kool kitty89
Senior Master Sergeant
It was mentioned in a few discussions some years ago that one of the reasons water-methanol injection took so long to be fully tested and approved for use (either in American or German aircraft applications) and initially saw only limited, restricted use as with boosted take-off power in the Bramo 323, was due largely to corrosion concerns, particularly long-term corrosion caused by residue left both at the intake and exhaust portions of the engine and manifolds.
This is reasonable given methanol (and even ethanol) can be pretty aggressive at catalyzing aluminum alloy corrosion when water is present, and exhaust moisture or ambient humidity exposure at the intake would be plenty to get water absorbed into residue between flight operations.
However, I haven't seen any discussion or references to experiments with alternative blending agents for water injection (both for anti-freeze and gasoline-compatible combustion properties: the latter more important in engines not employing direct fuel injection).
Acetone was the first one to come to mind given its ease of vaporization and good combustion qualities along with known use as a specialized aviation fuel additive (particularly British racing and air speed record setting fuel blends, as with the Rolls Royce R) and when heavily diluted with water, it's also relatively harmless to rubber hoses, gaskets, and seals.
But when looking into this, particularly looking for info on flash points of various water+flammable solvent mixtures, I found this: https://engage.aiche.org/HigherLogi...=e53a8ccc-48b1-4e3b-b59f-bb579cc5132b&ssopc=1
Which gives some nice charts for water and methanol, ethanol, isopropanol (2-propanol), acetone, isobutanol, and a few other solvents, though it's given in mole fractions (that's a ratio of the number of molecules), so you need to do a bit more calculation based on molecular weight to convert that into ratios by weight and then more to account for density differences to get it by volume. (if I've done my math right, 50/50 methanol/methanol at room temperature is roughly a .31 mole fraction of methanol in water)
And perhaps more importantly, freezing points and flash points for water-alcohol mixtures, mostly by volume:
Methanol - Freeze Protected Heat Transfer Liquid
Ethanol Freeze Protected Water Solutions
Isopropanol (2-Propanol) based Freeze Protected Water Solutions
So Methanol is the most potent antifreeze component of those, and if -40 (F or C) degree freeze protection was needed, that makes it pretty attractive over higher concentrations of ethanol or isopropanol from an economic point of view and for allowing a higher water concentration (good for increased charge-cooling due to water's high heat of vaporization) but more moderate freeze resistance combined with much wider range of flammability makes isopropanol attractive on top of its much better compatibility with various metals (especially aluminum). That would be all the more appealing for lower or medium altitude use and in warmer theaters of operation. (though extreme cold in winter even at lower altitudes in Northern Europe and especially on the Eastern front could obviously still be more demanding)
Most Isopropanol was being made as an intermediate chemical for industrial acetone production in the 1930s/40s, itself made from acid hydration of propylene (mostly a byproduct of oil refining, but also from gassification and thermal or steam cracking of coal, and from both hydrogenation and Fischer–Tropsch synthetic fuel plants in Germany) but could have been used directly itself for Anti-detonation injection (and charge cooling) as well as a possible fuel additive. (octane booster, water tolerance improver, and anti-oxidant/preservative for reducing gumming in storage: especially of aviation fuel with polymerization and oxidation-prone aromatics in them and especially if aniline is added, as the US started doing with 100 octane avgas during the war)
The relative resource wealth in the US would make the economics issue less pressing and the charge-cooling and anti-detonant potential for highly boosted, but non-intercooled (or poorly intercooled) supercharged and turbocharged aircraft engines seems like it would've been extremely useful earlier in the war, potentially well before water-methanol systems were ready for service use and with generally more flexible usage. It seems like the Allison engines in nearly all configurations would've benefitted a lot from this, from the limited intercooling on the P-38 (prior to -J models) to both single and aux-stage mechanical supercharging, and even with the more modest (and common early to mid war) 8.8 supercharger gear ratio of the integral supercharger. (and might have afforded more resources for establishing WEP ratings and potentially officially sanctioned use of higher RPM under load: if nothing else, Allison's rating of the V-1710 seems to have been consistently more conservative than either the British Rolls Royce and Ford or American Packard built Merlin engines: though the single-stage V-1650 models were nearly as conservatively rated)
Water injection for US naval aircraft could've been easier to get into service and the less aggressive anti-freeze requirements for Pacific Naval operations would have made dilute isopropanol blends quite attractive.
