Dual fuel engine and method of operating the same

In a dual fuel engine operating on a main liquid fuel and a gas fuel, a pilot injector (390) is used to inject a pilot liquid fuel in the gas mode. In order to avoid knocking in the gas mode, the compression ratio of intake air is relatively low. When, for example, heavy fuel oil is used as the main liquid fuel, the pilot injector (390) is used to also provide an injection of a pilot liquid fuel such as diesel in the liquid fuel mode prior to the injection of the main liquid fuel to facilitate combustion of the main liquid fuel with the relatively low compression ratio.