Ministers are preparing to tackle overpriced electric car charging over fears that it can cost as much to run a green vehicle as a diesel car.
Reforms set to be introduced next year will make roadside pricing for electricity – which can reach £7.50 for a half-hour charge – more consistent, so motorists are not put off buying environmentally friendly cars.
The new rules will give drivers easier access to public charge points and set common standards for pricing.
The environmental audit committee said that ministers would fall short of a target of ensuring that 9 per cent of new cars and vans were classed as ultra-low emission vehicles by 2020.
Its report predicted that without reform, green vehicles would at most account for only 7 per cent of the car and van market by 2020.
Motoring journalist and spokesman for the FairFuelUK campaign, Quentin Willson, told The Times: ‘We have seen some rapid chargers cost almost £7.50 for a half-hour charge. That strikes me as far too expensive and can almost bring costs up to a comparable level of running a diesel car.
Most motorists believe the Government should introduce technology to disable certain phone functions for the sake of safety, according to new research.
Fitting all cars with some form of blocking device was considered a more effective plan than harsher penalties or more education as road users reveal they cannot resist temptation.
The study of 1,000 UK motorists for Continental Tyres’ Vision Zero – a commitment to reduce road fatalities worldwide – uncovered that 11.3 million road users own up to using a mobile phone illegally.
Just under half of drivers (46%) admitted to researchers that they think it is OK to look at their phone when stopped or in slow moving traffic.
Reading texts, checking social media profiles and viewing emails is now more common than taking or making a phone call, meaning that as well as the evident distraction in concentration, people are taking their eyes off the road.
“Our research reveals that drivers know that their use of phones is illegal, distracting and dangerous yet they cannot help themselves,” said Continental Tyres’ safety expert Mark Griffiths.
“Nearly half, 45%, told us they struggle to be digitally disconnected and 28% felt that so many people now checked their mobile in traffic it had become normalised.”
In addition to the need to improve motorists’ behaviour, it is apparent that people want technology to help deliver the solution and enhance road safety – 66% think the Government should enforce a device to disable web-browsing, emails and the ability to send and receive texts.
Of those that admitted to breaking the current law, 31% said they had done so in the last month.
One in three drivers think the situation is getting worse and another 26% think advances in safety through new technology is being cancelled out by our unwillingness to put or phones out of reach.
Professor John Groeger, a specialist in driver psychology and author of ‘Sharing the Driving’ for Continental Tyres said: “It is really interesting that motorists want an enforced solution rather than to curb their own behaviour – yet there is no such system currently being promoted in the UK.
“It is imperative that we find a way to resolve this as the ‘switch cost’ – the critical time it takes us to shift our concentration from a task like reading a text to again fully engaging in driving is so important in reducing accidents.”
Even with the additional safety features being added to cars motorists believe the illegal use of phones when driving is decreasing road safety.
Mark Griffiths of Continental Tyres added: “There are enormous strides being made in autonomous vehicle technology to deliver even greater safety.
“Yet our study identifies that we are unsure about allowing cars to take even more control of driving. But when we recognise our obvious failing in relation to the use of phones we do want technology to step up and save us from ourselves.
“It points to the fascinating, probably unique, relationship we have with our cars and how the development of technologies is reshaping that.”
Stephen Cox blogs about Shelby American’s legendary Group 2 Mustang racers, Part 3 of 3.
John McComb ordered a new car for 1967. The choice was easy. Given his success in the 1966 Group 2 Mustang, he ordered a new notchback for 1967 to pick up where he left off with the Shelby program. The ‘67 Mustang was the model’s first major redesign and the car gained both size and weight. McComb didn’t care for either.
“Even though the ’67 car had a wider track, it was a heavier car, so I don’t really think the wider track helped,” McComb said. “The ’66 car was just a very reliable, quick car. I always thought the ’66 was better than the ’67 anyway.“
While awaiting delivery of the new car, McComb pulled his old mount out of the garage to start the new season. It still ran strong, competing at the Daytona 300 Trans-Am race on February 3, 1967 and in the 24 Hours of Daytona the following day. In March, McComb returned to familiar grounds and took second in the amateur A/Sedan race at Green Valley, and again participated in the Trans-Am event the following day. The car’s final race under McComb’s ownership was the Trans-Am at Mid-Ohio Sports Car Course on June 11th.
