Spray Process and Fuel Pyrolysis in the Initial Stage of Diesel Combustion

Abstract

To elucidate the spray processes in a diesel engine, with special regard to the gasification and thermal decomposition of the injected fuel at an elevated air temperature, a study was carried out on a simulated two-cycle engine using a fast gas-sampling technique. The results obtained suggest that already in the period before an appreciable pressure rise in the cylinder is observed, in other words, even during the so-called ignition delay period, the injected fuel quickly gasifies and decomposes, forming a large quantity of split hydrocarbons. This phenomenon may be partly attributed to the fact that the hot burnt gas formed in the vicinity of the spray jet is sucked into the spray core, thus promoting the gasification and thermal decomposition. It is also suggested that a quantity of decomposed products which undergo turbulent mixing will accumulate in the down-stream of the fuel jet.