By Steve Horne
Avgas, or aviation gasoline, grew out of the need to reduce detonation and increase horsepower in aircraft engines during WWI.
As military strategists realised how important aviation would prove, headlong improvements were made to aircraft and engine design. Improved performance and increased power were key – but while supercharged engines offered increased power, it soon became clear that the gasoline available at the time was not reliably up to a suitable standard to avoid detonation at high power settings.
The source of the fuel was important, with product from the Dutch East Indies offering relatively high aromatics and, critically, the aromatic Toluene, which gave aviation gasoline high anti-detonation properties. Toluene was also a key component of TNT, which meant the nascent aviation industry also faced competing demand for supply.
Shell was, at the outset, the Allies’ sole supplier of aviation fuel, with the product initially supplied in two gallon cans. By the end of WWI, fuel tankers had come into use.
In 1917 the British started receiving aviation gas from the USA, with Pennsylvania refined fuel offering the highest quality. Germany, meanwhile, had to source most of its fuels from Romania due to allied shipping blockades. The fuels used by both sides were in the 70 to 80 octane rating.
In early August 1917, the US Bureau of Mines, in co-operation with the Aviation Section of the US Army Signals Corps, began studying fuels for aircraft engines when it was found that no reliable data was available on the most suitable fuel. Flight tests were conducted at Langley, McCook and Wright airfields, while the US Bureau of Standards erected an altitude chamber to study performance at conditions encountered at high altitudes.
Results revealed that, in certain types of aircraft, motor gasoline gave as satisfactory a performance as Pennsylvania ‘high test’ gasoline, while in other types the pilots reported hotrunning with this fuel. An experimental fuel composed of 70% Cyclohexane and 30% Benzene appeared to be most satisfactory for fighting aircraft.
The war’s end changed the focus but not the world’s enthusiasm for the future of aircraft. The 1930s saw many new developments in aviation gasoline manufacturing processes. Knock engine tests would become part of all aviation gasoline specifications, as well as other quality control tests such as gum (actual and potential). Higher octane and performance would be achieved through the addition of Tetra Ethyl Lead.
There is a significant difference between aviation fuels and motor spirits used in automobile engines. The remarkable improvement in aircraft engines that took place in the years after WWI could not have been achieved without a correspondingly rapid improvement in the technology of fuel production. During this period, the power of the aircraft engine increased by 150% without any increase in cylinder capacity.
Brake-mean-effective-pressure increased by 100% and engine speed by 21%, whilst fuel consumption at cruising was reduced by 30%. By far the most significant leap forward would be the development of 100-Octane Aviation Gasoline.
WWII saw further advances in the refining and production of 100-Octane Avgas. Production of all grades of aviation gasoline expanded rapidly in the USA during 1943 and 1944, reaching an average of 500,000 barrels daily. During this period, 100-Octane gasoline constituted about two thirds of total production.
Post war, as aviation became dominated by jet aircraft, there was less demand for AVGAS 87 and AVGAS 115/145. A worldwide move towards unleaded gasolines, together with recognition of emerging environmental issues, also had an impact on the composition of motor gasolines.
The environmental pressure for low lead motor gasolines saw the development of a new grade of aviation gasoline, Aviation Gasoline 100LL (Avgas 100LL), which had a lower lead level than the traditional Avgas 100/130. To distinguish it from the green Avgas 100/130, the new grade was coloured blue. It was introduced in USA in 1975, but was not available in Australia and New Zealand until the 1980s.
Today significant progress has been made towards unleaded Avgas. At EAA Airventure this year, AOPA USA President Mark Baker noted this as the most important issue facing general aviation today. “The industry is committed to moving forward. We need to remember that this is not just about fuel; it’s about safety.”
The issue of unleaded fuel has been a hot button in the GA industry, with some regions in the US having banned or threatened to ban 100LL during the unleaded fuel transition.
In New Zealand we are starting to hear and, in some cases, see moves towards following suit. Kapiti Airport comes to mind. Since EAA Airventure 2022, a major step forward has been made in the manufacture and certification of an unleaded 100 Avgas. This has come after a decade-long effort from GAMI and
George Braly to develop and test a substitute.
According to Braly, Ann Arbor, Michigan-based fuel supplier of Avfuel, is standing by to manage the logistics and distribution of G100UL, and is open to partnerships. “Our arrangement is that any qualified refiner or blender of existing aviation fuels will be eligible to produce and sell it, subject to the quality assurance requirements that the FAA has approved.”
The timing for when G100UL will reach airports is still uncertain. “It’s going to take a while to manage the infrastructure, including manufacturing and distribution,” Braly says. The supply chain “is still a very wounded infrastructure, and that’s not going to make the process any easier, but we have a handle on how to do this and, with the support of the major players, I think we can. It’s going to be limited to begin with, but it can be ramped up rapidly.”
The question is, when will we see this in New Zealand?
AOPA NZ will be closely monitoring developments in the USA, and potential supply of G100UL to New Zealand. We are already in dialogue with CAA on this issue. However, there is another issue looming on the horizon for GA in New Zealand. Carbon neutral by 2050. A topic for another day!
This article first appeared in the Summer 2022 edition of Approach Magazine, the dedicated magazine of AOPA NZ, which is published quarterly.