Evaluation of various factors affecting nitric oxide formation and effectiveness of some emission-control systems

Abstract

Abstract Effects of fundamental factors, such as temperature, pressure, equivalence ratio and fuel type, which affect nitric oxide formation are evaluated; some emission-control systems are modelled analytically and their effectiveness for nitric oxide emission control are evaluated by chemical kinetics. The main results obtained are: 1. (1) by raising the temperature, the rate of nitric oxide formation is increased remarkably, and by lowering the temperature below about 1700 K it may be almost prevented; 2. (2) at the same temperature, rates of formation are larger for leaner fuel/air mixtures, and higher pressure results in a somewhat lower equilibrium concentration but a higher rate of formation; 3. (3) nitric oxide formation is little affected by the type of hydrocarbon fuel if the temperature and the equivalence ratio are the same, but it differs for each fuel at the adiabatic flame temperature of each; 4. (4) at the adiabatic flame temperature, the equilibrium concentration reaches its maximum at around φ = 0.85, but the rate of formation is highest at around φ = 1.0 for propane/air flames; 5. (5) reduction of nitric oxide emission by means of exhaust-gas recirculation and water-injection systems is attributable to the resulting lowering of temperature. A two-stage combustion system becomes more effective when the temperature drop or heat loss in the primary combustion region increases.