The spray combustion is applied to various practical combustors such as a diesel engine, a gas turbine, etc. However, the spray combustion is the very complicated, unsteady and inhomogeneous physicochemical phenomenon composed of preheating, evaporation, mixing, ignition, combustion and quenching, etc. Chiu et al. considered the spray combustion field with the concept of group combustion, and proposed that the group combustion can be classified into four modes in terms of group combustion number. In this paper, we examined to improve Chiu's group combustion mode using the numerical analysis on gas phase combustion process in three-dimensional inhomogeneous concentration and temperature fields of methane-air mixture. We arranged many fuel points using random variables instead of fuel droplets, and changed the initial equivalence ratio and fuel point diameter. We obtained the following results; 1) The group combustion is classified into five modes in terms of the initial equivalence ratio and fuel point diameter. 2) The ignition occurs in each fuel point when the mixture gas is lean, while the ignition occurs in the area with fuel point closely spaced when the mixture gas is rich. 3) "The initial equivalence ratio / fuel point diameter" is the appropriate parameter of the group combustion of gas phase.

The united model, which is applicable to the premixed and diffusion flame using of author's premixed combustion model[2-4], was proposed. It has the following features, 1) The model includes the laminar flame speed and the gradient of the mixing fraction. When the gradient of the mixing fraction is close to zero, then the model is also close to the existing premixed combustion model. 2) By the laminar flame speed, the effects of the pressure in the combustor, unburned gas temperature, and the flame stretch on the combustion were considered to the model. 3) The model is applicable with all the turbulence model like k-ε model, LES and direct simulation, on the case of the wrinkled laminar flame. The effect of the turbulence is considered through the eddy viscosity of each turbulence model.

To verify the accuracy, the numerical simulation of the one dimensional counterflow diffusion flame was performed using of the united combustion model, which is proposed on the 1^st report. The model is applicable to the premixed and diffusion flame. To compare the results, the two scalar Flamelet model was also applied to one dimensional counterflow diffusion flame. The main results are follows, 1) The distributions of the temperature and the mole fraction of each gas composition through the diffusion flame were in good agreement with experimental data, which was measured by Tsuji and Yamaoka[6]. 2) On the results of the two scalar model, some discrepancies on the distribution of the temperature and the mole fraction were found with experimental data. It depends on the estimation method of the temperature and the mass fraction using of G and the mixture fraction.