2019 Volume 61 Issue 198 Pages 313-319
The reduction of greenhouse gas such as CO2 has been strongly desired to prevent global warming. The reduction of GHG has become the urgent issue to be addressed in the maritime sector as well. For the GHG reduction from internal combustion engines (diesel engines), which most ships have, the use of alternative fuels such as natural gas, biomass fuels, and hydrogen (H2) is considered to be promising and the research to use such fuels is actively conducted. Among such fuels, we chose ammonia (NH3), because it is carbon free, has higher energy density per unit volume than hydrogen, and is liquefied below 240K at atmospheric pressure or above 0.857MPa at atmospheric temperature. We have proposed a mixed combustion system, in which ammonia is mixed into the intake air and liquid fuel is injected into the air-ammonia mixture to burn it in the cylinder. Such system can be retrofitted easily. The issues to be solved in this system are a) ammonia's low ignition performance and b) the high NOx emission due to nitrogen contained in the ammonia. To solve these issues, we conducted experiments and simulations. In this paper, we report the experimental results obtained through tests using a single cylinder engine and simulation results relating to the experiments. In the experiments, we found that the increase of the temperature was effective to decrease the leak of unburned ammonia due to the low ignition performance. In addition, pre-injection of the liquid fuel is found to be also effective to reduce the leak ammonia. These effects have also been observed in the simulation.