But by then, engines required it and there was no cheap alternative……similar to today’s piston aircraft fuel dilemma.

The ALPHA engine recommended octane number is 87, which should cover all normal ambient conditions.Operating with too low an octane number may cause a pinging noise (although the knock sensors should cause the ECM to adjust timing before pinging occurs), indicating a higher-octane rating fuel should be used under current conditions. I checked around and was delighted to find that autogas was available from the self-service pump at my home airport (Modesto, Calif.), and after checking with other pilots on the field, figured it was at least worth a try. Aviation fuel UL91; Main Content. Either bring up lean-of-peak mixture settings or ask whether you should use autogas in your engine. The simplest such molecules, methane and ethane, have just one or two carbon atoms respectively, and are gases. Most Continental O-200, O-300 and O-470 engines, and some of the fuel-injected IO-470 and IO-520 engines can run it as well.So, if you have a low-compression engine, can you just fill it up with autogas and take off? Fact – Modern gasoline remains stable for at least six months. When I asked about this, I was told that the short hose was a deliberate move by the FBO to prevent pilots from pumping autogas directly into their airplanes, though I was also told that “if you want to pump it into your own container, and then put it in your airplane, that’s your business.”Now that gave me pause. Are there any reasons why I shouldn't do this? The greater the humidity of the surrounding air, the greater the rate of contamination and shorter the safe useful life of the fuel.Ethanol also acts as a solvent that may break down other system materials such as rubber seals and hoses, fiberglass and other composite materials used in older aircraft fuel systems. 100LL AVGAS or Mogas?

John Ruley dissects the issues of autogas and introduces research (and problems) that didn't exist only a few decades ago.

The engine burns about 9 gallons/hr in cruise. We know this as detonation, or pre-detonation. Gravity fed fuel system in the 172, so the chance of vapor problems is very small. AVGAS VS. MOGAS. Unleaded Mogas, like the obsolete four-star Mogas fuel, has a much higher vapour pressure than 100LL or 80/87 Avgas. It’s said to have an Octane Rating of 62-64.The octane rating is significant because octane can withstand much higher compression than heptane, and high compression increases power. As nouns the difference between mogas and avgas is that mogas is (aviation) automotive gasoline suitable for use in piston-engined gasoline powered aircraft while avgas is gasoline fuel for piston-engined aircraft.

Vapor lock is a real issue when using autogas in aircraft engines, particularly at high altitudes on hot days — after all, it’s made for use at sea level, or at most lower altitudes. Rich Rosa, a contract Air Traffic Controller who flies a PA-20/22 Pacer conversion with the same engine as my first airplane, runs autogas. UL91 is suitable for around 55% of planes and is available at specific airports in Norway, Sweden, Denmark and France. Unfortunately, lead is a poison and after illness and deaths of many early engineers and workers producing leaded fuels, the government was pressured to outlaw it soon after its introduction. It’s found in aviation fuels in the following proportions:In the U.S., only the first two grades (80/87 and 100LL) are widely available, though 100/130 remains common overseas. I could have done the same thing, but that would have involved a lot of extra expense.I wound up following the line of least resistance and stuck to 100LL while I owned that airplane. Until recently, the most important such additive, for both automotive and aviation use, was tetra-ethyl lead (TEL). My local airport sells mogas. Eventually, water absorbed in the fuel will separate and collect on the bottom of the tank/plumbing/carburetor, which disrupts fuel flow to the engine and can degrade and corrode fuel system components. So, modifying older fuel systems to modern ethanol fuels often requires replacing components such as lines, seals, and possibly tanks. When most current piston aircraft engines were designed and certified in the 1950’s, lead was still a normal gas additive, mostly because it was a cheap way to increase octane number (by about 20%).

Ethanol absorbs water from surrounding air far more than earlier additives, which contaminates the fuel. “Straight-run” gasoline — directly as it comes out of a petroleum distillation plant — consists of 62-64% octane, and the rest heptane. So to get reasonable power from a lightweight engine for aircraft use, aviation gasolines have an octane rating of 80 or higher.The octane rating can be increased beyond the simple proportion of octane to heptane by adding anti-knock agents, which delay the onset of detonation. The colder and/or lower pressure of the intake air (such as on a cold day or at higher altitudes), the lower the cylinder temperatures will be during the compression stroke, decreasing the likelihood of detonation. The higher the octane number, the higher the compression and temperatures in the cylinder can be before fuel begins to self-ignite prior to the piston reaching the top of the cylinder and before spark plug ignition. This is one reason why gas station fuels available during winter months, or at higher altitude locations, may have lower octane ratings compared to stations in warmer or at lower altitudes.For example, a car -with a minimum octane requirement of 85 and recommended octane of 92- may run great with 85 octane fuel in Denver (elevation 5280 ft) during winter months; but experience “pinging”, detonation, or preignition with the same fuel when driven to Arizona (elev.

Both are liquids at room temperature.