What If Tetraethyl Lead additives were banned in the 1920s? Effects on WW2?

[Reluctant Poster]

Calum,

The difference is that benzene is just carbon and hydrogen, so it's not dangerous after combustion and degradation. Tetra-ethyl lead contains, well, lead, and you can't get rid of it.

Once the TEL goes through combustion, the lead is carried into the atmosphere by by the hot exhaust gasses and can be inhaled; it also ends up in soil and water where it can be directly ingested or take up by plants and then concentrated as it passes up the food chain.

So the difference is danger to people handling it vs. widespread environmental contamination no matter what. A gross simplification, but a good starting point.

Benzene became a concern in gasoline relatively recently

Reducing benzene in gasoline

Cost-effective solutions for the reduction of benzene in gasoline, particularly with regard to MSAT II requirement

www.digitalrefining.com

 

[Reluctant Poster]

Thank you for the information/correction.

Do you have any idea how long the 100/150 fuel specification lasted?
In 1947 according to one engine year book (secondary source) the US was using 115/145 while the British were rating a couple of Merlins/Griffons on 115/150.
I have no idea if the 115/150 was an invention of the author/editor.
In the 1948 edition the 115/150 references have gone away and been replaced by 115/145 but it appears the power ratings (Max power) stayed the same.

From Heron "Development of Aviation Fuels"

Grade 115/145 was specifically developed to suit air cooled engines as they did not see the same improvements in performance as liquid cooled when operating with lean mixtures

 

[Reluctant Poster]

Thank you for the information/correction.

Do you have any idea how long the 100/150 fuel specification lasted?
In 1947 according to one engine year book (secondary source) the US was using 115/145 while the British were rating a couple of Merlins/Griffons on 115/150.
I have no idea if the 115/150 was an invention of the author/editor.
In the 1948 edition the 115/150 references have gone away and been replaced by 115/145 but it appears the power ratings (Max power) stayed the same.

I haven't seen any record of 115/150 production. From "A History of The Petroleum Administration for War". You can get this for free on Google Books. It is essential reading.
You can also see that US production using 6 cc of TEL was miniscule

 

[Reluctant Poster]

From Army Air Forces Historical Studies: No 65 Aviation Production and Control

 

[Reluctant Poster]

And finally, from:

 

[special ed]

Benzene can be absorbed through the skin as well by the lungs. Hazard results are Leukemia, blood cancers and loss of bone marrow. Fortunately the 5 gallons I bought in the 60s (before restrictions) for mixing with model glow fuel evaporated so easily that I was only able to use only about a quart for actual fuel. At the time, it was available for hotrodders and drag racing at the chemical plant, five gallon minimum.

 

[AMCKen]

I seem to recall reading that one of the troubles the P-38 had in Europe was excess lead coating the spark plugs, naturally leading to ignition problems.

 

[kool kitty89]

It was well known that Tetraethyl Lead was toxic by the time that it became an additive to fuel for knock resistance.

After some deaths in a production facility, sales of TEL were suspended for a year and a conference held into its health issues. That, and other studies that were held in the following years, sometimes conducted by the lead industry, found that there was little health risk to the public.

But what if warnings from a few scientists were heeded and TEL sales permanently banned from 1925?

The other anti-knock additive being proposed at the time was ethanol. Had that been adopted what would aircraft performance have suffered?

How would ranges have been affected by petrol/ethanol blends? Fuel economy is ~3-4% worse with E10 compared with regular petrol.

It's worth noting that the acute toxicity of TEL was its best understood aspect, as was acute lead poisoning (and acute heavy metal poisoning in general, as with mercury). It's the chronic, low level lead exposure that was more poorly understood and being investigated and contended at the time. (particularly the fine particles of lead in exhaust from leaded gasoline)

That said, had the full dangers been understood, I suspect at most this would've led to restrictions on automotive gasoline, eliminating the vast majority of public exposure (and contamination of soil and ground water) presented by leaded fuel.

By the 1920s, a variety of octane boosting (and high octane fuel components) were available and it was mostly down to automobile manufacturers to design the engines and fuel systems to tolerate a wider range of blends with alcohols, aromatics, and other fuel additives or alternative fuels. It shouldn't have been too hard to find some compromise and set standards on the fuel/air mixture limits, lubricity, water tolerance, solvent properties (erosion or swelling issues for rubber based seals and tubing), volatility, flash point, etc for general automotive use and additional standards for different seasons and different regional climates. (regions with higher humidity might have stricter limits on water-attracting methanol and ethanol and/or higher requirements of cosolvents to prevent phase separation)

Also note: catalytic converters are a non issue here and restrictions of sulfur emissions (and acid rain) would likely be of limited concern, so the sulfur containing fraction of crude oil and resulting gasoline that has both octane boosting qualities and good lubricating qualities could be explicitly retained to improve those characteristics.

