Laser Illuminated Photographic Studies of the Spray and Combustion Phenomena in a Small High Speed DI Diesel Engine

A large number of high speed photographs have been taken of combustion in a high speed direct injection diesel engine. A frame rate of upto 20,000 frames/sec has been achieved at engine speeds up to 3000 rev/min. This has been achieved by computer controlled synchronization of a Cu-vapour laser illumination source, the high speed camera and the electronically controlled fuel injection equipment. In addition to the photography, the basic macroscopic parameters of combustion were recorded simultaneously: this enables the photographic information to be related to the heat release information.

The parameters investigated include the influence of swirl ratio, injection system, engine speed, load, injection timing, and combustion chamber shape on spray and combustion. The influence of various parameters on spray growth, ignition and combustion is discussed. Combustion processes in open and reentrant open bowl combustion chambers are examined. The relation between the illumination and pressure rise delays is studied. It is concluded that while there is an obvious relation between combustion improvement, levels of injection pressure and air swirl or turbulence, excessive swirl ratios and injection pressures have undesirable effects in small high speed diesel engines.