So what does this all mean? To compare the octane ratings we first need to understand what an octane rating means. Measuring octane ratings gets pretty technical but the basic takeaway is that the higher an octane rating, the more energy it takes for the fuel to combust. Higher performance engines require higher octane fuel because they create more compression and more energy, therefore they require fuel that can withstand the increased energy and not experience pre-ignition or detonation.
Pre-ignition can happen on its own or as a result of detonation, and occurs when the fuel mixture ignites prior to the spark plug firing. It can be caused by glowing carbon deposits within a cylinder, or other hot spots caused by detonation. Regardless of the cause, pre-ignition will cause a severe power loss as the piston is working against itself, and the cylinder temperature can rise dramatically as the burned mixture is compressed.
Since no power is extracted from the burn, all of the heat energy is absorbed by the cylinder components and can quickly cause a lot of damage. Detonation is distinguished from pre-ignition as it does not occur before the spark plug ignites.
In normal circumstances the fuel is supposed to burn evenly throughout the power stroke of the cylinder to providing pressure. If the entire mixture ignites all at once i. Detonation is usually caused by using fuel with too low of an octane rating because it requires less energy to combust and therefore combusts too rapidly. Aircraft engines are designed to be higher performance for their size and weight, increasing carrying capacity and overall engine performance.
The second major difference of avgas is that it contains lead the LL stands for octane fuel with low lead. Specifically, avgas uses a Tetraethyl Lead additive which is very effective in increasing the octane level of the fuel, thereby increasing the compression and temperature it can undergo before igniting so that it burns evenly throughout the combustion process and does not pre-ignite or detonate.
Aircraft engines are expected to be reliable, high performance relative to their weight, and be able to perform in extremely diverse conditions. All of these requirements lend themselves towards the use of high octane fuel in high performance engines, which is why the FAA is still permitting the use of small amounts of lead in aviation fuel. The FAA has created several different initiatives to investigate an unleaded replacement for aviation gasoline but has yet to find a sustainable solution.
As mentioned previously, diesel conversions have been pursued but not yet found real traction in the US marketplace due to the expense. Tens of thousands of airplanes have been issued an STC supplemental type certificate for automotive fuel conversion engines that are able to use the fuel you would put in your car. These engines are specifically made to be able to handle automotive fuel and their popularity seems to be mixed in the flying community.
Jet-A, the most common type of jet fuel, is made from kerosene and is similar to diesel fuel. Other discussion points in the conversation about jet fuel vs. Aviation gas still contains tetra-ethyl lead additives to lubricate the engine. Lead was taken out of automotive gas in Using leaded avgas in a modern car would ruin components such as the catalytic converter.
It would be like putting diesel fuel in your gas-powered car? However, Jet-A could be used in diesel-engine vehicles, but it lacks some of the lubricants found in road diesel fuel. Similar to a superpremium gasoline in formulation lots of high-octane alkylate!
Despite its formulation, it plays an analogous role in the aviation esp. GA world to the gasoline we put in our cars. Many light SLSA and ultralight aircraft, as well as some certificated types, can use this as it can be cheaper than LL; however, it's rarer to find it on the ramp, while LL is ubiquitous in the US and in other places where spark-ignition GA engines are common.
It is a highly refined kerosene that can be burned both in turbine engines and in diesel piston engines; spark-ignition engines can't use it though. It can be found anywhere commercial aviation is present, and thus is available worldwide. Role-wise, it is analogous to commercial diesel fuel, but furthermore can be substituted for diesel in some situations the military runs diesel engines on JP-8 all the time, but many jet fuels require a lubricity additive to be used successfully in diesel engines not purpose-designed to run on jet fuel.
JP-8 and JP-5 are the military kerosene-based jet-fuels JP-5 was the original naval jet fuel, with JP-8 being a modern derivative suitable for tri-service use. It was used in early jet aviation as it is easier to refine and ignite than Jet-A, but it has poorer safety properties than Jet-A. It can be found in extreme northern climes where Jet-A begins to crystallize or gelatinize. It is the fuel of choice for hot-air balloons, as it burns cleanly and lights off reliably with only a low-power ignition system fitted such as a piezo sparker.
As others have said, it's only seen in the occasional truckload headed to Reno. JP-7 -- A super-high-flashpoint jet fuel formulated for the SR Blackbird, but no longer made due to the discontinuance of the Blackbird program. It cannot be used in ordinary jet engines it won't ignite reliably.
RP-1 -- An ultra-refined kerosene, used for rocketry. Can be substituted for jet fuel, if you don't mind it costing more than ancient French wine on gallonage basis! These fuels are rather difficult to find now, and in some areas simply unavailable. A refinery might make a few truckloads on special order. Jet-A is basically clean Diesel, you can put it in your tractor or big truck with no harm to anything other than your wallet. Jet-B is regular jet fuel mixed with gasoline. Starts better in very cold weather, but also burns really, really well if you crash.
JetA is indeed a kind of diesel fuel prepared for use in turbines. There are a number of other jet fuels, such as JP1, JP2, etc, but these are fairly rare, since they are usually used for military turbines. Some engines can use 87 "mogas" buy they are mostly small engines and some converted ones. Even if 75 years old, this SAE paper contains useful information for those alien to the refining technology:.
Holaday, John Happel. Although flight operators can use both fuels interchangeably for flight operations, there are some differences in manufacturing specifications. For instance, Jet A1 has a lower freezing point OC than Jet A OC , making it suitable for long-haul international flights, particularly those overflying polar routes. Similarly, unlike Jet A, Jet A1 has static dissipater additives, which decreases any static charges that can form during the movement of the fuel.
Jet A1 is the most common type of jet fuel in the United States, and it can be used to power all jet aircraft.
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