As for Acetone, from WWI onward in the US, Canada, and UK (I'm not sure about mainland Europe or Germany itself) there was significant production of acetone via the Acetone-Butanol-Ethanol fermentation process using sugars, starches, and cellulose based biomass to supplement acetone production (this continued as economically competitive with petrochemical synthesis processes in the 1950s and 60s until the embargo on Cuba deprived the US of cheap cane sugar as high yield biomass feedstock and caused the gradual decline of that industry). That's also why n-butanol was researched as a gasoline substitute and additive along with ethanol and acetone during the 1940s in the US.
So Acetone itself, when in surplus (compared to isopropanol production) could still have been attractive as well in water solutions for ADI use.
I don't see any engineering toolbox pages on acetone solutions for freezing characteristics, but there's this:
Solid-Liquid Equilibrium Data of Acetone + Water from Dortmund Data Bank
I don't have the converted figures for that on-hand now, but I seem to remember acetone being less effective than isopropanol for antifreeze characteristics. (but will need to check that again)
I was using that chart or something similar to work out weight and volume % figures a couple years ago when I was researching this along with alternative fuel blends. (also for modern automotive use and the wide array of fuel alcohol and additive blending experiments that went on back in the 1970s and 80s following the oil crisis ... and prior to the MTBE and subsequent Ethanol standardization and/or mandates, especially in California)
If nothing else, acetone would have more issues with evaporating and needing pressure vents in storage, even in water solutions due to its high vapor pressure and low boiling point, even compared to methanol. Isopropanol is really appealing there for stability in storage over acetone, methanol, and ethanol.
Edit:
after some quick calculations, 50/50 acetone and water and 50/50 isopropanol and water are both pretty close in freezing point.
The molecular weight is pretty close and density is also pretty close, and the 50/50 volume conversion to mole fraction works out to also round to roughly .31 for Acetone in water at room temp.
So at 1:1 (50/50) by volume you get freezing at approximately:
Acetone50%= -23C (-9F)
IPA50%= -21C (-6F)
This is reasonable given methanol (and even ethanol) can be pretty aggressive at catalyzing aluminum alloy corrosion when water is present, and exhaust moisture or ambient humidity exposure at the intake would be plenty to get water absorbed into residue between flight operations.
However, I haven't seen any discussion or references to experiments with alternative blending agents for water injection (both for anti-freeze and gasoline-compatible combustion properties: the latter more important in engines not employing direct fuel injection).
Acetone was the first one to come to mind given its ease of vaporization and good combustion qualities along with known use as a specialized aviation fuel additive (particularly British racing and air speed record setting fuel blends, as with the Rolls Royce R) and when heavily diluted with water, it's also relatively harmless to rubber hoses, gaskets, and seals.
