Fuel comparison- road legal formula vs f1 formula

[hardingfv32]

Oxygen in real pump fuel is unavailable for gainful chemical reaction, i.e. that in the Ethanol or Oxygenate content

What in the world are you saying with this statement? Ethanol or Oxygenates ALWAYS perk up my dyno results.

Brian

[hardingfv32]

Here are some 1989 gasoline data. Compare it to the FIA rules as best you can. I look for something better.

http://www.atsdr.cdc.gov/toxprofiles/tp72-c3.pdf

Brian

[Tommy Cookers]

Thanks, I always like a good read. It says Air Force, is it road or Avgas (I'm thinking).

F1 would allow about 11% (bio)Ethanol if all the 3.7% oxygen was given to this (maybe 5% bioEthanol is now compulsory).
11% would allow almost the same power as plain best pump fuel, but the total fuel load would increase by about 6% (Ethanol has about half the energy of gas, you need to almost double the mixture strength of the Ethanol you use)
The other stuff classed as oxygenates is Ethers e.g.MTBE. This is no better in this respect.

So if the magic 3.7 % is used in F1 as in road fuel there is this weight penalty. There might be better cooling effect in the induced charge.

Compared to this, 'my way' gains about 3-4% in power (about half from the oxygen mentioned before and half from using 96.3% the best 'normal' ingredient , Iso-octane), without any increase in fuel quantity. Certainly there are other similar, known, compounds which occur naturally in the crude,and could legitimately be sythecized. There must another % or two here. I think the French did all this.


I think some Ethanol might well show a small power increase in an existing engine on ordinary pump fuel, mostly due to hugely better charge cooling causing a greater massflow of air, fuel, and more power. Ethanol is not a bad fuel, if someone else is paying.

If the Ethanol's oxygen was involved there would be a huge effect,we would have heard about it before. If it can be done with Ethanol, it could be done with water.

[Tommy Cookers]

NOTE TO SELF

THERE IS (NOW?) A PROHIBITION OF EXOTHERMIC REACTION NOT (WHOLLY?)INVOLVING EXTERNAL OXYGEN

[langwadt]

Seriously why should somebody buy fuel that is 5 times more expensive?

The specifications numbers in the rules are very similar to pump street fuel. For the F1 fuel you are paying to have every performance improving spec right at the legal limit at ALL times. These are very small production volumes requiring the best components. The is not a normal production run for the fuel manufactures.

Brian

I saw an interview with a shell fuel guy at the last grand prix, they mix and test many many fuels before they choose the few they make and use during the season. They had tried running a Ferrari F1 on standard shell V-power it doesn't damage the engine but it is about 1 second slower per lap

[aussiegman]

There is a substantial difference between any “pump” fuel from anywhere in the world and any proper race fuel, especially that used by F1 cars. They are only similar in that they are both used in an ICE and that some of the components may be related. That’s where it ends. The difference comes not only from the fuel profile or fingerprint as determined through gas chromatography (Prior to gas chromatography, a fuel was tested by measurement of its specific gravity), but from the exacting tolerances used in blending the % ratios of the fuel and the extraordinarily specific qualities of the fuels individual constituents.

As said already, any normal “pump” fuel will vary greatly in consistency from batch to batch for varying reasons such as climate, delivery method, storage period, available feed stock, refinery, methodology used to crack and blend fuel, the list is almost endless. The prime example is an E85 fuel, which can vary from under 70% to well over 85% ethanol content due to mixing variations, but primarily due to climate requirements. For improved cold starting, during winter and in colder latitudes the ethanol content is reduced anywhere down to 70%. My own testing on pump E85 in Australia has seen these variations due to season, while commercially available race fuel E85 (Sucrogen and Sunoco) has always been 85% ethanol give or take 0.1% or there about.

