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

This article focuses on an experimental study investigating the effects of injecting compressed natural gas (CNG) into an indirect injection (IDI) diesel engine on exhaust exergy and second-law efficiency. Conducted using a Perkins 4.108 IDI diesel engine at the Ferdowsi University of Mashhad, the study measured exhaust total exergy and chemical exergy by considering physical and chemical exergy of emissions, including the recovery of carbon monoxide (CO) and unburned hydrocarbons (UHC). Results showed that replacing up to 20% of diesel fuel mass with CNG generally increased exhaust total exergy due to rises in CO and UHC emissions, despite reductions in nitrogen oxides (NOx) and soot. When assuming recovery of CO and UHC, exhaust chemical exergy decreased with increasing CNG, leading to an improvement in second-law efficiency by up to 4.5% at 3000 rpm, 25% torque, and 10% exhaust gas recirculation (EGR). The findings are specific to IDI engines and highlight the thermodynamic benefits of dual-fuel operation with CNG under controlled emission recovery assumptions.