His new racecar became available just days later and McComb sold the #12 Group 2 Mustang to Keith Thomas, a Kansas native who had shown considerable ability winning club races throughout the region. Thomas campaigned the car against stiffening competition in the A/Sedan Midwest Division, ironically finishing second in the championship hunt only to John McComb’s new car.
This gave the #12 Group 2 Mustang a unique place in road racing history. Not only did it claim a share of John McComb’s A/Sedan championship by scoring points for McComb early in the 1967 title chase, but it also clinched second place in the same series in the hands of Keith Thomas. By virtue of Thomas’ runner-up standing in the series, the car earned a second invitation in the AARC at Daytona where it scored yet another top five finish.
Keith Thomas continued driving the #12 Group 2 Mustang in 1968 and 1969, finishing third in the series both years. Although the car was now well past its prime, Thomas set a new A/Sedan track record while winning at Wichita’s Lake Afton Raceway. He continued to rack up wins at places like Texas International Speedway, Oklahoma’s War Bonnet Park and the SCCA Nationals at Salina, Kansas throughout the late-1960s.
Now sporting a new livery, the car ran a limited schedule from 1971-73, after which it was retired from auto racing. The car traded hands later that year and again in 1978, each time distancing itself a bit more from its proud past while being repeatedly repainted and renumbered. Finally, in 1984, the car came into the possession of car collector Gary Spraggins. By this time its true identity had been lost and Spraggins was unsure of its provenance. He bought the car anyway.
Spraggins recalled that the Mustang had been repainted in “school-bus yellow” with black Le Mans stripes. There were no Shelby markings to be found anywhere on the car, but still Spraggins suspected that the vehicle might be something special. He noticed several items that were unique to Shelby GT350Rs, including the Cobra intake manifold, the Holley 715 carburetor and the A-arms that had been relocated to lower the car by one-inch. Mechanically, everything about the car screamed “Shelby” although no one really knew for sure.
The moment of truth came when Spraggins took the car home for a closer inspection. “When I raised the trunk lid up, of course, the inside of the trunk area was black, but you could see the Le Mans stripes overspray down in there,” Spraggins remembered.
“Oh, man, I knew what those colors represented – Shelby cars. And I got some paint remover and lightly put it over the black Le Mans stripe on the trunk and wiped it off, and there was the prettiest blue Le Mans stripe there. It’s like, oh, my gosh!”
Spraggins immediately wrote to the Shelby American Automobile Club, describing the car and asking if the VIN could be verified as a Shelby product. The response came on November 12th.
“Looks like you’ve found one of the original Shelby 1966 Trans-Am cars,” the letter began. “Your car was originally sold to Turner Ford in Wichita, KS. I think they may still be in business…”
SAAC national director, Rick Kopec, signed the letter. And so did Carroll Shelby.
Spraggins could barely contain his enthusiasm and quickly set to work restoring the car to its original 1966 livery and condition, not realizing that an aging John McComb had also entertained the idea of finding his old mount. He just didn’t know where to look.
“I was very excited at that time that I had found a needle in a haystack,” Spraggins said. “Nobody knew anything about these cars, so in order to track down the original driver – you know, John McComb – I just started calling information in the Wichita area.”
On a hot summer afternoon in late-July 1985, the telephone on John McComb’s desk rang again. On the other end was car collector Gary Spraggins calling with the surprising news that his famous #12 Group 2 Mustang had been found. When McComb saw photos of the newly restored Mustang, he said, “My immediate reaction was, ‘That’s my car!’ What a super job you have done on it.”
When asked to critique the restoration and help them convert the car to its precise 1966 condition, McComb confessed to a pair of secrets that he’d kept for nearly 30 years.
