What is Fuel System Icing Inhibitor?
Fuel Anti-Icing, or FSII (Fizzi, the slang for FSII) as it is often referred to, is an aviation fuel additive. Its primary chemical Diethylene glycol monomethyl ether, also referred to as DiEGME. DEGMME (Deggeme) has been around for over 50 years. CSD Aerospace is the original producer, having formulated the product at the request of the U.S Military. It is now produced and sold by two separate chemical brand names, Methyl Carbitol and Prist@
FSII is required to prevent entrained water in the fuel from freezing at sub zero temperatures, resulting in ice crystals which can plug fuel filters, causing fuel starvation and subsequent engine failure. Designed primarily for turbine aviation fuel, FSII may also be used in piston aircraft using IOOLL Avgas. The additive itself is exactly the same for both types of fuels and is produced to ASTM specification D4171 and to Military Specification MIL-DTL-85470B.
To find out if you require FSII in your aviation fuel, consult your aircraft engine or flight operations manual. This will specify year round use or use within a specified outside air temperature range.
Systems containing aviation fuel anodized with FSII must utilize a Coalescer/ Separator Filter. Monitor elements may not be used with aviation fuel containing anti-icing additives like FSII, as independent filter manufacturers have confirmed that the presence of these additives inhibit the performance of the monitors. If FSII is injected downstream of the final filtration point, monitor elements may be used on the fuel supply system.
The reasoning behind the filter manufacturer's recommendation of utilizing the filter coalescer/ separator is due to the fact that FSII does a good job of "hiding" water that is present in fuel by microencapsulating it, which makes it non-detectable to the filter monitor which is searching for water to absorb. The result is water will pass freely through the monitor element with the fuel. The filter coalescer/ separator will separate the water from the fuel during the 1st stage of the filtering process. The filter media inside the coalescer and "sock-like" outer layer work to coalesce moisture, allowing smaller droplets to grow larger, becoming heavier droplets which fall into the filter sump for drainage (sumping). Filter coalescer/ separators should contain a water defense system to automatically stop the flow of fuel when excess water is detected.
There are two types of water in fuel, free water and entrained water. The free or visible water in a fuel tank can be checked by utilizing water detection paste applied on the bottom of a gauging stick, or gauging tape. It is recommended that daily sumping of tanks to remove any water, or particulate assists in maintaining clean, dry and on-spec fuel to the flying public. Finding contamination in your storage tank is not necessarily a bad thing. If water is identified, it is important to isolate it and remove it. Failure to sump and analyze fuel samples for contamination can lead to excessive filter change-outs, and bacterial growth in fuel tanks.
Entrained water is moisture that remains suspended in the fuel. There are test kits available to measure amount of the entrained water and determining concentration range.
Whenever handling FSII, as well as all aviation fuels, use appropriate PPE (Personal Protection Equipment) to provide protection to skin or eye contact. Chemicals and solvents are great in aircraft fuel, but can be absorbed through your skin and cause health problems. In all cases, consult your product SDS to review storage and handling requirements.
Performing these, and any of the array of quality control tests takes training on how and why they are performed. As the quality assurance person, it is a great responsibility to maintain the quality of the fuel throughout the handling process. Keeping employees current through Aviation products quality assurance training courses will ensure you supply clean, dry and on specification fuel to your customers.