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The design parameters of a turbo-compound engine system affecting the thermal efficiency and engine output have been analyzed, considering the allowable limit of the maximum cylinder pressure, exhaust temperature and other factors. By adjusting the values of the engine compression ratio to 20, the cross sectional area ratio of the turbine inlet to 0.4, and the compressor pressure ratio to 2.2 at full load and to 1.7 at part load, the thermal efficiencies of approximately 40% at full load and 25% at part load have been obtained in turbo-compound engine. Furthermore, the changes the optimum values are comparatively small, even if the engine compression ratio is greatly changed from 22 to 14.

A turbo-compound engine system is considered to be an effective way to improve the thermal efficiency of diesel engine. In this study, the sensitivity of the design parameters of turbo-compound system, such as the compressor pressure ratio and the turbine expansion ratio, has been analyzed using a numerical analysis. And the potential of the improving effects of the thermal efficiency by turbo-compound system has been also examined. As the results, it was found that there are the optimum values of compressor pressure ratio and turbine expansion ratio to maximize the thermal efficiency of turbo-compound engine.

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.

With the aim of improving the air quality in large cities, the California Air Resources Board (CARB) has stipulated that non-methane organic gas (NMOG) composed of carbon numbers from C1 to C12 must be reduced for vehicle categories designated as Transitional Low Emission Vehicles (TLEVs), Low Emission Vehicles (LEVs), Ultra low Emission Vehicles (ULEVs), and Zero Emission Vehicles (ZEVs). Although considerable research work has been done on this issue to date, the entire picture is still not clear. Studies done by the authors have been aimed at providing a better understanding of the potential for reducing automotive tailpipe emissions by using several clean fuel candidates. The major questions of concern are the extent to which emissions of certain species can actually be reduced and what fuel can provide the best performance under a reduced NMOG condition.