Exergy analysis is conceptualized as an instrument for determining the attribute of an involved process in transferring availability of input to the system and the location in which useful energy reduction occurs. The aim of this study was to examine the effect of throttle valve opening positions on the exergy analysis of SI engine using bioethanol-gasoline blends. To this end, the definitions dealing with exergy and pertinent exergy equations as well as their applications for closed systems were provided. The results showed that the largest share of the irreversibility in the engine was the combustion process. In addition, the results showed that total exergy, burned fuel availability, availability with heat transfer and irreversibility for E0, E20, E40, E60 and E85 fuels, when the throttle valve is fully opened, were higher, compared to the 25%, 50%, and 75% throttle valve opening positions. Furthermore, it was found that the efficiency of thermodynamic second law in 25%, 50%, and 75% throttle valve opening positions was reduced to 18.7%, 29%, 60.6% for E0, 21.5%, 32.7%, 61.5% for E20, 23%, 35.4%, 62.5% for E40, 22.8%, 35.5%, 633% for E60, and 27%, 40%, 65% for E85 fuels, respectively, compared to 100% position. (C) 2016 Elsevier Ltd. All rights reserved.