Deflagration speed

[SamanPatou]

Is there a way to find an average speed for a deflagration?

Wikipedia states that they are typically far below 100 m/s, so this value can at most be a high end.

However, it doesn't provide alternatives, and I don't know how to determine such value myself, assuming it is possible.

 

[SamanPatou]

I've found an article that places the speed of flames between 1 m/s and 350 m/s, giving us a way to establish at least 3 ends, although the gap is quite high and 1 m/s is absurdly slow.

Still, does anyone have an idea about how to decide which end would be better, if they were to evaluate a calculation?

 

[SamanPatou]

Bump

 

[AbaddonTheDisappointment]

Only thing I would assume is if there isn't one accurate speed just use an average of the speeds or something. Really the only way to do this unless you want multiple ends for every single speed

 

[SamanPatou]

The problem here is to find an actual average.
Like, 175 m/s is the exactl half between the two proposed limits of deflagrations, would it be feasible as an average?

 

[AbaddonTheDisappointment]

I mean unless there's a concrete value in a reputable article you can find, averages are really the only way to go unless we want to straight up guess.

Also I do find it weird it points out the speed is subsonic then immediately claims a supersonic speed

 

[SamanPatou]

Supersonic is only for conflagrations, if I get it right.

The average would be 175 m/s, but Wikipedia also says that they typically travel far below 100 m/s, so I'm unsure if it would be the most reliable value.
Still, I'm far from being knowledge on this stuff, so I can't really cast a judgement, which is why I made this thread.

 

[AbaddonTheDisappointment]

Honestly, no idea either considering I don't know much about deflagrations. Only brought up averages since I thought it may be a solution but considering the two articles contradict each other with their info, wasn't really the best idea in hindsight.

 

[Jasonsith]

Noted.

1. This article says laminar flame speed sits at arounf 19 cm/s, i.e. 0.19 m/s...
2. A 12:1 compression ratio gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s, and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds are also very dependent on stoichiometry.
3. Real life wildlife fire spreading speeds are just 10 miles per hour or 2.778 m/s

So while yeah subsonic speeds are achievable, many flames are way slower.

But again, fireball speeds and flamethrower speeds are determined by wind speeds, air pressure ratios and a lot of other factors.

 

[SamanPatou]

Then I assume there isn't a way to establish an actual end.

This problem came out mainly because I noticed a flaw in this calc, which is assuming that the flames were travelling at 100 m/s, using Wikipedia as a source, despite it saying that usually they travel slower.
Since no further details are given about the fire (pressure and such), should the feat be considered not calculable?

 

[Jasonsith]

Well in that case it is important to know how fast the fireball can grow instead of blindly slapping in a stated value.

Or, how any real life flames the said fire projectile is the most comparable to.

Two more step actually.

 

[SamanPatou]

Do you think it would be useful to write some guidelines and put them into some page on the wiki, although I don't know how necessary it would be, and I'm totally unable to elaborate them.

Do you know a way to determine such steps?

 

[Jasonsith]

Where should we even put that in the first place?

Like it could just be as simple as another projectile dodging speed or a separate page.

 

[SamanPatou]

We could either create a page about explosions in general (conflagrations, deflagrations...) and how to handle them when performing a calc regarding speed, or maybe expand the Projectile Dodging Feats page, which I believe also covers reacting and such.

Or, how any real life flames the said fire projectile is the most comparable to.

Do you have any example of these real life flames?

 

[Armorchompy]

yeah we need to actually set up guidelines here since it's very muddy