In another thread we saw...
...and rather than drift the thread unmercifully, I thought it might make a good topic.
"Fuel cools" is one of those common beliefs, and although true after a fashion, it is interesting to quantify. I missed physics class, so ya'll check me. Quick 'n dirty, we have:
The BTU content of gasoline is about 114,000 per gallon. In very rough terms, about 30% of that BTU content gets wasted to the air by the cooling system, or about 34,200 BTU per gallon of consumption. That's the heat we're trying to dissipate for every gallon of gas we burn.
The latent heat of evaporation for gasoline is about 900 BTU per gallon. That's the energy absorbed in the phase change from liquid to vapor, assuming we start at about 60F. That heat comes from the local environment, in this case (to some degree) the cylinder heads. Reality is that it mostly cools the charge, but hey, lets pretend it's all CHT reduction.
So, on a per gallon basis, about 2.6% of heat dissipation (900/34200) comes from evaporation of fuel.
If we richen fuel-air ratio 20% (say from 10 GPH to 12 GPH) without changing power output (it actually goes down a tad), and assuming we evaporate all of it, we have 900 x 1.2 = 1080. 1080/34200 means evaporative cooling is now a whopping 3.2%, or 0.4% additional cooling.
I conclude that extra fuel doesn't cool..not really. For sure it lowers combustion temperature, and HP at the same time. Get real lean, and the result is the same.
If it (ed; a fuel injection nozzle) is not fully functioning, the decrease in fuel need paradoxically causes heat, as fuel cools.
...and rather than drift the thread unmercifully, I thought it might make a good topic.
"Fuel cools" is one of those common beliefs, and although true after a fashion, it is interesting to quantify. I missed physics class, so ya'll check me. Quick 'n dirty, we have:
The BTU content of gasoline is about 114,000 per gallon. In very rough terms, about 30% of that BTU content gets wasted to the air by the cooling system, or about 34,200 BTU per gallon of consumption. That's the heat we're trying to dissipate for every gallon of gas we burn.
The latent heat of evaporation for gasoline is about 900 BTU per gallon. That's the energy absorbed in the phase change from liquid to vapor, assuming we start at about 60F. That heat comes from the local environment, in this case (to some degree) the cylinder heads. Reality is that it mostly cools the charge, but hey, lets pretend it's all CHT reduction.
So, on a per gallon basis, about 2.6% of heat dissipation (900/34200) comes from evaporation of fuel.
If we richen fuel-air ratio 20% (say from 10 GPH to 12 GPH) without changing power output (it actually goes down a tad), and assuming we evaporate all of it, we have 900 x 1.2 = 1080. 1080/34200 means evaporative cooling is now a whopping 3.2%, or 0.4% additional cooling.
I conclude that extra fuel doesn't cool..not really. For sure it lowers combustion temperature, and HP at the same time. Get real lean, and the result is the same.