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Source: © The Indiana Observer www.IndianaObserver.com
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Early in the evolution of automobiles, engines, and gasoline, engine “knock”, “pinging”, became a problem. It is also referred to as “detonation”, “pre-ignition”, “spark knock”, “valve noise”, and other terms, misnomers or not.
If the gasoline in an engine burns (combusts) prematurely (in terms of mere milliseconds), or combusts spontaneously, or too rapidly, or too violently, it is inferior combustion, and makes a pinging or rattling noise from the engine, usually when accelerating. Severe pinging can quickly destroy an engine. Chronic mild pinging can eventually result in serious damage to an engine. A sturdy engine can withstand occasional light pinging, though maybe with slightly accelerated wear on certain parts. When any pinging occurs, efficiency and power are reduced, and fuel consumption is increased. Put simply, pinging is not good.
In the 1920s, gasoline companies began offering a new, improved, and slightly more expensive type of gasoline that resisted pinging, knock. The new gasoline contained an “anti-knock” additive, a chemical called tetraethyl lead, “TEL”, that actually made gasoline slightly “reluctant” to burn, which helped to remedy inferior combustion, “pinging”. The more TEL that was added to gasoline, the more knock-resistant the gasoline became. The manufacturer of TEL, who supplied it to the gasoline companies, was the Ethyl Corporation. Gasoline that contained the most TEL, that (thus) was the most knock resistant, was widely referred to as “ethyl”. Into the 1960s, drivers who preferred that premium type of gasoline told “service station attendants” to “fill it with ethyl”.
But the TEL anti-knock additive in gasoline caused engines to emit in their exhaust tiny amounts of lead, which pollutes the air, and which cannot be controlled by automobile emissions-control systems because lead damages them. So, TEL was phased out during the 1970s and was replaced by other anti-knock additives. Of course, at gas stations in recent decades, gasoline that is more knock-resistant is referred to, not as “ethyl”, but as “premium”.
A gasoline’s knock resistance can be measured in the laboratory, and the gasoline is assigned a numerical value that is referred to as its “knock rating”, or “octane number”. The more resistant a gasoline is to knock, the higher its octane number. Today, octane numbers at gas stations range, roughly, from 85 to 95.
Of course, it is particularly catastrophic if an aircraft engine fails. So, “premium”-type aviation gasoline (“avgas”, for piston-engined aircraft) has an octane number of around 115. Too, many racing cars use avgas or special super-high-octane racing gasoline. Whether or how higher octane makes them go faster is a complicated matter that I will not go into here, but it certainly helps to increase the probability that the engine will finish the race. Of course, some types of racing cars do not use gasoline. For example, Indy cars use methanol (wood alcohol), which is weird stuff. For example, it is extremely corrosive to engine parts. But methanol is water soluble, which makes extinguishing fires easier, and it has excellent natural anti-knock properties.
It might surprise some people that, in jet aircraft fuel, high octane is not desirable, and jet fuel would have a low octane rating. Jet fuel and diesel fuel, which are similar, feature, not an octane rating, but a “cetane” rating, which is the opposite of an octane rating. Jet fuel would run very poorly, if at all, in a gasoline engine, and would quickly ping it to destruction. Jet fuel would not make a gasoline engine “really take off”. Conversely, high-octane gasoline would run poorly, if at all, in a jet engine. I do not know anything about rocket fuel.
There are several myths about engine pinging and gasoline octane. One myth is that the pinging noise is from “the valves rattling in the engine”.
Another myth is that higher octane gasoline “burns hotter”. For example, it is not an old “wive’s tale”, but, rather, a common “husband’s tale”, that if you put premium gasoline into a lawn mower, or into a low performance car like a decades-old VW Beetle, you will “burn up the engine”. News reporters often excitedly describe some blazing inferno as “burning furiously!, like it was fueled by high-octane gasoline!”. In reality, higher octane gasoline not only is slightly more “reluctant” to burn, but actually has a slightly lower energy content. Technically, it is perfectly sensible to run premium gasoline in a lawn mower or an old Beetle. Technically, it would be more correct to exclaim that some blazing inferno was “burning furiously!, like it was fueled by low-octane, regular-grade gasoline.....the cheap stuff!”. But, you can’t let facts throw cold water on a hot news story! That’s why they call them “stories”.
Automobile manufacturers like to suggest, especially regarding their economy models, that the cars are “designed to operate on” regular-grade fuel, which is a carefully worded statement, and a true statement, and which portrays the cars as economical to operate. But, more than a few car owners have observed that “it might have been designed to operate on regular-grade fuel, and the engine does operate on regular-grade fuel, but it pings, so I have to use premium”. Of course, the phrase “designed to operate on” remains true.
In recent decades, a few “consumer advocates” have persuaded a few consumers that premium gasoline is “a ripoff, that is sold simply to make more money for oil companies”. In my years as an auto mechanic I have seen several engines that were consumed because their owners refused to be “ripped off” by premium gasoline. The engines pinged to death. Those consumers spent more money, and all at once, for major engine repairs, than the total additional money that they would have spent, and pennies at a time, on premium gasoline. Pinging can cause, for example, “blown” head gaskets, damaged heads, damaged pistons, damaged cylinder bores, “blown” engines, etc.
Some people who own cars with engines that ping on regular-grade gasoline use it anyway, but they buy premium every other fill-up, or every third fill-up, or once a month, or whatever. They believe that octane has a residual beneficial effect that gives the engine some ongoing protection, to get it through the lean times. It does not.
One old story was that if you put moth balls in a car’s gas tank it would keep the engine from pinging. The story had a basis in fact. Moth balls contained a chemical that has a powerful anti-knock effect. I have seen moth-balled gasoline tested in the laboratory for its octane rating. The moth balls would dissolve in the gas tank and become an anti-knock additive. The trick was to put enough moth balls into the tank to increase the octane enough to prevent pinging. Modern moth balls do not contain that chemical and will not stop engine pinging.
Each piston-type gasoline engine has some minimum octane requirement, below which it will ping. Ping and octane requirement are a function of engine design, manufacturing tolerances, engine condition, specific engine part malfunctions, and certain engine adjustments. If your car’s engine does not ping, you do not need to buy higher octane gasoline. If it does ping, then, first, have a mechanic check it and make any necessary repairs or adjustments. Then, in my opinion, if it pings at all, or if you do not know whether your engine pings (because, for example, your hearing is fading, like mine), or if you just like to be on the safe side, you should routinely use premium gasoline. There are no harmful effects on an engine of using higher octane gasoline than the engine needs.
