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Following on from my previous blog post on Hybrid Rockets, I’ve been working on putting together a functional prototype. The core aim of my thesis is to evaluate the performance of various 3d printed Fuel grains.  As such, this prototype had to be able to handle a variety of different fuel cores.  The results weren’t perfect, but I was able to get some fantastic data from my research. This blog will provide an overview of my prototype rocket engine with a nice video at the end of it being fired.

In the image below it can be seen that hybrid rockets consist of a few distinct parts:

  • Oxidizer tank – Holds a variety of oxidizers for the system. For this test I am using Gaseous oxygen, but Hydrogen peroxide or Liquid oxygen are also great choices.
  • Pumping unit – Pressurizes the oxidizer. The Oxidizer tank that I am using is already pressurized so I can skip this stage.
  • Solid Fuel core – A Tube or hollowed out section of a fuel material. There are many types of fuel that a hybrid rocket can utilize, from paraffin wax to Polyethylene. For my thesis I am examining 3d printed fuel cores, so I have chosen to use ABS plastic.
  • Nozzle – Channels the expanding gasses from the system, accelerating them to supersonic speeds. The test prototype in this article has a ceramic nozzle, but due to a lack of a pre-combustion ignition stage, it cannot be used.

 

Diagram depicting a hybrid rocket engine. From left to right: Oxidiser Tank, Pumping unit, solid fuel core, nozzle
Hybrid Rocket Engine

The first step of this project was to 3D print a fuel core. The construction of the core is quite simple, being a 50mm tube of ABS plastic with a 10mm hollow core. Both the lead in and lead out of the core had a bevel to allow for better oxidizer flow.  The print took 8hrs total and used 150g of ABS plastic.

A 3D Printer printing a fuel core.
3d Printing Fuel Grain

 

With the core printed, the components could be assembled. From left to right we have the rockets nozzle, the fuel core and housing unit, the oxidizer inlet and a oxidiser lead-in to prevent blowback.  All parts are commonly available pipe fittings.

 

From left to right: rockets nozzle, the fuel core and housing unit, the oxidizer inlet and a oxidiser lead-in to prevent blowback.
Engine Components

With the parts assembled, I secured them to an aluminium bed attached to an elevated stand. The oxygen tank was then attached to the system.

The rocket engine parts assembled and attached to an aluminium plate.
Engine Test bench

For the test itself I removed the nozzle. Experimentation with igniting the system revealed that the nozzle prevented initial combustion. Future experiments will have a pre-combustion ignition stage, likely using a spark plug assembly near the oxidizer inlet.

The assembled rocket engine with the nozzle removed ready to fire.
Ready For Firing

With the system assembled it was ready to fire. I recommend turning on captions in the video for more information about the process.



 

The results of this experiment have been good. I was able to demonstrate that the ABS fuel core could be ignited and that the experimental setup works as intended.  Pay attention to this blog in the next few months as I continue to improve on this experimental setup.