Between the development of new synthetic processes to produce methanol by the late 1920s and an increasing array of liquid alcohols, ethers, ketones, and hydrocarbons using synthesis gas as a starting point, plus the ongoing advances in catalytic cracking of crude oil into higher yields of desirable high octane components, and the competing fields of biofuels (namely fermentation derived ethanol and acetone-butanol-ethanol fermentation) all should've helped work towards a quite viable set of standards to work with during the 1930s and into the 1940s.


Also note: certain combinations of the above components can also mitigate issues with metallic corrosion or erosion of rubber (plus corrosion inhibators can be added as well) plus combinations of light alcohols like ethanol, and especially methanol with normal gasoline (and hydrocarbons in general) will actually increase volatility and lower the flash point beyond that of either of the starting materials due to the semi-polar nature of the alcohols vs non-polar hydrocarbons, plus the formation of azeotropes with several common hydrocarbons present in gasoline (like hexane, plus aromatics and benzene), increasing the vapor pressure and lowering the boiling point of the mixture. At some point adding more alcohol will stop increasing the volatility and start reducing it (usually somewhere between the 40 and 60% alcohol mark) and taper off down until you reach the same vapor pressure of 100% alcohol. (note: methanol is more volatile in itself and more aggressive in increasing volatility of hydrocarbon blends both due to its lower boiling point and more polar nature than ethanol, albeit this also means it can phase separate with lower water content than ethanol and thus benefits more from having ethanol, propanol, and/or butanol present, or other co-solvents, to reduce this behavior)

This behavior is also partly why it's uncommon to see E20 to E50 blends in modern gasoline since the EPA has fairly strict limits on vapor pressure and those intermediate blends exceed this. (this was also a major point holding back methanol blends tried in the 1970s and 80s in the US, including some that were initially granted waivers and later revoked, namely concerns over VOCs emitted by fuel evaporation from the tank). This is a bit frustrating and ironic as it's these blends that are most efficient and tend to greately improve break thermal efficiency (to the extent that many engines have better per-gallon fuel economy than with straight gasoline, with 30 to 50% generally being optimal, though much over 35% not being tolerated by typical non-flex-fuel engines simply due to inability to correct the fuel/air mixture and ending up running lean, thus triggering a fault from the oxygen sensor). Much beyond 50% and the efficiency drops again, and by the time you get to E85 the brake thermal efficiency is much closer to the same a sit is with normal gasoline or E10.

Alcohol blends also reduce flame temperature and allow engines to run cooler.

Ethanol and methanol are also especially corrosive to aluminum (and many aluminum alloys), but interestingly this is most true for anhydrous (water-free) alcohols which can dissolve aluminum oxide and form a gel of aluminum hydroxide and alcoholate that accelerates further corrosion so long as any dissolved oxygen is present. However, a small fraction of water is enough to inhibit this, with less than 1% being needed to achieve this and prevent dissolving of the protective oxide layer of aluminum. Of course, the presence of water itself can have other corrosion issues (and phase separation issues), moreso for steel components than aluminum, though there may be a happy medium for very low, non-zero fractions of water, possibly even within the convenient hydrous (190 proof, ~95%) ethanol range.

Experimentation with different steel and aluminum alloys, various fractions of water, different fuel blends, and corrosion inhibitors likely would've worked around this, along with maintenance procedures specific to these issues, especially for extended periods of inactivity. (problems from fuel sitting in float bowls and such causing issues)

On the plus side, alcohol blends and acetone tend to greatly reduce gum and varnish problems in fuel (where aromatics tend to make this worse), and the intermediate alcohol blend proportions that tend to optimize fuel economy also tend to have some of the best water tolerance. (small amounts of water would also further increase octane rating without, plus further reduce flame temperature, allowing engines to run even cooler than the alcohol blend already allows)