“We cheated in two places on the bodywork. One was on the lower front valance where the license plate goes. We took those two little tabs off and opened it up a little. We also opened up the front fenders just a little. We rolled the inner lip around a welding rod to give it more strength for nerfing. We never got caught on either one.”
Eventually, even Carroll Shelby was reunited with the newly restored #12 Group 2 Mustang at a car show in the mid-1990s. He recognized it instantly. “This was the last year I was really interested in racing,” he lamented to Mustang Monthly.
“We had won Le Mans in 1966 and then the Trans-Am series came along. A lot of our good guys had moved on to other things because we had been winning for so many years.”
When it came to North American road racing, the Group 2 Mustangs were Shelby’s last stand. Largely forgotten by car collectors worldwide, these amazing racecars won the first Trans-Am title for Ford and were among the most dominant sportscars their era. They left an indelible imprint on the American road-racing scene of the 1960s. Then they simply disappeared.
Standing at the car’s freshly repainted rear fender, Shelby crossed his arms, took one last glance at the #12 Group 2 Mustang and gave a long sigh. “After 1966, we were concentrating on building volume. Unfortunately, the racing programs didn’t have much priority after this.”
NOTE:All photos are courtesy of Mecum Auctions. The driver in the cockpit photo is owner/driver John McComb preparing for a race in the late-1960s.
The friction generated by an automobile tyre is crucially dependent upon the roughness of the road surface over which the tyre is moving. The theoretical representation of this phenomenon developed by the academic community over the past 20 years has been largely predicated on the assumption that the road can be represented as a statistically self-affine fractal surface. The purpose of this article is to explain what this means, but also to question whether this assumption is in need of some generalisation.
To begin, we need to understand two concepts: the correlation function and the power spectrum of a surface.
Surfaces in the real world are not perfectly smooth, they’re rough. Such surfaces are mathematically represented as realisations of a random field. This means that the height of the surface at each point is effectively sampled from a statistical distribution. Each realisation of a random field is unique, but one can classify surface types by the properties of the random field from which their realisations are drawn. For example, each sheet of titanium manufactured by a certain process will share the same statistical properties, even though the precise surface morphology of each particular sheet is unique.
Let us denote the height of a surface at a point x as h(x). The height function will have a mean <h(x)> and a variance. (Here and below, we use angular brackets to denote the mean value of the variable within the brackets). The variance measures the amount of dispersion either side of the mean. Typically, the variance is calculated as:
Var = <h(x)2> − <h(x)>2
Mathematically, the height at any pair of points, x and x+r, could be totally independent. In this event, the following equation would hold:
<h(x)h(x+r)> = <h(x)2>
The magnitude of the difference between <h(x)h(x+r)> and <h(x)2> therefore indicates the level of correlation between the height at points x and x+r. This information is encapsulated in the height auto-correlation function:
ξ(r) = <h(x)h(x+r)> − <h(x)2>
Now the auto-correlation function has an alter-ego called the power spectrum. This is the Fourier transform of the auto-correlation function. It contains the same information as the auto-correlation function, but enables you to view the correlation function as a superposition of waves with different amplitudes and wavelengths. Each of the component waves is called a mode, and if the power spectrum has a peak at a particular mode, it shows that the height of the surface has a degree of correlation at certain regular intervals. Related to the auto-correlation function is the height-difference correlation function:
C(r) = <(h(x+r)−h(x))2>
This is essentially the variance in height as a function of distance from an arbitrary point x. This is a useful function to plot graphically because it represents the difference between the auto-correlation function and the overall variance, as a function of distance r from an arbitrary point x:
C(r) = 2(Var−ξ(r))
Which brings us to self-affine fractal surfaces. For such a surface, a typical height-difference correlation function is plotted below, (Evaluation of self-affine surfaces and their implications for frictional dynamics as indicated by a Rouse material, G.Heinrich, M.Kluppel, T.A.Vilgis, Computational and Theoretical Polymer Science 10 (2000), pp53-61).
