Queries Regarding Rocket Engine Design

[Handsome Rob]

1.    Name two advantages and two disadvantages of using a regeneratively cooled nozzle extension for an upper stage engine.

 

2.    Which materials would you consider for a radiatively cooled nozzle extension?

 

3.    Assume a nozzle extension consisting of two parts: one made of Ti6Al4V and one of C-103. Which of the two would you use close to the throat and which one further downstream and why?

[sevenperforce]

Is this from an exam?

6 hours ago, Handsome Rob said:

1.    Name two advantages and two disadvantages of using a regeneratively cooled nozzle extension for an upper stage engine.

The primary disadvantages are weight and complexity. All other things being equal, a regeneratively-cooled nozzle extension will be heavier and more complex (and thus more expensive and prone to failure) than a radiatively-cooled one. The advantages are potential for reuse (if you're going to try to recover and reuse) and preheated fuel that lowers the stresses on the engine. 

6 hours ago, Handsome Rob said:

2.    Which materials would you consider for a radiatively cooled nozzle extension?

Reinforced carbon-carbon, niobium superalloy, or some other ceramic.

7 hours ago, Handsome Rob said:

3.    Assume a nozzle extension consisting of two parts: one made of Ti6Al4V and one of C-103. Which of the two would you use close to the throat and which one further downstream and why?

The niobium alloy is better for the nozzle extension. It melts at 2624 K while Ti6Al4V melts at a paltry 1299 K. Remember that heat rejection via radiation is proportional to the fourth power of the absolute temperature, so a radiative nozzle made out of a niobium alloy will allow almost 17 times as much radiative cooling as the titanium alloy would.

Close the throat with the titanium alloy; it has better convective heat transfer properties (since it will be regeneratively cooled) and a higher strength-to-weight ratio.

[YNM]

I hope you're not asking to an online forum to try and make your own liquid propellant rocket engine. Not to say we know entirely nothing, or that no one else have tried in the past, but unless you really know what you're doing I suggest starting from an easier point first, like solid fuels (and the easier ones at that like sugar or maybe blackpowder if you're more than confident with sugar).

[magnemoe]

Well as upper stage engines are single use outside of starship. Starship plan to cool the entire vacuum engine nozzle. This is needed as unlike most upper stage engines it will burn inside the skirt so you can not radiate away the heat. 
As I understand the upper stage engine on falcon 9 is basicaly an standard engine designed to bolt on the vacuum nozzle extension who is radiantly cooled. 
Benefit of this is that its easy to test the engine in an atmosphere and then add the extension. 
 

[RealKerbal3x]

@Handsome Rob I would recommend you get this book as it has pretty much everything you need to know about rocket motors. This one might also be useful, and is a fun read to boot.

[DDE]

3 hours ago, RealKerbal3x said:

@Handsome Rob I would recommend you get this book as it has pretty much everything you need to know about rocket motors. This one might also be useful, and is a fun read to boot.

Why do I know what these two are without looking?