Investigation of performance and emission characteristics in natural gas dual fuel marine engines with a novel Burned Zone Ammonia Combustion strategy

Adding ammonia to natural gas engines is a promising method for meeting future carbon emission targets, suppressing engine knock tendencies, and supporting sustainable engine development. However, ammonia addition significantly increases NOx emissions, presenting new challenges. This study proposes a novel Burned Zone Ammonia Combustion (BZAC) strategy, which achieves an approximate 94.3 % reduction in NOx emissions compared to conventional methods, thereby meeting IMO Tier III standards without the need for after-treatment systems. The results indicate that by promoting extremely rich-fuel ammonia combustion in the burned zones, BZAC shifts the ammonia combustion reaction pathway from NH3→NH2→H2NO→HNO→NO to NH3→NH2→NNH→N2, significantly lowering fuel NO formation. Additionally, the generation of NH reducing radicals under these conditions facilitates the NH + NO=N2+OH reaction, further reducing NO emissions. The BZAC approach also minimizes unburned ammonia and N2O emissions and avoids increases in peak pressure, thus preventing mechanical stress, noise, and knock. Overall, the BZAC strategy is expected to increase power output by up to 25 % and reduce carbon emissions by 40–45 %, thereby meeting the IMO's mid-term carbon emissions target, all while ensuring compliance with stringent IMO Tier III emission standards and preventing knocking.