But when looking into this, particularly looking for info on flash points of various water+flammable solvent mixtures, I found this: https://engage.aiche.org/HigherLogi...=e53a8ccc-48b1-4e3b-b59f-bb579cc5132b&ssopc=1
Which gives some nice charts for water and methanol, ethanol, isopropanol (2-propanol), acetone, isobutanol, and a few other solvents, though it's given in mole fractions (that's a ratio of the number of molecules), so you need to do a bit more calculation based on molecular weight to convert that into ratios by weight and then more to account for density differences to get it by volume. (if I've done my math right, 50/50 methanol/methanol at room temperature is roughly a .31 mole fraction of methanol in water)
And perhaps more importantly, freezing points and flash points for water-alcohol mixtures, mostly by volume:
Methanol - Freeze Protected Heat Transfer Liquid
Ethanol Freeze Protected Water Solutions
Isopropanol (2-Propanol) based Freeze Protected Water Solutions
So Methanol is the most potent antifreeze component of those, and if -40 (F or C) degree freeze protection was needed, that makes it pretty attractive over higher concentrations of ethanol or isopropanol from an economic point of view and for allowing a higher water concentration (good for increased charge-cooling due to water's high heat of vaporization) but more moderate freeze resistance combined with much wider range of flammability makes isopropanol attractive on top of its much better compatibility with various metals (especially aluminum). That would be all the more appealing for lower or medium altitude use and in warmer theaters of operation. (though extreme cold in winter even at lower altitudes in Northern Europe and especially on the Eastern front could obviously still be more demanding)
Most Isopropanol was being made as an intermediate chemical for industrial acetone production in the 1930s/40s, itself made from acid hydration of propylene (mostly a byproduct of oil refining, but also from gassification and thermal or steam cracking of coal, and from both hydrogenation and Fischer–Tropsch synthetic fuel plants in Germany) but could have been used directly itself for Anti-detonation injection (and charge cooling) as well as a possible fuel additive. (octane booster, water tolerance improver, and anti-oxidant/preservative for reducing gumming in storage: especially of aviation fuel with polymerization and oxidation-prone aromatics in them and especially if aniline is added, as the US started doing with 100 octane avgas during the war)
The relative resource wealth in the US would make the economics issue less pressing and the charge-cooling and anti-detonant potential for highly boosted, but non-intercooled (or poorly intercooled) supercharged and turbocharged aircraft engines seems like it would've been extremely useful earlier in the war, potentially well before water-methanol systems were ready for service use and with generally more flexible usage. It seems like the Allison engines in nearly all configurations would've benefitted a lot from this, from the limited intercooling on the P-38 (prior to -J models) to both single and aux-stage mechanical supercharging, and even with the more modest (and common early to mid war) 8.8 supercharger gear ratio of the integral supercharger. (and might have afforded more resources for establishing WEP ratings and potentially officially sanctioned use of higher RPM under load: if nothing else, Allison's rating of the V-1710 seems to have been consistently more conservative than either the British Rolls Royce and Ford or American Packard built Merlin engines: though the single-stage V-1650 models were nearly as conservatively rated)
Water injection for US naval aircraft could've been easier to get into service and the less aggressive anti-freeze requirements for Pacific Naval operations would have made dilute isopropanol blends quite attractive.
As for Acetone, from WWI onward in the US, Canada, and UK (I'm not sure about mainland Europe or Germany itself) there was significant production of acetone via the Acetone-Butanol-Ethanol fermentation process using sugars, starches, and cellulose based biomass to supplement acetone production (this continued as economically competitive with petrochemical synthesis processes in the 1950s and 60s until the embargo on Cuba deprived the US of cheap cane sugar as high yield biomass feedstock and caused the gradual decline of that industry). That's also why n-butanol was researched as a gasoline substitute and additive along with ethanol and acetone during the 1940s in the US.
So Acetone itself, when in surplus (compared to isopropanol production) could still have been attractive as well in water solutions for ADI use.
I don't see any engineering toolbox pages on acetone solutions for freezing characteristics, but there's this:
Solid-Liquid Equilibrium Data of Acetone + Water from Dortmund Data Bank
I don't have the converted figures for that on-hand now, but I seem to remember acetone being less effective than isopropanol for antifreeze characteristics. (but will need to check that again)
I was using that chart or something similar to work out weight and volume % figures a couple years ago when I was researching this along with alternative fuel blends. (also for modern automotive use and the wide array of fuel alcohol and additive blending experiments that went on back in the 1970s and 80s following the oil crisis ... and prior to the MTBE and subsequent Ethanol standardization and/or mandates, especially in California)
If nothing else, acetone would have more issues with evaporating and needing pressure vents in storage, even in water solutions due to its high vapor pressure and low boiling point, even compared to methanol. Isopropanol is really appealing there for stability in storage over acetone, methanol, and ethanol.
Edit:
after some quick calculations, 50/50 acetone and water and 50/50 isopropanol and water are both pretty close in freezing point.
The molecular weight is pretty close and density is also pretty close, and the 50/50 volume conversion to mole fraction works out to also round to roughly .31 for Acetone in water at room temp.
So at 1:1 (50/50) by volume you get freezing at approximately:
Acetone50%= -23C (-9F)
IPA50%= -21C (-6F)
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