PeachParts Mercedes-Benz Forum - View Single Post - Why does diesel engine idling consume to little fuel?

lrg · #2 04-10-2003, 01:49 AM

It's because of pumping losses, or more accurately the lack thereof. A gas engine has throttle plates that constrict the intakes when the engine is idling. This is necessary because it is the only way to keep a relatively constant fuel air mixture that is required to get the gasoline vapors to ignite. Much of the work a gas engine does at idle is to suck (or pump) mixture into the cylinders which uses fuel. Diesels have no throttle plates because a diesel will happily burn the fuel(as opposed to explode like on a gas engine) with excess air in the cylinder. Diesels don't worry about a mixture, only having enough air available to burn all the fuel injected into the cylinder. As a result, the intakes on a diesel are wide open all the time and idle is achieved but merely injecting only the small amount of fuel necessary to overcome frictional losses and keep the engine turning over. That makes diesels very efficent....80X more than a gasser? Probably not, but still much more efficient.