Liquid Fuels Explained

If you ever wondered where liquid fuels come from, here is a short primer.


A 16 hp Witte engine, S/N 34498, with a hit-and-miss governor 9" bore16" stroke. Restored and displayed by Col. Houston L. Herndonat the fall meeting 5 Nov. 1966 of the Florida Gas and SteamEngineers Club at the Sarasota Bradenton Speed way. An idea of thesize of this engine can be had by comparison with Mrs. Herndon whois 5' 2' tall. Courtesy of Houston L. Herndon, Sarasota, FL


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The liquid fuels we use today were unknown until petroleum or crude oil was first discovered at Titusville, Pa. in the year 1859. Even then it took more years of experimentation to identify all the useful compounds a gallon of black goo could yield. Texas is at present the largest producer in the U.S. Some has to be pumped from the ground, some flows freely, or spurts out in the form of a gusher like an artesian well. Have you wondered how it got there? It is believed to result from the decomposition of plants and animals that lived in the sea, which was originally in the areas where it is found.

While the fermentation process was going, a tremendous build-up of internal pressure caused bulging of the earth's crust, which in turn formed pockets. The upper parts of these pockets harbor natural gas, still sometimes at great pressure. It is a thick brownish green oil and as found is a mixture of Carbon and Hydrogen in varying proportions.

For instance, the formula for cylinder oil is C23H48, which means 23 parts Carbon in a chemical mixture with 48 parts Hydrogen. Petroleum and all products made from it are thus known as hydro-carbons. When properly refined, 100 gallons of crude oil will normally yield liquid fuels and byproducts in the following measure: about 44 gallons of gasoline, 6 gallons of kerosene, 36 gallons of fuel oil, 3 gallons of lubricating oil, and 8 gallons of liquid paraffin wax or asphalt. While refining is going on the temperature is raised in steps, so that different byproducts having different boiling points may be collected separately.

Gasoline, having the lowest boiling point, is collected from 160° to 390° Fahrenheit temperature. Next in line is Kerosene, which is boiled off at temperatures from 390° to 570°. And so on down the line. Lubricating oil is mixed with soaps and various other compounds to make non-fluid greases. Pennsylvania crude oils yield paraffin wax and so are said to be paraffin bases. Those from the west yield asphalt instead and are called asphalt. The formula for gasoline runs from C7H16, 5.83 pounds per gallon, containing 122,721 British Thermal (or heat units) per gallon to C9H20 (for the heavier gasolines) 6.04 lbs per gal., containing 125,450 Btu's. Kerosene has a formula of C13H28 weight per gal is 6.82 lbs, and a gallon contains 135,922 Btu. Notice the heavier the fuel, the more the heat units per gallon. This does not necessarily mean more power, but instead means more hours of operation on a tankful, when burned under proper conditions. The heavier the fuel, the less volatile. The more heat must be used to aid in it's vaporization. This heat may be taken from the exhaust pipes and manifolds of the engine in use and applied to the intake air, as well as to the mixture after it leaves the carburetor to prevent condensation within the manifold and so keep in it a state of vaporization.

Considerable refrigeration goes on right within the carburetor. You may have noticed the frost that forms next to the carburetor of a tractor, particularly just after first starting. This is due to freezing of moisture in the external air brought on by this refrigeration. No additives in the gasoline will prevent this, they are merely to keep the moisture in fuel lines from freezing. The more volatile (more easily vaporized) the fuel the less pronounced this effect will be. Air by volume, in the country (without smog) is about 78% Nitrogen (gas which under ordinary conditions will not unite with any thing else) 21% Oxygen which we need to breathe, and combines with the hydro-carbons in fuels during combustion also contains carbon-dioxide, and other trace elements in small amounts. It takes about 15 lbs of air to burn one lb. of gasoline. More gasoline is necessary at lower than normal temperatures. Thus it is necessary to choke a cold motor to start it.

When burning within a cylinder, the mixture reaches a temperature around 2,700° Fahrenheit, and carbon-dioxide (carbon-monoxide in lesser amounts, due to imperfect combustion) and water are formed, the latter not being noticeable as it is in the form of steam. It is the expansion of the mixture within the cylinder due to heating (while burning) which forces the piston outward and so produces the power. If this burning takes place too rapidly the piston receives a sledge-hammer blow instead of a more steady push, and we then have what we call detonation, knocking, or pinging. This was effectively overcome in years gone by, by feeding water within the mixture, by means of an extra jet in the carburetor. This greatly helped to keep the interior of the cylinders clean and free of carbon also. Kerosene had an octane rating of zero and made this very necessary.

Modern engines mostly use gasoline, the octane rating depending on the crude oil it's made from. The octane rating of untreated gasoline would be about 60. After the addition of tetra-ethyl lead and other anti-knock compounds, it can be raised to 100 or so, Most of the older engines will perform very well on untreated gasoline. There's nothing to be gained by burning higher octane gas in them. The average compression when they were built was 75 lbs. for gasoline, and 85 lbs. for kerosene when feeding water. Use the lowest octane gasoline that will give good performance and you will get the best economy and all around results.

Years ago we used to hear about oil companies watering their gasoline. If you believe that just take a small amount of gasoline and like amount of water, put them in a bottle, shake it up good, try to mix them and see what happens. You will find them impossible to mix. In chemistry, it is called non miscible. It used to amuse me, years ago, to hear some people who had trouble starting their cars (particularly Model T Fords) tell they were going to get one of these hot spot manifolds to overcome their difficulty. The heat from the exhaust would warm the mixture, but there would certainly be no heat until they got the motor started—quite obviously they did not understand.