Again commercially available race fuels from companies like Elf, Sunoco and Sucrogen (available I MON numbers up to 117+) are manufactured to specific profiles to perform in specific engine types with regard to compression ratio, maximum RPM and forced induction. A fuel that works in a low RPM (under 7,000rpm) and medium compression (12.5:1) will need a very different fuel to a high RPM, high compression or forced induction engine.

Fuel profile is altered through optimisation of the four major attributes of all fuels:
1: Octane: The rating of a fuels’ detonation resistance expressed as a Research Octane Number (RON) or Motor Octane Number (MON)
2: Flame Speed: This determines the speed at which fuel releases its energy. High RPM engines provide a very small “time” window for the fuel to release its energy. Peak cylinder pressure should occur at approximately 20° ATDC. If a fuel is not fully combusted by this time, its energy is not contributing to peak cylinder pressure.
3: Energy component/value: The potential chemical energy in the fuel, measured in BTUs by mass value (grams, kilograms, pounds etc) not volume. This is critically important as AFR is measured by weight, not volume.
4: Fuel vaporization (cooling) quality: Directly related to the fuels “heat of vaporization”. A higher value provides a larger cooling effect on intake charge. This can show substantial power gains (up to 5%) on a high rpm naturally aspirated engine due to cooler temperatures, increased density and higher levels of atomized (vaporized) fuel in the mixtures. Also a fuel with good vaporization will provide increased sensitivity to throttle inputs.

The general principles Article 19: Fuel of the FIA F1 regulations are “intended to ensure the use of fuels which are predominantly composed of compounds normally found in commercial fuels and to prohibit the use of specific power-boosting chemical compounds.”

Rules 19.7 and 17.8 set down

Before any fuel may be used in an Event, two separate five litre samples, in suitable containers, must be submitted to the FIA for analysis and approval.

Fuel samples taken during an Event will be checked for conformity by using a gas chromatographic technique which will compare the sample taken with an approved fuel. Samples which differ from the approved fuel in a manner consistent with evaporative loss, will be considered to conform. However, the FIA retains the right to subject the fuel sample to further testing at an FIA approved laboratory.

So optimisation of F1 fuels for specific tracks or as a trade off of any or all of the below is possible where you are looking for as an example:
1: improved throttle response where there are low-mid speed cormers
2: power where there are longer straights or the need to run with higher downforce
3: evaporative cooling at warmer tracks

These are all in theory possible while remaining in the fuel profile required by the FIA. Shell, Total and the other fuel suppliers have more than one fuel available for teams to use with optimised qualities based on engine design, requirements of the track and needs/wants of the team decision makers.

Modern Avgas was designed in 1936 to allow a power gain with mixture enrichment around 10 times that of modern pump fuel, yet would meet the F1 spec (apart from the lead).

What is the constant preoccupation with Avgas and early to mid 20th century anecdotal evidence?! As said before, Avgas is generally less dense than the majority of racing and modern pumps fuels, and as a result, tuners must compensate by resorting to richer mixtures when using Avgas.

Avgas also has a very different hydrocarbon profile to a normal pump or race fuel to optimize volatility properties at high altitude, typically through the concentrations of high level of aromatics, which can contribute to poor throttle response when used in engines that require constant throttle variations such as an F1 engine. Aviation engines typically are not required to have constant high speed throttle variations, they generally run at long periods and constant RPM's and as such, throttle response is a secondary concern.

Also Avgas has poor octane quality compared to modern fuels due to the specific requirements for high altitude/lower oxygen use. Low octane quality is one of the quickest ways to destroy an engine. Aluminum piston forgings can be severely eroded or cracked during acceleration events where detonation is present due to the inherent properties of low quality Avgas octane.

Avgas would also fail on:
Lead content: Avgas has various concentrations from 0.125% (0.56g/Lt) to 0.189% 0.85g/Lt) vs.FIA - 0.005%)
Octane number of 99.5 vs. FIA - 87.0
Benzene profile: Avgas has allowable Benzene up to 5.0% v/v (volume concentration) vs. FIA - 1.0%

I think some Ethanol might well show a small power increase in an existing engine on ordinary pump fuel, mostly due to hugely better charge cooling causing a greater massflow of air, fuel, and more power. Ethanol is not a bad fuel, if someone else is paying.

