temp-mpg relationship

[James Marriott]

>Why do you think the less thermally efficient diesel engine gets
so much
>better fuel economy under cruising conditions than an Otto cycle

Errr, because it's _more_ thermally effiecient? A higher
compression ratio leads to better efficiency (defined here as
turning heat energy into work energy), either in power or
economy.

And because it has no throttle, and because virtually all
hydrocarbons have about 19500 Btu/lb of combustion energy; we buy
vehicle fuel by the gallon, and diesel (oil) is a bit more dense
than gasoline.

cu, James Marriott
'87 4kq (alias "late-B2 90q") with rare NG engine, 181k
'89 200q (MC1, ProconTen/no bag, 1.8 blah blah), 132k
Boise, ID, USA     http://www.webpak.net/~marriott/