Reduction of Cooling Loss in Hydrogen Combustion by Direct Injection Stratified Charge

Hydrogen can be readily used in spark-ignition engines as a clean alternative to fossil fuels. However, a larger burning velocity and a shorter quenching distance for hydrogen as compared with hydrocarbons bring a larger cooling loss from burning gas to the combustion-chamber wall. Because of the large cooling loss, the thermal efficiency of a hydrogen-fueled engine is sometimes lower than that of a conventionally fueled engine. Therefore, the reduction of the cooling loss is very important for improving the thermal efficiency in hydrogen-combustion engines.

On the other hand, the direct-injection stratified charge can suppress knocking in spark-ignition engines at near stoichiometric overall mixture conditions. Because this is attributed to a leaner end gas, the stratification can lead to a lowered temperature of burning gas around the wall and a reduced cooling loss.

This paper proposes the direct-injection stratified charge as a technique for reducing the cooling loss in hydrogen-combustion engines. The characteristics were experimentally analyzed in a constant-volume combustion chamber. The direct-injection stratified charge has a very high effect to reduce the cooling loss in hydrogen combustion especially at larger excess-air ratios. Adequate degree of stratification and excess-air ratio can reduce the cooling-loss fraction without deteriorating the degree of constant volume.