Calculating Gas Expansion Ratio for Fireball Formation

[burnit]

Hi All,

How to work out the expansion ratio of a gas fireball.

Eg:
Just say we have a ball of gas-- no container, 1 liter in volume suspended in mid air & we ignite it, how far would the flame front extend to form the fireball, what volume would it occupy once ignited?.

An example of the equations would be helpful, i haven't specified what gas, density etc etc as i am not sure exactly what is needed to calculate this.

Thanks

 

[burnit]

Just to elaborate a little further on the above questions as it may have been taken for an out of the blue query--not so & any help would be greatly appreciated.

We have setup an experiment on a small controlled scale to find the volume occupied by the ignition of various gasses compared to the starting volume of the gas.

In our controlled experiment we have been using a gas confinement chamber with high Elasticity so once ignition occurs the confinement chamber expands to X area & volume.
This works very well except for the tension of the elastic chamber itself, the tension increases with increasing diameter & confines the true volume change of the gas fireball in normal atmospheric conditions.

I need to be able to calculate the volume change of ignited gasses compared to our results & hence the question.


Thank You

 

[sir-pinski]

Calculating the expansion ratio of a gas fireball is a complex process that requires knowledge of various factors such as the type of gas, its initial temperature and pressure, and the surrounding environment. Here are some general steps you can follow to estimate the expansion ratio of a gas fireball:

1. Determine the initial volume and temperature of the gas: In your example, you have specified that the gas is 1 liter in volume. However, you also need to know the initial temperature of the gas, as it will affect its expansion once ignited.

2. Calculate the initial pressure of the gas: If the gas is contained in a container, you can use the ideal gas law (PV = nRT) to calculate its initial pressure. If the gas is not contained, you may need to make some assumptions about the pressure based on the surrounding environment.

3. Determine the energy released during ignition: This step requires knowledge of the type of gas being used. Different gases have different energy release values, so it is important to know this information in order to accurately calculate the expansion ratio.

4. Use the energy release and initial conditions to calculate the expansion ratio: Once you have all the necessary information, you can use the energy conservation equation (E = Q + W) to calculate the expansion ratio. Q represents the energy released during ignition, and W represents the work done by the expanding gas.

5. Estimate the flame front distance and final volume: The expansion ratio will give you an idea of how much the gas will expand, but to determine the actual flame front distance and final volume, you will need to take into account other factors such as heat transfer and convection.

It is important to note that this is a simplified approach to estimating the expansion ratio of a gas fireball. The actual calculation may involve more complex equations and may vary depending on the specific scenario. It is always best to consult with a fire safety expert or perform extensive research before attempting to calculate the expansion ratio for a specific gas fireball.