BMW’s F1 ‘rocket fuel’ and aromatic hydrocarbons

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…


Proof that Formula 1 was better in the past

If you’re a long-time Formula 1 fan, then the chances are that you believe the sport was better in the past. However, the chances are that you will have also read arguments from younger journalists and fans, to the effect that Formula 1 in the modern era is better than it was in the past.

Fortunately, there is an objective means to resolve this dispute: churn.

In sport, churn provides a straightforward measure of the uncertainty of outcome. Churn is simply the average difference between the relative rankings of the competitors at two different measurement points. One can measure the churn at an individual race by comparing finishing positions to grid positions; one can measure the churn from one race to another within a season by comparing the finishing positions in each race; and one can measure the inter-seasonal churn by comparing the championship positions from one year to another.

The latter measure provides an objective means of tracking the level of seasonal uncertainty in Formula 1, and F1 Data Junkie Tony Hirst has recently compiled precisely these statistics, for both the drivers’ championship and the constructors’ championship, (see figures below). In each case, Hirst compiled the churn and the ‘adjusted churn’. The latter is the better measure because it normalises the statistics using the maximum possible value of the churn in each year. The maximum can change as the number of competitors changes.

The results for the drivers’ championship indicates that churn peaked in 1980. Given that the interest of many, if not most spectators, is dominated by the outcome of the drivers championship, this suggests that Formula 1 peaked circa 1980.

The results for the manufacturers’ championship are slightly different, suggesting that uncertainty peaked in the late 1960s, (although the best-fit line peaks in the middle 1970s).

One could, of course, make the alternative proposal that the churn within individual races is more important to spectators’ interest, but at the very least we now have an objective statistical measure which provides good reason for believing that Formula 1 was better in the 1970s and early 1980s.

Source: mccabism

Qatar GP: Dovizioso and Crutchlow finish the race in fifth and sixth

The two Ducati Team riders, Andrea Dovizioso and Cal Crutchlow, finished the Qatar GP at Losail, the opening round of the 2014 MotoGP World Championship, in fifth and sixth place respectively.
Andrea Dovizioso, Duc … Keep reading


Another step forward for Scott in Malaysia

Scott Redding successfully completed the third and final day of testing at Sepang, aboard the Honda RCV1000R that he will campaign in Team GO&FUN Honda Gresini colours in this year’s MotoGP World Championship.
Keep reading

Special thanks to:

Ferrari plan ‘Red’ rally for Michael Schumacher

While Michael Schumacher remains in critical condition, Ferrari have announced via their Facebook page that they would like to host a silent and respectful rally at the hospital in Grenoble to honor the 7-time champion on his birthday Friday January 3rd.

“In these difficult days and on the occasion of his birthday the SCUDERIA FERRARI CLUBS want to show their support for MICHAEL SCHUMACHER, organising tomorrow a silent and respectful event all in Red at the Grenoble University Hospital Center.”

Schumacher remains in critical condition today and the hospital is planning no media updates. That does bring to mind the notion that the hospital does have other patients and duties and should the event garner a large participation, it could be challenging for the hospital to manage.

I would hope the Ferrari clubs will also provide some sort of crowd management and security for the event. We’ve already seen a journalist impersonate a priest in order to try and sneak into Schumacher’s room so having a throng of ardent fans may be a challenge as well.

Having a throng of supporters is most likely appreciated by Corinna but at this moment, the only thing she’s likely to really care about is her husband.