Light weight Euro-diesels

"Bill Daniels" wrote

Why would the fuel boil? Glycol/water coolant doesn't boil if the engine
temps are normal.

How are the temps going to stay normal, once the fuel has gotten up to
engine operating temperature? Remember the premise that the skins will not
get rid of the heat fast enough? Someone has proven it here before. The
fuel will then get hotter and hotter, until it is boiling. The change of
state may then keep the engine from melting down, at least until all of the
fuel is gone.

Using fuel as a coolant is a respected technique used by rocket engines
and
the SR-71.

Rocket engines only use the fuel one time for cooling, and that is on the
way into the combustion chamber. If it had to recirculate to keep the
engine cool, the fuel would over pressure and over temp in a short period of
time.

The SR-71 does not use the fuel to cool the engine, but uses the fuel to
cool the hot parts of the airframe, or in other words, redistribute the hot
skin temps. It should also be noted that the fuel was very special, and
only available at a few sites around the world. Are you planning on cooling
your skins, and where are you going to get SR-71 fuel?

Sorry, but your examples are not valid. If it worked, racers would do it,
and so would some others. It does not work. those are my final words on
the subject. See ya. -)
--
Jim in NC

"Morgans" wrote in message
...

"Bill Daniels" wrote

Why would the fuel boil? Glycol/water coolant doesn't boil if the
engine
temps are normal.

How are the temps going to stay normal, once the fuel has gotten up to
engine operating temperature? Remember the premise that the skins will
not
get rid of the heat fast enough? Someone has proven it here before. The
fuel will then get hotter and hotter, until it is boiling. The change of
state may then keep the engine from melting down, at least until all of
the
fuel is gone.

You know, I just don't buy the "skin radiators won't work" theory. The
pre-war Schneider Cup Seaplane racers did use skin radiators to cool some
really big engines. There are LOTS of reasons skin radiators weren't used
on WWII fighters - bullet holes being one. Since then, piston aero engines
have been air-cooled.

About 10 years ago I did a crude experiment. The fuel tanks on a PA-28 are
wet leading edge cells with only the wing skin between the fuel and the
airstream. I filled the tanks on my Archer II from a fuel truck that had
been sitting in the summer sun all day, measured the fuel temperature in the
right tank and went flying in the cool evening air using the fuel in the
left tank. 15 minutes later, after landing, I measured the right tank fuel
temperature again. It was a LOT cooler than when I started. This is an
experiment that anybody can do.

Using the tank wetted area, the before and after fuel temperature, the OAT
and the specific heat of AVGAS, I calculated the heat rejection of the tank
as if it were used as a radiator. There was huge heat flow from the fuel in
the tank to the airstream. It looked as if it would be larger than the
heat rejection of the O-360 in the Archer's nose if the fuel temperature
were as high as coolant would be.

Now maybe if the fuel were at 200 F, the heating of the boundary layer would
trip it to turbulent flow and create a lot of drag but I doubt that an
Archer has much laminar flow anyway. If the fuel tank/radiator were in the
propeller slipstream where it belongs there wouldn't be any laminar flow to
trip.

Bill Daniels

Bill Daniels wrote:


You know, I just don't buy the "skin radiators won't work" theory. The
pre-war Schneider Cup Seaplane racers did use skin radiators to cool some
really big engines. There are LOTS of reasons skin radiators weren't used
on WWII fighters - bullet holes being one. Since then, piston aero engines
have been air-cooled.

I don't either.

A diesel fuel-cooled plant would NOT use raw fuel in its coolant
passages. It would have a conventional glycol "primary loop", with a
radiator-behind doors or (in front of) cowl flaps, a cabin heat
exchanger ("heater core" in autoese), and an intercooler with fuel
circulated through it and returned to tanks. It would be designed so
the fuel loop could be shut off-bypassed- when the rad had its doors
open as would be done when the aircraft was very low on fuel, or in
high thermal load situations.

At altitude (this is a turbodiesel and flies at high FL) the ambient
temperature is very cold and the normal radiator could be blanked off
largely or entirely. If the tanks are designed with a lot of surface
area they will cool a large percentage of the engine's total heat
rejection and additionally provide anti-icing.

The main requirement as I see it is the system has to be default
failsafe and provide single lever power control. Unless you want to
make it a two person flight crew aircraft and haul a FE along.