The exhaust total exergy analysis of compressed natural gas used in an indirect injection diesel engine in different working conditions

Abstract

Deficiencies of energy resources, air pollution, and climate change have led to some threats to energy security and human health, making natural gas to be offered as one of the most widespread alternative fuels. The novelties of this experimental study are (i) injecting the Compressed Natural Gas (CNG) into the indirect injection diesel engine and measuring the exhaust total exergy, and 2nd law efficiency of a dual-fuel engine via considering the physical and chemical exergy of emissions. (ii) Injecting the CNG with a reduced mole fraction of byproducts decreases the chemical exergy of exhaust emissions that are considered to be wasted in the atmosphere which means the destruction of exhaust exergy that cannot be recycled is declined, and the 2nd law efficiency has been increased. The testbed is provided in the internal combustion engine laboratory of the Ferdowsi University of Mashhad. Replacing 20% diesel fuel mass fraction with natural gas showed that, by the CNG enhancement, the exhaust total exergy has an upward trend which faces maximum variation at 1200 rpm. Also, assuming that excess CO and unburned hydrocarbon can be recovered to reach the level observed in the absence of CNG, the maximum decline in exhaust chemical exergy is related to the speed of 3000 rpm, 25% torque, and 10% exhaust gas recirculation (EGR) by 11.7% between 0% and 20% CNG. Also, the most significant increase in second-law efficiency is reported for 3000 rpm, 25% torque, and 10% EGR with a 4.5% increase.