Control strategy for engine operation

A method of operating an internal combustion engine system having a fuel injection system including a fluid delivery means operable to deliver a fuel entrained in gas directly into a combustion chamber and a gas supply system for supplying pressurised gas to the fluid delivery means without a gas pressure regulator, the method comprising:

• cranking the engine to initiate a start-up phase;
• generating compressed gas in the gas supply system for delivery of gas to the fluid delivery means, the compressed gas being generated in response to cranking the engine;
• generating a supply of electrical energy in response to cranking of the engine;
• energising an electrical fuel pump for delivery of fuel to the fluid delivery means, the electrical fuel pump being energised using electrical energy generated in response to cranking of the engine, wherein there is a lag period between commencement of engine cranking and the delivery of fuel at a requisite fuel pressure to the fluid delivery means;
• and regulating gas pressure in the gas supply system during the lag period by interrupting an initial increase in gas pressure in response to cranking of the engine prior to delivery of fuel into the combustion chamber, wherein regulating gas pressure in the gas supply system comprises opening the fluid delivery means to selectively allow gas to pass into the combustion chamber to relieve pressure in the gas supply system.