Search Results

Temperature stratification plays an important role in HCCI combustion. The onsets of auto-ignition and combustion duration are sensitive to the temperature field in the engine cylinder. Numerical simulations of HCCI engine combustion are affected by the use of wall boundary conditions, especially the temperature condition at the cylinder and piston walls. This paper reports on numerical studies and experiments of the temperature field in an optical experimental engine in motored run conditions aiming at improved understanding of the evolution of temperature stratification in the cylinder. The simulations were based on Large-Eddy-Simulation approach which resolves the unsteady energetic large eddy and large scale swirl and tumble structures. Two dimensional temperature experiments were carried out using laser induced phosphorescence with thermographic phosphors seeded to the gas in the cylinder.

The UNIBUS (Uniform Bulky Combustion System) based on the HCCI (Homogeneous Charge Compression Ignition) concept uses an early injection quantity, timing, boost pressure, EGR, etc. for ignition control [1]. To further expand the operation range from the present level, the effects of the atmospheric conditions on ignition and combustion were calculated using CHEMKIN in the present study. When controlling the start timing of the high temperature reaction to suppress the early ignition, it is more effective to apply EGR than boost pressure. If fuel quantity is increased to expand load, it is possible to suppress a sharp cylinder pressure rising rate by increasing the boost pressure. Furthermore, it has become apparent that the cause of this is an increase in heat capacity.