Jet fuel oil has to perform an important job. It lubricates various parts of an engine so that losses due to friction are kept to a minimum. The correct oil may change with the time of year or depending on the engine usage. There are several different types of jet engine oil and they all have different properties. These are the 7 most important properties to consider when testing jet fuel lubrication.
- Lubrication and molecular size
The oil forms a barrier between various engine components and reduces friction. The size of the molecules of the oil will determine how good it is at lubricating.
- Viscosity and temperature
The viscosity of an oil is not a fixed parameter because it varies with temperature. Oil is thicker in colder temperatures. Whatever the outside temperature, it is vital that the correct oil pressure is reached within 30 seconds or engine damage can occur.
- Additives and contamination
You often read that additives clean an engine, but what they actually do is keep any contaminants suspended within the oil itself, so that they do not build up in a particular part of the engine and cause damage. The additive ZDDP is one example.
- Cooling the engine
Heat from the engine is transferred to the oil as it flows around the hotter parts of the engine, such as the pistons and cylinders. The oil must be capable of being cooled by a thermostatically controlled oil cooler so that it can be maintained at the optimum operating temperature.
- Oil grade
In the past, jet engine oil provided by jet fuel suppliers was a single grade oil (usually 80 grade or 100 grade), but now multigrade is more popular. This means that it will work well over a wide range of temperatures. It is not possible to mix mineral oils with synthetic oils. You must stick to one or the other.
- Noise reduction and sealing
To keep noise levels down, gas blow-by between the piston rings and cylinder walls must be prevented. The oil achieves this by forming a thin film which creates an air-tight seal. Gas blow-by is prevented and noise levels are maintained within acceptable limits.
- Corrosion protection
Oil becomes contaminated by various products of combustion (soot and coke) and by water vapour and gasoline products. The contaminants can cause an acidic and corrosive sludge. This can be very damaging to the jet engine.
The ashless dispersant oils are used after the first few hours of engine break-in. The dirt remains suspended within the oil and is removed by the oil filter as the oil circulates.
However, the additives do get used up and the oil has to be changed regularly. Each aircraft has a recommended frequency for oil changes. This helps to prevent corrosion and damage.
By paying careful attention to the 7 most important properties of jet fuel lubrication provided by jet fuel suppliers, the best performance can be obtained from jet engines.