If the Ethanol's oxygen was involved there would be a huge effect,we would have heard about it before. If it can be done with Ethanol, it could be done with water.

Sorry but I am truly bewildered by your logic here in relation to the evaporative cooling aspect or in relation to the substitution of Ethanol for water (unless you’ve cracked the water based internal combustion engine, then I can’t see your logic).

You have argued previously that there was no benefit to using EC from rich fuel mixtures, yet here you are espousing exactly the same from the use of non-energy bearing substances that reduce fuel and oxygen volume in the intake charge to provide the exact same benefit which you said previously does not exist.

So which is it? Does EC is any form, from either water or fuel (ethanol) provide any benefit?

Firstly on your ethanol substitution claim:

While generally having a lower calorific content than the fuel in which it is blended (but typically higher octane), it still contains available chemical energy. Water does not as any potential energy is tied up in the bonds between the two (2) hydrogen and one (1) oxygen atoms that make it up. It’s that simple. You can’t displace a potential chemical energy bearing substance with a non-energy bearing substance and get a similar result.

Secondly in water substitution:

If you are referring to the band-aid, anti-detonation system that is water injection, this only works where you have a serious problem in the first place that you can not fix properly. That is namely excessively high intake charge temperatures or low/poor quality fuel octane issues such as where regulation requires or results in the same.

Absurdly high intake temperatures such as was the case in WRC where water injection re-gained popularity was the domain of such a need due to limitations on fuel octane and the use of a ever reducing turbo inlet restrictor that saw stupidly high low RPM boost levels to produce maximum low RPM torque prior to hitting the super sonic flow limit of the restricting orifice.

So water injection was used by the WRC teams as they were restricted in air flow, had high boost levels with low air flow for intercooler efficiency, limited fuel octane and high compression engines. The perfect, non-perfect scenario where a normally inefficient and temporary solution could work as they had no other options available. Remove one of the regulatory restrictions and the effectiveness of water injection would plummet.

So water injection works on the principal whereby the evaporation of injected water through the process of evaporative cooling reduces the temperature of the engine components and intake charge and then when converted to steam which takes energy from the combustion process, absorbs this energy and slows the speed of the flame front preventing or lessening detonation. It actually takes energy from combustion in the final phase of its use and there is a constant need to ensure proper water ratio's to ensure that you don't loose engine output due to fuel/oxygen displacement, over saturate the intake charge to the stage that combustion is not sustainable or further to result in hydraulic lock. Further what happens when it runs out and the engine that was relying on it can no longer sustain the high temperatures?? Either loose power or loose reliability.

That says nothing of the weight penalty of dragging around 10 to 20 kgs of water plus associated equipment like pumps, filters, lines, tanks etc.

I have seen all from the fool hardy and ill advised use of water injection by those that were told it was a safe and easy system. It is a band-aid fix and potentially very dangerous if not controlled and monitored carefully.

In an engine using proper fuel, proper fuelling for a given compression ratio or boost level and not forced to run overly high inlet or in cylinder BTDC temperatures, water will see a negligible net gain or a power loss due to its displacement of fuel AND oxygen in the form of air leading to incomplete combustion if fuel tables (or jetting in the case of carburetor engines) or reduced fuel/oxygen available in cylinder due to the water present.

Conversely, the use of ethanol for its evaporative cooling (“EC”) properties allows it to be effectively used as a tool when base heat loads such as those under high load conditions materialise and in which base fueling and intake temperature control is insufficient. As such, fuel EC performs a similar function of water injection through the use of fuel to increase net effect of fuel evaporation to control temperatures. Using a fuel for EC however allows that fuel to use all of available oxygen for combustion.

