Combustion experiments of synthetic gas and pulverized coal were carried out by the method of two free-impinging-streams as shown schematically in configuration "b" of Figure I. In combustion of gas, the complete behaviour of impinging jets versus the fuel/air ratio was revealed and explained on the basis of the dependence of the burning velocity of the gas mixture on the above ratio. This behaviour consists of three distinct and stable modes of operation as follows: In mode I, no combustion takes place along the path of the free jets fed into the reactor (Figure 3a). In mode II, combustion begins roughly near the impingement plane of the two jets (Figures 3b, 4 and 6). Mode III is a third situation in which combustion takes place immediately at the entrance of the jets into the reactor (Figures 3c and 5). For combustion of pulverized coal, a correlation based on a diffusion-convection model was obtained for the prediction of the combustion efficiency as a function of available operational parameters.