Combustion processes in a diesel engine
The effects of in-cylinder and injection pressures on the formation and autoignition of diesel sprays at realistic automotive in-cylinder conditions was investigated. A two-stroke diesel Proteus engine has been modified to allow optical access for visualisation of in-cylinder combustion processes. Various optical techniques were used to investigate the combustion processes. These include high-speed video recording of the liquid phase, high-speed schlieren video recording of the vapour phase and laser-induced incandescence for soot imaging. The spray cone angle and penetration with time data extracted from photographic and high-speed video studies are presented. The effects of droplet evaporation, breakup and air entrainment at the initial stage of spray penetration were studied theoretically using three models. It was found that the predictions of the model combining bag breakup and air entrainment are in good agreement with the experimental measurements. Spray autoignition was investigated using video, in-cylinder pressure, and schlieren recordings. Pseudo three-dimensional visualisation of the autoignition was achieved by simultaneous use of two high-speed video cameras at right angles to each other. The effects of elevated injection and in-cylinder pressures on the ignition delay and ignition sites have been investigated. Laser-induced incandescence was performed to obtain maps of soot concentration for a range of engine conditions. The influence of in-cylinder and injection pressures on soot formation sites and relative soot concentration has been studied. The work has been mainly focused on the specificities of soot formation under extreme in-cylinder conditions.