As you are fond of aviation analogies, the Harrier jet used water injection to allow it to hover to stop the Rolls-Royce Pegasus 6 to 11 series engines (UK variant) or Rolls Royce F402-RR-408 (US Marine Corps variant) from overheating and increase take off power as the blade metallurgy problem could not be solved. 30 to 45 seconds constant flow was all it could sustain. Once gone its hover was very limited and the weight of the water severely impacted performance to the point pilots I know that flew them typically went up without a water load. The now defunct US Joint Strike fighter VSTOL had none of these issues as the metallurgy issues had been solved.

What you have said previously is that the addition of extra fuel under load to these high AFR's has no net tangible benefit with relation to in cylinder heat management. If that is the case then water injection should make no difference. If this is the case then OEM and motorsport engine tuners need to go back to school.

[Tommy Cookers]

Again you seem to be defending your commercial interests against attacks that exist only in your imagination !

I have always said that all evaporation of fuel (and water) causes cooling, you accuse me of saying the opposite.

Perhaps I should change my username to 'Straw Man' ??

In recent weeks I have pointed out in other threads that the thing called Water Injection is in 99.9% of cases actually Methanol/water mix(50/50), and that true WI is pretty poor, largely due to displacement of useful stuff like air.

You should know that what you call WI in the Harrier is actually MWI.

So it is bizarre that you are presenting me as an advocate of true WI, and irritating that you have manipulated quotes.

BTW hydrogenation, then alkylation were in worldwide use prior to WW2, even in the E Hemisphere (Sumatra, but it was then bombed), not as you said (50s).

BTW there seems to be a surprising amount of interest in (competing?) improved methods of making 'Triptane'.
For the record, I assume that its very high response to organometallic 'octane boosters' is of interest to the industry, that has in mind a (relatively non-toxic) modern equivalent of TEL ('Lead')
(Iso-octane being relatively unresponsive to such)

[Tommy Cookers]

Seriously why should somebody buy fuel that is 5 times more expensive?

The specifications numbers in the rules are very similar to pump street fuel. For the F1 fuel you are paying to have every performance improving spec right at the legal limit at ALL times. These are very small production volumes requiring the best components. The is not a normal production run for the fuel manufactures.

Brian

I saw an interview with a shell fuel guy at the last grand prix, they mix and test many many fuels before they choose the few they make and use during the season. They had tried running a Ferrari F1 on standard shell V-power it doesn't damage the engine but it is about 1 second slower per lap

[aussiegman]

Again you seem to be defending your commercial interests against attacks that exist only in your imagination !

Tommy (I am assuming your name is Tommy or Tom and your reference is somehow linked to either the German slang for the Sherman Tank in WW2 or the portable alcohol fueled stoves they used to cook food in the helmet on), I have no commercial interests in any of the aforementioned subjects. My motorsport experience and interests extend only to that which my own wallet, private facility, academic interests and friends in the business with experience in these matters allow.

As for what exists in my imagination, I firmly believe that is a topic best left for another adult rated forum, preferably discussed after a number of beverages.

In recent weeks I have pointed out (in other threads) that the thing called Water Injection is in 99.9% of cases actually Methanol/water mix(50/50), and that true WI is pretty poor, largely due to displacement of useful stuff like air.

From my experience in motorsport uses, Water Injection (WI) is exactly that, water and not the water/methanol mix due to regulations. Apologies I have not seen any previous post regarding H2O/ Methanol pre-mix use. Regardless, where used by the general public, a 50/50 mix is popular such as that available from places such as Snow Performance with their "Boost Juice" and even their "Nitro Juice" with Nitro-methane. Aquamist is the other UK based WI company.

However it still does not detract from the simple physics that two elements or compounds cannot occupy a finite space and the chemistry that water contains no potential chemical energy available for combustion. By injecting H2O in any quanity it is a case of the law of diminishing returns as far as a ICE is concerned. You are removing a portion of that finite space that could be better utilised for fuel or air in simply covering up significant, fundamental problems with the system.

