Ejection Temp

Well-Known Member
Does anyone have any data regarding ejection temps? I am looking at temperatures at the forward end of the motor mount and a few inches forward as well.

Stymye

Well-Known Member
woah...lots of factors involved but you can get a basic idea

for black powder the combustion gas temp is 3307 degrees

you have to divide this number by a constant (R)
the constant for black powder is 22.16 per foot
or 1.846 per inch

so if you wanted to know the(theoretical) temp say 6" from the charge you would multiply 6(inches) X 1.846....=11.076

divide the combustion gas temp 3307 by 11.076...
= 298 degrees,,but you would have to factor in the volume of the chamber,diameter of charge ...ect .but you can be sure that the temp will be no higher than these calculations

hope this helps some

KenParker

Well-Known Member
The knowledge base available on this forum never ceases to amaze me. I learn something new nearly every time I read the new posts.

stymye, that info on black powder gas temperature, and how it changes over distance.... very useful. Thanks.

Stymye

Well-Known Member
thanks butl I forgot about ejection charge weight

a 24 estes engine is .85 grams
an 18mm is .5 grams

but I forget how to add that to the mix. lol

you can actually figure out how much pressure is generated from these equasions also ...like figuring how much FFFF you might need for a highpower bird

I'll post this formula to the forum later

bobkrech

Well-Known Member
Stymye

I think you got your equations from InfoCentral article on Black Powder sizing by Ted Apke https://www.info-central.org/recovery_powder.shtml

These equations assume the gas temperature is 3307 R and are used to predict the peak pressure obtained when a certain weight of BP are burned in a given volume. A temperature of 3307 R is about 2850 F or 1564 C. That hot.

Calculating the gas temperature during the gas expansion is far more complicated and requires solving a bunch of time dependent differential equations to get an accurate answer. Ted's equations don't touch that aspect of the problem.

When you go through the equations describing the chemistry of the BP decomposition, you will find that 1 gram of BP generates about 120 cubic inches of hot gas at the combustion temperature and atmospheric pressure which will fill the parachute compartment and damage or melt an unprotected parachute. After the gas cools to room temperature the volume is 20 cubic inches, a factor of 6 reduction to the the lower temperature.

Baffles, wadding and chute protectors preventing hot particles from impinging on a chute and by providing surface area to cool the gas.

Bob Krech

Stymye

Well-Known Member
Thanks Bob

actually I wrote most of the equasions down from a post some one made on rmr about a year ago and just went from there.. I guess It must have been Ted Apke,,so he should get the due credit for it

I wasn't aware of the article
and It explains some things that I was not fully understanding
in far more detail..plus it has a calculator! sure makes things much easier!

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