Science: Gas and Supergas

For 25¢ a gallon the U.S. oil industry can now produce quantities of aviation gasoline so powerful that present airplane engines in production cannot make full use of it. Fuel technology has outstripped mechanical progress, inverting the aviation picture of 16 years ago.

In those days engine designers were frustrated for want of high-test gasoline. Mail planes roared along on 60 octane pap. As late as 1929 designers and flyers never dreamed of using 100 octane gasoline, the presumably unattainable “perfect” fuel.

Not until 1931 was the first 100 octane gasoline made—and then only in laboratory flaskfuls at a cost of $10 a gallon.

Today 100 octane gasoline costs only 15¢ a gallon f.o.b. refinery. It powers all first-line U.S. and British warplanes, gives them 20% more power per gallon than Germany’s usual 90 octane. But even this supergas—70% more powerful than 1931’s best 87 octane fuel—is a back number with fuel technologists, who have recently concocted “no octane” gasoline—50% more powerful than 100 octane. Of this liquid dynamite the U.S. could produce overnight several hundred thousand gallons a day.

Its use would give planes smaller fuel loads, lighter engine weights per horse power, less head resistance, lower cooling loads, greater speed. But this is one case in which the war is not stimulating aviation progress but hampering it, and “no octane” gas will not be harnessed now for two big reasons: 1) To build stronger engines capable of using “no octane” gasoline would require retooling, and thereby much lost production which the U.S. cannot afford while Hitler is on the rampage.

2) Every two gallons of “no octane” gasoline contain the vital ingredients of three gallons of 100 octane. And right now the U.S. and Britain are having a hard time wringing enough 100 octane gas out of their refineries.

Into the Octane Stratosphere. This month U.S. oil companies, greased by a promise of some $150,000,000 from the RFC, are moving fast to triple their 1,818,000-gallon-a-day capacity for 100 octane gas. As late as last May 0PM’s Petroleum Consultant, Dr. Robert Erastus Wilson, thought the oil industry “with its genius for overbuilding” could produce “twice the present domestic and foreign demand,” though at a meeting of the Society of Automotive Engineers he advised “a 25% expansion in 100 octane capacity” to be on the safe side. But that was before Britain began bombing Germany, before the U.S. began helping Russia, before the new U.S. bomber program sent high octane demand estimates soaring.

Development from World War I’s 55 octane gas to World War II’s 100 octane plus came slowly. Octane rating is the index of antiknock qualities.* Before 1922 the only way to raise this rating was to increase the percentage of isooctane (and similar compounds). Isooctane is a hydrocarbon, C8H18, which is one of the hundreds of compounds which make up the chemical mixture called gasoline. But isooctane alone makes a poor fuel because it is not volatile enough, does not readily carburet into explodible vapor.

Next came tetraethyl lead, introduced in 1922, which acts like a high content of isooctane. Added to the best leadless gasoline, it raises the octane rating to around 90.

Third came the synthesizing of a group of liquid hydrocarbons called alkylates out of either 1) natural gas or 2) the gaseous by-products of the cracking process for making ordinary gasoline. Alky-lates alone have an octane rating of about 93, but they respond quickly when lead is added, making possible ratings well above 100.

Today octane rating may depend on the presence of any or all of these substances, and there can be several formulas for gasoline of any given rating. Power output increases much faster than octane rating (see graph). So the octane limit seems to be 129, where power theoretically becomes infinite.*

Push v. Punch. Oldtime flyers look back amazed at the changes in aviation brought about by cheap 100 octane gas. In 1930, typical engine weight per horsepower was 1.6 Ib. Now it has dropped to 1.25 Ib.

One reason is that the same high octane factors which prevent knocking, i.e., lost power, also deliver greater power to the cylinders.

Knocking is caused by premature explosion of gasoline vapors before the piston has returned to the cylinder head. These out-of-rhythm explosions can ruin a motor, perhaps break its crankshaft. High octane materials—octane, lead, alkylates—prevent these premature explosions by slowing down the rate of explosion. Though all gasoline explosions are a matter of split seconds, some are “slow,” others “fast.” Each kind of hydrocarbon in gasoline ignites at a slightly different temperature and compression. Igniting slowly and in order, they give the piston a firm, continued push instead of a brief, wrenching, power-wasting punch. So high octane gas can give more power to airplane engines—if they are designed to harness it.

One hundred octane gas may well win the war in the air, for Hitler cannot produce in quantity anything better than 90 octane. Reason: the vital ingredient of the higher octane gas is alkylate, which is made from natural gas or from by-products of petroleum cracking, on both of which Germany is as short as the U.S. is long.

Hitler can produce oceans of 90 octane by adding lead to his synthetic gasoline derived from coal.

After the war, 100 octane and other super-gasolines will be among the great technological developments let loose upon industry and society. For example, with “no octane” gas, 50% more powerful than 100 octane, a plane will some day be able either: >To fly from New York to London on the same amount of gasoline it now takes to fly from Newfoundland to London, or > To carry about 30% less gas and therefore carry a much larger payload.

* Rating is determined by feeding the gasoline to be tested to a test motor, whose spark is advanced until knocking appears. An identical motor is then run on various mixtures of 1) heptane (a bad knocker) and 2) isooctane (once thought to be the perfect knockless fuel) until its knocking corresponds to that of the other. If the unrated gasoline knocks at the same point as a mixture of 30% heptane and 70% isooctane, it is rated as “70 octane.”

* Yet ratings of 130 to 150 are often reported. Such confusion arises because ratings over too (the former maximum) cannot be measured against isooctane knocklessness. Best meaning of ” 110 octane” is 110 on the extrapolated power-octane scale.But “no octane” sometimes loosely means 10% more powerful than 100 octane—or the equivalent of only 10¢ octane on the extrapolated scale.