Comparative thermodynamic analysis of LNG, LPG, methanol, ethanol, biodiesel and hydrogen as alternative fuels in HCCI engines

Abstract

Aiming to mitigate the problem of harmful emissions arising from the use of conventional fossil fuels, the performances of alternative fuels, namely LNG, LPG, biodiesel, ethanol, methanol, and hydrogen in an HCCI engine have been analyzed. Thus, a thermodynamic model that considers the gas composition of combustion products and the specific heat temperature dependency of the working fluid has been developed. It allows examining the influence of key engine parameters such as the compressor pressure ratio, ambient temperature, equivalence ratio, engine speed, and the compressor isentropic efficiency on the performance of the HCCI engine. The reliability of the model has been successfully verified against various theoretical and experimental data from the literature. Results showed that LNG performs the best in terms of brake efficiency, exergy efficiency, and placed second in terms of brake specific fuel consumption. With the exception of the latter, although it is associated with a higher energy value, hydrogen produces lower performance compared to the other fuels assessed. For all fuels, the largest exergy destruction rates occur in the HCCI engine. It ranges between 78.4 and 87.8 % of the total exergy destruction rate according to the fuel used. The order of exergy destruction rates within the other components differs from one fuel to the other.