Semi-Diesel adj. Designating an internal-combustion engine of a type resembling the Diesel engine in using as fuel heavy oil 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.
