Comprehensive analysis of combustion behaviors of hydrogen (H2)/diesel reactivity-controlled compression ignition (RCCI) in a light-duty diesel engine

Abstract

In this study, a comprehensive analysis of the combustion behaviors of hydrogen (H2)/diesel reactivity-controlled compression ignition (RCCI) was conducted toward the achievement of reliable and flexible combustion control of H2 RCCI. The interplay between H2 and the direct-injection (DI) high-reactivity fuel in RCCI combustion was revealed under various operating conditions, and the potential of H2/diesel RCCI in enhancing engine performance was excavated. The results suggested that under the single DI strategy, the maximum indicated thermal efficiency (ITE) of H2 RCCI is considerably higher than that of gasoline RCCI. Compared with the single DI strategy, using the double DI strategy can significantly improve ITE and nitrogen oxides (NOx) emissions simultaneously for H2/diesel RCCI. Under the double DI strategy, the ignition and combustion of H2 are more sensitive to intake boost than gasoline in RCCI. Meanwhile, compared with gasoline, H2 can inhibit to some extent the low-temperature heat release from the DI high-reactivity fuel in RCCI. By evaluating the emission performance of H2/diesel RCCI under different double DI strategies, it was found that NOx emissions of H2/diesel RCCI are mainly dominated by the homogeneity of the DI fuel/air mixture but not the combustion rate. In addition, increasing the premixed ratio can effectively improve combustion stability, ITE, NOx, and soot simultaneously with reduced peak pressure rise rate for H2/diesel RCCI. Attributed to the absence of carbon elements in H2, the soot emissions of H2 RCCI are considerably lower than that of gasoline RCCI.