Points only a small distance away from an arbitrary starting point x can be expected to have a height closely correlated with the height at x, hence C(r) is small to begin with. However, as r increases, so C(r) also increases, until at a critical distance ξ||, C(r) equals the variance to be found across the entire surface. Above ξ||, C(r) tends to a constant and ξ(r) tends to zero. ξ|| can be dubbed the lateral correlation length. In road surfaces, it corresponds to the average diameter of the aggregate stones.
To understand what a self-affine fractal surface is, first recall that a self-similar fractal surface is a surface which is invariant under magnification. In other words, the application of a scale factor x → a⋅x leaves the surface unchanged.
In contrast, a self-affine surface is invariant if a separate scale factor is applied to the horizontal and vertical directions. Specifically, the scale factor applied in the vertical direction must be suppressed by a power between 0 and 1. If x represents the horizontal components of a point in 3-dimensional space, and z represents the vertical component, then it is mapped by a self-affine transformation to x → a⋅x and z → aH⋅z, where H is the Hurst exponent. In the height-difference correlation function plotted above, the initial slope is equal to 2H, twice the value of the Hurst exponent.
Note, however, that a road surface is considered to be statistically self-affine surface, which is not the same thing as being exactly self-affine. If you zoomed in on such a surface with the specified horizontal and vertical scale-factors, the magnified subset would not coincide exactly with the parent surface. It would, however, be drawn from a random field possessing the same properties as the parent surface, hence such a surface is said to be statistically self-affine.
Attempts have been made within the academic literature to adopt the self-affine model of surface roughness to road surfaces, which are known to be characterised by two distinct length-scales: the macroscopic one determined by the size of aggregate stones, and the microscopic one determined by the surface properties of those stones. One such attempt, which introduces two distinct Hurst exponents, is shown below, (Investigation and modelling of rubber stationary friction on rough surfaces, A.Le Gal and M.Kluppel, Journal of Physics: Condensed Matter 20 (2008)):
This doesn’t seem quite right. The macro-roughness of a road surface is defined by the morphology of the largest asperities in the road, the stone aggregate. Yet as the authors above state themselves, a road surface only displays self-affine behaviour “within a defined wave length interval. The upper cut-off length is identified with the largest surface corrugations: for road surfaces, this corresponds to the limit of macrotexture, e.g. the aggregate size.”
It’s not totally clear, then, whether the macro-roughness of a road surface falls within the limits of self-affine behaviour, or whether it actually defines the upper limit of this behaviour. At first sight, the notion that a road surface is statistically self-affine seems to have been empirically verified by the correlation functions and power spectra taken of road surfaces, but perhaps there’s still some elbow-room to suggest a generalisation of this concept.
For example, consider mounded surfaces. These are surfaces in which there are asperities at fairly regular intervals. In the case of road surfaces, this corresponds to the presence of aggregate stones at regular intervals. Such as surface resembles a self-affine surface in the sense that it has a lateral correlation length ξ||. However, there is an additional length-scale λ defining the typical spacing between the asperities, as represented in the diagram below, (Evolution of thin film morphology: Modelling and Simulations, M.Pelliccione and T-M.Lu, 2008, p50).
In terms of a road surface, whilst ξ|| characterizes the average size of the aggregate stones, λ characterizes the average distance between the stones.
In terms of the height-difference correlation function C(r), a mounded surface resembles a self-affine surface below the lateral correlation length, r < ξ||. However, above ξ||, where the self-affine surface has a constant profile for C(r), the profile for a mounded surface is oscillatory (see example plot below, ibid. p51). Correspondingly, the power spectrum for a mounded surface has a peak at wavelength λ, where no peak exists for a self-affine surface.
The difference between a mounded surface and a genuinely self-affine surface is something which will only manifest itself empirically by taking multiple samples from the surface. Individual samples from a self-affine surface will show oscillations in the height-difference correlation function above the lateral correlation length, but the oscillations will randomly vary from one sample to another. In contrast, the samples from a mounded surface will have oscillations of a similar wavelength, (see plots below, from Characterization of crystalline and amorphous rough surface, Y.Zhao, G.C.Wang, T.M.Lu, Academic Press, 2000, p101).
