A320 Neo gravity fuel feed ceiling

[vilas]

A320 CEO gravity fuel feed ceiling if the aircraft was below 30000ft is 15000ft. But in same case the Neo ceiling is 20000ft. Can anyone provide authentic explanation please? Thank you

[Check Airman]

The NEO has a larger mass than the CEO, so from Newton's gravitational equation, we can see that the bigger engine can more easily attract the fuel.

Sorry vilas. I couldn't resist. I'll get my hat.:}

[vilas]

Following from a safety first article
Limitations of fuel gravity feed. The altitude limitations linked to gravity feed are due to the application of Henry’s law. The law states that the concentration of a solute gas in a liquid is directly proportional to the partial pressure of that gas.Therefore, as the airplane climbs and as the atmospheric pressure decreases, so does the amount of air dissolved in the aircraft’s fuel. The excess air vents into the fuel tanks and engine fuel lines. At some point, the quantity of vapour present in the fuel, when it reaches the engine, may exceed the engine inlet maximum allowable vapour /liquid ratio and the operation of the engines is compromised.
This may give an idea that if an engine is handling higher volume of air may be it can handle more bubbling than the smaller one. But it is not authentic.

[pattern_is_full]

I don't know if this counts as "authentic," but at least some of the NEO aircraft have different fuel tank configuations than their CEO cousins.

And possibly more to the point, the center tanks on NEOs use jet-ejector-venturi pumps rather than electric feed pumps.

And those pumps themselves can "suck out" dissolved or entrained vapor. Rather like a reverse version of using a hypobaric chamber to cure the "bends" in deep-divers. While at the same time sucking in more fuel though a side-port to replace the vapor.

It is also the case that the performance of the venturi pumps and resulting gravity-feed limitations/calculations may vary per airframe. Which may be enough to explain the 5000-foot difference.

https://hursts.org.uk/airbus-nonnormal/html/ch07.html

https://encyclopedia2.thefreedictionary.com/jet+pump

Ejector Pumps are used to help ensure liquid fuel is always at the pump’s inlet, maintaining a constant flow of fuel from the pump to the tank. These make sure vapor pockets do not form, which could cause structural damage to the aircraft.

https://www.aviationsourcingsolutions.com/blog/aircraft-fuel-pumps-made-simple/

https://www.youtube.com/watch?v=0KsGD9XyW1s