A small quantity of Nitromethane is often added to the glow-plug engine’s fuel to enhance the power output of an engine. The present work is aimed at characterizing performance enhancement and analyzing the in-cylinder combustion parameters to understand the reasons for the improved performance of a small glow plug-assisted compression ignition engine. The experimental tests involved the measurement of in-cylinder pressure with respect to the crank position at various equivalence ratios for different nitromethane blends. The thermodynamic analysis was carried out to obtain the heat release rates and combustion durations. Results showed increased heat release rates with nitromethane addition. Emission measurements were carried out to quantify the effect of nitromethane addition on nitric oxide (NO), hydrocarbon (HC), and carbon monoxide (CO) emissions. It was observed that the HC and CO emissions drop with nitromethane addition; however, NO emissions increase drastically. © 2020 SAE International