View Single Post
Old 07-20-2009, 04:03 PM   #21 (permalink)
ConnClark's Avatar
Join Date: Jun 2008
Location: Richland,WA
Posts: 967

Das Schlepper Frog - '85 Mercedes Benz 300SD
90 day: 23.23 mpg (US)

Gentoo320 - '04 Mercedes C320 4Matic
90 day: 22.44 mpg (US)
Thanks: 46
Thanked 227 Times in 156 Posts
Originally Posted by bombloader View Post
Are you referring to the case of carbureted engines? Most non-aviation carbureted engine have fixed jetting for mixture, so yeah efficiency does decrease because the mixture becomes richer. You have to rejet the whole carburetor to fix the problem. Modern injected engines maintain a stoichometric mixture constantly, so that wouldn't be a problem.
Trapped mass due to egr plays a role as well. At part throttle at low altitude you have more egr in the cylinder than you would at a higher altitude forthe same amount of fuel burned. The egr absorbs some of the heat of combustion that would otherwise be transferred to the engine block. This allows that heat to be converted to work instead of being dumped through the radiator.

  Reply With Quote