Rumblings, August 1940
Racing Fuels
WE should really be most thankful that after nearly a year of war we can still obtain petrol for a certain amount of motoring, and that the price of this precious fluid has not risen excessively. Petrol is strictly rationed and has depreciated materially in octane value, because our mechanised fighting units burn this fuel in very large quantities. It is a profound thought that if modern aero-engines ran on fuels of the sort that have been deemed essential for first-line racing cars for the past seventeen years, doubtless we should now be able to tank-up with good fuel, just as if the war had never happened. Modern racing fuels contain some 50 per cent. and upwards of alcohol for ordinary racing, and sprint fuels approach a 100 per cent. alcohol content. A fuel composed of 60 per cent. methyl alcohol, 30 per cent. benzole and 10 per cent. aviation petrol is generally suitable for a racing engine with a b.m.e.p. of 180-200 lbs. per square inch. For sprint or short record runs the alcohol content may be increased at the expense of the benzole, but for normal racing this would be likely to result in damping out after corners, and, fortunately, the let-up for cornering will compensate for the lower cooling characteristics of the fuel. The Derby-Miller which Mrs. Stewart used to handle so successfully was started on straight petrol, and the throttle could not be fully opened until the alcohol fuel was brought in. Even so, alcohol fuel used to deposit in the lower part of the centrifugal blower casing to an extent sufficient to cause corrosion, and the casing had to be drained carefully before the car was put to bed. Similar trouble was experienced in a Schneider Trophy Napier “Lion” motor, in which the magnesium alloy filters disintegrated; they were replaced in gun-metal. In spite of this shortcoming, starting difficulties, and the very heavy consumption because so much is only coolant, alcohol is the base of modern racing fuels and is responsible for the very high output possible from present-day racing engines. Its use was favoured by motorcyclists at Brooklands around 1922, and at this period the famous 3-litre T.T. Vauxhall cars were run on an alcohol-blended fuel. Other major components of racing fuels include benzole, petrol, toluol, and acetone, and, to a minor degree, ether, water, naphtha, oil, xylene, cyclo-hexane, tetra-ethyl-lead, and oxygen gas. Benzole can be employed in much greater quantities than petrol on account of its higher anti-knock value and better latent heat value. It is an excellent binder of alcohol and petrol, and increases the water tolerance of such mixtures. Its high freezing point (about 5ºC.) makes it of small use for aero-engines. Petrol is really only valuable in a racing fuel on account of its wide boiling range, which assists starting and improves distribution. Air Ministry D.T.D. 224 specification fuel is preferable, or D.T.D. 230 in a leaded variety. Toluol is akin to benzole, but has a freezing point of —70°C., which obviates freezing troubles. Its value as a dye and a war material renders it costly and difficult to obtain. Acetone is of value in binding an alcohol-benzole-petrol mixture, and has an anti-knock value between that of benzole and alcohol. It attacks certain light alloys, however. Ethyl ether has been used to assist starting with fuels of very high alcohol content, but having an anti-knock value only about half that of commercial petrol, it was not generally successful. Water has a great cooling effect, and at one time was used in as great a proportion as 25 per cent. In an alcohol mixture it was necessary to use benzole and probably acetone also, to obtain a blend, as petrol will not blend with alcohol otherwise, if more than 4 per cent. of water is present. Even then, low temperatures or a little extra water result in separation. Injection was rather a different story, but even then the effect on lubrication was severe, and the only satisfactory way to inject water without washing oil from the cylinder walls and diluting the sump contents seems to be by the Arnott method, described in MOTOR SPORT last May. Naphtha appears useful only as a binder of alcohol and petrol if benzole is not available, and xylene likewise, with possibly a slightly wider boiling range. Cyclo-hexane is very rarely used, being