P07105: METEOR Launch Vehicle
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Overview of the Hybrid Rocket Design

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Overview of the Hybrid Rocket Design Drawings Section Preperations for Hybrid Rocket Testing Testing of the Hybrid Rocket BOM and Parts List Deliverables for Senior Design

Design Overview

Hybrid Rocket Definition & Current Design Materials

Hybrid rocket engines are classified as those that utilize a liquid oxidizer and solid propellant to achieve thrust. This team is currently using Hydroxyl Terminated Poly-Butadiene, or otherwise known as HTPB, as the solid fuel. This material is essentially the same form of rubber that is in everyday car tires, minus a couple of elements. The liquid oxidizer in this system is Nitrous Oxide. These two components together in a hybrid rocket system are not necassarily the most efficient. However, it is considered to be one of the safest combinations and considering that this is a school project, safety is of the utmost concern for all of the parties involved.

Overview of Components of the Current System

To describe the system, it is best to start from the beginning, the feed system, to the end, the snap ring that holds everything in place. Because the goals of this project are dependent upon testing a hybrid rocket engine, safety is a primary concern. As you will see, every component keeps this in mind.

Feed System

The feed system is comprised of two tanks: a Nitrous Oxide tank that deliivers the liquid oxidizer to the rocket chamber during a fire and a Nitrogen tank that is utilized to purge the entire system after a fire. Nitrogen is an inert gas so it will extinguish any flames that are left over after the NOX is turned off. Seperate solenoid valves are utilized to open and close the appropriate feed lines. All that these need are the necassary amount of voltage to open so this means they can be operated from a safe distance away. Other components include filters, reducer couplings, pressure relief valves, and a cylinder warmer. The cylinder warmer is used to heat up the Nitrous Oxide Tank, therefor increasing its available pressure.
Feed System Setup

Feed System Setup

Above is an example of how this set up looks during a round of testing. You will note that the tanks are on the outside of a large concrete "bunker" that serves as the housing for the rocket chamber. It serves as a means of protection to the environment and surrounding people in case an emergency occurs.

Steel Chamber

The chamber includes all of the major components of the hybrid rocket engine. Reinforcing the safety concern, it is a half-inch thick peice of 304 Stainless Steel tube, hence the name "Steel" Rocket Team. The final set-up, prior to testing is pictured On this Link. A graphic is pictured below. Overall, the chambe encompasses an injector plate, pre-combustion chamber, igniter ring, fuel grain, nozzle, and the snap ring that secures all components.
Hybrid Rocket Chamber

Hybrid Rocket Chamber

Injector Plate

The injector plate serves as the interface between the feed system and the engine itself. It consists of small holes that particulate the liquid nitrous oxide. This increases the overall surface area of the oxidizer, allowing it to combust more efficiently. A lot of properties about the injector plate can affect this process; including but not limited to the total inlet area, the number of holes, the diameter of the individual holes, the orientation of the holes, etc...

Pre-Combustion Chamber

The pre-combustion chamber gives the liquid nitrous oxide time to separate before it reaches the solid fuel. Too short and it will not have separated enough. Too long and the NOX will lose momentum, decreasing mass flow and thus efficiency of the engine. The current material for this chamber is a ceramic known as Garalite.

Igniter Ring

The igniter ring is what initiates a rocket burn. Nitrous oxide will not ignite until approximately 575 degrees Celsius. The job of the igniter is to get temperatures above and beyond this point in a vaccuum atmosphere. It consists of several components. The main portion of the igniter is a mixture of HTPB and Amonium Perchlorate powder. What initiates the flame is a wire/black powder/AP set-up. The wire heats up enough to ignite the black powder when current is supplied to it. From here, the AP and HTPB begin to burn. After a few seconds, the Nitrous Oxide is supplied to the system, initiating the rocket burn.

Fuel Grain

The HTPB fuel grain is what makes up the majority of the rocket. The goal for an HTPB/NOX Hybrid Rocket is to have an Oxidizer to Fuel (O/F) Ratio of between 6/1 and 8/1. Studies have shown that this range is where this form of engine is the most efficient.

Post-Combustion Chamber

The post-combustion chamber allows for the combustion process between the HTPB and NOX to complete. It is very similar to the pre-combustion chamber in that it can't be too short, and it can't be too long. Too short and not enough time will be given for combustion to take place. Too long and the flow could potentially lose momentum. Because garalite does not survive the high temperatures seen at this end of the rocket, graphite is being used to provide this spacing.

Nozzle

The Rocket Nozzle is regarded as the most difficult portion of the design. It is also the most important, having up to a 30% affect on the thrust capabilities of the engine. Prior to optimization of the nozzle, certain temperatures and pressures within the system are needed. Here is a sample of a Nozzle Drawing and an example of the Nozzle Calculation spreadsheet being used for design.