In order to consider Jet A1 fuel safe to use, it should have no contaminants present. Given that information, water is a very common type of contaminant, but how much water is there supposed to be in the fuel for it to be considered as contaminated.
1
-
4$\begingroup$ A little water being fed into a turbine may not be such a bad thing, but freezing in the fuel lines would be. $\endgroup$– Robert DiGiovanniCommented Nov 13 at 22:23
Add a comment
|
4 Answers
$\begingroup$
$\endgroup$
There are standards to test fuel contamination, applicable to fuel check methods and detection kits (e.g. ATA 103, EI 1530, GOST 10227 for the Russian Federation), but no standard for the limit itself, only accepted values. For free water, the accepted value varies between 15 ppm (military) and 30 ppm (civil aviation).
The limit used by refuellers and operators, 30 ppm, is set by the International air transport association (IATA).
Principle
Water is not miscible with fuel but they can form an emulsion up to saturation at 40 to 80 ppm of water. The warmer the temperature, the higher the ratio of dissolved water that can be present in the emulsion. When the emulsion temperature is lowered, water in excess separates as free water. This also happens when the emulsion is at rest. This free water is a hazard, e.g. it can freeze and it can allow microbiological growth, with a risk of filter blockage and tank and pipe deterioration.
FAA
FAA just says in AC 20-125 - Water in Aviation Fuels:
Aircraft engines will tolerate a small amount of free water (30 ppm. is usually considered to be the maximum) if it is in a fine, uniformly dispersed state.
IATA
For commercial transport, the criteria is the recommended limit provided by IATA, the international carriers syndicate, in:
- IATA Guidance Material for Aviation Turbine Fuels Specifications, Part III ─ Cleanliness and Handling
For Jet A-1 the tolerance is 30 ppm of undissolved (free) water.
ICAO
ICAO position confirms there is no standard (SARP) for commercial aviation:
The Current Regulatory Provisions on Aviation Fuel Safety: There are no SARPs yet on the aviation fuel. Following an accident met by A330 aircraft of Cathay Pacific Airlines in Hong Kong in 2010, the International Air Transport Association (IATA) had developed a manual on Civil Aviation Jet Fuel Supply which was later on circulated by ICAO as Doc 9977, Manual on Civil Aviation Jet Fuel Supply. However, this publication is not yet associated with any one specific ICAO Annex.
In Doc 9977, Manual on Civil Aviation Jet Fuel Supply ICAO defines fuel contamination referring to IATA criteria:
Fuel contamination. For the purpose of this document, fuel that is cross-contaminated by other products, [...] fails the visual clear and bright check or exceeds the cleanliness limits set out in IATA Guidance Material for Aviation Turbine Fuels Specifications, Part III, Cleanliness and Handling [...]
Fuel Providers
- The IATA value considered as the reference is mentioned in fuel specifications from providers, e.g. in this Total Energies article on fuel contamination, when discussing about storage tanks and delivery:
Maximum content of free water tolerated by IATA is 30 ppm at ambient temperature at point of delivery into the aircraft tank.
- also by Chevron:
IATA publishes a document entitled Guidance Material for Aviation Turbine Fuels Specifications. The guidance material contains specifications for four aviation turbine fuels: three kerosine-type fuels (Jet A, Jet A-1, and TS-1) and one wide-cut fuel (Jet B). Jet A meets the ASTM requirements, Jet A-1 meets the Joint Checklist requirements, TS-1 meets the Russian GOST requirements, and Jet B meets the Canadian CGSB requirements.
$\begingroup$
$\endgroup$
1
A water contamination of 30ppm in jet fuel is considered the threshold for concern. Once the amount of water is above this the fuel is considered unfit for use due to concerns such as the fuel freezing and blockages. (This is the case for Jet A and Jet A-1 fuels. Other fuels safety thresholds may differ) Sources: Code7700.com Trustedfuel.com
-
$\begingroup$ Is that based on a lab test? My post was more from the pilot's perspective, or the mech doing a DI and seeing a slug of water coming out a sampling drain. $\endgroup$– John KCommented Nov 13 at 23:07
$\begingroup$
$\endgroup$
4
From the perspective of the pilot finding water on a pre-flight or mechanic on a DI, kerosene and water separate out similar to water and gasoline. This means that water in the fuel will slosh around the bottom of the tank as kind of blob or slug of water, since the kerosene is lighter.
When fuel is sampled from the low point drains, if you get water in the sampling cup you will keep draining fuel until there is no more water. It's normal to find small amounts of water in the tank because condensation forms on the inside surfaces above the fuel level, especially if the airplane is left outside overnight.
If you get very large amounts of water (you'd be getting only water for several samplings before kerosene starts to appear) you would need to investigate the source (such as a leaking overwing fuel cap (called a "bung") after sitting in the rain).
However, I'm not aware of any go-no-go standard on water volume in a drain sample for deciding to dispatch an aircraft.
A more common problem is ice crystal formation in fuel when temperatures are low and micro droplets of water are present in the fuel. Most transport aircraft use fuel heaters (normally an engine-oil-to-fuel heat exchanger) to warm it up before it enters the fuel control system of the airplane, to deal with low to moderate ice crystals. Heavy crystal formation can block filters.
The usual mitigation is fuel additives that lower the freezing point of water so that microdroplets in the fuel (that haven't settled to the bottom yet) won't crystalize as free floating particles in the fuel.
-
2$\begingroup$ This seems to contradict the other answers: Up to some low ppm, water can mix with fuel (may be a suspension/emulsion, may be true mixing) $\endgroup$ Commented Nov 14 at 12:33
-
2$\begingroup$ @Peter-ReinstateMonica Some can be suspended as micro drops, but eventually it settles out and migrates to the drains, water having about twice the Sp Gravity. In any case my post was based on what a pilot draining sumps would have to deal with, and suspended microdrops would not be apparent. Testing fuel samples for contam is another story. I made some edits to clarify. $\endgroup$– John KCommented Nov 15 at 1:50
-
$\begingroup$ deep draining until... looks like a typo for "keep draining", but I don't have the rep to make a 1-char edit. $\endgroup$ Commented Nov 15 at 17:52
-
$\begingroup$ @PeterCordes I was going to concoct a story about how "deep draining" is a thing, but just decided to fix it. lol Thanks $\endgroup$– John KCommented Nov 15 at 23:26
$\begingroup$
$\endgroup$
In Compression Ignition (Diesel) Engines, water emulsion up to 2 % improved noise, emissions, power (see M Reza Seifi, 'Fuel' magazine, 2016), it's similar to Water Injection in WW II Aircraft Engines, allowing top power increase for a while without risk of heads and pistons melting, but water injection damages engines.
Total in France had patents on how to prepare Water in Diesel fuel emulsions. This reduces NOx emissions as it reduces flame, combustion temperatures.
Bacteria thrive in the interface of fuel and condensation water in fuel deposits, its metabolism generates corroding acids, a problem for Industrial Microbiologists to solve.
Heating the fuel was implemented long ago in the Iskra training Jet, was also proposed by an Spanish Utility Model for car engines; if heating fuel is an alternative to carburetor heating to avoid carburetor icing, I don't know. Blessings +
