This is now a fuel composition debate rather than an F1 engine relevance debate, however it seems interesting so here we go.
Tommy Cookers wrote: No 'pump fuel' has or ever has had any spec for effect of mixture strength (independent of temperature) on detonation (and thereby on power from a forced induction engine).
I would have to disagree with this.
Firstly, I would like to know how you can make that definite assumption as modern pump fuels are definitively produced with detonation resistance due to reduced mixture strength as a primary goal which gives evidence that is in direct conflict with your statement.
Never-the-less, as you seem preoccupied with Avgas and early 20th century ICE's, the addition of tetraethyl lead into pump fuels goes as far back as the 1920’s where it was used as an inexpensive agent to increase fuel octane ratings, which allowed for engine compression ratios to be increased, more advantageous ignition timing to be used
AND mixtures to be leaned off, all of which increased power and economy. This specifically resulted and allowed the reduction of mixture strength.
Secondly, various international regulations have specifically required fuels that provide the ability for leaner burning engines (Japan, Australia and the State of California in the USA for instance), which in turn require detonation resistance due to “lean mixture strength”. The proliferation of these high efficiency engines has required specific types of higher octane pump fuels to be available where they are in usage.
Additionally, “Clean Air” policies have now mandated that “pump fuels” are of specific compositions and octane (RON/MON) values to allow for exactly what you are saying these fuels have not set out to achieve. This is a specification to allow detonation resistance at mandated leaner mixtures.
Unleaded fuels which cannot rely on tetraethyl lead have resorted to various means to specifically increase fuel detonation resistance to allow for these lean burning requirements and not those mixture strengths related to out dated and out modded engines such as to those seen in 1917, WWI and WWII automotive and aircraft engines.
If this is not the case, what has been the basis for refineries producing more expensive and complex pump fuels of increased octane from the usually prevalent leaded 91 octane to now ubiquitous unleaded 95, 98, 99 and 100 octane blends and even the ethanol based 108+ rated E85 fuels. These fuels were specifically provided after regulatory mandate to allow leaner burning engines (reduction in pollution) which require leaner mixtures that necessitate increased detonation resistance.
Tommy Cookers wrote: Although in principle all fuels show such a benefit, the effect is highly variable with composition eg source of crude. The huge research that led to the mandatory RON then MON was driven by this; aircraft engines around 1917 had huge problems at full power with the introduction of fuel from Western hemisphere (US) crude. RON & MON intentionally disengage from this effect.
I am not sure why you are repeatedly showing anecdotal evidence from the very early to mid 20th century, however current requirements and technologies have moved on. Variation based on crude feed stock with modern thermal decomposition and catalyst derived cracking technologies are now considerably more efficient. This includes Catalytic Reformation or Reforming.
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.
As such, the largest issue with crude feed stock variation is the efficient production of the resulting end-product (fuel) for specific short to medium hydrocarbon chains (fractions) as a percentage of feed stock utilised, rather than any individual issue with specific qualities of hydrocarbon compositions.
Different feed stocks will allow for more or less efficient production of a higher or lower percentage quantity of certain short to medium hydrocarbon fractions. The quality of these fractions is rarely impacted, only the quantity produced. Poor quality feed stock generally results in greater numbers of the longer chain hydrocarbon fractions that cannot be cracked like bitumen etc due to impurities.
Personally, I fail to see the relevance of a 1917 issue that resulted in the RON/MON classifications which are present today. By their very existence, they negate the argument and are not relevant. Modern fuels are governed legislative mandate based on specific RON/MON rating requirements, not the will and whim of the refineries.
Tommy Cookers wrote: Today's Avgas was designed (for British air defence ie short range use) in 1936 to maximise the effect, and was thus difficult to make from US crude, hence at that time required a novel process (not needed today, especially with Far East crude? ).