Such blend may have been appealing enough to even use for aircraft during war-time given the higher octane and potentially competitive fuel economy, though real-world experimentation would've been needed to confirm this and the higher maintenance requirements (and potential inability to allow unsealed fuel systems to sit with fuel in them) would've been concerns for anything involved in front line combat service. However, the lubricating qualities of TEL would still likely be desired for aircraft use along with the octane boosting quality, albeit TEL tends to be less effective at boosting octane of alcohols than hydrocarbons, this also varies somewhat with blending. OTOH a minimum amount of TEL required just for the valve lubrication and wear qualities should've allowed stretching of limited TEL supply during war-time as well.
The earlier you put pressure on designing engines and fuel systems around alternative/competitive fuels, the fewer problems with logistics you'll have later on. And, given benzol and ethanol were the earliest competitive alternatives to TEL for automobiles (and to high octane straight gasoline from California oil wells and the like), optimizing around a range of alcohol-benzol-gasoline blends would've made sense, and from there you'd already have a lot of the general difficulties being worked on, so a wider array of blends later on wouldn't change all that much. (ie the difficulties with just benzol and ethanol would account for the vast majority that would be encountered with other alternative blends that might come later as synthetic chemical technology expanded) Acetone and n-butanole available through fermentation following WWI would also have been early considerations (the ABE process developed in the UK as a source of acetone for cordite created a new bio-chemical industry for ABE fermentation in the US that lasted up through the 1950s when access to cheap sugar cane from Cuba was cut off).

And, of course, during prohibition in the US, you have a further surplus of industrial alcohol (and underutilization of distilleries) that would've made ethanol fuel blends more attractive to all segments of the agriculture and alcohol production industries otherwise marginalized by the lack of (legal) demand for ethyl alcohol in consumables.

Racing aircraft throughout the 1920s and 30s had been experimenting with various alcohol fuel blends, ethanol and methanol both, plus benzol and acetone, and the Italians used ethanol blends for at least some of their fighter aircraft during the 1930s. The Fiat CR.32 and its A.30 engine, apparently ran on a mixture of: 55% petrol, 23% ethanol, and 22% benzol.


Additionally, aircraft using pressure injection carbs (single point fuel injection) or direct injection would've avoided the issues associated with fuel sitting in carb float bowls, exposed to the atomosphere. (and sealed fuel systems of that sort should've been easier to allow for alcohol fuel blends to sit in the tanks and in the fuel lines for extended periods between operation)

 

[kool kitty89]

People were also adding benzene to the gasoline in late 1920s/early 1930s (at least?). The mixure of benzene/gasoline 80/20 was used on the BMW VI 7,3 (denotes 7.3:1 compression ratio), for 750 HP. The VI 6,0 was using the benzene/gasoline 40/60 mix, for up to 660 HP. The BMW VI 5,5 that used only the gasoline of the day was good for 650 HP.

All per data from January 1929. I don't know what kind of octane rating can we 'attach' to the gasoline used in that time.

I had the impression it was "benzol" being used as fuel component (or straight as fuel) rather than pure benzene, though I think "Benzol" itself was a British brand and "Benzene" may have also been a generic term for a mix of liquid aromatic hydrocarbons. Those types of mixes were typically a combination of benzene, toluene, xylene (or xylene isomers, rather since there's 3 different configurations of that molecule), trimethyl benzene, ethyl benzene, and other alkyl benzenes. (ie all with a single 6-carbon benzene ring structure, but with different hydrocarbon chains or groups bonded to it) It was generally derived from bituminous coal tar.

Some grades might have also contained some polycyclic hydrocarbons like naphthalene or methyl naphthalene. (some are solid at room temperature, but extremely soluble in liquid aromatic hydrocarbons, and sometimes form eutectic mixtures, like with Benzene and Naphthalene, where a mixture of the two results in a freezing point lower than either of them)

This is broadly similar to the blends of aromatics used to boost octane in modern gasoline, albeit without any polycyclic compounds and with incresingly strict limits on benzene content due to its toxicity, carcinogen properties, and persistence in groundwater.


Also, benzol type mixtures are much more aggressive solvents than straight-run gasoline, naphtha, or catalytically cracked alkylate (all three predominantly containing saturated chain or branched hydrocarbons), as well as having poor lubricity, and you run into similar issues as acetone, methanol, or ethanol fuels in engines or fuel systems not designed around this. Albeit certain blends of regular gasoline and some or all of the above can mitigate this and some of the above have more specific solvent properties than others (alcohols and acetone are good at dissolving shellac, for example, so cork floats and seals treated with that would fail when the shellac is dissolved, while metal floats have no such issues; also aromatics and acetone tend to cause rubber tubes and seals to swell, and some systems are even dependent on this propery: hence why synthetic jet fuel can cause leaks if an aromatic fraction isn't added to it as the seals will contract when the more typical aromatic-containing kerosene based fuels are absent).

