OHKLA Design/Combustion chamber material
From CSTART Wiki
This page is part of an implementation of the CSTART Engineering Process. Anyone can edit it, but it should only be modified in accordance with the procedures and guidelines of the Process. Please check before editing if you are in doubt.
This document is a leaf node in the Design Task Tree for the OHKLA project.
Contents |
[edit] Decision
A decision on this design task was made on 23/10/2010. The OHKLA combustion chamber will be manufactured from 6061 T6 Aluminium
[edit] Summary
The purpose of this design task is to select a material from which to construct the OHKLA hybrid rocket engine's combustion chamber.
[edit] Background
One of the two major components of a hybrid rocket engine is the combustion chamber, which contains the solid fuel grain. One end of the combustion chamber is connected to the oxidiser tank, while the other is connected to the exhaust nozzle. Oxidiser liquid or gas is injected into one end of the chamber, and burns with the fuel through the length of combustion ports in the fuel grain, before exiting the chamber through the nozzle.
[edit] Features/Considerations
[edit] Chamber mass
A lighter combustion chamber will contribute to a lighter dry mass of the entire rocket, and hence to a lower required propellant mass, making the rocket smaller and each launch cheaper. Thus, all else being equal, materials which result in lower chamber masses should be preferred over those which result in heavier chambers.
[edit] Tensile strength
The combustion gases that the combustion chamber contains will be at a higher pressure than the ambient atmospheric pressure, so the combustion chamber is a pressure vessel. Thus the chamber must be made from a material with a sufficiently high tensile strength that the pressurised gases can be contained safely using a practical thickness of material.
[edit] Ease of melting
High temperature combustion will take place inside the combustion chamber, and some of this heat energy will be conducted to the structure of the chamber. The lower the melting point and the lower the heat capacity of a material, the more care that will need to be taken in insulating the inner walls of the chamber from the fuel grain.
[edit] Ease of construction
Since combustion chambers of the required size cannot be purchased as off-the-shelf components, the combustion chamber will need to be manufactured from raw materials. Thus there needs to be a preference for materials which are easier to work with. For instance, steel is easier to weld than aluminium.
[edit] Cost
All else being equal, cheaper materials are preferred over more expensive materials.
[edit] Available Solutions
[edit] 304 Stainless Steel
Pros:
- High ultimate tensile strength (505 MPa)
- Easy to weld
Cons:
- High density (8.00 g/cc)
- Low yield tensile strength (215 MPa)
[edit] 6061 T6 Aluminium
Pros:
- High yield tensile strength (276 MPa)
- Low density (2.70 g/cc)
Cons:
- Less easy to weld
- Less ultimate tensile strength than 304 Stainless Steel (310 MPa)
[edit] Nickel Chromium Alloy
Pros:
- Extremely high yield tensile strength (875 MPa)
- Extremely high ultimate tensile strength 1275 MPa)
Cons:
- Extremely expensive
- High density (8.22 g/cc)
[edit] Carbon Composite
Pros:
- Extremely low density
Cons:
- Expensive
