Effects of ammonia addition on the performance and emissions for a spark-ignition marine natural gas engine

The application of natural gas (NG) and ammonia in internal combustion engines contributes to reducing greenhouse gas (GHG) emissions. The present study aims to discuss the optimization direction and evaluate the GHG emission reduction potentials of NG engines blending with ammonia. In the present study, the effects of ammonia volume fraction (XNH3) and excess air ratio (λ) on the performance and emission characteristics of a spark-ignition marine NG engine were experimentally and numerically investigated. The in-cylinder pressure, heat release rate, brake thermal efficiency, and emissions (e.g. CH4, NH3, NOx, CO, CO2, N2O) were analyzed. Results show that the peak values of the in-cylinder pressure and heat release rate decrease with the increase of XNH3 and the optimum brake thermal efficiency increases by 1% compared with the pure NG engine. As for emission characteristics, it is found that NOx emissions increase first and then decrease with ammonia addition and the main NOx is produced from ammonia. With the increase of XNH3, CH4 emissions fluctuate, NH3 and N2O emissions monotonously increase. Moreover, the addition of ammonia can reduce CO2 emissions and the maximum reduction of CO2 emissions is approximately 44.1%.