Combustion Performance of Methane Fermentation Gas with Hydrogen Addition under Various Ignition Timings 2022-32-0043

Hydrogen (H2) addition is widely used for natural gas combustion to improve the engine efficiency. However, less attention was paid on the various ignition timings for the maximum brake torque (MBT) and brake thermal efficiency (BTE). In order to check the ignition timing effect, experiments were performed in a spark ignition engine with engine speed fixed on 1500 revolutions per minute (rpm). Firstly, CH4 was only used for combustion with excess air ratio (λ) changing from 0.8 to 1.4. Then, co-combustion of 50 vol% CH4 and 50 vol% CO2 was checked to simulate methane fermentation gas. Finally, H2 was added with volume percentage varying from 5% to 20%. Among these discussions, torque, brake mean effective pressure (BMEP), BTE and cylinder pressure were evaluated. Based on the results, high efficiency can be achieved by advancing the ignition timing with H2 addition at λ=1.4. However, with H2 addition, the ignition timing should be retarded to obtain higher BTE. At the lean-burn condition, through delaying the ignition timing at -20° CA TDC, BTE of 20% H2 addition reaches to 22%, which is even higher than that of CH4 only combustion at stoichiometric condition. Furthermore, the optimal working region for the mixed gas combustion is mapped under various conditions. Besides, H2 addition could improve the combustion stability and decreases CCV and COV in Pmax.