Using Fuel as a Combustion Engine Coolant?

In summary, it is possible for a combustion engine to use its own fuel as coolant, but it may not be viable due to the relatively small amount of heat that can be absorbed by the fuel compared to the amount of heat generated by the engine. Additionally, most piston aircraft engines are air cooled due to the high cooling drag associated with using a liquid coolant. Further research into aircraft cooling drag may provide more insights into the feasibility of using fuel as a coolant for combustion engines.
  • #1
Delta Force
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Some jet and rocket engines use their own fuel as coolant. Hydrocarbons have even been used to cool electronics and nuclear reactors. Would it be viable for a combustion engine to use its own fuel as coolant instead of water or another liquid?
 
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  • #2
Start a problem like this with some ball part calculations. I'll suggest some assumptions and a path to help you get started.

1) Assume a power, say 100 hp.
2) Assume typical efficiency of 0.45 lb of fuel per horsepower-hour for a small (automotive size) gasoline engine.
3) Assume 1/3 of the fuel goes to work (power from the crankshaft), 1/3 as heat out the exhaust, and 1/3 as heat out the water jacket.
4) Assume typical operating temperature of 190 deg F.
5) Assume a starting temperature (tank temperature) for the fuel.
6) Choose your fuel, and search the specific heat.
7) How much heat goes into the water jacket?
8) What is the fuel burn rate?
9) Given the starting temperature, ending temperature, and specific heat of the fuel, how much heat is absorbed?
10) Compare.
 
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  • #3
100 horsepower * 0.45 pounds of gasoline per horsepower-hour = 45 pounds of gasoline per hour
45 pounds of gasoline per hour * 1/3 of energy content to the radiator = 15 pounds of gasoline energy content to the radiator per hour

Gasoline requires 0.53 British Thermal Units to raise 1 pound of fuel by 1 degree Fahrenheit (source). Gasoline contains 114,000 BTU of energy per gallon (source), with a gallon of gasoline weighing 5.91 pounds or more (source), giving an energy content of 19289.34 BTU per pound.

15 pounds of gasoline energy content to the radiator per hour * 19,289.34 BTU per gallon of gasoline = 289,340.1 BTU to the radiator per hour

72 degrees Fahrenheit seems like a good starting temperature for the fuel, which means the gasoline can't warm more than 118 degrees Fahrenheit before it starts warming the engine instead of cooling it.

I'm not sure how to continue from here. I'm not from an engineering background so I'm not sure of the equation to use going forwards. There's a formula for heating energy where I found the specific heat content for gasoline (here), but it seems overly simplistic for this calculation. It's quite literally not taking place in a vacuum and some of the heat should be lost to the atmosphere through the radiator. After all, engines more powerful than this theoretical one have been cooled purely by air, with no liquid at all.
 
  • #4
@Delta Force, good so far.

Next step: You have 45 pounds per hour of gasoline flowing from the tank at 72 deg F, then heated to 190 deg F in the engine. The heat to do that is 45 lbs/hr X 118 deg F X 0.53 BTU/(lb-deg F) = 2810 BTU/hr. Check the units, you will see that they balance.

Result: The engine is sending 289,000 BTU/hr to the water jacket, and the fuel could theoretically absorb 2810 BTU/hr, or 1%.

Most piston aircraft engines are air cooled. A rough rule of thumb is that cooling drag (power required to force air over the engine) is about 10% of engine horsepower. Here is a good link to a person who studied the cooling drag on his homebuilt airplane: http://www.n91cz.net/Interesting_Technical_Reports/106-111_BuildingBasics.pdf. Good search terms for further information are aircraft cooling drag.
 
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Related to Using Fuel as a Combustion Engine Coolant?

1. What is the purpose of using fuel as a combustion engine coolant?

Fuel is used as a combustion engine coolant to prevent the engine from overheating. It absorbs heat from the engine and carries it away, allowing the engine to maintain a safe operating temperature.

2. Is using fuel as a coolant safe for the engine?

Yes, using fuel as a coolant is safe for the engine. Fuel is designed to withstand high temperatures and has a high boiling point, making it an effective coolant for engines.

3. How does fuel compare to traditional engine coolants?

Fuel is not as effective as traditional engine coolants such as water or antifreeze. However, in emergency situations where other coolants are not available, fuel can be used as a temporary solution.

4. Are there any potential drawbacks to using fuel as a coolant?

One potential drawback of using fuel as a coolant is that it can be expensive and wasteful. Additionally, fuel can also be flammable and pose a safety risk if not handled properly.

5. Can any type of fuel be used as a coolant?

No, not all types of fuel are suitable for use as a coolant. Generally, only high-octane gasoline or diesel fuel should be used as a coolant for engines. Other types of fuel, such as ethanol or biodiesel, may not have the same cooling properties and could potentially damage the engine.

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