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Recently, environmental problems come to be taken prosperously, and the reduction of environmental effects is demanded in an automobile section. The alternative fuels for diesel engines have been also developed for emission regulations. In this study, the authors proposed and estimated the validity of the hybrid system, which combines a dimethyl ether (DME) diesel engine and a DME fuel cell for commercial vehicles such as buses and tracks. DME is adopted as the both fuels for good environment and high efficiency of the system. DME has received a lot of attention recently as a possible alternative to diesel engines for a little environmental effects and stable distribution. It has the same cetane number as that of diesel fuel and emits no smoke from diesel engines. The conventional LPG stations are possible to provide DME because of the same handling as LPG.

In recent years, trans-esterified vegetable oils have been widely applied to diesel engine in order to suppress greenhouse gas emissions. However, “neat” vegetable oils are expected to be directly used to resolve some difficulties faced in their use, such high viscosity and slightly high fuel consumption. In this study neat linseed oil has been investigated as a neat vegetable oil. It was found to show higher fuel consumption than diesel fuel, however at the same time it showed lower indicated fuel consumption than diesel fuel. These results suggest some increase in engine friction loss in a neat biofuel diesel engine. Studies have been extensively investigated the difference in friction loss and a newly developed “improved deceleration method” has been applied.