What and how to prevent the freezing of an aircraft fuel?

Welcome to today's blog...

We have discussed a lot about an aircraft and the possibilities which might happen. Today let's discuss the danger of freezing fuel. The freezing of the fuel can lead to a decrease in the engine output and makes the engine to flame out. There are two types of diesel available based on the freezing point, i.e., 

Summer diesel and Winter diesel which is chemically treated to have lower cloud point and vice versa.

Basically, the commercial fuel for an aircraft is categorized into three types: Jet-A1 fuel is available outside the U.S, Jet-A only available in the U.S, and Jet-B used for military aircraft and sometimes available in Canada and Russia because of its low freezing point. Freezing point is similar to the cloud point temperature it is defined as when the jet fuel becomes cloudy/moisturised and the temperature gets nearly 6 deg lower than the freezing point temperature; thus, solidifies as wax.

Jet-A1 = -47 deg (freezing point temp) 

Jet-A = -40 deg (freezing point temp)

The fuel is filled into the wings at ambient temp (e.g. 25 deg), however, it depends where you're. In extremely cold weather, the fuel is preheated and then filled into the aircraft so that the aircraft can cruise and the fuel temp gets lower while in contact with the atmosphere air. Based on the research, the cooling rate of the fuel can vary from 3 to 11deg/hr. The fuel temp is measured using a sensor called Thermometric Fuel Temp Sensor and the sensor reading can be monitored in the Cockpit. It is mandatory for the pilot to monitor the fuel temp so that no unwanted situation will rise up. Considering Jet-A fuel at -37deg the sensor will trigger and responds to the situation to be critical which is 3 degrees less (prior) than the actual value. Then pilots have to monitor when and at what temp the fuel has been filled in the flight. Based on that they have to calculate the decrease in the temp by looking at the flight distance left for the destination to have a safe flight. The Aviation board recommends pilot to monitor the indicated fuel temp and the air temp as the difference of the temp allows them to take further action. 

Following steps can be taken to reduce the fuel temperature:

1. Increase in speed. Results have shown that 0.01 Mach increase in the speed will increase the total air temp respective to fuel temp by 0.4 - 0.7 degrees, thus, requires more fuel to burn.

2. Descend to normal air temperature. Based on the rules and regulations it is recommended to have 2000-3000 feet below the optimum altitude (Best Cursing Altitude). Research shown that at around 4000 feet lower altitude 8 degrees increase in the total air temp which respectively lowers the fuel temp.

3.  Divert the flight to warmer air mass. It is recommended to fly away from the jet stream. 

These are the major points to be noted, but still, the fuel can freeze as the fuel contains water and some kerosene in it whereas, the water particles freeze below zero degrees. To prevent this, a heat exchanger is placed before the fuel goes to the combustion chamber which warms up the fuel as per the requirement. The hot tubes lines run adjacent to the fuel tubes to make them warm as required so that the engine can work effectively.  

Thanks for reading it....