Effect of high compression ratio on thermal efficiency and unburned ammonia emissions of a dual-fuel high-pressure direct injection marine ammonia engine
Cheolwoong Park, Ilpum Jang, Minki Kim, Gyeongtae Park, Yongrae Kim
Abstract
• High compression ratio improves combustion stability of ammonia dual-fuel engine. • High compression ratio does not greatly reduce unburned ammonia emissions. • Heat release of diesel is low, but it burns ammonia more efficiently with a high compression ratio. • Combustion of ammonia varies depending on the state of the ignited diesel flame. • Heat release by combustion of diesel and ammonia is advanced with high intake air pressure. For marine ammonia dual-fuel engines, the pilot fuel that helps contributes to the ignition of the ammonia must be controlled, and the injection timing and amount of pilot fuel must be optimized according to the operating conditions. However, for marine engines that use a high-pressure liquid ammonia injection system and micro-pilot diesel fuel for ignition, it is difficult to meet the combustion performance of a marine engine that requires high power output by optimizing pilot fuel injection alone; therefore, improvement of the design is required. In this study, a high compression ratio piston was applied to experimentally observe its effects on combustion stability and exhaust emissions in a high-pressure ammonia direct-injection marine dual-fuel engine. A 12.5 L medium-sized single-cylinder marine engine was used to determine whether the combustion stability could be improved by increasing the compression ratio from 13 to 14 under various load conditions. Efficiency increased by more than 5.8 % and combustion stability improved under high compression ratio conditions. Unburned ammonia emissions were reduced by approximately 10 % owing to the stable combustion of the lean mixture at a higher compression ratio.