holes in the injection nozzle and even the effect of the swirl flow inside the cylinder is observed. Since those luminosity effects occur in the near UV and blue spectral range they are caused by light emissions from stoichiometric or lean hydrocarbon pre-combustion. The heat release derived from internal pressure values indicated a first combustion phase of the pre-injected diesel fuel. Further evidence was supplied by an analog recording high-speed film technique in the visible spectral range showing a slight flickering in an area of 20 mm around the injection nozzle.
Engine operation parameters under investigation were high and low swirl flow inside the combustion chamber and 60 and 40°CA BTDC control of the pre-injection, respectively.