OTOH benzene and benzol type blends also works as a co-solvent for alcohols, improving their water tolerance and delaying phase separation by allowing more water to be dissolved into the fuel mixture. (heavier molecular weight alcohols like propanol and butanol also help with this)

Alcohol has several problems for aircraft fuel, only one of which is the reduction in heat energy per gallon.
While gasoline and water do not mix, alcohol mixes with both and can pull water into the "mix" rather than allow water to collect at the bottom of a tank.
Alcohol has a higher freezing temperature than gasoline and a higher auto ignite temperature which makes cold weather operation more difficult. Operation can be cruising at higher altitudes, not just staring up.
Benzene also has cold temperature problems

It's high flash point that can be a problem, not high auto-ignition temp. You want a low flash point and high auto-ignition temp as the latter goes along with high octane rating. Diesel oil generally has a high flash point, but a low autoignition temperature, and straight-chain hydrocarbons generally have increasing flash points and decreasing auto-ignition temperatures as they get higher in molecular weight, hence why propane has a high octane rating and dodecane has a low one along with a low autoignition temperature and high flash point.

Several of the problems with alcohol fuels are mitigated (partially or entirely) when optimally blended with other fuel components, the same goes with benzene itself (aside from toxicity). Benzene's high freezing point is mitigated by being present in mixtures of other aromatics (toluene, xylene, etc) but perhaps more interestingly, it's also mitigated by mixing with napthalene (normally solid at room temperature) as they form a eutectic mixture with a suppressed freezing point. (it's the same property that makes lead-tin solder melt at a lower temperature than either of the individual components) That said, with a complex mixture of aromatics, alcohols, and normal gasoline (plus potentially acetone or other ketones), you'd want to evaluate acceptable upper and lower limits of each component and how they interact in combination to maintain optimal chemical and physical properties.

Mixing of alcohols with hydrocarbons tends to increase the volatility of both until a maximum point is reached (usually between 40 and 60 %, but depending on the alcohol in question and the exact mix of hydrocarbons), so it should be very possible to maintain an optimal blend by adjusting the blending components chosen. The increased volatility and vapor pressure of alcohol-gasoline mixtures is one of the potential reasons for improved brake thermal efficiency seen in intermediate blends (in the 25 to 50% ethanol range) and why its often possible to get better MPG with modern cars and trucks (non-flex-fuel and flex fuel alike) running around 30-35% ethanol even though such blends aren't generally available. (some cases get even better MPG than with normal gasoline, other cases at least get much better than expected based on the theoretical energy content of the given blend) Albeit for the cases of non-flex-fuel cars, some gains may be due to the engine running slightly lean more often in instances where the ECM isn't quick enough to compensate through feedback from the O2 sensor, thus tricking the engine into running in a more efficient manner that might compromise emissions standards. (albeit the vehicle would likely still pass emissions testing as the transient scenarios where lean burn occurs would likely be outside of the normal testing requirements at a smog certification station)

Higher volatility = more complete vaporization and more even combustion, but also means increased charge density due to the cooling effect of vaporization, though the latter doesn't really benefit engines using direct (in-cylinder) fuel injection, but would apply to single and multi-port fuel injection inside the intake manifold. (or for conventional carburetors)
The reasons we don't see such fuels on the market or a push for such is likely due to the vapor pressure and volatility being way too high for EPA standards (ie VOC output would be too high from fuel tank venting), so there's probably not some sort of conspiracy going on to prevent this and it's also likely not a huge issue with such blends being too corrosive or too hard on fuel lines (though running them will likely void your warranty as well, unless it's a flex-fuel vehicle). This is the same reason that butane content is limited in gasoline and summer blends tend to be more expensive than winter blends and cheaper in colder climates than warmer ones. (butane is a very cheap, high octane, high volatility component of gasoline, and can make up a significant fraction of winter blends due to its high solubility at lower temperatures, but it boils at just about -1C or 30F, and its solubility in gasoline drops as the temperature increases, and at any temperature, too much butane will increase the vapor pressure of a fuel blend beyond EPA limits)

OTOH, from a WWII standpoint, with pressurized fuel tanks and operations at altitutde over cold European skies, butane-rich aviation fuel should've been quite attractive, using up an otherwise low value component of oil refining (and coal hydrogenation for the Germans), especially during the winter months.