You should know that what you call WI inthe Harrier is (like the other 99.9%) actually MWI.

From discussions with pilots and engineers I know that used the Harrier, it had the capability to use a mix of 33.3% methanol/66.6% water, like 99.9% of WI systems however they are adamant it was primarily only distilled water for a number of reasons.

The maximum take-off thrust available from the Pegasus engine is limited, particularly at the higher ambient temperatures, by the turbine blade temperature. As such there were three separate injection ports installed from memory, with water injected into the engine aft of combustion to increase the volume of gas generated going thru the power turbine section. The water tank was installed behind the Pegasus engine into a V-shaped cavity rearward of the hot exhaust nozzles. They found having the methanol mix in such close proximity to the hot sections of the turbines was "sub-optimal" was the description. There was also the issue of the corrosive effect of the methanol mix on certain alloys used in the engine and injection systems from the explanation I had. The extra cost and maintenance required made this "price prohibitive" and as such while it had the capacity it was very rarely used. There were also logistical issues of carting around not one but two separate liquids (they were not supplied pre-mixed AFAIK), mixing them in the right ratios etc.

So it is bizarre that you are presenting me as an advocate of true WI, and irritating that you have manipulated quotes.

Apologies if I have given you the itches, however I only write it like I read it. No manipulation however perhaps I am simply slow and misreading what you've written. In this particular instance it was simply a discourse on what you had written here.

BTW hydrogenation, then alkylation were in worldwide use prior to WW2, even in the E Hemisphere (Sumatra, but it was then bombed), not as you said (50s).

As quoted from previous discussions:

"This chemical process is used to convert typically low octane naphthas into more valuable and usable high-octane fractions. These are called “Reformates”. The end result is a Reformate that contains hydrocarbons with more complex molecular shapes holding higher octane values than the original naphtha feedstock fractions is derived. This is all totally independent of crude feed stock source and was first implemented on a commercial scale in the 1950’s after WWII and where you seem to be gathering most of the basis for you argument."

Yes, alkylation using strong acid catalyst such as sulfuric or hydrofluoric acid as well as hydrogenation using metal catalysts such as platinum, palladium, rhodium, and ruthenium and elevated temperatures above 480C were both in use prior to 1950, perhaps in Sumatra I have no idea. However, as stated it was first first implemented on a commercial scale in the 1950’s due to the limited availability of the the precious/rare earth metals and resource priorities (gearing up to WW2) limited its use. Perhaps I should have written on "a large commercial scale" and maybe included "outside Sumatra/South East Asia" as well, however I did not say it was not used, only the scale at which is was implemented.

BTW there seems to be a surprising amount of interest in (competing?) improved methods of making 'Triptane'.

I have not looked into triptane outside of general usefulness as an anti-knock agent primarily in aviation. Care to share more??

For the record, I assume that its very high response to organometallic 'octane boosters' is of interest to the industry, having in mind a (relatively non-toxic) modern equivalent of TEL ('Lead')
(Iso-octane being relatively unresponsive to such)

As a non metallic, low toxicity octane booster, triptane would be of huge interest. Since there has been increased scrutiny of other alternatives to TEL like Methylcyclopentadienyl Manganese Tricarbonyl or MMT any possible solution that may work in replacement of TEL and MMT would be a god-send to the industry.

When all said and done, all that is written here by myself is nothing more than interested and animated technical discussion between like minded persons. I am always happy to be learned when proved wrong and will apologise no issue when it happens. Please never take anything to heart, it is simply discussion.

Cheers

Glenn

[Tommy Cookers]

Triptane is 2,2,3-trimethyl butane (not so different from 2,2,4-trimethyl pentane aka isooctane),it was discovered by Kettering's group over 80 years ago, apparently as a minor natural constituent of (US?) crude.

