I've been looking for this for quite some time now, and I can't find anything other than calculations where they already assume a chamber pressure. So my questions are two:

  • What are the equations for calculating the chamber pressure for a bipropellant engine? In case it's the opposite, how do you find out the needed propellant flow rate so that you achieve the design chamber pressure?

  • When you have a pressurized gas thruster, that is, with no combustion, what do you have to take into account in order to calculate the parameters of the injector?

  • 1
    $\begingroup$ Your second question is already answered at space.stackexchange.com/questions/21577/… $\endgroup$ – Nathan Tuggy Jun 2 '17 at 15:10
  • 1
    $\begingroup$ No, it's not. That's why I am asking again. Yes, you have a regulator that you can control, but you should be able to calculate before even running the engine how much feed pressure you need. And I doubt you would feed it with the chamber pressure you want, cause the chamber is open, therefore you won't achieve as much pressure. $\endgroup$ – mariohm1311 Jun 2 '17 at 19:16
  • $\begingroup$ If you're not satisfied with the answer(s) because you think they're wrong, asking a new question isn't the way to handle it. With more rep you can add a bounty for better answers, or you can edit the question to be clearer. Otherwise, we're just going to give the same answers again, or nothing. $\endgroup$ – Nathan Tuggy Jun 2 '17 at 19:19
  • 1
    $\begingroup$ What else can I do? It's not like I can add a bounty, and I don't really understand what's not clear about the question. $\endgroup$ – mariohm1311 Jun 2 '17 at 19:22
  • 1
    $\begingroup$ With no combustion there's no point to having a combustion chamber and as result no combustion chamber pressure. The pressure fed from the regulator IS the pressure reaching the nozzle, directly. $\endgroup$ – SF. Mar 18 '20 at 13:49

I can only answer your first question. You can use the following equation:

$$ \dot{m} = \frac{P_{c}A_{t}}{C^*} $$ where $$C^* = \frac{\sqrt{RT_{c}}}{\sqrt{\gamma}(\frac{2}{\gamma+1})^\frac{\gamma+1}{2(\gamma-1)}}$$

  • 3
    $\begingroup$ Could you give a source and/or define the variables? $\endgroup$ – Steve Linton Jun 1 '18 at 13:11
  • $\begingroup$ link. Here you can find the notation I use. Also the main source for introduction to rocket propulsion is Sutton's Rocket Propulsion Elements. You can find the same formula if you check equation 3-32. $\endgroup$ – Kaan Güven Jun 1 '18 at 13:37

By chamber Pressure, you mean stagnation/Steady state Pressure.

Here's the Equation

$$ P_0 = p\left[1 + \frac{1}{2} \left(k - 1\right)M^2\right]^{\frac{k}{k-1}} $$

$P_0$ = Stagnation Pressure or Steady-state Pressure your chamber Pressure

$p$ = let's call it environmental pressure (Atmospheric pressure, but it changes with altitude)

$k$ = ratio of specific heat at constant pressure to specific heat at constant volume

$M$ = is the Exit velocity in Mach number

The equation above assumes that the Mach of the chamber/before the nozzle throat is negligible

Ask me more if you still confuse

You might ask me what is Stagnation Pressure and Steady-state Pressure?

And you might question me why I used the word Environmental pressure?


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.