I have already referenced synthetic hydrocarbons earlier in my blog and the important question on whether Sustainable Aviation Fuel, such as Neste MY Renewable Jet Fuel, is safe to operate in turbine engines. To understand this better, you will have to brush up on your chemistry a little bit.
Conventional jet fuel is primarily composed of chains of hydrogen and carbon, or hydrocarbons, in the range of C8 to C16. During manufacture, crude oil with various hydrocarbons is distilled to produce various cuts of specific hydrocarbon ranges, which are classified as diesel, gasoline etc.
The C8 to C16 hydrocarbon chain is designated as kerosene or jet fuel. All of the jet engine turbines and fuel systems are designed to utilize this composition of hydrocarbons for optimum combustion and operation. Neste MY RJF is also comprised of the same chain of hydrocarbons that are designated for conventional jet fuel.
These hydrocarbon chains are produced from the HEFA process with feedstock which is not natural crude oil, hence the term ‘synthetic hydrocarbons’. Since the hydrocarbon chain matches that produced from crude oil, there is no impact on the turbine operation when Neste MY RJF is used.
Why does sustainable aviation fuel need to be blended with conventional jet fuel?
A few of you have probably already caught on to the fact that if the hydrocarbon chains are identical then why does Neste MY RJF need to be blended with conventional jet fuel? The answer to this is aromatics. Aromatics carry a bad reputation as the cause of pollution, and rightfully so. When combusted, these aromatics generate soot and particulate matter that can be harmful to the environment. But in a jet engine a minimum amount of aromatics are necessary in order to ensure the proper swelling of the elastomeric seals in the fuel systems and prevent leakage, which can be a fire safety hazard.
ASTM D1655 specifies a minimal level of aromatic content to be present in the fuel. While aromatics are found naturally in crude oil and subsequently in conventional jet fuel after fractionation, the feedstock used to produce Neste MY RJF using HEFA process does not contain these compounds. Hence HEFA fuels are typically less dense than conventional jet fuel. In order to meet the minimum aromatic content requirement, Neste MY RJF has to be blended.
Safety of Neste MY Renewable Jet Fuel
This brings us back to the topic of safety. As it currently stands, sustainable aviation fuel, such as Neste MY Renewable Jet Fuel, cannot be used in neat form and needs to be blended with conventional jet fuel. The ASTM D7566 certified synthetic component is blended with an ASTM D1655 fossil component and then re-certified as ASTM D1655.
The blended jet fuel is analyzed again to ensure that all ASTM D1655 properties are met and all subsequent documents are updated or amended. This allows the fuel to be transported in the existing infrastructure and loaded on to the aircraft without requiring any special handling or segregation.
Prior to the blending operation, neat Neste MY RJF does require segregation and cannot be placed in and unblended form in the existing infrastructure. Neste MY RJF complies with EI JIG 1530 guidelines for quality assurance and handling procedures related to blending and distribution.
In aviation, safety is never compromised. Sustainable aviation fuel, such as Neste MY Renewable Jet Fuel is ASTM D7566 certified and is safe to be used in flights when blended with conventional jet fuel.