It is 112 octane, but very responsive to TEL .
Pump petrol, like/largely isooctane, is relatively unresponsive to TEL.
By mid WW2 Avgas had the TEL level raised to the limit of safety to give 115/145 PN

Because Triptane was very responsive to TEL, blending it eg 30/70 or 50/50 with 100/130 or 115/145 Avgas would raise the rich mixture PN to 200, 250, or even 300 (hence the name).
This meant that a supercharged test engine with boost set to give the same mep as 100 Octane on the worst (detonationwise) mixture strength, could have its boost raised on the best (detonationwise) mixture strength (ie v rich) to double or even triple the mep.
This is all based on free supercharging air from a big tank, with temperature control so cancelling any effect of evaporative cooling (Avgas already being specified for best rich mixture effects on detonation independent of cooling benefits).
There was no guarantee that real aero engines would develop such huge power increases (or that such power would be useful)

So the plan was with lots of Triptane added and the same high or max TEL, to increase compression ratios and boost for greater takeoff and emergency power combined with better range.
In WW2 the envisaged large scale production would have been critically in conflict with other production (it needed huge amounts of Chlorine).
Most of the Triptane work seems to have been done in the early postwar years.

Improved methods of Triptane manufacture seem to have been recently developed, presumably because it would attain very high octane number using trivial levels of (current or improved) non-lead organometallic octane boosters.

Europe (and the USA?) is forcing itself down the maize/wheat route to bioalcohol. This is expensive and gives little or no Carbon benefit (unlike tropical ie sugar derived bioalcohol).
Maybe we Europeans need an alternative.



Regarding the MWI, I'm (now) sure the mix you mention is the standard mix still available to both military and civil aviation (usually for hot-and high airfield conditions, try Santa Fe NM !)
In principle any turbine engine can benefit regardless of the metallurgical limits, but' as you show, there are practical considerations.

A turbine will always have spare air (beyond combustion needs), so displacement by water vapour is no problem.
In 2014 F1 (pure) WI would only be useful if injected into the combustion chamber after valve closure (to avoid such displacement), eg if emulsified with fuel. IMO
People have asked why (pure) WI is banned for 2014.

[mariano]

How much weighs a F1 gasoline litre (a litre of F1 gasoline)?

[Tommy Cookers]

IIRC the current F1 fuel rules have, amazingly, waived the established upper limit of Octane number
and introduced, amazingly, a minumum ON that some road fuel would fail (presumably to prevent the dieselisation of F1 from 2014)

high Octane fuels were primarily for aviation, the present worldwide standard originating in UK and USA 70+ years ago
this standard is the PN (performance number) rating, which goes beyond the (terrestrial) MON and RON Octane ratings
PN rating tests at a the mixture strength most inclined to detonate, and at the (richer) mixture least inclined to detonate
eg currently usual Avgas is rated 100/130 (until recently there was also 115/145 etc)
this means that it behaves like 100 Octane at normal mixture strength, but will allow 30% more mep/power with rich mixture
(by raising the induction pressure, test running being on an adjustable, temperature-standardised supply of air from a reservoir)
PN rating was related to the development of fuels that allowed greatly increased mep (supercharging) by mixture richening

where does this leave 2014 F1 ?

PN ratings suggest that mixture richening (although wasteful of fuel) will allow engines to run at higher supercharge/power, or with higher CR/efficiency at the same supercharge pressure
PN ratings should not be taken at face value, they are an effect of the type of test engine standardised for PN rating
they fairly represent the behaviour of typical WW2 and post WW2 era engines (2 valve, aircooled, 3 litres/cylinder)
showing benefit from mixture richness independent of the increased evaporative cooling (the induction mixture being conditioned to standard temperature)
but (as Sam Heron wrote c 1949), engines with better internal cooling, the RR and Allison (4 valve, liquid cooled, 2 litres/cyl)
did not need any richening at max power ie the makers regarded 115/145 fuel as if it was 145/145
(though RR were known to use richening for internal cooling)

