whats in a gallon

Gasoline, like oil, is a product 'bilers discuss over a cup of java. Many look for the best price and leave it at that. Today's superbly engineered snowmobile motors are designed to run on mid-grade fuels, oxygenated fuels and summer time fuels. The designers have gone through deep snow to make your sled's engine think. But, you should do your part.

An elementary rule to follow is to purchase fuel from a high-volume national station that also lists the fuel's alcohol content and mixture ratio (if a state law so requires).

Major fuel brands offer the needed quality for your engine, turnover in the storage tank ensures fuel is fresh and blended for current seasonal temps, and lastly, the snacks are fresh.

Short History
The last century can easily be called the petroleum age. Oil and gasoline make up our economic lifeblood. Without oil and gas our world would look very different. Around 1900, only 11 gallons of gas came from a barrel of oil. Today, over 25-gallons of gas are produced from the same barrel.

To produce gasoline from oil, a thermal and distillation process is used to produce the product. Oil is not the only product from which we can distill gasoline, other products like coal, shale oil, tar sands and even recycled plastics and rubber tires can be used. But these processes are complicated and expensive.

Consequently crude oil is the most economical source for the distillation and refinement of gasoline.

Petroleum has a variety of chemical consistencies. It can be thin and light-colored or it can be thick and black. Thin crude has high gravity, whereas thick crude has low gravity. Their molecular size makes them one or the other. Low-gravity crude has small carbon chains; high-gravity crude has long carbon chains. This chemical makeup means when the petroleum is heated to a boiling point, the lighter crude percolates to the top faster than heavier crude because the smaller carbon chains separate faster than the long chains.

But the composition of the heavy low-gravity crude contains more natural gasoline and its low sulfur and low nitrogen content makes it easy to refine. Modern refining techniques turn low-gravity crude petroleum into high-gravity crude. However, refining low-gravity crude requires complex and expensive equipment. This makes it costly. Here is how gasoline is refined.

All petroleum crude is composed primarily of three hydrocarbon classes: paraffin, naphthen, and aromatic. Each class contains a broad range of molecular weights because, as mentioned, the carbon chain is different.
Distillation is a process that involves boiling the crude to remove the lighter elements. Boiling is followed by condensation to capture the vapor from the remaining crude.

The refining industry discovered a process whereby high-boiling point hydrocarbons could be broken down into lower boiling point hydrocarbons. This process is called cracking. Cracking is a way to increase gasoline production since it now uses the remaining discarded crude from the distillation process. The hydrocarbon is subjected to a very high temperature to break the carbon molecule chain and leave a carbon molecule product that is easier to distill at lower temperatures.

It may be said that gasoline is as much a government-created product as it is a petroleum refining process product. This is due to government regulations that treat gasoline that comes out of the refinery as a product that must meet additional social policy conditions. Many of these policies were introduced for the first time in the 1970s. For instance, gasoline must not contain lead, it must have a high-octane (no-engine knock) rating, and it must meet air pollution regulations. To comply with myriad government regulations, a gasoline must be blended with up to five or more refining streams.

These streams are used to produce commercially and governmentally sellable products. They meet different government regulations for quality and pollution control. Usually the final gasoline blends are the result of combining different streams to meet quality or governmental regulations.

The gasoline refining business has been the product of some intense chemistry research over the last 90 years. But it is not enough to have a good product, it must meet social policy regulations. The process is now remarkably efficient; but major oil refiners are still looking for ways to get more gas from a barrel of oil.

What's in a Number?
Octane ratings have been a part of the coffee shop talk for many, if you are bored enough to have such talk. Joe Motorhead has often said, "My '70 Pontiac Judge really kicks #$% on av gas. I buy it all the time." Uh uh.

Regular unleaded gas has an average octane rating of 87 or 88. Mid-grade unleaded has a rating of 89. Premium or Supreme packs a rating of 91 to 93.

Some believe the higher the octane number the more the wallop. Octane numbers are a measure of the fuel's ability to prevent engine knock. This number is an average of the Research and Motor Octane number, and best indicates the response to fuel in normal use. The higher the number, the more the fuel is needed in non-normal use, such as high-compression two-stroke motor use. High compression motors, those that are prone to engine knock, will give their best performances on high octane fuels.

Properly tuned, motors will burn fuel in an orderly manner. When a piston cycles up a cylinder, a mixture of atomized gasoline and air is pulled in through the intake port, rattled around in the crankcase and eventually forced up the transfer port and dumped into the combustion chamber. As the piston moves to top-dead-center (TDC) the air and fuel is compressed and then ignited by the spark plug at an optimum time.

As the mixture burns it expands and forces, through great gaseous pressure, the piston to jump down the cylinder in what is called the power stroke. Once the piston reaches bottom-dead-center (BDC), (forcing a new charge out the crank case and up the transfer port as the crank case volume decreases), and starts back up, the exhaust port is left wide open and the expended fuel is pressured out the motor. This is an over simplified view, but in its generality this is how a two-stroke motor uses its fuel.

In a knocking engine, this tightrope process has gone amuck. Heat generated from the compressed fuel and oxygen, or hot glowing carbon deposits, ignite the fuel/air mixture before TDC. Pre-detonation trips up this orderly fashion and sends shock waves through the motor, which is called knock. Higher octane fuels resist knock by burning slower. They are knock resistant. Yet, slower may not be the word. High octane fuels simply prevent knock - mostly.

With this information about fuel and octane ratings, you should be able to gab your way out of tight situations when your pal testifies his stock sled is faster on aviation fuel than it is on super-unleaded. Also, when building and tuning a high-performance high-compression motor, you should be able to make wise fuel choices.