Today’s Avgas is not classified as a “commercially available pump fuel” by regulation and is therefore specifically outlawed for road use in most countries and even for use in motorsport in most others. This is specifically due to the tetraethyl lead content of the fuel. Today’s Avgas has a very different profile (to my understanding of previous incarnations) as both the currently commercially available variations have lower concentrations of tetraethyl lead than previously found.
Tommy Cookers wrote: The spec is 100/130 PN , this means that with best enrichment 30% more mep and power can be obtained supercharged from Avgas that tests like 100 Octane when supercharged at a disadvantageous mixture strength. The US fuel at that time tested at 100/108 PN or so.
Agreed, they still conform to pre-determined mixture ratio requirements of 100/130, however this is more a case of regulatory standardization that the use of feed stock which has zero bearing on the end product, only the quanity oif the end product produced. The use of Far East crude coupled with modern distillation techniques allow for greater purities, if not greater quantities, of certain fractions and control during the blending of the end product fuel.
Tommy Cookers wrote: 100/130 became the standard, even a country making Avgas from coal followed this. Some British planes had takeoff power increased in 1940 from 1050 to 1310 bhp by adjustment only of automatic throttles (and carburation ?) to allow higher mep. Fuel consumption was of course increased.
Yep OK, I agree on the standardization however my knowledge doesn’t extend to 1940’s aircraft so defer to your experience.
Tommy Cookers wrote: F1 ran on this fuel in 1958-1960 (with little or no power gain, as naturally aspirated).
OK, but they sure couldn’t run on Avgas now due to tetraethly lead content, simple.
As for any power gain, a modern NA engine with digital control would allow for increases in compression ratio to take advantage of the increased detonation resistance. Of course, simply pouring a higher octane fuel into a carburetor based engine not designed to take advantage of it will give a net small or no increase in performance, even with mixtures adjusted.
Tommy Cookers wrote: Presumably some of the benefit with mixture richness is from the TEL (so what ?) We've had this Avgas in the low lead version for 40 years now (for the benefit of light aircraft engines not designed for high lead content). It's still 100/130 PN. Lower grade are/were 80/87 PN and 91/98 PN(still leaded but specifying only minimal effect of richness). So there's some value in the use of 100/130 Avgas in supercharged engines.
Avgas is generally less dense than most racing fuels and modern pumps fuels, and as a result, tuners must compensate by resorting to richer mixtures when using to Avgas. Avgas also has a very different hydrocarbon profile to optimize volatility properties at high altitude and can contain high level of aromatics, which can contribute to poor throttle response when used in engines that require constant throttle variations which typically aviation engines due not. They generally are required to run at long periods and stable RPM's and as such, throttle response is a secondary concern.
Another primary differential is Avgas' octane quality. Avgas is short on octane compared to modern fuels due to the specific requirements for high altitude use. Inadequate 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.
All being said, Avgas, today/right now, is not a standard pump fuel (unless you are fueling an aircraft at an aerodrome or have specific licensing permits to purchase in bulk for distribution depots) and will never return to usage as a staple in motorsport or as a road legal fuel. It is even outlawed in amateur level motorsport classes in some countries. The tetraethyl lead content will always see to this.
Tommy Cookers wrote: Avgas may have less margin when rich for imperfect carburation (eg with a race camshaft) causing poor combustion due to further (accidental) richness, alcohols may be more tolerant of this.
OK again, however, motorsports is not aviation nor does it require operation at altitude or ensure as close to perfect reliability as possible. A person’s existence does not rely on it in motorsport as it does in aviation. At worse it’s a long walk home, not a long fall from 15,000 feet. Regardless of this, digital fuel, ignition and knock control as well as closed loop running allow for reduced concerns such as those above.
Tommy Cookers wrote: Regarding the benefits of evaporative cooling (eg with alcohol), every molecule evaporated causes cooling, so EC is largely generated by the basic fuelling (extra fuel causes some more cooling which could be useful of course).
Again, I strongly disagree.
