Comparative Analysis of CNG and Hydrogen Effects on Exhaust Emissions in Dual-Fuel Single Cylinder Diesel Engines

This study provides a comparison between the impact of two gas fuels, compressed natural gas (CNG) and hydrogen (H2), on the exhaust emissions of a single-cylinder diesel engine operating in dual-fuel mode. The analysis is conducted with a constant and maximum achieved gas-to-total-fuel ratio (K = 20% and K = max) under varying load conditions, specifically at an engine speed of 2000 min−1 and brake mean effective pressures ranging from 0.2 to 0.43 MPa. The results reveal that H2 significantly improves the engine’s emissions profile compared to CNG. When H2 is used as the secondary fuel, reductions in soot, carbon monoxide (CO), carbon dioxide (CO2), and unburned hydrocarbons (CHs) are more pronounced. However, under certain load conditions, nitrogen oxide (NOx) emissions are higher with H2 than with CNG and can even surpass those observed during diesel-only operation. These findings suggest that while H2 demonstrates superior overall emissions performance, its impact on NOx emissions under specific conditions requires further optimization to maximize environmental benefits.