Numerical investigation into the influence of hydrogen energy ratio on the combustion characteristics of ammonia fuel in a marine engine

Abstract

This work carries out a numerical study to investigate the effect of changing the hydrogen energy ratio (HER) on the combustion performance, pollutant formation, and the thermal-structural stresses in a large-scale marine engine running with a mixture of ammonia-hydrogen fuel. The combustion of the ammonia-air mixture is studied by using a pre-chamber ignition system to enhance the combustion of the ammonia-air mixture. Hydrogen content varies from 5% to 30% in the case of maximum load. It is observed that a higher hydrogen proportion increases the maximum in-cylinder pressure and the pressure gradient, and decreases both the ignition delay and the total combustion time. When the HER is more than or equal to 25%, the cylinder pressures are more than the safety limits, and the pre-mature ignition takes place before the spark. If the HER is kept less than 20%, the nitrogen oxide emissions grow moderately, the ammonia slip is decreased significantly, and the thermal stresses of the engine parts (piston, cylinder wall, and head) are in order of operation. In the case of 30% hydrogen concentration, it shows that the thermal burden and the phenomena of spontaneous ignition, which take place in the pre-combustion chamber, have been investigated. The experimental results show that keeping the energy contribution of the hydrogen between 5% and 20% is the best compromise of engine stress, thermal output efficiency, exhaust emissions, flame homogeneity, etc. This result provides useful operating parameters to design marine propulsion using a mixture of ammonia-hydrogen as fuel.