Abstarct: Seeks to reduce energy sources and growth of environmental pollutants, many efforts to optimize thermal processes around the world have begun. Among these, vehicles are a major contribution to fuel consumption and polluting the environment. In order to evaluate the performance of the vehicle systems which depends on the performance of its subsystems, Thermodynamic analysis especially the second law analysis provides better understanding of the performed processes. To Analysis the second law, Exergy considered as a key concept. Exergy is indicative of the potential to do useful work. Although the first law guarantees the conservation of energy, But the second law enforcement indicates that Exergy in phenomena like combustion, friction, mixing and strangulation in collection of vehicle subsystems destroyed. In this study, in the first test of accessories including power generation system, air conditioning system, hydraulic system and electrical charging system have been investigated in the test chamber. This test, is designed to obtain the information of EF7 engine performance in different operating conditions, including three speeds of 2000 rpm, 3500 and 5000. The fuel used in combustion applications has a significant impact on production of irreversible and therefore exergetic efficiency of the system. In the remaining of the research, degradation of availability and exergetic efficiency of combustion for two different fuels have been studied. Thus, in the second test using two gasoline and compressed natural gas in an EF7 engine have been tested separately at different speeds. The results of both tests to check the energetic and exergetic efficiencies have been used. After collecting data, its analytical solution in conditions of full load system has been calculated separately for each fuel and components. The main objective of this study is determination of accessories effects and also comparison of fuel on energy and Exergy efficiency of the EF7 engine. Obtained results indicate that the type of fuel and engine operating conditions have applied a greater impact on exergetic and energetic efficiency in comparison with system components. As an example in the first test speed of 3500 rpm full load of engine has larger energy and Exergy efficiency than speeds 2000 rpm and 5000, but Exergy destruction in 5000 rpm engine speed is more than speeds 2000 rpm and 3500. In the second test, the percentage of unaccounted Exergy destruction mainly due to the Irreversibility of combustion and friction losses, at engine speeds 2000 rpm and 3500 for compressed natural gas and at engine speed of 5000 rpm for gasoline was higher. The highest Exergy efficiency of engine with gasoline fuel at the speed of 4000 rpm equal to 32.94% and for compressed natural gas fuel equal to 32.12% at the speed of 3000 rpm have been measured.