Characteristics of the Expansion of Reactive Gas Mixtures as Occurring in Internal Combustion Engine Cycles

The influence of nonequilibrium in the expansion gases of spark ignition engines has been studied theoretically to determine how power output and exhaust gas composition might be affected. Comparing a gas which is frozen in composition during expansion with a composition which continuously is in equilibrium shows the difference in expansion work can be as large as 10%. Maximum influence is in the fuel-air ratio range of chemically correct mixture. It was found that carbon monoxide and nitric oxide concentrations in the exhaust more nearly reflect the frozen composition than the equilibrium expansion. This is particularly true for the range of mixture ratios -- from lean to chemically correct.