Yes, every molecule that “evaporates” removes heat from its surrounding area agreed. However, I again disagree with your assertion that this “
is largely generated by the basic fuelling” or more correctly base fueling.
EC is a tool used specifically when the base heat loads that appear under high load conditions and in which base fueling is insufficient requiring additional fuel to increase net effect of fuel evaporation to control temperatures.
So EC is primarily a tool used by the implementation of overly rich mixtures within the fuel tables. If this was largely achieved by “base” fueling, there would be no need to force overly rich mixtures (10.5:1 or greater, way outside the optimum 14.7:1 to 12.5:1 generally accepted) under load when in cylinder heat management becomes an issue.
What you are saying 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 OEM and motorsport engine tuners are simply pouring extra fuel into the combustion process for no net tangible benefit.
As said I strongly disagree and have substantial experience garnered while testing various engines at various states of tune that definitively shows otherwise, especially where forced induction is utilised.
Tommy Cookers wrote: Toluene; I could believe that it was introduced as part of the fuel blend to allow higher powers with turbo etc development without having to redesign the car for greater tankage (in 1988 I heard forecast a 38 bhp immediate gain to Williams for Hungary). Presumably this blend didn't need heating. I don't think they went straight at very high Toluene content, but that it soon progressed to a point where the teams were vulnerable to rule changes (to contain power growth).
Toluene was certainly used in F1 fuels as an anti detonation agent and rose to prominence during the turbo era. This is an undisputed and inconsequential fact.
Tommy Cookers wrote: I don't think it is outstanding apart from its density (ie more power for 280 litres not more power for say 200 kg). What matters is the heat content of the amount of fuel burn allowed by a cylinderful of air.
Toluene has many advantages for forced induction engines aside from energy value.
Yes, Toluene is denser than ordinary pump fuel (0.87 g/mL vs. 0.72-0.74gr/ml) with a higher caloric content per unit volume {standard molecular entropy of 220.6J/(mol K)}and high latent heat of evaporation being 351kJ/kg vs. Heptane at 318kJ/kg. Toluene also compares favorably against oxygenated fuel types such as ethanol or MTBE, which contain lower energy per unit volume when compared to pump fuel.
The high calorific content of Toluene results in higher exhaust temperatures which contain more kinetic and thermal energy available for harvesting by the turbine of the turbo. This provides the practical effect of allowing larger A/R housings without detrimental effects to boost response or boost threshold usually associated with large A/R turbine housings on small capacity engines.
Additionally, as Toluene has a RON octane rating of 121 and a MON rating of 107, it is catagorised as a low sensitivity fuel with a sensitivity rating of 14 (121-107=14), which compares well against alcohol fuels such as ethanol and methanol which have sensitivities in the 20-30 range. All this results in a fuel that matches the performance profile for a heavily loaded engine which maybe prone to detonation, such as forced induction engines running high boost pressures.
The high octane allows the use of more favourable ignition tables before retardation is required due to the onset of detonation, which is detectable by the ECU via “knock sensors” that can be set on a per cylinder basis. This also allows the use of higher static compression ratios in forced induction engines as seen by the increase over the past 20 years where standard engines have gone from 7.0:1 up to and in excess of 10.0:1 for standard road cars due to fuel detonation resistance and ability to run on "
leaner mixtures".
Tommy Cookers wrote: It was ok costwise and hazardwise in my school chemistry days. There's a lot of lurid but vague 'information' from one basic source, unqualified to write on such subjects. IMO of course There's a lack of solid 'who did what,when' type information.
I am not sure when you went to school, but i sounds like a long time ago (no offense).Toluene is definitively not OK in school chemistry now without substantial precautions.
Toluene is rated as:
1: Teratogenic (reproductive toxicity);
2: Mutagenic (genetic toxicity);
3: Carcinogenic (cancer causing); and
4: A strong skin irritant.
It can be absorbed through inhalation (acute vapor toxicity) and skin contact and as such requires a respirator at a minimum and usually goggles, gloves and protective clothing.
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