My not as glorious Silver State ORR adventure
09-28-2009, 11:54 AM
#31
Race Car
Is the stock fuel cooler not up to this task? Or does the car no longer have A/C? It's only about 5hp to drive the compressor, and the weight shouldn't matter that much in ORR.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
09-28-2009, 01:05 PM
#32
Chronic Tool Dropper
Lifetime Rennlist
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Cooling the fuel actually makes a very small difference in intake charge temps. It's about 8% of the total charge (by weight), and only the sensible heat in the liquid can be considered when predicting the change in total charge temperature. Like water to steam and freon liquid to vapor flashing to absorb heat, the actual amount of heat absorbed in the state conversion of the fuel is much more dependent on the conditions (temp and pressure) downstream of the injector than it is in the upstream part.
Cooling the fuel will obviously make a huge difference if the conditions (temp and pressure again) in the fuel piping upstream of the injector cause the fuel to go to vapor state there. Chilling the fuel before it gets to the fuel rail helps keep it in liquid state all the way through the injector nozzles. That may be the most important contribution.
Keeping the tank cold is likely the best way to get the most benefit, so that the chilled fuel is less likely to flash to vapor at a pump inlet, for instance. George, I didn't see your final configuration for pumps. Is the first pump sitting well below the normal liquid level in the tank? Are there any check-valves or other potential pressure drops in the line between the tank well and that first pump? Big pipes, no sharp elbows, protected from external heat sources like exhaust or sunlight. In a perfect world, the inlet of the pump would see only liquid under all conditions, and have enough suction head to make sure that there is no fuel boiling in the first couple stages of the pump. Just a small amount of fuel vaporizing in the first pump sections can cause the pump to stop drawing liquid. This is commonly called 'cavitating' but really it's trying to recompress the fuel vapor in a pump section not intended for vapor.
Cooling the fuel will obviously make a huge difference if the conditions (temp and pressure again) in the fuel piping upstream of the injector cause the fuel to go to vapor state there. Chilling the fuel before it gets to the fuel rail helps keep it in liquid state all the way through the injector nozzles. That may be the most important contribution.
Keeping the tank cold is likely the best way to get the most benefit, so that the chilled fuel is less likely to flash to vapor at a pump inlet, for instance. George, I didn't see your final configuration for pumps. Is the first pump sitting well below the normal liquid level in the tank? Are there any check-valves or other potential pressure drops in the line between the tank well and that first pump? Big pipes, no sharp elbows, protected from external heat sources like exhaust or sunlight. In a perfect world, the inlet of the pump would see only liquid under all conditions, and have enough suction head to make sure that there is no fuel boiling in the first couple stages of the pump. Just a small amount of fuel vaporizing in the first pump sections can cause the pump to stop drawing liquid. This is commonly called 'cavitating' but really it's trying to recompress the fuel vapor in a pump section not intended for vapor.
09-28-2009, 01:14 PM
#33
Nordschleife Master
I am suggesting both, for the locations that you can get dry ice, or even regular ice.
Take into consideration where we race. I haven't checked but places like Ely, Wendover, Arnold and other locations probably will not have access to dry ice. That would mean picking up the ice on a Wed transporting it and hoping it would last until Sunday when we race. I would think a cooler based off of ambient would be the better choice if it was available.
