On Mon, 18 Jun 2001 10:13:37 EDT, Stefanv@aol.com said:
>Flames shooting out of the back of a car (especially running in endurance
racing) is not a good thing!
>Flames out the back is fuel in the exhaust igniting.
>Fuel in the exhaust is fuel not burned in the combustion chamber.
>Fuel not burned in the combustion chamber is fuel wasted.
>Fuel wasted means poorer fuel mileage than if you'd managed to use that
fuel.
>Poorer fuel mileage means more pit stops.
>More pit stops means you lose the race.
>In general, flames out the exhaust is indicative of underdeveloped, "off",
or improper fuel management in the >engine management computer/black box
area.
>As I understand it.
To add to your understanding: The flames out the exhaust were only on
"overrun", or closed-throttle conditions. In an endurance race, it's
customary to set the fuel mixture into the "comfortably rich" zone, a bit
richer than the best fuel/air ratio for peak power production, in order to
assist the longevity of the engine for 6, 10, 12, or 24 hours. This is
particularly true for turbocharged engines (like the Audis, Cadillacs,
Bentleys), but is also done on normally-aspirated engines (I've seen
overrun flames from the Corvettes and Vipers, for example).
The reason for "comfortably rich" as opposed to stoiciometric or even
slightly lean in an endurance racing engine is simple: lean means higher
combustion temperatures, and a far greater potential for Bad Things to
happen to pistons (like holes getting torched in the piston crowns).
Running a little rich will actually cool the burn slightly, and having more
fuel than oxygen means there's some leftover fuel -- very little under
load, but there's a bit more on an overrun condition where the throttle
closes and there's a wee bit of lag between that action and the injection
system reducing the fuel shot. That extra bit of fuel passes through the
cylinders, the turbocharger (if equipped) and lights off in the exhaust --
or right at the exit of the exhaust where there's more oxygen available.
You won't see the flames out the exhaust under load, except in Hollywood
movies.
Yes, it uses a wee bit more fuel than running stoic or lean, but it's also
cheap insurance that the engine will be running in a fit state at the end
of the race (because, of course, you have to be running at the end to be
classified as a finisher...).
I watched an awful lot of SpeedVision this weekend...
Jim "Yeah, I'm an engineer" Crider
autojim@att.net
****************************************************************************
The information contained in this transmission, which may be
confidential and proprietary, is only for the intended recipients.
Unauthorized use is strictly prohibited. If you receive this
transmission in error, please notify me immediately by telephone
or electronic mail and confirm that you deleted this transmission
and the reply from your electronic mail system.
****************************************************************************
|