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This paper describes experiments to determine the effect on exhaust emissions of starting on compressed natural gas (CNG) and then switching to gasoline once the catalyst reaches operating temperature. Carbon monoxide, oxides of nitrogen, and detailed exhaust hydrocarbon speciation data were obtained for dedicated CNG, then unleaded gasoline, and finally CNG start -gasoline run using the Federal Test Procedure at 24°C and at -7°C. The result was a reduction in emissions from the gasoline baseline, especially at -7°C. It was estimated that CNG start - gasoline run resulted in a 71 percent reduction in potential ozone formation per mile.

Seven motorcycles, ranging in size from 100 to 1200 cm3, were tested for emissions characterization purposes. They were operated on the federal seven-mode test procedure (for 1971 and older light-duty vehicles), the federal LA-4 test procedure (for 1972 and later LDVs), and under a variety of steady-state conditions. Four of the machines tested had 4-stroke engines, and the other three had 2-stroke engines. Emissions which were measured included hydrocarbons, CO, CO2, NO, NOx, O2, aldehydes, light hydrocarbons, particulates, and smoke. Emissions of SOx were estimated on the basis of fuel consumed, and evaporative hydrocarbon losses were also estimated. Crankcase “blowby” emissions from one 4-stroke machine were measured. The impact of motorcycles on national pollutant totals was estimated, based on the test results and information from a variety of sources on national population and usage of motorcycles.