Source : Webster's Revised Unabridged Dictionary (1913)

Semi-Diesel \Sem`i-Die"sel\, a.
   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.