Vaporization pressure in a fuel can

In summary, the normal behavior of a plastic jerry can used for gasoline is that it expands by the pressure caused by vaporization of the gas. To reduce this pressure during storage, the best alternative would be to fill the can nearly full, leaving some air at the top. This is because the can's non-rigid structure allows for slight expansion in the head room, counteracting the pressure caused by fuel vaporization. However, if the fuel and can have different coefficients of thermal expansion and the can is very rigid, filling it completely could result in high pressures. In any case, the pressure in the can's head space will always be higher than the vapor pressure alone due to the presence of air.
  • #1
Anders L
1
0
A normal behavior of a plastic jerry can used for gasoline is that it expands by the pressure caused by vaporization of the gas.

Which option below will be the best alternative to reduce the pressure caused by vaporization in a jerry can during storage? :

- Fill up the can as much as possible

- Fill up to let say 80% of the total volume, leaving some air at the top

Regards Anders
 
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  • #2
I think the vapour pressure depends only on the temperature, so my guess is that the fluid level won't have any effect.

Cheers,
Terry
 
  • #3
If one treats the can as being perfectly rigid, that is correct -- the fluid level will not have any effect. The increase in pressure will be exactly equal to the vapor pressure of the fuel.

If the can is non-rigid then leaving a lesser amount of head room means that a small expansion in the can results in a (relatively) larger expansion in the head room. So the expected increase in pressure due to vaporization of the fuel is countered by a slight expansion in the can and the pressure only increases slightly.

So... in the real world my answer would be to fill the can nearly full up.

However... if the coefficient of thermal expansion of the fuel is different than the coefficient of thermal expansion of the can and if the can is very rigid and if the temperature rises or falls then a completely full can could be subject to very large pressures. (e.g. consider what happens to a glass bottle completely full of water in the freezer). Jerry cans are not that rigid. Still, it can be unwise to fill a rigid container completely.
 
  • #4
I think that even in the non rigid container case the pressure will always settle at the vapour pressure for the temperature.

Cheers,
Terry
 
  • #5
Not if there is any air in the head space.
 
  • #6
OK.
Could you please provide the "why is it so"?

Cheers,
Terry
 
  • #7
The pressure in the head space is the sum of the air pressure plus the vapor pressure. When you initially tighten the lid on the can the head space is full of air at atmospheric pressure. Fuel eventually evaporates so that the partial pressure of fuel vapor in the head space is equal to the vapor pressure of the fuel at the current temperature. But the air is still there, so the resulting pressure will be strictly higher than the vapor pressure alone.
 

1. What is vaporization pressure?

Vaporization pressure is the pressure at which a substance transitions from a liquid state to a gaseous state at a given temperature.

2. Why is vaporization pressure important in fuel cans?

Vaporization pressure is important in fuel cans because it determines the point at which the fuel will vaporize and ignite. If the vaporization pressure is too low, the fuel may vaporize too easily and cause a fire or explosion.

3. How is the vaporization pressure of a fuel can measured?

The vaporization pressure of a fuel can be measured using a variety of methods, such as the Reid vapor pressure test or the distillation method. These tests involve heating the fuel and measuring the pressure at which it begins to vaporize.

4. What factors can affect the vaporization pressure of a fuel can?

The vaporization pressure of a fuel can be affected by factors such as temperature, pressure, and the composition of the fuel itself. Higher temperatures and pressures can increase the vaporization pressure, while the presence of certain additives or impurities can lower it.

5. How can the vaporization pressure of a fuel can be controlled?

The vaporization pressure of a fuel can be controlled through proper storage and handling techniques. Keeping the fuel at a stable temperature and pressure can help prevent it from vaporizing too easily. Additionally, using high-quality, pure fuels can also help maintain a safe vaporization pressure.

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