Conceptually, what’s particularly interesting about mounded surfaces is that they’re generalisations of the self-affine surfaces normally assumed in tyre friction studies. Below the lateral correlation length-scale ξ||, a mounded surface is self-affine (M.Pelliccione and T-M.Lu, p52). One can say that a mounded surface is locally self-affine, but not globally self-affine. Note that whilst every globally-affine surface is locally self-affine, not every locally self-affine surface is globally self-affine.
A self-affine road surface will have aggregate stones of various sizes and separations, whilst a mounded road surface will have aggregate stones of similar size and regular separation.
In fact, one might hypothesise that many actual road surfaces in the world are locally self-affine but not globally self-affine. For this to be true, it is merely necessary for there to be some regularity in the separation of aggregate within the asphalt. If the distance between aggregate stones is random, then a road surface can indeed be represented as globally self-affine. However, if there is any regularity to the separation of aggregate, then the surface will merely be locally self-affine. If true, then existing academic studies of tyre friction have fixated on a special case which is a good first approximation, does not in general obtain.
The story of BMW’s turbo ‘rocket fuel’ has long since passed into Formula 1 legend, but there’s a longer and deeper story here, involving the German war effort, some organic chemistry, and the history of oil refining techniques. But let’s begin with the legend, and the breakthrough which enabled the Brabham-BMW of Nelson Piquet to win the 1983 Drivers’ Championship:
[BMW motorsport technical director, Paul] Rosche telephoned a contact at chemicals giant BASF and asked if a different fuel formulation might do the trick. After a little research, a fuel mix was unearthed that had been developed for Luftwaffe fighters during World War II, when Germany had been short of lead. Rosche asked for a 200-litre drum of the fuel for testing and, when it arrived, he took it straight to the dyno.
“Suddenly the detonation was gone. We could increase the boost pressure, and the power, without problems. The maximum boost pressure we saw on the dyno was 5.6 bar absolute, at which the engine was developing more than 1400 horsepower. It was maybe 1420 or 1450 horsepower, we really don’t know because we couldn’t measure it — our dyno only went up to 1400.” (‘Generating the Power’, MotorsportMagazine, January 2001, p37).
An aromatic hydrocarbon called toluene is commonly held to have been the magic compound in this fuel brew, but erstwhile Brabham chief mechanic Charlie Whiting goes further:
“There were some interesting ingredients in it, and toluene has been mentioned. But it would have had far more exciting things in it, I think, than toluene. I suspect – well, I know – that it was something the BMW engineers had dug out of the cupboard from the Second World War. Almost literally rocket fuel,” (‘Poacher Turned Gamekeeper’, MotorsportMagazine, December 2013, p74).
Before we delve into the chemistry of fuels, let’s establish some context here. The current F1 turbo engine regulations require detonation-resistant fuels with a high calorific value per unit mass. Detonation resistance enables one to increase the compression ratio, and thereby increase the work done on each piston-stroke, while the limits on total fuel mass and fuel mass-flow rate require fuel with a high energy content per unit mass.
In contrast, in the 1980s the regulations required detonation-resistant fuels with a high calorific value per unit volume. From 1984, the amount of fuel permitted was limited, but the limitation was defined in terms of fuel volume rather than mass, hence fuel with a high mass-density became advantageous. By this time, the teams had already followed BMW’s lead and settled upon fuels with a high proportion of aromatic hydrocarbons.
To understand the significance of this, we need to start with the fact that there are four types of hydrocarbon:
(i) Paraffins (sometimes called alkanes) (ii) Naphthenes (sometimes called cycloalkanes) (iii) Aromatics (sometimes called arenes) (iv) Olefins (sometimes called alkenes)
Methane, ethane and propane. Each larger disk represents a carbon atom; each white disk represents a hydrogen atom; and each black disk represents a covalent bond.
Each hydrocarbon molecule contains hydrogen and carbon atoms, bound together by covalent bonds. The hydrocarbon types differ from each other by the number of bonds between adjacent atoms, and by the overall topology by which the atoms are connected together. So let’s briefly digress to consider the nature of covalent bonding.
