Reducing agent supply method for SCR system of ammonia engine

The invention discloses a reducing agent supply method for an ammonia engine SCR (Selective Catalytic Reduction) system. For a high-pressure direct injection ammonia engine, an ammonia injector of a cylinder is used for injecting a reducing agent required by an SCR system when the temperature in the cylinder is lower than the spontaneous ignition point of ammonia at the starting stage of engine exhaust or scavenging. The method can be used for an ammonia engine and can also be used for an ammonia/diesel oil dual-fuel engine. For an ammonia/diesel dual-fuel engine, the method can be used in a diesel mode and can also be used in an ammonia mode. The air cylinder has the advantages that ammonia used as a reducing agent of the SCR system can be fully mixed with exhaust gas in the air cylinder, the denitration reaction of an SCR catalyst can be fully carried out, the denitration efficiency of the SCR system is improved, and the ammonia escape amount is reduced. For an ammonia/diesel oil dual-fuel engine, the ammon