Testing Rocket Grain Mixture and Designs with Sucrose Propellant

Student: Kourtney Adkisson

Mentor: Darci Snowden

Abstract

A solid rocket motor is composed of a cylinder full of fuel which typically has a hollow core. After being ignited with a fuse, the fuel at the surface of the hollow core burns and produces hot gas that is released through the nozzle of the rocket in order to produce force. The surface area of the burning propellant affects the thrust force and pressure output of the motors; the more fuel that burns at one time, the more thrust and pressure is produced. The purpose of this project was to investigate the effect of surface area on thrust and pressure. In order to accomplish this, a safe technique was devised and carried out in order to make motors with potassium nitrate and sucrose propellant. Four different surface areas were tested, each with different geometric shapes of propellant, which is called the propellant grain. The motors were tested on a thrust table, which is an apparatus that measures the pressure and thrust output while the motor is burning. Sixty percent of the tested motors had a short burn time that averaged 0.5s. Due to the collection rate of data, the short burn time resulted in minimal data points. As a result, the project pivoted towards creating grains that burn for longer by reducing the oxidizer to fuel ratio from 65:35 to 60:40 and investigating more efficient ways to mix the fuel.

Presentation:

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11 thoughts on “Testing Rocket Grain Mixture and Designs with Sucrose Propellant”

  1. I was a bit lost, but for the most part understood. You did a great job of explaining . So very proud of you.

  2. Hello Kourtney!
    Well done on your poster and project overall. Could you elaborate a bit on the physical reasons why a multiperforated grain design results in progressive or regressive outputs (compared to those grain designs that give neutral outputs)? Also, can I ask which characteristics of a multiperforated grain design determine whether the output will be progressive or regressive (size, shape, number of perforations, the distance between perforations, etc)?

    1. Kourtney Adkisson

      Thank you, Kahmina.
      Sure; essentially, the progressive, regressive, or neutral burning motors depend on the amount of surface area that is burning at one time.
      If you start with a smaller surface area of propellant and end with a larger surface area (like a circular core that burns a smaller cylindrical area at the beginning and the cylinder gets larger over time, see figure 1), then this should result in a progressive burn.
      If you start with a larger surface area burning and decrease the area over time, then this would result in a regressive burn; these types of motors are uncommon, but an example would be if you had a cross shape in the cylinder that was void of propellant where each quarter of the motor burns down over time.
      Neutral burns is where it gets interesting; depending on the exact shape inside, you can create a neutral burn with a star or finocyl shaped grain design. There are models that one can use (or create) in order to determine if the exact shape you are using will burn neutrally. As you can imagine, completely filled motors would also burn neutrally due to the same amount of surface area burning from the bottom up.

      1. Very interesting! Are there different applications where each of these designs and resulting outputs would be most useful?

        1. Kourtney Adkisson

          Hi Dr. Craig,
          That is a great question! There are different times where each type of design would be useful. For example, if your rocket boosters (typically solid motors) are helping you get off the ground, but you will activate engines part of the way through the flight, then a regressive grain design may be most useful. Though, if you wanted your booster to help accelerate your rocket at a constant value, then perhaps neutral burning motors would be the best. I all depends on what application you prefer.

  3. Kourtney,

    Great job on your research! Before testing, did you perform any analysis on the grain designs to predict the thrust curves? Which design resulted in the most optimal curve?

    1. Kourtney Adkisson

      Hello Joseph. Thank you.
      I was using models set up by my source before synthesis (see my literature cited), and throughout the project I worked to develop a model of my own to predict the thrust output over time. The model is still in progress as more variables need to be included in my equations in order to represent the expected values correctly. My data was not characteristic of what I expected. However, I believe my data will yield more consistent results if I am able to get the motors to burn for a longer amount of time.

  4. Kourtney great presentation!

    Do you want to continue to work with rockets in the future, or are you mostly interested in comustion and propulsion?

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