The electrons in an atom are stacked in so-called ‘shells’, each of which can contain a maximum number of members. The first shell can contain only two electrons, while the second can contain eight. If the outermost electron shell possessed by an atom is incomplete, then the atom will be disposed to interact or bond with other atoms.
A neutral hydrogen atom has one electron, so its one and only shell needs one further electron to complete it. A neutral carbon atom has six electrons, two of which fill the lowermost shell, leaving only four in the next shell. Hence, another four electrons are required to complete the second shell of the carbon atom.
In covalent bonding, an electron from one atom is shared with an adjacent atom, and the adjacent atom reciprocates by sharing one of its electrons. This sharing of electron pairs enables groups of atoms to complete their electron shells, and thereby reside in a more stable configuration. In particular, a carbon atom, lacking four electrons in its outermost shell, has a propensity to covalently bind with four other neighbours, while a hydrogen atom has a propensity to bind with just one neighbour. By this means, chains of hydrocarbons are built.
Methane, for example, (see diagram above) consists of a single carbon atom, bound to four hydrogen atoms. The four shared electrons from the hydrogen atoms complete the outermost shell around the carbon atom, and each hydrogen atom has its one and only shell completed by virtue of sharing one of the carbon atom’s electrons.
If there is a single covalent bond between each pair of carbon atoms, then the hydrocarbon is said to be saturated. In contrast, if there are more than one covalent bond between a pair carbon atoms, the molecule is said to be unsaturated.
Saturated ethane in a state of unconcealed glee compared to the glum unsaturated ethylene, and the vexatious triple-bonded acetylene, (this and the above taken image from ‘BP – Our Industry’, 1958, p69).
Now, to return to our classification scheme, paraffins are non-cyclic saturated chains, (there is a sub-type called iso-paraffins in which the chain contains branching points); naphthenes are cyclic saturated chains; aromatics are cyclic (semi-)unsaturated chains; and olefins are non-cyclic unsaturated chains, (with a sub-type of iso-olefins in which the chains have branching points).
Aromatic compounds possess a higher carbon-to-hydrogen ratio than paraffinic compounds, and because the carbon atom is of greater mass than a hydrogen atom, this entails that aromatic compounds permit a greater mass density. This characteristic was perfect for the turbo engine regulations in the 1980s, and toluene was the most popular aromatic hydrocarbon which combined detonation-resistance and high mass density.
To put toluene into context, we need to begin with the best-known aromatic hydrocarbon, benzene. This is a hexagonal ring of six carbon atoms, each one of which is bound to a single hydrogen atom. Toluene is a variant of this configuration in which one of those hydrogen atoms is replaced by a methyl group. The latter is one of the primary building blocks of hydrocarbon chemistry, a single carbon atom bound to three hydrogen atoms. The carbon atom in a methyl group naturally binds to another carbon atom, in this case one of the carbon atoms in the hexagonal ring. Hence toluene is also called methyl-benzene.
Closely related to toluene is xylene, another variant of benzene, but one in which two of the hydrogen atoms are replaced by methyl groups. (Hence xylene is also called dimethyl-benzene). If the two methyl groups are bound to adjacent carbon atoms in the ring, the compound is dubbed o-xylene; if the docking sites of the two methyl groups are separated from each other by two steps, then the result is dubbed m-xylene; and if the docking sites are on opposite sides of the ring, the compound is called p-xylene.
Most teams seem to have settled on the use of toluene and xylene. By mid-season 1987, for example, Honda “reached an 84% level of toluene,” (Ian Bamsey, McLaren Honda Turbo – A Technical Appraisal, p32).
With respect to the Cosworth turbo used by Benetton in 1987, Pat Symonds recalls that “the problem was the engine had been developed around BP fuel, and we had a Mobil contract. Fuels then weren’t petrol, they were a chemical mix of benzene, toluene and xylene. We kept detonating pistons, and it wasn’t until mid-season that we got it right,” (Lunch with Pat Symonds, MotorsportMagazine, September 2012). In fact, Pat attests that the Cosworth fuel was an equal mix of benzene, toluene and xylene, (private communication).
