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The effects of engine operating parameters on the unburned hydrocarbon in the residual gas in a cylinder of a spark ignition engine were investigated. Since the residual gas was not homogeneous in the cylinder, a method was developed to estimate the mean hydrocarbon concentration in the residual gas by the gas sampling technique. It was shown that the mean hydrocarbon concentration in the residual gas was much higher than in the emissions. In addition the analysis of net and gross combustion efficiencies was made. The influence of compression ratio on the hydrocarbon in the residual gas and combustion efficiencies was also studied.

The effect of the introduction of low-emission vehicles on potential air quality improvement in the Los Angeles area was predicted using a three-dimensional airshed simulation model. The simulations were based on ozone concentration estimates made on the basis of data released by the California Air Resources Board concerning projected quantities of emissions from various sources in 2010. Analyses were made of three scenarios. One assumed that LEV, ULEV and ZEV regulations were enforced as planned, a second assumed that these planned regulations were modified; and a third assumed that emission levels from various sources were reduced in line with the goals of the Air Quality Management Plan formulated by the South Coast Air Quality Management District.

This paper presents the results of several studies conducted on a natural gas vehicle. In one study of engine-out emissions performance, the exhaust emissions of the CNG engine were lower than those of the base gasoline engine. In another study of the conversion characteristics of three-way catalysts, it was found that the conversion efficiency of total hydrocarbons (THCs) was much lower in the lean-mixture region for the NGV. The reduced efficiency was traced to lower conversion and poor reactivity of low-end hydrocarbons and to a higher concentration of H2O.