Abstract: To calculate the combustion temperature in direct-injection diesel engine the mixture fracture space is presented. The mixture fracture function is introduced and the connections between species and mixture fraction are deduced. The classic non-premixed flame structure is analyzed based on flamelet assumptions and the connections between temperature and mixture fraction are carried out in the adiabatic condition. So the temperature equation is deduced with mixture fraction equation through the space coordinates change, and a way of separating the numerical effort associated with the solution of the turbulent flow field from that of solving the chemistry is offered. The connections between temperature and scalar dissi-pation rate and between temperature and mixture fraction and the flame temperature profile are carried out through a series of parameters. Further the calculational results are compared with the experiment data. A new way to simulate combustion tem-perature and further for pollutants in direct-injection diesel engine is presented.

Key words: Direct-injection diesel engine, Flamelet assumptions, Mixture fraction, Turbulent combustion