By Mike Schlee
Photo courtesy Petro Canada
First off, a couple basic definitions, as per Wikipedia: Octanes are a family of hydrocarbons that are typical components of gasoline; Octane Rating is a measure of how likely a gasoline or liquid petroleum fuel is to self-ignite. The higher the number, the less likely an engine is to pre-ignite and suffer damage.
A good portion of the Allies’ air supremacy in World War II, especially the battle of Britain, can be attributed to octane rating. Yes, you read that right, octane rating—as in a gasoline measurement. It seems that everyone who was involved in World War II tries to stake the claim that they were the difference maker during the war, but there is a legitimate claim that advances in fuel helped push the Allies to victory in World War II.
In 1940, when the Battle of Britain was about to begin, the German planes outnumbered the British Royal Air Force (RAF) fleet by a ratio of roughly 4 to 1. The Germans were set to dominate British airspace and there wasn’t much the Brits would be able to do in defense as both were using similarly equipped air forces. At the time, the Germans were using 96 octane fuel in their aircraft, like the ME-109, with output around 1,000 hp. The British were using a roughly 60 octane fuel at the time and planes like the Spitfire were also making in the neighbourhood of 1,000 hp.
However, just as the Battle of Britain began, the Brits converted to American 100 Octane fuel and they could suddenly increase their engine’s superchargers from 6.5 psi to 12 psi. Engine output soared by roughly 30 percent and the Spitfire now had a faster climb rate and top speed (by 27 mph). Suddenly, the RAF planes were hard to catch and even harder to beat, giving the Brit and Allies air superiority, and the Germans ultimately lost the war. Okay, there was a bit more going on between the octane boost and the Allies winning the war, but we don’t have space for that here.
Octane and Automotive Applications
Previous to the war, octane ratings were even lower as gasoline refinement was not up to today’s standards. When the automotive industry was in its early stages, four-cylinder engines well in excess of 10 L in displacement were hard pressed to make the power engines smaller than 2.0 L do today. Although design and materials are the biggest factors in the low output numbers of these antique monsters, low octane grades also hampered these engines.
Fast-forward to the 1950s and octane, although improved, still didn’t mean much, especially in North America where big-displacement monster V8s ruled the roads. In fact, it wasn’t until recently that octane has become very important to automobile manufacturers. Increased compression ratios, turbocharging, supercharging, engine downsizing, direct injection, and attainable 500-hp sports cars are putting a heavy reliance on consistent, if not higher-octane gasoline.
So what’s the big deal if you do not put the required level of octane into your vehicle? Well, ‘knock’ occurs. Knock is one of those things many people have heard of, and know is bad, but do not actually understand why. Basically, knock is the sound you hear when your engine produces uncontrolled combustion. In other words, knock means tiny explosions are occurring in your engine when they shouldn’t be.
If left to operate this way for long periods of time, unwanted issues like piston crown spalding, sticking rings, and holes in pistons may develop that will either cause a loss in engine performance, or downright catastrophic failure. This is why it is important to see what the minimum octane requirements are for your engine and whether premium fuel is required, or merely recommended. The latter meaning an engine can adjust its timing for lower octane fuel.
Not All Octane Ratings Are Equal
The above tidbits of history and technical insights were presented to a group of us by Petro Canada during our day at the Bridgestone Racing Academy. Petro Canada is proud of their Ultra 94 Fuel (formerly Sunoco 94) as it is the highest Research Octane Number ‘normal’ fuel in the world; in other words, the highest rated non-race fuel.
Presently, octane is measured in a few different ways. There is Research Octane Number (RON), Motor Octane Number (MON), and Anti Knock Index (AKI). RON is used in most of the world and tests octane numbers on an engine dynamometer (“dyno”) at various compressions and speeds. MON is a more accurate depiction of what octane level a fuel has as it is tested for octane under load conditions. AKI is a rating system used by averaging the RON and MON ratings.
In Europe and a lot of the world, RON is used for the octane rating labeled on fuel pumps. However, in North America we used the AKI system, which is also referred to as the Pump Octane Number. For the most part, North America and Europe use the same level of octane in their gas even though it may appear that Europe has a higher octane gasoline due to the RON rating they use.
For example, Petro Canada’s 91 grade octane gas has a MON rating of 85.6 and a RON rating of 97.2. So here in North America we split the difference and call it 91 octane, whereas in Europe the exact same gasoline would be labeled 97 octane. Petro Canada’s Ultra 94 gasoline, which features ethanol, is similar in that has a MON rating of 88 and RON rating of 101.5 octane.
And that brings us to Ethanol and its effects on engines both new and old, but that is a topic for another day.
* – special thanks to Brian Kenney, Senior Advisor, Fuels and Additives at Petro Canada for the facts and data.