Ways And Means
Ways and means
TDC
Kevin Cameron
A BIG TOPIC IN THE DAYTONA GARAGE area this year was fuel. For many years it was an article of faith that, although racing gasolines might vary in octane number and volatility, all gave essentially the same horsepower. Particular fuels were chosen because they worked best in particular engines. For example, a hot-running two-stroke with a high compression ratio might require a fuel of very high detonation resistance, which is measured as octane number. Another engine, turning very high rpm and so providing little time for fuel vaporization, might require a fuel that evaporates extra-quickly. This is revealed by the fuel’s volatility curve, end point or other measures.
The relative equality of horsepower arises from the fact that hydrocarbon fuels are made of nothing but carbon and hydrogen atoms. When these fuels combine with oxygen from the atmosphere, a definite, measurable amount of energy is released. It has been a comfortable truth that fuel energy, measured as heat released from combustion of a cubic foot of fuel-air mixture, varies little.
Tuners knew that there were ways to play with this. The energy required to evaporate liquid fuel into vapor comes largely from the air that mixes with the fuel. Because this evaporation lowers the temperature of the resulting mixture, its density increases and so power rises. This “refrigeration effect” is particularly strong with the alcohols. Their use in racing gasolines is prohibited by most sanctioning bodies, and they are easily detected with the commonly used dielectric meter.
Another class of potentially power-increasing fuels are the oxygen-releasing agents such as nitropropane and nitromethane. These are actually explosives, each molecule of which consists of a hydrocarbon fuel (such as propane), and oxygen, barely kept from violently and energetically combining with each other by a “spacer”-a nitrogen atom between them. These compounds are also easily detected by the dielectric meter. The oxygen releasers are different from so-called “oxygenates,” in which the oxygen is present but its bonding energy is not available. Oxygenates include the alcohols and ethers, both of which are, in effect, partially burned, which explains why their energy release is lower than that of normal gasoline hydrocarbons.
Now imagine the surprise of race
teams when they discovered, a few years ago, that certain quite expensive and bad-smelling racing gasolines from Europe actually boosted horsepower by 5-8 percent while easily passing standard tests for alcohols and oxygen-releasers. Never mind how it works, let’s use it!
Some of this fuel came from the French ELF company, whose blue-andblack drums of “Spirit 1203” have become a common sight at U.S. motorcycle races. This year, they were joined by the aqua-colored drums of a new maker, Nutech. At least one team at Daytona this year was using a fuel that made their exhaust smell of styrene. This kind of thing stimulates curiosity.
How can fuels containing only hydrocarbons make increased power? When fuels are burned, energy must be supplied to first break apart the structure of the fuel molecules-to strip off the hydrogen atoms and break up the chains or rings of carbon atoms. This energy comes, ultimately, from the heat generated as the resulting carbons and hydrogens joyously rush to combine with oxygen. This break-up energy therefore reduces the net energy produced. One scheme for increasing the power of fuels works by making the fuel molecules easier to break up. Doubleand triplecarbon bonds are more easily broken than are single bonds, so compounds containing them, such as dienes and acetylenes, can release more net energy than “normal” hydrocarbons.
Another way to play with this idea is to assemble hydrocarbon molecules
with their atom-to-atom bonds bent or twisted to angles that would not otherwise occur. Already under strain, such bonds take less energy to break, so these compounds can also release increased net energy.
Extra power from fuel is very attractive, but there are complications. The components that deliver the extra energy do not necessarily also meet the normal fuel requirements for detonation resistance and volatility. Octane number lost by adding the blender’s mystery ingredient must then be recovered by adding other components of exceptionally high detonation resistance. Unfortunately, these components are often larger molecules which evaporate poorly, so the volatility of the resulting fuel suffers. That, in turn, may mean loss of some performance at top rpm, and possibly degraded throttle response.
There is another important effect, as well. Honda, in a paper published in 1964, showed that as engine rpm rises over 12,000, the combustion process begins to outrun the heat-driven and timedependent chemical changes that cause detonation. As revs rise above 12,000, the fuel-octane number necessary to prevent detonation falls steadily. This effect probably makes high-energy fuels easier to use in small, high-revving cylinders. In larger cylinders and at lower revs, high-energy fuels may work less well-possibly encountering detonation.
How were these higher-energy compounds discovered? Although such fuels were the rage among well-funded Formula One teams a decade ago, it’s likely that the original research money was spent back in the 1950s. Then, concern over the high fuel consumption and short range of early jet engines stimulated a lot of high-energy fuel research.
Formula One gave up high-energy fuels after 1991 because the high profile of that sport magnified everything associated with it. All motor fuels today-racing or pump-bear warnings that users must not breathe fuel vapor, expose skin to liquid fuel or use fuel for washing parts. These are reasonable precautions. Some high-energy fuel components may arguably be carcinogenic in some degree, but so are many of the aromatic components used now in ordinary pump gasolines to make up the octane loss caused by the legislated absence of lead. Life itself is risky, so enjoy every moment.
