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Salient: Victoria University Students' Paper. Vol. 28, No. 11. 1965.

Science Feature: Petrol — Key To Revolution

Science Feature: Petrol — Key To Revolution

As with most revolutions, the transport revolution was founded on dreams. One was the vision of a certain Colonel Drake; the other that of an earnest young man by the name of Henry Ford. The Colonel had a dream of oil, a dream which came true on a hot August day in 1859.

After months of fruitless searching and back-breaking labour, his primitive drilling rig struck into a hidden pocket of "black gold," and produced the first oil gusher.

By the time that the next quarter century had rolled by, Henry Ford had made his dream out of wood, wire, metal and bicycle wheels, pushed in and out of a backyard shed in Detroit, and smiled delightedly as the forerunner of the first family production car sputtered its way to history. Together these unrelated events added up to revolution—a new way of life made possible by one oil product—gasoline.

Early Models

Early model petrol engines were extremely large and temperamental pieces of hardware, with power outputs out of all relation to their size. Simple in design and slow in operation, they could be coaxed to run on what we would today regard as very poor quality gasoline.

Revolutions per minute, if they were measured at all, were scaled in hundreds and not thousands, and horsepower seemed a rather optimistic term to apply to a machine that often needed a strong wind and the will of God behind it for smooth operation.

But that is all history. Over the years, encouraged by economic goals and by wars, the internal combustion engine and the fuels that drive it have undergone changes that make them as similar to their predecessors as we are to cavemen—structurally similar, but much more refined.

The modern engine is a complex piece of highly engineered machinery that produces a high power output through sophistication of design, not from brute force and ignorance like its forebears.

And this has meant a continual improvement in fuels, to keep pace in the constant race for technical perfection.

Today, there are five main requirements for an acceptable gasoline conforming to contemporary standards. It must be clean (more important than it sounds), it must be volatile, have a definite octane quality, be stable and should, preferably, have its performance rating improved by positive performance additives.

Dirty Fuel

Dirty fuel makes its presence felt in a very marked way, usually involving rough running and often stoppage of the engine. Severe contamination will not only stop an engine, but keep it stopped until it has been dismantled and cleaned out. There are two main types of contaminants—foreign matter, such as water, rust and dirt, and fuel-derived contaminants formed by the interaction, under abnormal conditions, of elements contained in the gasoline.

Occasionally a mysterious temporary fuel blockage will occur through the formation of ice-crys-stals in water held in suspension in the fuel, but this usually clears itself as heat soaks back from the engine.

Since customer reaction to dirty gasoline is usually fairly strong, suppliers run constant checks on cleanliness from refinery stages right up to the point where it is pumped into cars on service station driveways. Even small amounts of contamination can reduce a high quality gasoline to one of comparatively low standard.

Even in the good old days, volatility was taken as one of the most important basic requirements of a satisfactory gasoline. They even had a disarmingly simple test for this property. You took a can of petrol up to the second storey and poured it through the window. If enough of it reached the ground to make a splash, then the petrol wasn't good enough. Needless to say, somewhat more refined techniques have been adopted.

The subject of volatility is one that is fraught with hazards. For instance, it would be natural to assume that the greater the volatility, the better the petrol. It would also be wrong. During winter periods, a high degree of volatility would certainly help cold starting, because the temperature at which the petrol vapourises is low enough to combat the atmospheric conditions.

But in summer, this high volatility would mean that the fuel vaporised too readily, causing vapour locks in the feed lines, and a consequent blockage of fuel from the carburettor.


The wrong degree of volatility can also cause another irritating complaint known as "carburettor icing." When petrol evaporates, it takes its latent heat of vaporisation from the surrounding air. Under certain conditions of temperature and humidity, such as those found in certain South Island areas for up to six months of the year, moisture condenses out of the air, and forms ice on carburettor surfaces.