the extensively documented benefit (to detonation resistance) would appear to be an artifact of PN ratings and earlier tests
IMO it is explicable by fuels variously evaporatively cooling after reaching the cylinder, induction temperature standardisation thereby being unable to cancel the effects of cooling
EDIT aromatics eg Toluene and Benzene show great PN gain from rich mixture (but no benefit from TEL)
and are relatively slow to evaporate
and have rather poor energy/kg
most paraffins eg Octane show no PN benefit from richening (but gain from TEL)
have better energy/kg
'Triptane' has high PN and good energy/kg (and is a legitimate ingredient in an F1 fuel blend)

aircraft engines even pre the PN era ran eg from 8% lean economy cruise, to 15% rich normal cruise and 28% rich at take-off
such general use of rich mixtures was stated to reduce thermodynamic losses due to dissociation
as well as giving consistent combustion by swamping imperfections in mixture strength


there seems no benefit to rich mixtures in F1 from 2014
(currently c 20% rich mixtures are used for much of the race, stated to help combustion at the current very high rpm)
2014 rpm and cylinder bore are so much less, combined with the direct very high pressure injection
that IMO mixtures over 1 or 2% rich amount to simply throwing fuel away
IMO as the engines will (unlike aircraft engines) run at relatively constant mep and in-cylinder temperature
the dissociation will be constant (and anyway managed by the fuel chemistry ?), and factored in to the choice of CR and boost

[seventhsin]

Haha, I can just imagine driving past a Shell and seeing the Ferrari race transporters bumper to bumper filling up hundreds of jerry cans on a monday morning

[olefud]

Maybe there’s a little more confusion that can be added to the fuel discussion. As I read the differing views they seem to be opposite sides of the same coin, i.e. fuel combustion in the IC engine.

Generic gasoline combustion is primarily driven by the state of the oxygen in the mixture. At ambient temperature and pressure the mixture is rather stable. However, as temperature and pressure increase, electrons in the oxygen move progressively into higher reaction states, or spins. When in such states the oxygen becomes a highly reactive free radical. In the highest state it produces a very rapid reaction, or detonation. In proper balance, the spark “ignites” a kernel of oxygen free radicals that progressively produce more such free radicals for an even burn.

Engine efficiency increases with increased compression ratio and power increases with a greater fuel mixture charge as through boosting, both of which increase temperature which, in turn, may promote catastrophic detonation. Water (a hydrocarbon end combustion product) or alcohol (a partially oxidized hydrocarbon) can be advantageously included in the fuel mixture despite the energy dilution if their high -water highest- heat of evaporation cools the fuel mixture below the catastrophic detonation temperature with greater boost/higher compression ratio gaining back some or more of the energy dilution. Mixture cooling is just one way of skinning the cat.

Fuel detonation resistance is provided by two differing mechanisms. TEL additive readily disassociates at relatively low temperatures and pressures yielding free lead. Lead has the quality of soaking up the oxygen free radicals, particularly the high energy ones, thereby protecting the hydrocarbon from an overly high rate of oxidation. Hydrocarbon fuels having larger, more complex structures –longer chains or cyclic- tend to have more resistance to free radical oxidation and thus are more resistant to detonation.

Av gas generally needs low vapor pressure for use at altitude. Heavier hydrocarbons fit this requirement and afford a high octane rating. But Av gas is slow burning and suitable primarily for slow turning Av engines. That’s not to say that the “competition” military engines didn’t benefit from water and/or alcohol injection or nitrous oxide injection.

[Tommy Cookers]

there might have been a case for (in 2014 F1) using a rich mixture to reduce dissociation
(which delays the release of some heat till late in the power stroke, reducing efficiency, often when we most seek it ?)

however (my guess) the race fuel people fixed this years ago, with some clever chemistry they all have and keep quiet about

only if burning was allowed post-cylinder but pre-turbine (it isn't) could a rich mixture have value