1.NounAn internal combustion engine of a type resembling the diesel engine in having heavy oil for its fuel, which is injected in a spray just before the end of the compression stroke and is fired without electrical ignition. The fuel is sprayed into an iron box (called a hot bulb or hot pot) opening into the combustion chamber, and heated for ignition by a blast lamp until the engine is running, when it is ordinarily kept red-hot by the heat of combustion.