Experimental study on heat and exergy balance of a dual-fuel combined injection engine with hydrogen and gasoline

In this paper, a dual-fuel engine test rig with gasoline injected in the intake port and gasoline (or hydrogen) injected directly into the cylinder is built up; therefore, two injection models are realized. One is port fuel injection + gasoline direct injection (PFI + GDI), the other is port fuel injection + hydrogen direct injection (PFI + HDI). And the effects of two injection models on heat and exergy balance are investigated experimentally. The results show that, from the perspective of the first law of thermodynamics (heat balance), no matter what the injection mode is, the heat proportion of cooling water is the largest, the exhaust heat ratio and brake power are the second, which two are roughly equivalent, and the uncounted loss is the least. In PFI + GDI mode, the local mixture is too dense due to the increase of mixing ratio, which leads to insufficient combustion and a slight decrease of brake power ratio. However, due to the special characteristics of hydrogen, the increase of direct injection ratio improves the brake power ratio in PFI + HDI mode. Moreover, because of the short quenching distance of hydrogen, the cooling loss rises up with the increase of hydrogen ratio. The engine speed and load also have great impacts on heat distribution, but on account of the different physical and chemical properties between gasoline and hydrogen, resulting in varying degrees of impact and trends. On the basis of the second law of thermodynamics (exergy balance), it is found that no matter what injection mode is, the ratio of exergy destruction is always the highest, accounting for half of the total fuel energy, and the exhaust exergy ratio is lower than the brake power ratio. However, the proportion of exergy contained in cooling water is the smallest, which is quite different from the result of the first law of thermodynamics. The influences of several factors on engine energy balance are analyzed, and the differences and similarities between heat balance and exergy balance are compared. The two analytical methods are interrelated and complementary, and the purpose is to find a reasonable and comprehensive energy balance analysis method for internal combustion engine. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.