過濃燃焼ガスの希薄化過程における窒素酸化物の生成と分解

抄録

Production and destruction of nitrogen oxides in the dilution process of fuel-rich burnt gases are investigated based on detailed chemical kinetics. From the analysis of combustion processes with mixing of methane-air fuel-rich burnt gas and air, it is shown that fast mixing due to strong turbulence enables a great deal reduction in NO_x concentration, and that a further reduction cannot be achieved for a rich mixture of equivalence ratio higher than 1.2. The NO production rates of elementary reactions indicate that NO is formed by the destruction of HNO at low NO concentration and is deoxidized into HNO at high NO concentration. It is also shown that NO_x concentration can be halved if the temperature decreases with the volume expansion in a high-speed piston-engine motion prior to the heat release due to dilution. Furthermore, the effect of temperature fluctuation on the dilution path is discussed from the practical point of view for reducing NO_x in two-stage combustion.