Heat Generated by a V8 Gasoline Engine?
Heat Generated by a V8 Gasoline Engine?
(OP)
Does anyone out there have some rule of thumb numbers or better yet technical information for how much heat a 300 cubic inch V8 will produce at an iddle. I want to determine how much heat the radiator or an equivalent heat exchanger would need to remove from the coolant loop to maintain a somewhat constant engine temperature when the engine is iddling. The engine in question is a 1978 AMC 304 with a 2 barrel carburator and dual exhaust.





RE: Heat Generated by a V8 Gasoline Engine?
Blacksmith
RE: Heat Generated by a V8 Gasoline Engine?
RE: Heat Generated by a V8 Gasoline Engine?
One way to figure out the amount of heat is to actually measure the amount of fuel used at idle-for your engine.
The efficiency is very low at idle-no load, probably less than 10%. That leaves ~90% of the heating value being converted to heat, and I'd guess that ~20-30% of the 90% goes out the exhaust when unloaded.
So, if you use ~70% of the total heat in the fuel, you should be fairly close. You might try to recover some of the exhaust heat too.
RE: Heat Generated by a V8 Gasoline Engine?
RE: Heat Generated by a V8 Gasoline Engine?
If you intend to heat a house this way, why not add a big generator/alternator and make your own electricity?
RE: Heat Generated by a V8 Gasoline Engine?
Typical pump gas will produce about 19,000-21,000 BTU per pound. Figuring a weight of 5.8-6.5 lbs per gallon, gives you anywhere between 110,200 and 136,500 BTUs per gallon.
How many BTUs you have available to power your alternate device, is largely dependent on how effectively this device can remove heat from the engine. The more energy your device can safely remove, the lower the requirements of the cooling system will need to be.
Bryan Carter
RE: Heat Generated by a V8 Gasoline Engine?
RE: Heat Generated by a V8 Gasoline Engine?
RE: Heat Generated by a V8 Gasoline Engine?
If you want to reject heat to some other device, you may want to replace the thermostat with a different flow control device so that under a steady state idle rpm that you always circulate warmed coolant to the radiator. A thermostat replacement used by many racers is a disk with a center hole pierced in it. You could experiment with different diameter holes. You could plumb in a flow control valve like a plumber might use as well.
RE: Heat Generated by a V8 Gasoline Engine?
For extra brave points - lag the engine, or at least run it in an enclosed box. You might want to recover the heat in the exhaust (easy) and the cooling air (tricky).
Cheers
Greg Locock
RE: Heat Generated by a V8 Gasoline Engine?
What I am actually doing is using the 304 V8 from my 1978 CJ-7 Jeep to provide hot water for a shower while I am camping or in hunting camp. I have a small plate and frame heat exchanger that I will mount under the hood. I will then mount a 12V self priming RV pump beside it to pull around 2gpm of water from the creek and pump it through the heat exchanger to a shower head outlet. The other side of the heat exchanger will be plumbed into the coolant loop just like the heater core and will have a cable operated adjustable valve to control the flow. What I wanted to find out was if the engine could produce enough waste heat at idle to heat the water for my shower. My gut feeling said it would and the ballpark numbers also indicate it should. I guess we will see. The engine may produce around 114 mbh, the heat exchanger is rated at 90 mbh with an inlet of 180 deg which should give me around a 90 deg delta T on the water from the creek assuming a 2 gpm flow. This arrangement should be able to continually heat water from 35 to 125 deg for the shower. Not the most efficient use of gasoline but it would be worth if for a nice long hot shower in the middle of the winter in the middle of the wild. I thought about using a control valve with a sensing bulb to regulate the flow from the coolant loop but this arrangement just seemed simpler. The temperature should be fairly stable once the engine is up to temp and additional temperature control while showering will be available by increasing or decreasing the flow at the shower head.
Once again, Thanks for the input.
RE: Heat Generated by a V8 Gasoline Engine?
If you are plumbing the secondary heat exchanger in the bypass circuit of the engine, you will have more luck maintaining the shower water temperature. If you plumb the secondary loop into the main heat exchanger hoses, you'll have to deal with the continual thermostat cycling. This cycling is approximately 10 deg F. If the thermostat is set to open at 190 F, it will be fully open at 200 F. I'd say with cold winter air across the idle that the inlet water back to the engine would be below 150 and that there may be a bit of thermostatic cycling.
RE: Heat Generated by a V8 Gasoline Engine?
Sorry I didn't include all the details in the first posting, but I wasn't sure what I would do with the "design/idea"(other people have done this also). I even toyed with the idea at one time of building a compact little package that could be sold. I have since decided to just build one for my Jeep and probably another for my brother. I think these things will be too expensive for many people to be interested. I will let you know how it works if anyone is thinking of building one.
The bypass from the water pump goes around the thermostat and it appears that the loop for the heater/defroster coil does also. I am planning on connecting into the heater loop right off the pump. I think this may be a higher pressure tap from the pump that would maintain flow even if the thermostat for the main loop opens. If I cannot get enough heat out because the thermostat cycles and the radiator dissipates the heat, I may need to look into temporarily restricting the radiator flow, or installing a diverter valve (expensive) that would divert water through the heat exchanger vs the radiator(need to be carefull though). I am hoping the heat exchanger will get as much heat as it needs and any extra would be removed by the radiator once the thermostat opens. I may even put in a higher temperature thermostat to help things out, but I don't want to do that unless I have to. I probably only need 105 - 110 deg for a shower so it may work with a lower inlet temp.
RE: Heat Generated by a V8 Gasoline Engine?
'Think outside the box!'
Get some flexible exhaust duct hose & run your tailpipe exhaust through the HXer.
If you didn't already have the HXer, you could just bubble the exhaust up through a drum of water (make sure to remove exhaust hose before shutting off engine). The basic principle is used in Vertical Tubeless hot water heaters from Fulton
http://www.fulton.com/hotwater.htm
and or 'DIRECT CONTACT WATER HEATERS' from Ludell
http://www.elliscorp.com/ludell/whtr/whtr.htm
RE: Heat Generated by a V8 Gasoline Engine?
Regards
pat
RE: Heat Generated by a V8 Gasoline Engine?
Burning 1 gallon of gasoline would produce ~1 gallon of condensate (+ additional BTUs).
Ken