"To develop a fuel, you have to essentially be a partner with an enginebuilder," Burns said. "You want the cars to be competitive when they'reout there. The fuel needs to have enough octane so there won't bedetonation."

Detonation and pre-ignition are the biggest enemies of any fuel'sperformance. The spark within the internal combustion engine needs tooccur at the right time. The perfect time is when the piston is startingits downward stroke. If the fuel ignites too late, the piston hasalready begun the process and efficiency is reduced. Ignition that's tooearly will create a force opposite of the piston force, again reducingefficiency.

In the case of detonation, the fuel becomes heated to the point ofexplosion without the needed controls. A common cause of detonationcomes from amounts of uncombusted fuel, still in liquid form, remainingafter normal ignition has taken place. When this fuel ignites, it isoften out of synch with the expected process and reduces efficiency. Bytheir nature, racing engines can be highly susceptible to detonation, aconstant concern of engine builders and fuel manufacturers.

Properties

Most fuels are known for their octane number, a point to be discussed inmore detail in short order. There are additional considerations in fueldevelopment that must be met in order for the product to make it tomarket.

A figure sought by engine builders is the burning speed of the fuel.This is the time it takes for the fuel to totally release its availableenergy. If the fuel is still burning after the peak cylinder pressurehas been attained, that fuel is not contributing total efficiency.

"Gasoline does not burn, it vapor-burns. It's a liquid but it must beconverted to vapor before ignition," said Burns. "The vaporization helpsthe fuel release its energy. The gasoline goes through the intake trackand never vaporizes. You want the engine to suck in air and the fuelvapor will displace the air. The fuel is vaporizing fast as the pistoncomes up. Before you set the torch to it, you want it to be vaporized.You have to get the fuel to release the energy and you should have thatat 17 to 22 degrees after top dead center. You have to be careful thatit doesn't vaporize so quickly that you lose volumetric efficiency andpower. Burn speed is an important consideration."

Another fuel test comes from the energy value; a measure of the fuel'spotential. It is measured against the oxygen consumed in the process.It's a delicate balance because there are materials that will enhancethe fuel's energy value, but something has to give, and it is often thefuel's octane number. "It's a trade-off," said Burns about energy value."If you want one thing to go up, something will have to come down."

A final consideration is the cooling effect, directly related to theheat of vaporization. The cooling effect on the intake mixture is betterif there is a higher heat of vaporization.