Diesel \Diesel\, Diesel engine \Die"sel en`gine\ or Diesel motor \Die"sel mo`tor\ (d[=e]"zel). [After Dr. Rudolf Diesel, of Munich, the inventor.] A type of internal-combustion engine in which the air drawn in by the suction stroke is so highly compressed that the heat generated ignites the fuel (usually a heavy oil), the fuel being automatically sprayed into the cylinder under pressure. The Diesel engine has a very high thermal efficiency. [Webster 1913 Suppl.]