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Performances of gasoline engine fueled by gasoline into cylinder and pure hydrogen or simulated reformer gas (H2, CO, CO2, and CH4) into intake manifold were evaluated in view of improvement of thermal efficiency of spark ignition engine. Commercial spark ignition direct injection gasoline engine was modified to install injection system of commercial CNG vehicle. Test engine can be controlled by homogeneous and stratified charged combustion for gasoline. Thermal efficiency of the engine operated with gasoline and hydrogen or reformer gas is much higher than that with gasoline under low and mid load conditions. Especially the improvement of thermal efficiency with gasoline and hydrogen on lean burn condition is less than 40% that with gasoline on stichometric condition under low load condition. The operating range of the engine operated with hydrogen is limited due to knocking, but the range is extended by the addition of gasoline.

The addition of soybean methyl ester (SME) to diesel fuel has significantly reduced HC and PM emissions, but it increases the NOx emission slightly when measured with exhaust emission evaluation mode for heavy-duty DI diesel engines or D-13 mode in Japan. Also, under partial load conditions, the SME addition increases the PM emission due to an increase in the SOF emission. However, the addition of lighter fractions or kerosene to diesel fuel reduces NOx and PM emissions but increases HC and CO emissions measured by D-13 mode. In addition, under full load conditions, the lighter fuel seldom reduces PM emission. Therefore, the exhaust emissions emitted from the blends of SME, kerosene, and cetane improver to low sulfur diesel fuel are evaluated using the latest DI diesel engine with a turbo-charger and inter-cooler. The clean fuel reduces over 20% of PM under a wide range of engine conditions including D-13 mode without an increase in NOx, HC, and CO emissions.

The application of biodiesel fuel (BDF) to diesel engines is very effective at reducing CO2 emissions, because biodiesel is considered to be carbon neutral in principle. Gas-to-liquid (GTL) fuel, a synthetic fuel, is expected to reduce emissions from diesel engines. This study focused on the effects of driving conditions and fatty acid methyl ester (FAME) and GTL blended fuel on emissions from diesel engines/vehicles meeting Japan's new short-term regulations, or '03 regulations. FAME including rape methyl ester (RME), palm oil methyl ester (PME) and soybean methyl ester (SME) were studied. Major technologies for emissions reduction may include common-rail high-pressure fuel injection system, cooled exhaust gas recirculation (EGR) system, diesel oxidation catalyst (DOC) and diesel particulate filter (DPF).

Smoke emission from single-cylinder DI and IDI diesel engines was shown to strongly depend on oxygen content in fuel regardless of oxygenate molecular structure. Thus, with cetane improver and oxygenate used in combination in a proportion determined from blending properties and potential cost for modern heavy-duty DI diesel engines were assessed. The combined use of nitrate type cetane improver with glycol ether type oxygenate reduced particulate, HC, and CO emission but not that of NOx. Particulate reduction depended on oxygenate content. Oxygenate at less than 5% with cetane improver seldom worsened volume-based fuel economy compared with the base hydrocarbon fuel.