Definition of hot bulb in English:

hot bulb

noun

Mechanics
  • (In a semi-diesel engine) an uncooled chamber connected to the cylinder head which is maintained at a sufficiently high temperature to vaporize fuel oil injected into it prior to compression in the cylinder; any mass of metal that performs the same function in such an engine; frequently attributive.

Origin

Early 20th century; earliest use found in U.S. Patents.