expensive, difficult to obtain, and tending to pre-ignite before detonating, but it can be employed to adjust distribution characteristics. Oil is added merely for purposes of lubricating supercharger components, valve stems and upper piston rings, but it has a severe pro-knock tendency, and should never be used in greater than 2 per cent. quantities. Tetra-ethyl-lead imparts a high anti-knock value to petrol, up to the addition of about 5 c.c. per gallon. It does not improve alcohol or benzole, so there is little point in using lead with blends in the region of 90 per cent. alcohol/benzole: 10 per cent, petrol, to an extent greater than 1 or 2 c.c, per gallon. In any case, the fluid is not available to ordinary mortals, and would only be used in fuels blended by the petroleum companies. Lead dope seriously harms overheated exhaust valves and frequent examination is necessary. At Indianapolis, where the rules confined competitors to petrol fuels, it was said that lead fluid to the extent of 10 c.c. per gallon was used to obtain the desired anti-knock values, but in this country such methods are regarded with suspicion, because such a high content would have no additional anti-knock value, it would result in valve and plug failures, while, even if it were to permit higher compression pressures without knocking, they would not be realised, because internal overheating would lower volumetric efficiency so that the h.u.c.r. would never be reached. Hence the use of alcohol, which requires only half the weight of air and keeps engine temperatures much lower by its higher latent heat of vaporisation. When petrol was the only available fuel it was thought that oxygen-injection would enable more fuel to be burned, and Eldridge carried a cylinder on the big Fiat when he went out for the Land Speed Record at Arpazon. His passenger turned the tap on for the first run, but forgot to cut off the supply thereafter, consequently it was exhausted before the second run. As the speed was identical, it was concluded that oxygen had no particular value. The experiment was repeated, if memory serves correctly, on an Austin Seven engine at an Inter-‘Varsity speed trial, but didn’t the engine blow up?
The Rolls-Royce aero-engines used in the record-breaking motor boats “Miss England” and “Miss England III,” piloted respectively by Segrave and Don, ran on a 50/50 toluol/ethyl alcohol fuel. The Rolls-Royce engine used in the seaplane which won the 1931 Schneider Trophy Race used a 70 per cent. benzole : 20 per cent. petrol : 10 per cent. methyl alcohol blend, on which it developed some 2,350 b.h.p. Given more throttle, this engine gave about 300 more b.h.p. when it took the World’s Speed Record, in which form it used a blend of 60 per cent. methanol : 30 per cent. benzole : 10 per cent. acetone. In both cases tetra-ethyl-lead dope was added. Damping-out at around 200 m.p.h. was experienced if acetone was not used. Sir Malcolm Campbell used similar fuels in “Bluebird,” but Eyston’s RollsRoyce “Kestrel” motor in “Speed of the Wind” and Cobb’s Napier “Lion” in the Napier-Railton ran on non-alcoholic fuels. M.G. used 50 per cent. methanol: 20 per cent. ethanol : 15 per cent. benzole: 12.5 per cent. petrol : 2.5 per cent. distilled water, with a b.m.e.p. of 335 lbs. per square inch. The l½-litre Delage of 1927 was run on “Eleosine,” composed of 50 per cent. ethyl alcohol and 50 per cent. benzole, with 1 per cent, addition of castor lubricant.
Having emphasised the extremely important part which alcohol has played in the development of the present-day racing engine, it may be as well to point out that two distinct types of alcohol are employed— Ethanol and Methanol. Ethanol is a product of the fermentation of grain alcohol, a by-product of the manufacture of molasses, or a product of other vegetable matter. Methanol is usually a synthetic product which may be made by passing carbon monoxide and hydrogen over a catalyst at an elevated temperature. Ethanol = C2H5OH. Methanol = CH3OH. Methanol possesses advantages in respect of latent heat, calorific value, and volatility and is not subject to Excise Duty. Ethanol seems less prone to pre-ignition, and is less extravagant, but it has to be denatured with 25 per cent. benzole, or similar, to avoid duty, in which case the latent heat value might be improved by admixture with methanol.
