Method of combustion and fuel injection system for hydrogen gas

A method of combusting hydrogen gas in an engine cylinder to initiate a diffusion combustion process, the engine cylinder having a cylinder piston which is driven by means of a crankshaft between bottom dead centre (BDC) and top dead centre (TDC) to perform a compression stroke. The method comprises delivering a pilot injection of hydrogen gas into a combustion chamber during the compression stroke so that the pilot injection of hydrogen pre-mixes with the air and forms an ignitable air/hydrogen gas mixture in the vicinity of an engine cylinder spark plug; generating a spark with a spark plug to ignite the ignitable air/hydrogen gas mixture to generate a primary combustion event which results in a fuel burn and a cloud of primary gas; and delivering a main injection of hydrogen gas directly into the burning cloud of primary gas so that the main injection of hydrogen gas ignites in the compression stroke to deliver a secondary combustion event.