Due to the economic growth, the energy demand of the world increase every year. In the energy conversion process in power plants and small engines, energy efficiency is a key factor. The equipments with higher efficiency, the more work output. Therefore, a number of researches studied on thermodynamics of efficiency, irreversibility and exergy in both spark-ignition and compression-ignition engines were found during the last century.
The thermal efficiency and the energy loss in the system are normally calculated from the 1st law of thermodynamics, while the maximum work output or exergy is characterized by the 2nd law of thermodynamics. The exergy of a system from the 2nd law is defined as the maximum useful mechanical work as can be produced as the system is brought to thermal mechanical and chemical equilibrium with its environment through reversible processes . Unlike energy, exergy is not a conserved quantity and can be destroyed during the process due to irreversibility.
Rakopoulos and Giakoumis , Caton J.A. , Som and Datta  studied the destruction of exergy in a diesel engine for various operating parameters with different types of fuel. From their research works show that the exergy loss is mainly occurred by the irreversibility of the combustion process comparing with the exergy losses from the heat transfer through the combustion chamber and the cooling water system. By the second-law analysis of internal combustion engines fuelled with n-dodecane (n-C12H26), light gaseous fuel (CH4) and an oxygenated (CH3OH), Rakopoulos and Kyritsis  found that the lighter molecular weight fuel can achieved the higher efficiency at the same equivalence ratio of operation due to the less entropy generation in the combustion product.
Sayin and Gumus  investigated the influence of...