Simulation study on the new combustion strategy of pre-combustion-assisted compression ignition for internal combustion engine fueled by pure ammonia

Abstract

In recent years, with the increase in the spread of the renewable energy and the development of its technologies, the necessity of development of energy storage medium technology for storing renewable energy which is intermittent. Hydrogen is one of the energy storage media that has received much attention. There have been many studies on the use of hydrogen as fuel and energy storage in the form of hydrogen. However, since hydrogen has an extremely low boiling point, it is difficult to store the hydrogen as a liquid phase, and when stored in a high-pressure gas phase, the energy density of the hydrogen based on volume is somewhat lowered. Ammonia is an energy storage medium that can compensate for the drawbacks of hydrogen. Since ammonia does not contain carbon in its molecular structure like hydrogen, it does not produce carbon-related emission during combustion, and has a merit of storability and transportability because it is in a liquid phase under a condition of room temperature and 10 atm. Focusing on the possibility of using ammonia as a hydrogen carrier, a combustion strategy for pure ammonia as an engine fuel to convert the stored energy into a usable form has been proposed, which uses ammonia itself as a combustion promotor. Under this strategy, the conditions of sufficiently high temperature and pressure to cause the spray combustion of ammonia are obtained by the auto-ignition of a pilot-injected mixture of air and ammonia. To confirm the feasibility and the operating characteristics of an engine with the ammonia combustion strategy proposed in this study, engine modeling has been conducted, the combustion strategy has been simulated, and a parametric study has been performed. To analyze the mechanisms of NO production in an engine with the proposed combustion strategy, the NO production process has been classified into four phases, and the NO production in each phase has been analyzed under various start of injection timing and fuel amounts.