Ignition timing effect on the combustion performance of hydrogen addition in methane fermentation gas in a local energy system

Nowadays, the reduction in carbon emission becomes the big issue in the world. In order to achieve the target of “carbon neutral” in the middle of 21st century, a regional energy system is designed to develop a carbon recycle system with the help of fermented gaseous fuels for electric power generation. Hydrogen (H₂) addition is widely used for methane (CH₄) combustion to improve the engine efficiency. However, less attention was paid on the various ignition timing for the maximum brake torque (MBT) and brake thermal efficiency (BTE) at a certain power output. In order to check the ignition timing effect on CH₄ combustion with H₂ addition, 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 1.01 to 1.42. Then, H₂ was added with volume percentage varying from 10% to 50%. Among these discussions, torque, brake mean effective pressure (BMEP), BTE and brake specific fuel consumption (BSFC) were evaluated. Based on the results, high efficiency can be achieved by advancing the ignition timing when CH₄ only at larger λ. When H₂ added, the ignition timing should be retarded to obtain higher BTE from 10 % to 50 % H₂ addition. Under the lean-burn condition, through delaying the ignition timing at −15° CA TDC, BTE of 50% H₂ addition reaches to 22%, which is even higher than that of CH₄ only combustion at stoichiometric condition. Furthermore, working and optimal regions for the co-combustion of H₂ and CH₄ are mapped under various conditions.