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In order to clarify the effects of fuel properties on the mixture formation under the stratified-charge combustion condition in a direct-injection gasoline engine, fuel concentration measurement in the vicinity of the ignition plug was established using a fast response flame Ionization detector (FID). A single-cylinder direct-injection gasoline engine, for which a Toyota D-4 engine was modified, was used. Paraffin, olefin, naphthene and ether having a boiling point of approximately 50°C, and paraffin, olefin and an aromatic compound having a boiling point of approximately 100°C were used as candidate fuels. As a result, the effect of boiling point on the mixture formation was clarified.

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.