Abstract
Effects of air-fuel ratio and hydrogen fraction on engine combustion at the conditions of locally rich hydrogen and lean-burn mode have been experimentally carried out on a hydrogen direct-injection (HDI) and gasoline port-injection engine. The test results showed that both excess-air ratio and hydrogen affect the HDI combustion. The peak cylinder pressure was decreased by 45% (3.9% hydrogen fraction) and 23% (10.5% hydrogen fraction) when the excess-air ratio was increased from 1 to 1.5. Hydrogen, which compensates the loss of cylinder pressure and heat release rate caused by lean burn, effectively improves the engine performance at lean burn operation. In addition, when the excess air ratio was set at 1.2, the rise in hydrogen fraction from 3.9% to 10.5% caused a 51.2 % increase in peak cylinder pressure and 101% increase in maximum heat release rate. The maximum cylinder temperature and exhaust temperature was increased firstly and then decreased afterwards with an increase in excess-air ratio. The increase in hydrogen fraction resulted in the acceleration of maximum cylinder temperature, but the exhaust temperature is not that much affected.
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