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It has been known from multi-zone simulations that HCCI combustion can be significantly affected by temperature stratification of the in-cylinder gas. With the same combustion timing (i.e. crank angles at 50% heat release, denoted as CA50), large temperature stratification tends to prolong the combustion duration and lower down the in-cylinder pressure-rise-rate. With low pressure-rise-rate HCCI engines can be operated at high load, therefore it is of practical importance to look into more details about how temperature stratification affects the auto-ignition process. It has been realized that multi-zone simulations can not account for the effects of spatial structures of the stratified temperature field, i.e. how the size of the hot and cold spots in the temperature field could affect the auto-ignition process. This question is investigated in the present work by large eddy simulation (LES) method which is capable of resolving the in-cylinder turbulence field in space and time.

With the increasing efficiency of D.I. Diesel engines, the heat power needed to warm the passengers compartment becomes too low during the warm-up period. So the temperature increase of oil and water may be accelerate. This paper is devoted to the understanding of the phenomena involved in this process and their modeling. A diesel engine enclosed in a calorimeter is mounted on a test bench and largely instrumented. From the recorded data, the instantaneous energy balance is set up for different running conditions. Some general trends may be pointed out. During the first minute, 50% of the fuel energy is absorbed by the heat capacity of the heavy metallic components. This part progressively decreases to the benefit of heat transferred to the coolant. Furthermore, for increasing distance from the combustion chamber in the block, the rate of temperature rise decreases. Concerning the oil temperature evolution, it lags behind the water one.