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The objective of this study is to improve the ignition quality of LPG (liquefied petroleum gas) in order to utilize LPG as a diesel fuel. First, the relationship between the cetane numbers and ignition delay periods of primary standard fuels (mixtures of n-cetane and heptamethylnonane) and diesel fuels were investigated by measuring the ignition delay periods using a constant volume combustion chamber. As a result, it was found that a good relationship between the cetane numbers and ignition delay periods could be obtained for a 550°C combustion chamber temperature and 4MPa pressure. Also, the cetane number estimation equation was established using the ignition delay data of n-paraffins. Next, the constant volume combustion chamber was modified to evaluate the ignition delay period of LPG with a cetane number improver, and these cetane numbers were then estimated.

The objective of this study is to clarify the effects of fuel properties on the stratified-charge combustion of direct-injection gasoline engine with EGR. A single-cylinder direct-injection gasoline engine, based on a Toyota D-4 engine, was used. First, the effects of EGR on the stratified-charge combustion of direct-injection gasoline engine were investigated under various conditions. As a result, 20% EGR can drastically reduce NOx emission without reducing the IMEP under the stratified-charge combustion. Next, paraffin, olefin, naphthene and ether having a boiling point of approximately 50 °C and paraffin, olefin and aromatic compounds having a boiling point of approximately 100°C were used for fuel to investigate the effects of fuel properties on the stratified-charge combustion of a direct-injection gasoline engine with EGR. As a result, the effects of fuel properties on the stratified-charge combustion of direct-injection gasoline engine were maintained by the use of EGR.