Rocket Fuel

Rocket fuel

TDC

Kevin Cameron

AT ONE TIME, MOTORCYCLE ENGINES led the world in four-stroke design, but Formula One car engines have now taken that role. Because car and bike engines alike are encountering the same problems, it’s useful to look at F-l car engine development.

The current roadblock is that short strokes and high compression ratios-to allow high rpm and high combustion pressure, respectivelyyield wide, thin “crawl-space” combustion chambers that leave no room for the mixture turbulence that leads to quick, efficient combustion. Shortstroke engines like Ducati’s 851 and Yamaha’s OWOl 750 are therefore fired at a too-early 43-45 degrees BTDC. Bike racers accept this.

By contrast, F-l car teams have so much money to spend that if they don’t like a certain law of physics, they have it repealed. Accustomed to firing their big 85-90mm cylinders in an efficient, quick 25-27 degrees BTDC, they aren’t about to accept a horrible 45 degrees just because their latest super-short-stroke designs have these cramped combustion chambers.

How could they maintain combustion speed in such tight chambers? Perhaps broad vistas of chemistry beckon them beyond the narrow definition of conventional hydrocarbonbased gasoline.

Two years ago, Ferrari reportedly contracted for a special “gasoline” from the Italian Agip company. The rumors hold that this fuel contained “unusual power-producing ingredients” that made the red cars instantly competitive. Obvious power-boosters like nitromethane and nitropropane can easily be detected in gasoline by the polarity of their molecules, using a $200 dielectric meter. However, chemists suggest that limited amounts of such good but illegal oxygen-toting stuff might be smuggled past the meter inside larger, non-polar molecules.

Another well-tested scheme is to dissolve hydrocarbon gases such as propane and butane in gasoline. Normal motor fuels contain some dissolved gas-it’s put there to aid cold-starting-but using more has desirable flame-speed-increasing effects.

For some time, special qualifyingonly fuels have been used in F-l, but mileage with these is too poor for race-day use. They probably contain alcohol, whose evaporation cools the intake charge enough that more of it can fit in the cylinders.

Now the next round of rumors, seen in the magazines Autosport and Road & Track: The French ELF gasoline firm is reputedly supplying a highly potent substance to the Renault team-a fuel that both boosts power and reduces fuel consumption. Grab your handy desk reference on fuels and flip to the table comparing energy per cubic foot of correct mixture for liquid hydrocarbons. Search though you will, you won’t find any answer here; all the hydrocarbons have closely equivalent energy release.

Next rumor: Fumes from the ELF fuel are said to cause cancer in laboratory animals. There was an explosion of an unidentified fuel (caused by mis-handling) during recent winter F-l testing, resulting in the destruction of a track-side building. ELF’s fuel is reputed to cost $665 a gallon-most of the cost covering special transportation precautions.

What kind of stuff has more energy per pound than hydrocarbons, is both toxic and unstable, and costs too much? Governments love this kind of thing. The SR-71 “Blackbird” spyplane has recently been declassified, but its turbo-ramjet J58 engines and fuel system remain secret. A longtime rumor was that high-energy fuels or additives containing the element boron had been considered for the purpose of extending the plane’s range. Boron combines with hydrogen to produce toxic gaseous and liquid hydrides, some with specific gravities close to the bottom end of the gasoline range. Some of these are pyrophoric-they can ignite spontaneously in contact with air-and they are also liable to vigorous hydrolysis in the presence of even small amounts of water. Toxicity is high and handling calls for extreme care. Metal hydrides-those of beryllium, aluminum and lithium, for instancehave also been considered for use as high-energy fuels.

Bad stuff, but the incentive is the pleasantly high energy content and flame speed. Gasoline hydrocarbons yield about 19,000 BTU of heat per pound, but boranes range from 2530,000. More power, and better mileage, too. Laminar burning speed is also high-about 100 times that of normal hydrocarbons. Ugly combustion chambers got you down? Fill up at the sign of the skull and crossbones.

With the evident risks, would any sane person consider using such fearsome substances? You bet. How many kart and drag racers eagerly blew themselves up with hydrazine/nitromethane mixtures back in the 1960s while seeking a competitive edge? When leaks developed in the fuel systems of prototype German Mel63 rocket interceptors during World War II, their unfortunate pilots were dissolved by the propellantsbut there was no shortage of volunteers to fly these 600-mph machines.

Now, this is all just circumstantial speculation. It’s possible that these rumors of weird chemical brews are just sophisticated psychological warfare among the teams. It is also possible that no useful, exotic, high-energy boron or metallic hydrides are compatible with hydrocarbon fuels. They may be violently pro-knock, or produce abrasive exhaust products. They may be easy to detect (one sniff and you know). Surely, it’s all just a nasty nightmare and there’s a sensible, rules-abiding hydrocarbon explanation. Those multi-million-dollar F-l teams wouldn’t use such questionable propellants, anyway.

Unless they worked.