Why are you using nHeptane? Dump it immediately. It has a boiling point of 209F and a MON of....zero.RDY4WAR wrote: ↑Sat Jun 11, 2022 1:49 pm Circling back to Butane...
Here's data for Butane that I was able to obtain online.
Stoich AFR = 15.42:1
BTU/lb energy = 21,300
BTU/lb HOV = 165.6
21,300 / 15.42 = 1,381 BTU/lb of air energy
165.6 / 15.42 = 10.7 BTU/lb of air heat of vaporization
Let's take a (purely hypothetical) fuel formula that's (before additives)...
Iso-octane - 54%
n-heptane - 13%
toluene - 25%
cyclohexane - 8%
This combination (if my math is correct) should have the following properties...
- AFR = 14.66
- AKI = 89.39
- HOV = 138.86 BTU/lb, 9.47 BTU/lb of air
- BTU = 18,658 BTU/lb, 1273 BTU/lb of air
- BP = TBD
- RVP = 1.69 psi
- SpG = 0.742
If we add 2% butane...
- AFR = 14.68
- AKI = 89.44
- HOV = 139.39 BTU/lb, 9.50 BTU/lb of air
- BTU = 18,684 BTU/lb, 1,273 BTU/lb of air
- BP = TBD
- RVP = 2.70 psi
- SpG = 0.739
If we add 5% butane...
- AFR = 14.70
- AKI = 89.52
- HOV = 140.20 BTU/lb, 9.54 BTU/lb of air
- BTU = 18,724 BTU/lb, 1,274 BTU/lb of air
- BP = TBD
- RVP = 4.21 psi
- SpG = 0.734
If we add 10% butane...
- AFR = 14.74
- AKI = 89.65
- HOV = 141.53 BTU/lb, 9.60 BTU/lb of air
- BTU = 18,790 BTU/lb, 1,275 BTU/lb of air
- BP = TBD
- RVP = 6.72
- SpG = 0.725
If we add 15% butane...
- AFR = 14.78
- AKI = 89.78
- HOV = 142.87 BTU/lb, 9.67 BTU/lb of air
- BTU = 18,856 BTU/lb, 1,276 BTU/lb of air
- BP = TBD
- RVP = 9.24 psi
- SpG = 0.717
Now let's add 10% ethanol to the 15% butane blend...
- AFR = 14.20
- AKI = 90.75
- HOV = 168.08 BTU/lb, 11.84 BTU/lb of air
- BTU = 18,130 BTU/lb, 1,277 BTU/lb of air
- BP = TBD
- RVP = 8.52 psi
- SpG = 0.724
What if we blended the 15% butane blend with 85% ethanol for E85...
- AFR = 9.88
- AKI = 98.04
- HOV = 357.11 BTU/lb, 36.14 BTU/lb of air
- BTU = 12,682 BTU/lb, 1,284 BTU/lb of air
- BP = TBD
- RVP = 3.09 psi
- SpG = 0.778
What about the 15% butane E10 blend with 60% methanol...
- AFR = 9.56
- AKI = 107.7
- HOV = 351.03 BTU/lb, 36.72 BTU/lb of air
- BTU = 12,303 BTU/lb, 1,287 BTU/lb of air
- BP = TBD
- RVP = 6.11 psi
- SpG = 0.765
I think I may be having a little too much fun with this.
Anyway, what I can't figure out quite yet is how butane stays in solution in any of these and where the IBP and 10% BP will fall. It would seem adding 10-15% butane would be excellent for a naturally aspirated drag racing engine.
And it has a negative response to TEL; add lead and the MON goes down.
Substitute neoHexane; it has a boiling point of 121F and a MON of 93, has a high RVP and responds positively to TEL.
Dump the cyclohexane; bad news. Replace with cyclopentane.Same story; lower BP, higher RVP, higher MON.
Butane is a gas at normal temperatures (BP 31F). Limited amounts can be put into race gas under pressure and
low temperature. The upper practical limit is typically 4%. As soon as the container cap is opened or exposed to room temps, the butane leaves the room. Not many refineries were capable of adding butane to gasoline from a production perspective. The problem is one of keeping the gas in solution under a variety of operating conditions.
OK, back to the drawing board. Consider some combination of the following:
isooctane
isopentane
neohexane
MTBE
cyclopentane
xylene
Other factors to consider are the speed index and the driveability index. Octane and energy are only part of the program.
A winning race fuel has a fairly wide distillation curve which produces a smoother throttle response across the rpm range.
Limited component fuels do not produce smooth throttle response and must be designed for a specific operating condition.