At Ferrari, AGIP later recalled that their toluene and xylene based fuel reached density values of up to 0.85, in some contrast with the paraffinic fuels of the subsequent normally-aspirated era, with density values of 0.71 or 0.73. “Given the ignition delays of heavy products, we had to add more volatile components that would facilitate that ignition,” (Luciano Nicastro, Head of R&D at AGIP Petroli, ‘Ferrari Formula 1 Annual 1990’, Enrico Benzing, p185).
Renault, in contrast, claim to have used mesitylene, as Elf’s Jean-Claude Fayard explains:
“We found a new family of hydrocarbons which…contained a strong proportion of mesitylene [trimethyl-benzene] and they had a boiling point of 150C, but with a combustion capability even higher than that of toluene,” (Alpine and Renault, Roy Smith, p142).
Mesitylene is a variant of benzene in which three methyl groups are docked at equal intervals around the hexagonal carbon ring, (naturally, mesitylene is also called trimethyl-benzene).
Now, the fact that Paul Rosche grabbed a barrel of aviation fuel used by the Luftwaffe is significant because German WWII aviation fuel differed substantially from that used by the allies. Faced with limited access to crude oil, and a poorly developed refining industry, the Germans developed war-time aviation fuels with a high aromatic content.
Courtesy of the alkylation process, the original version of which was developed by BP in 1936, the allies could synthesise iso-octane from a reaction involving shorter-chain paraffins, such as iso-butane, and olefins such as butene or iso-butene. By definition, iso-octane has an octane rating of 100, defining the standard for detonation-resistance. Using 100-octane fuel synthesised by the alkylation process, the British were able to defeat the Luftwaffe in the 1940 Battle of Britain.
In contrast, German aviation fuel was largely obtained from coal by applying hydrogenation processes. With limited capacity to produce paraffinic components, the initial B-4 grade of aviation fuel used by the Germans had an octane range of only 87-89, a level which itself was only obtained with the addition of the anti-detonation agent, Lead Tetra-Ethyl. A superior C-3 specification of aviation fuel was subsequently produced, with an octane rating of 95-97, but only by substantially increasing the proportion of aromatic hydrocarbons:
“The B-4 grade…contained normally 10 to 15 percent volume aromatics, 45 percent volume naphthenes, and the remainder paraffins…The C-3 grade was a mixture of 10 to 15 percent volume of synthetic isoparaffins (alkylates and isooctanes)…[and] not more than 45 percent volume aromatics,” (US Navy, Technical Report No. 145-45. Manufacture of Aviation Gasoline in Germany, Composition and Specifications).
The Germans, however, also included some interesting additives:
“The Bf 109E-8’s DB601N engine used the GM-1 nitrous oxide injection system…Injected into the supercharger inlet, the gas provided additional oxygen for combustion at high altitude and acted as an anti-detonant, cooling the air-fuel mixture,” (‘The Decisive Duel: Spitfire vs 109’, David Isby).
“Additional power came from water-methanol and nitrous-oxide injection,” (‘To Command the Sky: The Battle for Air Superiority over Germany, 1942-44‘, Stephen L.McFarland and Wesley Phillips, p58).
At which point, one might recall Charlie Whiting’s suggestion that the 1983 BMW fuel brew “had far more exciting things in it”than toluene. This, despite regulations which explicitly stated that fuel should be 97% hydrocarbons, and should not contain “alcohols, nitrocompounds or other power boosting additives.” Still, there’s breaking the rules, and then there’s getting caught breaking the rules. Perhaps BMW were a little naughty in 1983, before settling down with an 80% toluene brew.
The current turbo regulations, however, require a much lower aromatic content, stipulating the following maxima:
Aromatics wt% 40 Olefins wt% 17 Total di-olefins wt% 1.0 Total styrene and alkyl derivatives wt% 1.0
Which entails, in a curious twist, that the current maximum aromatic content almost matches that of the C-3 aviation fuel developed in war-time Germany…