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Improvements in the fuel economy of passenger cars and trucks contribute directly to CO2 reductions. Recently low fuel consumption cars are being developed, however most cars are still old types. This study estimates the effect of new engine types, light weight cars, kinds of fuel, and running conditions on fuel economy and CO2 emissions with a new calculation method of fuel consumption. In this calculation method the fuel consumption and CO2 emissions are easily calculated from the indicated thermal efficiency and friction mean effective pressure for different engine types and sizes. By this method the overall fuel consumption and CO2 emissions from small passenger cars to heavy duty trucks were estimated for roads through the center of a small city. As a result, the influence of new type engines, light weight cars, fuel properties and driving patterns on fuel economy and CO2 was made clear.

Early stage combustion systems, with lean homogeneous charge compression ignition (HCCI), have been studied, with the intent to decrease the pollutant emission characteristics of DI diesel engines. Early stage combustion enables drastic reductions in both nitrogen oxides (NOx) and smoke emission, but the operating load range is restricted, due to combustion phenomena, such as unsteady combustion and knocking. In this study, we explored the possibility of broadening the operating load range in HCCI and reducing pollutant emissions using Dimethyl Ether (DME) fumigated through the intake pipe. However, the improvements in load range were found to be less than 0.1 MPa in brake mean effective pressure (BMEP), even when compression ratios were reduced and Methane with high octane number was mixed. Therefore, a DME premixed charge could be used only at light loads. At heavier loads a hybrid fuel system with a DME premixed charge and diesel fuel injection is necessary.