I got into researching a ton of this for both the historical and modern standpoints (and relatively recent history, like from the 1970s oil crisis to present) following an older discussion on stretching the German fuel supply some years back (probably over a decade ago) on the forums here and found a lot of interesting studies and research papers. If I have time, I might be able to dig up some useful charts and graphs relevant to vapor pressure of different blends, plus other relevant subjects. (though on the vapor pressure end, you can probably find such info in related articles on alternative fuels via a google search, at least for methanol, ethanol, and butanol)

Isopropyl alcohol gets overlooked more often than butanol as an alternative fuel (either of synthetic or fermentation origin), possibly because it tends to increase NOx emissions slightly where methanol, ethanol, and butanol don't (neither does acetone as I recall from related studies), but is otherwise an excellent octane booster and co-solvent for ethanol or methanol and is the lightest alcohol to avoid most of the worst corrosion and erosion (or swelling) issues. (I think it's mostly the NOx emission issue that killed its potential back in the 1970s and 80s as a competitive fuel blending component as it's otherwise cheap to make from relatively plentiful fractions of petroleum and natural gas feedstocks, though also possible to make from synthesis gas and certain fermentation processes, including a modified drivative of the Acetone-Butanol-Ethanol process that produces isopropanol rather than acetone)

 

[elbmc1969]

All I know is that the nearest gas station to work has E85 and it was less than half the price of regular unleaded a few months ago. (With falling gas prices it's probably "only" 60%.) Anyhow, talked to a guy who was filling up his Flexible Fuel Vehicle Ford. His mileage on E85 was only about 80% what he got on unleaded, but he was still coming out far, far ahead of anyone not driving an electric. Best was that he could mix fuels freely; no need to empty the tank of one to use the other.

Oh, and on fuel quality: my father worked as a gas chromatography lab tech for Shell in the early 50s when they were first using it in oil refineries. It absolutely revolutionized quality control and the consistency of fuels. Anyhow, if piston engine fighters were still a thing in the 50s, it would have been another little "boost."

 

[bf109xxl]

my father worked as a gas chromatography lab tech for Shell in the early 50s when they were first using it in oil refineries. It absolutely revolutionized quality control and the consistency of fuels. Anyhow, if piston engine fighters were still a thing in the 50s, it would have been another little "boost."

The most important development in the high octane gasoline production since 1930s was introduced in 1949 prior to the GC era. I mean catalytic reforming. Afterwards some new alkylates came into production, but it was rather a consequent improvement than a "boost". GC was very useful to optimize technological processes, but the key factor was the development of new catalysts.

 

[z42]

One class of chemicals usable as octane boosters are aromatic amines, particularly monomethyl aniline (MMA), N-methyl aniline, toluidine and xylidine. IIRC MMA was used in some WWII avgas formulations.

As for banning TEL, hard to see how it could have been banned for military use. For civilian use, sure. Removing lead from the current 100LL avgas would apparently result in about 96 octane. Though that is with current day refinery processes, I'm sure the hit back in WWII days would have been bigger. Maybe something like an unleaded 87 octane avgas could have been possible in that timeframe..?

From a public health perspective, IIUIC the biggest danger is to children whose brains are still developing. The public health tragedy came with the explosion of automobile use post-wwii using leaded automotive gas. Banning leaded autogas would have been a lot easier than avgas, with a much bigger public health impact as well.

 

[wuzak]

As for banning TEL, hard to see how it could have been banned for military use. For civilian use, sure. Removing lead from the current 100LL avgas would apparently result in about 96 octane. Though that is with current day refinery processes, I'm sure the hit back in WWII days would have been bigger. Maybe something like an unleaded 87 octane avgas could have been possible in that timeframe..?

The dangers of TEL were known before its widespread adoption in the 1920s.

If TEL had been banned at that time, leaded fuel would not have been developed for military aircraft since no-one would be making TEL.

 

[z42]

The dangers of TEL were known before its widespread adoption in the 1920s.

If TEL had been banned at that time, leaded fuel would not have been developed for military aircraft since no-one would be making TEL.

Indeed the dangers of TEL were known, and they still went ahead and used it. Even in the civilian automotive market, where other ways of improving octane were well known; TEL was just the cheapest way to do it (cheapest ignoring negative externalities, that is).

