Combustion and emission characteristics of lean-burn natural gas engines with a high compression ratio

Based on the lean-burn technology, to enhance the compression ratio will explore the potential of lean-burn natural gas engines and further improve their thermal efficiency. In view of this, an experimental study was made on how the combustion and emission characteristics of a port-fuel-injected natural gas engine were affected by excess air ratios (γ) and compression ratios (Ε). The experiment condition was that when the compression ratio increased up to 10 and 12 respectively, the excess air ratios ranged from 1. 0 to 1. 4. The following results are obtained in this experimental study. On one hand, with the increase of the excess air ratio, the maximum cylinder pressure, the maximum rate of pressure rise and the maximum combustion temperature increased at first but then decreased, on the contrary, the gas consumption rate firstly decreased but then increased; the cyclical fluctuation coefficient of mean indication pressure did not exceed 8%, CO emission sharply declined, HC emission decreased firstly but then increased, and NOx emission increased a little bit but then significantly decreased. On the other hand, with the increase of the compression ratio, the heat load of the engine rose, the gas consumption rate decreased, and the cyclical fluctuation coefficient of mean indication pressure increased, the CO emission decreased, the HC emission increased, but the NOx emission changed little.