At this point it might be argued that, as alcohol blends permit satisfactory combustion under the highest conditions of supercharge and compression pressure that engines have been able to withstand mechanically at present—up to the equivalent of a compression ratio of 19 to 1 or more—exact design of combustion chambers cannot any longer be of much importance. In other words, inefficient head design could be masked by increasing the alcohol content. While this may be true to some extent, it must be remembered that the greater the alcohol content, the higher the fuel consumption, and the greater the distribution and starting difficulties. The former may be of little consequence for sprint work, but could matter quite a lot in road-racing or record breaking. This was very nicely demonstrated by Seaman with his rebuilt Delage, which used to get through 200 mile races without a pit-stop, at a time when the E.R.A.s had to refuel in that distance, because the Delage used a lower boost and could run on a “milder” fuel, and so achieve a better consumption. On the other score, the need to use an extreme alcohol blend will court the possibility of faulty pick-up from corners and even failure to restart after a pit-stop, detrimental in both road and track racing. Considerations of this sort will obviously make a designer strive to achieve good head formation and port layout, and/or reduce compression-ratio, even with alcohol fuel at his disposal. The fact that supercharging reduces the volatility of the fuel, as Banks pointed out in connection with his work on special fuels for the Rolls-Royce Schneider Trophy engines in 1933, has considerable bearing on this aspect, as the better the combustion chamber design, the more petrol may be blended in, and if the head design will not permit of this on account of either detonating or dangerous overheating of valves or piston, pre-heating, with consequent reduction in volumetric efficiency, is the only cure. This question of the effect of supercharge on volatility is happily overlooked by persons who say that the fuel is atomised by the churning it gets in the blower, but perhaps they are only concerned with boosts of a few lbs. per square inch.
Not every race organiser of recent times has permitted special fuels. Until 1928, Le Mans regulations stipulated ordinary French petrol, inferior even to British No. 1 spirit. This kept compression-ratios to under 6 to 1, and very rich settings were used to keep down detonation. Later, an unlimited proportion of benzole was permitted, and race speeds rose accordingly. In our own sports-car races and motor-cycle T.T. races, a 50/50 petrol/benzole mixture is usually allowed. Such a mixture can be safely employed with compression-ratios of up to 7 to 1 unblown, or up to a little over 6 to 1 using a very slight boost (in engines of up to 70 mm. bore). If the regulations allow standard leaded petrol to be mixed with the benzole, slightly higher ratios are possible.
Alcohol is of little use to the R.A.F. because heavy consumption and icing-up must be rigorously avoided, nor are extremely high compression-ratios deemed desirable, so that leaded petrols of 100 octane value are largely employed. Which is why we are rationed these days to limited supplies of a fuel variously called cess-pool, puddle fuel and ruder things, although it says much for modern sports engines that they protest really very moderately at being deprived of the anti-knock elements found in the better commercial fuels.
One final point about racing fuels. The reason why weather conditions can so thoroughly upset carburetter tuning is because the nearer a mixture approaches chemical purity, the more constant its boiling point becomes, and special fuels often boil over a very close temperature range, such as a range of 100 C., as against petrol’s range of 170° C. Thank you, boys. Class, dismiss!
Why Not Termites?
If the war really is due to go on for another two years or more, some of us will be looking around for fresh interests. Why not start thinking in terms of termites, which is Yank for model racing cars? Out there, petrol-driven model racing cars are all the rage, and the speed record is up to 63 m.p.h. Casually picking up a copy of the “National Auto Racing News” you find reports of race meetings at Michigan, Pennsylvania, Chicago, and New York. Lots of clubs seem to have banked concrete or board tracks on which to race the termites, electrically timed, round the pole. It must be fun, and good to watch. Alas, in this country, Mr. Hamley never gave a public demonstration of the petrol-models he was importing, and only one reader has written to us of a model he has built. We do not like the evident sameness of the models America races, but we might find some good entertainment on more varied lines for practically Pool-less days, had we her facilities. I don’t profess to know how much a track costs, but a pole set up on a bit of open space from which troop-‘plane traps have been rolled away would do for a start. Models are the problem. You can buy a ready-to-run termite from go-ahead America for $49.50, but it would look odd to us because, while at first sight it would pass as a scale model Indianapolis car, actually, it seems that fans across the pond build only replicas of midget racing cars, and so their models look odd to us. But in case you feel this way, the firm making the De Palma Special is De Palma Industries, 3347 Baychester Avenue, Bronx, New York. Who will be the first racing-driver to start the craze?