Re: OT- fuel mileage & fuel injection questions



Dave Hinz wrote:

On Mon, 19 Jun 2006 16:16:15 GMT, William Wixon <wwixon@xxxxxxxxxxxxxxx> wrote:


i recently happened to acquire a stack of Life magazines, 1937-1941, one of the things that struck me was the ads for automobiles of the time touting "30 mpg". i was incredulous thinking "jeez, you'd think in 69~65 years we'd be getting at *least* double what they were getting then!" or, they were lying big time.


Well, that was probably with manual transmission, and on a constant-speed
level cruise. Those cars were huge boats, not terribly aerodynamic, with the
frontal area of a billboard. The engines ran the cooling water much cooler,
and the compression was lower. (Of course, they didn't have EGR, or keep the
timing retarded to lower Nitrogen Oxide emissions, either.)

Today's EPA milage requires driving a prescribed course, although pro drivers
can get VERY good milage when doing it.

There just isn't much more energy to be had. At this point, you're not
getting unburned hydrocarbons out the tailpipe, the fuel is all being
burned. And unless you come up with a cycle other than Otto's, the heat
losses are going to be about the same. Thermal losses are all we have
left to work with at this point, from the engine perspective, because
the fuel delivery angle of things has been optimized as far as it's
going to, other than small incremental changes.


Huh? Have you heard of pumping loss? That is the loss of having to pump
100+ CFM of air past a restriction (throttle plate) with 15 - 20 inches of mercury
pressure drop, when cruising. If you want to check it out, sometime, try
shutting off the ignition and coasting down, both with the gas pedal at the
normal cruise position and with it floored. The car will coast WAY farther
with the pedal floored. (This works best with a manual transmission, or at
least an all hydraulic automatic. The modern electronic ones will go into
neutral when the power is turned off.)

This loss is QUITE substantial, and is one of the reasons Diesel engines get
higher thermodynamic efficiency at part power, while the Otto engine goes
in the trash can at part throttle. It is also why the need "retarders" on large
trucks, because there is no engine braking with a normal Diesel.

Stratified charge engines can operate with no throttle or other restriction
on the air intake, varying power by varying fuel flow. There are some problems
taming the emissions like is now done with exhaust gas recirculation, or so

I've read.

Jon

.

Relevant Pages

  • Re: News 24 and Heathrow Incident .
    ... was on final approach over Hounslow when he reported complete loss of ... power - engines, avionics everything. ...
    (uk.media.tv.misc)
  • Re: News 24 and Heathrow Incident .
    ... BBC is now reporting, from an anonymous airport source, that the pilot ... was on final approach over Hounslow when he reported complete loss of ... power - engines, avionics everything. ...
    (uk.media.tv.misc)
  • Re: News 24 and Heathrow Incident .
    ... BBC is now reporting, from an anonymous airport source, that the pilot ... was on final approach over Hounslow when he reported complete loss of ... power - engines, avionics everything. ...
    (uk.media.tv.misc)
  • Re: Worlds First Fuel Cell-Powered Train Locomotive Slated for 2008
    ... continue on using diesel engines but develop biodiesels supplies. ... desert could potentially provide enough biodiesel fuel to power the U.S. ... the hybrid systems. ... >> So they are diesel electrics, ...
    (sci.energy.hydrogen)
  • Re: Worlds First Fuel Cell-Powered Train Locomotive Slated for 2008
    ... continue on using diesel engines but develop biodiesels supplies. ... desert could potentially provide enough biodiesel fuel to power the U.S. ... the hybrid systems. ... >> So they are diesel electrics, ...
    (sci.energy)