Study on the Effects of Ignition Timing and Excess Air Ratio on Lean-Burn Performance of Small-Bore Natural Gas Engines

This study investigates the effects of ignition timing and excess air ratio on combustion and emission performance under lean-burn conditions using a small-bore intake manifold injection natural gas engine test bench. Results indicate that as the excess air ratio increases, ignition delay period and the combustion center shift backward; combustion duration first shortens, then lengthens; NOx emissions initially rise, then decrease, while THC and CO emissions first decrease, then increase; COVIMEP increases, and effective thermal efficiency first rises, then falls. As ignition timing advances, the ignition delay period shortens and the combustion center advances; the combustion duration first shortens, then lengthens; NOx emissions significantly increase, CO emissions slightly decrease, then increase, and THC emissions vary under different excess air ratios; COVIMEP decreased initially, then increased, while effective thermal efficiency rose initially, then decreased. Compared to stoichiometric combustion, lean-burn technology combined with ignition advance improved engine thermal efficiency, reaching a maximum of 40.47% at an excess air ratio of 1.4.