Theoretical investigation of the effect of thermal barrier coating on ammonia combustion of marine medium speed engine

In recent years, with the introduction of dual carbon policies and ship emission regulations, marine engines are facing strict decarbonization standards. As a zero-carbon fuel, ammonia has a higher energy density than hydrogen and a high degree of industrialization, with relatively complete production, storage and transportation technologies. It is suitable for application in marine engines for long voyages. But at the same time, ammonia faces difficulties in igniting and organizing combustion due to its high ignition point and slow combustion rate. This article is based on a high-power density medium speed marine engine, and uses numerical simulation methods to explore the combustion performance of the engine under four different combustion modes and study the influence of piston coating on engine performance and thermal performance. The conclusions are as follows: the engine achieved normal combustion in all four different combustion modes; At high premixing ratios, ignition of ammonia using ignition method can achieve the highest cylinder burst pressure(31 MPa) and thermal efficiency (44.6 %), but at the same time, there will be a high pressure rise rate(21.1 bar/CA), which is not conducive to the safe operation of the engine; In terms of heat flow, under high premixed ratio conditions, due to the short combustion duration and heat transfer time, the heat transfer loss is relatively small. The analysis of wall thickness ratio shows that under high premixed conditions, the heat flux of the piston is relatively high(60 %), which is caused by the concentration of heat release near the top dead center; After adding the coating, the cylinder pressure and thermal efficiency of the engine were improved in various modes, and the temperature inside the cylinder also increased 18 °C at the end of compression and expansion, because the insulation performance of the coating reduced heat transfer losses. The addition of the coating reduces the heat flow of the piston by 50 % and the heat flow proportion by 20 %. The NOx emissions of all four combustion modes meet the Tier II standard, while the NOx emissions of L-10 and L-30 meet the Tier III standard, and the addition of coating will increase NOx emissions. The steady-state thermal analysis of the piston shows that adding coating can reduce the temperature of the piston surface by about 80 °C, reduce the thermal stress of the piston surface by about 21 %, and extend the service life of the piston parts.