P18102: RIT Launch Initiative Hybrid Rocket
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Feed System

Table of Contents

Overall Feed System Summary

The main purpose of the feed system is to deliver the oxidizer fluid to the injector plate so it can combine

Main Feed System Components:


Tank Design

Fluid Flow

Feed System Requirements

  1. Avoid 2-phase flow
  2. Provide a constant flow rate to the injector plate
  3. Store the oxidizer and any pressurant for up to 1 hour
  4. Be capable of offloading all fluids prior to landing
  5. Should be able to purge the lines and engines after engine shut off
  6. Contain burst valves for all pressure vessels

Feed System Design

Figure 1: Feed System Schematic

Figure 1: Feed System Schematic

The feed system utilizes a 2-tank design, with one tank responsible for storing the N2O and the other tank storing the pressurant for the system. Solenoid valves between the tanks and the injector plate will be used to turn various flow paths on/off during operation for the filling, supply, and expelling of the oxidizer. One of the main requirements for the system is to deliver the N2O to the injector plate as a sing-phase liquid. In order to do this, the system has been designed to deliver the N2O at 780 psi to the injector. To account for head loss through the piping and valves, the N2O tank is pressurized to 900 psi. This is done with the pressurant gas. For testing purposes, we plan on using N2 gas because it is readily available, cheap, and easy to store. For flight purposes, there is the potential to change to helium, as it will weigh less, but this will not be decided on until multiple tests have been conducted.

In order to control of the flow of both fluids, each section will have 2 solenoid valves controlled by the microcontroller. The first will be responsible for filling and draining the tanks, while the second if responsible for flowing the fluid downstream. In order to provide a constant pressure of gas to the oxidizer tank, a mechanical regulator will be used to drop the N2 pressure down to the operating oxidizer pressure.

Pressurization Selection

When selecting the design for the pressurization system, a few different designs were considered:
  1. Single Tank, blowdown system
  2. 2-tanks regulator system
  3. Single-tank, bladder sysetm
  4. 1 or 2-tank heater system

Ultimately, simplicity was the driving factor behind our decision to go witht he second option; simplicity in the design itself as well as simplicity in the analysis. The bladder system was removed due to the complexity of the tank design and the lack of resources to implement the design. The heater design was eliminated due to the short operating time of the system. Since the rocket is only firing for approximately 7 seconds, there would not be a quick enough response time of the heater system to provide a constant pressure during the fire. Finally, the single-tank, blowdown system was eliminated due to the fact that it required a very large single tank, could not provide a constant oxidizer pressure, and had a more complex analysis in regards to the interaction between the oxidizer and pressurant within the single tank.

Pressurant Sizing

Valve Selection

In order to control the pressurant and the N2O, the feed system deisgn incorporates various valves for conrtrol and safety.

N2O Control Valve For the lower portion of the feed system, a large valve must be used to start and stop the flow of the N2O into the injector. The requirements for this valve include:

Tank Analysis

In order to store the oxidizer and pressurant, 2 tanks will be used. The oxidizer tank is expected to have a volume of 24.1 L and a max operating pressure of 1200 psi. The pressurant tank will be INSERT VALUE in3. The oxidizer tank was sized by from the needed oxidizer mass, with 5% margin, and the density of N2O at 295K to give an estimate for the volume of N2O that would be present. The tank was then sized to hold this, plus a 10% ullage space. For the pressurant tank, the tank was sized to minimize the mass of our system, while being bounded by manageable pressures that would need to flow into the oxidizer tank

For both tanks, we are planning on using a composite material do to the high strength/weight ratio. This means that the tanks must be designed with a FoS of 3, due to IREC requirements.

Current CAD Model

public/Engine Specifications/Feed System/Images/20180307_1.PNGpublic/Engine Specifications/Feed System/Images/20180307_2.PNG

Potential Improvements

  1. Lighter Oxidizer Tank, potentially composite
  2. Optimization of pressurant tank sizing
  3. Smaller N2O control valve
  4. Simulink analysis of fluid flow
  5. More consistent mass flow rate of N2O (maybe larger N2 lines)
  6. Separate fill and drain valves (1 way flow)
  7. Quick disconnect fittings for rocket
  8. Valve mounting in rocket
Link to Orifice https://neutrium.net/fluid_flow/calculation-of-flow-through-nozzles-and-orifices/

ASME Pressure Vessels https://www.asme.org/products/codes-standards/bpvcviii1-2017-bpvc-section-viiirules

5 Things about Sizing a Pressure Regulator https://blog.craneengineering.net/5-things-you-must-know-for-sizing-a-pressure-regulator-correctly

Carbon Fiber Composite Cylinders http://www.acecare.cn/product/60710142809-211919342/PCP_Paintball_Air_Gun_3L_6_8L_9L_12L_Carbon_Fiber_Scuba_Tank_Aluminum_Composite_Gas_Cylinder.html?spm=a2700.8304367.prewdfa4cf.8.47ad64ccy8j2O7

Peter Paul Solenoid Valves https://peterpaul.com/valves/2-way-normally-closed/series-20-model-h22/

McMAster Solenoids https://www.mcmaster.com/#1190n24/=1a65g6l