# Fuel pressure change in closed fuel tank

• themindflayer
In summary, the conversation discusses the difficulties of measuring pressure at the bottom of a fuel tank and the effects of temperature on the fuel volume and pressure. The person is seeking advice on how to accurately measure the fuel volume and eliminate discrepancies. Suggestions are made to take average readings or measure the height of the fuel as well. The conversation also touches on the use of a pressure sensor at the top of the tank to compare readings.

#### themindflayer

Hi,
I am measuring pressure at the bottom of a fuel tank and temp variations are giving me a tough time. I wish to clear my head so here goes my reasoning as temp increases

- Tank Volume increases causing - height of fuel to decrease, pressure at the bottom of tank to decrease
- Fuel density decreases causing - volume of fuel to increase, height of fuel to increase, pressure at bottom of tank to increase
- Fuel vaporization increases causing - volume of fuel to decrease, height of fuel to decrease, pressure of fuel to decrease, however this leads to an increased pressure on the fuel, so since I am measuring relative to ambient pressure this should show an increase in pressure, right? The mathematics involved / equations are unknown to me, a few pointers here would be great!
- Any other effect?

What would the net effect of a temp rise be? Currently my data shows that as temp increases, pressure decreases.

Tank is 300ltrs, fuel is diesel.

Regards

Welcome to PF, Themindflayer.
I am in no way qualified to answer your question, but I have one of my own which might help to narrow down the scope of the problem.
What is your purpose in this measurement? Could you perhaps figure out some way to take an average so as to eliminate the thermal fluctuations? Maybe freeze-frame a measurement at an average point? Just thinking out loud...

I need to measure the fuel volume in a tank. I am using a pressure sensor to do that. My data shows pressure variation when no fuel is being consumed (hence change in volume), after compensating for temp the pressure variation still shows enough variation to appear as a liter or two discrepancy in fuel.

Sometimes in an entire day with no fuel consumption there is still a discrepancy of a liter of two which is boggling me.

Sometimes in an entire day the fuel variation sums up to zero.

Regards

You do know, I assume, that the fuel itself will change in volume, but not mass, due to thermal effects. I seems to me that you're trying to nail down a non-existent change in the actual amount of fuel in the tank.

Pressure equals density times height so the fuel expanding with temperature will not affect the pressure.

Dr_Morbius said:
Pressure equals density times height so the fuel expanding with temperature will not affect the pressure.

What in the living name of hell does height have to do with this? If you light a stick of dynamite, the pressure is a lot higher during detonation than it is before, with no change of altitude.

What is the sensitity of your sensor? 1 % may mean a fuel variation of 297l to 303l
Perhaps it has some hysterisis.
Next readings take a stick and measure the height of the fuel in the tank Take temp readings too. And then try to correlate your stick, temp and pressure sensor readings.

How are you measuring the pressure?

BTW if you light a stick of dynamite it burns like the wood pulp it mostly is. Blasting cap or its equal or no boom.

Danger said:

What in the living name of hell does height have to do with this? If you light a stick of dynamite, the pressure is a lot higher during detonation than it is before, with no change of altitude.

Really? The depth, height of the level, of the liquid. Come on it's not that hard.

You might try putting a pressure sensor at the top of the tank, above the fule. Look at the difference between sensors.

## What is fuel pressure?

Fuel pressure is the force exerted by the fuel inside a closed fuel tank. It is measured in units of pressure, typically pounds per square inch (psi) or kilopascals (kPa).

## Why does fuel pressure change in a closed fuel tank?

Fuel pressure can change in a closed fuel tank due to a variety of factors such as temperature changes, changes in altitude, and fuel consumption. These factors can cause the volume of fuel inside the tank to expand or contract, which in turn affects the pressure.

## What are the potential consequences of a significant fuel pressure change?

If the fuel pressure changes too drastically, it can lead to problems such as fuel leaks, fuel pump failure, or engine performance issues. It is important to monitor and maintain appropriate fuel pressure levels to ensure efficient and safe operation of the vehicle.

## How can fuel pressure be measured in a closed fuel tank?

Fuel pressure can be measured using a fuel pressure gauge, which is attached to the fuel line and provides a reading of the pressure inside the tank. The fuel pressure can also be monitored using a vehicle's onboard diagnostics system.

## What steps can be taken to prevent significant fuel pressure changes in a closed fuel tank?

To prevent significant fuel pressure changes, it is important to regularly maintain the vehicle and its fuel system. This includes checking for fuel leaks, ensuring the fuel tank is properly sealed, and monitoring the fuel pressure levels. Additionally, avoiding extreme temperature changes and properly storing the vehicle can also help prevent drastic fuel pressure changes.