A thickening film of ice in the carburettor can immobilise a car somewhat better than a vapour lock, because when the ice goes, the water that forms it remains to contaminate the fuel. The risk of carburettor icing can be reduced by lessening the volatility of the fuel, but it is generally much more effective to use anti-icing compounds, such as "surface active ingredients." which prevent ice forming on surfaces.

The volatility range of a gasoline must be carefully chosen, and tailored to meet the prevailing elimatic conditions.

In certain continental areas such as the United States, gasoline varies from region to region. The product you fill your tank with in Los Angeles will probably be quite different from that you buy in Dallas. Similarly, a gasoline ideal for New Zealand would be worse than useless in Aden.

Octane Rating

Next to volatility, the most important single property of a petrol is its octane rating, a subject filled with mystery for the uninitiated, but nevertheless fairly easily explained in terms of gasoline and engines.

The archetypal combustion engine had a remarkable ability to produce some pretty ghoulish noises. Among the disharmonies of piston slap, tappet rattle, big-end thuds and other percussive variations, the discerning ear could frequently pick out a muted and high-pitched knocking.

Occurring most in cars with fairly high compression ratios, research proved that it was caused by the premature burning of the fuel-air mixture. It was also discovered that a relationship existed between compression ratios, knocking, the octane number of the gasoline and the energy output of the engine.

In brief, the octane number of the gasoline can be taken as a measure of its anti-knock qualities. Using a standard single-cylinder engine, it is possible to determine the octane number of a specific gasoline by comparing its performance in that engine with carefully measured quantities of heptane (its octane number is 0) and iso-octane (its octane number is 100).

The higher the octane number, the less will a gasoline knock. It is particularly important that high octane gasolines be used in cars with high compression ratios.

High compression means that cylinder temperatures are hotter, and premature burning of the fuel/air mixture is more likely. High octane fuel reduces the tendency of the fuel to burn before it is ignited by the spark, and eliminates the consequent loss of power. So if the little old bomb ain't what she used to be, change to high octane gasoline!


Stability is an important aspect of gasoline performance. If a gasoline is as good on the day it is pumped into a car tank as it was when it left the refinery, then it is alright.

In the early days of New Zealand motoring, stability was an important factor in selecting the right brand to buy. In those days gasoline was shipped to the Antipodes from the producing countries in crates of four-gallon tins. By the time it reached here, its stability had been tested to the utmost. Failure to produce gums and other insoluble deposits meant that the gasoline was good.


Positive performance additives are the sophistications of gasoline, designed to enhance the characteristics of the basic components. Additives are a subject in themselves, ranging from necessary elements to others that are little more than refinements. For instance, one additive to motor gasoline in New Zealand is a dye—a different dye for each grade of petrol.

This provides grade identification and also fulfils an international requirement that all "leaded" products be dyed.

Gasolines are "leaded" by the introduction of another additive, organic lead compounds. These chemicals, usually in the form of tetra-ethyl-lead or tetra-methyl-lead, raise the octane rating of straight-run refinery gasoline, and increase power and economy. Tetra-methyl-lead has the advantage of being a light and volatile lead alkyl, and improves the anti-knock quality of the base gasoline over the whole range of temperatures at which the different components of the gasoline boil.

Generally speaking, the addition of lead compounds gives gasoline improved performance characteristics, and a greater degree of flexibility in operation.

The only drawback to using lead compounds to improve gasolines is the fact that they combine with oxygen to form ash residues on combustion chamber surfaces. Under normal conditions, operating temperatures never get hot enough to burn these deposits off, so another additive is put into leaded gasolines to prevent ash deposits from accumulating.

These additives are called "scavengers." which react with the lead deposits to form chemical compounds which can be burnt off within the heat range of the combustion chamber. The obvious benefits include improved engine operation and longer service life.

These are the most important additives. Others include antioxidants, anti-rust compounds, carburettor detergents, pre-ignition and plug-fouling entrols, and the anti-icing compounds mentioned earlier.

Gasoline, the bread and butter product of the oil industry, is remarkable stuff. Without it, the transport revolution that has taken only 60 short years to reach its present form of sophistication would never have been possible.

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