Even if a ban on TEL in the civilian market had been successful, I find it hard to imagine that it would have been possible to extend to the military as well, the potential performance improvements were just too great to pass over. If the enemy was using leaded avgas and you weren't, that would be a great benefit to the enemy.

Now, if TEL had never been discovered, that's of course another argument. In that case, other ways to improve octane would have been explored, and perhaps ultimately we'd have made do with lower octane avgas than historically.

 

[FALC0N]

Indeed the dangers of TEL were known, and they still went ahead and used it. Even in the civilian automotive market, where other ways of improving octane were well known; TEL was just the cheapest way to do it (cheapest ignoring negative externalities, that is).

Even if a ban on TEL in the civilian market had been successful, I find it hard to imagine that it would have been possible to extend to the military as well, the potential performance improvements were just too great to pass over. If the enemy was using leaded avgas and you weren't, that would be a great benefit to the enemy.

Now, if TEL had never been discovered, that's of course another argument. In that case, other ways to improve octane would have been explored, and perhaps ultimately we'd have made do with lower octane avgas than historically.

That is not entirely accurate. The dangers of TEL were PARTIALLY understood. The full scope was not. Yes, it was toxic on contact. Everyone knew that. The question was would it be toxic in motor fuels. Mercury is toxic, but people walked around with it in filling all the time. The world is replete with things that are otherwise toxic, are substantially less so in certain combinations and applications. Such was the view of TEL at the time.

The Surgeon General even commissioned a panel to examine the question in the Mid-1920's. And they concluded that it would be safe to use in fuel.

Even TEL opponents didn't really see coming how bad it ended up being. That's why finding the scope of the environmental contamination was so shocking. Nobody was really looking for it. Not even TEL opponents.

TEL didn't become dominant because it was cheap. It became dominant because it was, by far, the best octane booster out there. It still is. If we found a magic potion tomorrow that would fix TEL's toxicity issues, it would be back in every motor fuel under the sun inside of a year.

 

[Engineman]

Not certain that a "safe TEL" would be used. Modern automotive ICE tech is giving around 10:1 C/R, 25psi boost, 150bhp/l on standard car engines using E10 fuel.

Eng

 

[FALC0N]

Not certain that a "safe TEL" would be used. Modern automotive ICE tech is giving around 10:1 C/R, 25psi boost, 150bhp/l on standard car engines using E10 fuel.

Eng

It is 110% certain. Maybe 120%. The toxicity was the only reason the industry moved away from TEL. It would be the easiest call in the history of calls. Do you remember (of course you don't. Nobody is that old) what TEL primary competitor was back in the late 1910's, early 1920's? Ethanol! Yep! And that competition wouldn't go any differently if they rematched today.

 

[Engineman]

ICE technology has moved on, leaving TEL and other highly toxic fuels unusable today in Western style countries. Saying that such-and-such toxic fuel would be used today if only it wasn't toxic is a waste of time, and misleading. Many of these more toxic chemicals do have a certain usability in ICE but they are not satisfactory for emission or cost reasons.

Eng

 

[ThomasP]

FWIW

Current catalytic converters are not compatible with TEL, via a combination of lead/lead oxides coating of the surfaces (resulting in poor 'converting') and causing heat buildup within the catalytic converter (said heat build-up sometimes resulting in melting of various bits and/or fires).

Since 2 of the main purposes of the catalytic converter are to effectively convert harmful combustion byproducts to non harmful ones, and not start cars on fire in the process, TEL would not currently be acceptable even if it were not as toxic as it is.

It may, however, be possible to produce acceptable catalytic converters that would use different designs/materials/processes, thereby avoiding the current potential problems.

 

[tomo pauk]

An interesting graph can be seen here.
It basically says that the gasoline that otherwise has the octance rating of 68 can be 'improved' wrt. the resistance to knocking via the addition of water, alcohol+water, only alcohol, as well as with water+alcohol mix together with the TEL. The later (w+a+TEL) addition can increase the octane rating to about 97 if it represensts 30% of the total fuel (ie. 70% is the 68 oct gasoline). Alcohol can do 94 oct if it is 30% of the total fuel. 80% alcohol + 20% water can do 92 oct under the same conditions. Last but not least, 30% of water (rest 70% being gasoline) moves the oct rating from 68 to 76-77.

French were experimenting with adding the water to the gasoline in the late 1930s with good results, but the benzene lobby was successful in prventing this to be implemented across the country. During the ww2, German authorities in Paris noted that the French were pouring water into the tanks of their gasoline-powered cars to gain as much mileage as possible.