Effect of Some Spark Ignition Engine Operating Variables on NOX Production and Control

A spark ignition engine two-zone simulation code was used to conduct a systematic study of the effects of combustion chamber wall temperature, start of heat release/ignition timing, fuel-air equivalence ratio, engine speed, indicated mean effective pressure and exhaust gas recirculation on an individual basis on emissions in a 5.734 l, V8 spark ignition engine. The two-zone model which incorporates heat transfer, blow-by and other losses was used. In this model, the flame traverses the charge resulting in burned and unburned zones. The unburned zone contains the reactants (fuel and air), and there is no reaction between the constituents. The burned zone consists of the products of combustion and dissociation. The formation of nitric oxide was obtained using the extended Zeldovich nitric oxide reaction mechanism. The simulation program computes both equilibrium thermodynamics and rate-limited values of the concentration of oxides of nitrogen ( in parts per million (ppm) as a function of crank angle as well as its concentration in the exhaust gas stream. The study shows that the equilibrium NO is formed immediately after the start of combustion, and because of its strong dependence on temperature it rises rapidly to a maximum value of 8454.75 ppm, and declines rapidly as the pressure and temperature fall during expansion stroke to a final concentration value of 28.7 ppm. The results also show that spark retard and exhaust gas recirculation are effective strategies for emission control. The complete results from this study are summarized in the conclusion.