Detecting Water in Jet Fuel
With Capacitive Sensing

What is jet fuel?

Jet fuel,or aviation turbine fuel, is a type of fuel designed for use in gas-turbine powered aircraft. The term “Jet Fuel” does not refer to a specific chemical composition, or mixture of hydrocarbons. Instead, jet fuel is defined by its performance specifications – being required to meet the unique challenges posed by use in high-altitude aircraft.

Why is water in jet fuel a problem?

For a hydrocarbon mixture to be defined as jet fuel, one of the most important criteria it must meet is a low freezing point. As an aircraft climbs higher into the atmosphere, it is subjected to lower and lower temperatures. This is why a low freezing point is imperative in jet fuel, and it is also why the presence of unexpected water in jet fuel is problematic.

As the temperature drops due to gains in altitude, free water in aviation fuel can begin to precipitate, and drop to the bottom of the fuel tank. This happens because water is denser than the fuel in which it is located. Once the water is no longer suspended in the fuel it can begin to form droplets. These droplets can be incredibly dangerous, because they can freeze when exposed to subzero temperatures. Once ice is present in the tank it can result in blockages and interfere with the fuel delivery system. In order to avoid this, it is generally accepted that jet fuel must stay below a 30ppm water to hydrocarbon ratio.

This phenomenon is the suspected cause of the accident involving British Airways Flight 38. In this incident on January 17th, 2008, an international passenger flight from Beijing to London crashed while attempting to land on the runway at Heathrow International airport.

After numerous investigations, it has been theorized that a compromised fuel delivery system was responsible for the crash. There was no evidence of a mechanical failure, and it is thought that the problem arose due to a blocked fuel line,caused by frozen water in the aircraft’s fuel system. Fortunately, none of the passengers on board were killed, and relatively few were injured, but the incident serves as a stark reminder of the dangers of water contamination in aviation fuel.

How does water get into jet fuel?

Water contamination occurs in jet fuel for reasons that are not unique to it, but are present across all fuel types and systems. The most common of which is simply weather.When a tank, truck, or storage system is exposed to wet weather, such as rain or snow, it is possible for water to find its way into the fuel tank,especially if it hasn’t been sealed properly.

Another potential source of contamination is human error. Although the individuals who work in aviation are highly trained and competent, mistakes happen. Something as simple as forgetting a gas cap, or failing to notice a cracked tank can have dire consequences when it comes to fueling a modern aircraft.

Likely the most common source of unaccounted for water in jet fuel is condensation. Just like any standard gas tank, the empty portions of a tank of jet fuel can begin to form condensation. Moisture is attracted to the cold, and because jet fuel evaporates very quickly it tends to result in the walls of the tank being colder than the surrounding area. This causes the water vapor in the air to be attracted to the walls of the fuel tank.

How is water in jet fuel detected?

Due to the factors detailed above, removing all of the water from jet fuel can be impractical. Therefore, commercial aircraft often use fuel heaters to prevent the water in fuel from reaching subzero temperatures.

As for detecting water contamination in the first place, there are chemical tests that can be done to ensure that a fuel’s water levels are within safe operating standards, but the primary alarm system is one of manual, visual inspection. Most of the discrepancies in the fueling, and fuel storage processes are caught by observant pilots and technicians, but if not for these individuals’ training and expertise it is possible that many problems resulting in higher than normal water content would go unnoticed. This problem is exacerbated by the fact that when in a suspended state, water in most fuels is only noticeably visible around the 1000ppm mark, which is well above the 30ppm water that jet fuels are required to maintain.

Using capacitance to detect water contamination

On-line capacitive sensing can help to remedy this problem by providing a live, real-time readout of the fuel’s water content wherever it is installed – from storage tanks to transport trucks, or anywhere else in the process that is desired. Capacitive measurement technology does not serve to replace the existing tests and standards for determining water content in jet fuel, but to exist alongside these established technologies and serve as a secondary alarm system to notify technicians when water content is approaching an unsafe level. This is why this non-destructive technology can play a crucial role in the maintenance and safe usage of this vital fuel type.


Delta C Technologies

Delta C is a specialized water cut meter manufacturer based in Western Canada. We develop advanced capacitance technology for water cut metering and build field-ready water cut meters and sampling systems. Delta C’s expertise on watercut measurement in the oil and gas industry spans over 30 years, with a specialization in low PPM measurements.