N2O Flow Analysis (cont.) Major Loss from SS Hose 15.5 PSI Minor Losses T-Fittings 5.4 psi / T Solenoid Valve 30 psi Check Valve 38 Total Minor Loss 96 psi TOTAL LOSS 111 psi 53
Pressure Loss for Stainless Hose https://www.hoseflex.com/wp-content/uploads/2014/07/Stainless-Steel-Hose.pdf 54
Oxidizer Tank Sizing N2O Mass 37.25 lbm Tank Volume 0.85 ft^3 Tank ID 6.5 in Tank Internal 46 in Height Wall Thickness 0.25 in MEOP 900 psi 55
Nitrogen Pressurant System Analysis based on ideal gas law, adiabatic, constant pressure through regulator Volume of Volume of Volume and Tanks & N2O Tanks & N2O pressure of N2 Tank Pressure Tank Pressure tank initially 56
Nitrogen Pressurant System 57
Pressurant Tank Model Number: CRPIII-161-9.0-30-T Working Pressure: 30Mpa Length: 570mm Diameter: 174mm Water Capacity: 9L Empty Weight: 5.1kg Cylinder Thread: M18*1.5 58
N2 Valve Selection - 24 VDC - ¼” Pipe - 3500 psi N2 - 47 GPM 59
Regulator Inlet Pressure: 3500-4000 psi Outlet Pressure: 900 psi 60
Feed System Support - Can utilize an “interstage” as described previously - Will contain cutouts for - fill/drain ports - power/data when testing - Can act as a support for oxidizer tank - Will protect feed system - Materials and Design TBD 61
Final Equipment List Mass Mass w/ Growth Component Total $ Qty Unit $ Growth [lbm] [lbm] TOTAL $4700 70 77 7% Oxidizer Tank 1 $800.00 $800.00 28.10 10% 30.91 Pressurant Tank 1 $284.00 $284.00 11.24 10% 12.37 Gas Pressure Regulator 1 $615.00 $615.00 3.09 10% 3.40 N2 Solenoid 2 $120.00 $240.00 2.18 5% 2.29 N2O Solenoid 2 $700.00 $1,400.00 10.00 10% 11.00 Check Valve 2 $350.00 $700.00 3.09 10% 3.40 Relief Valve 3 $100.00 $300.00 9.92 10% 10.91 Stainless Steel Hose 1 $0.00 0.27 10% 0.30 Cross Fitting 2 $54.84 $109.68 0.59 5% 0.62 Tee Fitting 4 $33.16 $132.64 0.93 5% 0.97 Pressure Sensor Adapter 2 $10.98 $21.96 0.55 5% 0.58 62
Next Action Items - Source N2O solenoid and check valve - Create Simscape model of fluid flow - Purchase valves and regulator - Initial flow tests - Order custom N2O tank 63
Safety Considerations Main Concerns with N20: - Exothermic decomposition - Contamination reduces energy threshold - 2 phase at standard room temperature - N2O saturating tank and combustion chamber 64
Safety Protocols Safety through Design - Operating as a liquid - Pressure relief valves - Check valves - High pressure drop over injector - Use stainless steel, PTFE, and compatible grease throughout system Safety through Procedures - Inject N2O after ignitor has already fired - Thorough cleaning of all tubes and tanks between Fill oxidizer tank at less than 20 psi/sec - - Wear goggles and gloves 65
Controls 66
Microcontroller - Teensy 3.6 was ordered and received - Meets basic goals: - Large pinout - High speed - UART, SPI, I2C - ADC with minimum 8 inputs - Programming using Teensyduino add-on for Arduino IDE - Begun familiarizing ourselves with board and reference manual - Next steps: Integrating uC into test circuits and programming functions GIF demonstrating uC controlling LED 67
Controller Flowcharts ● Controller tasks have been broken down into various functions and ISRs ● After DDR, we will be moving to polling rather than ISRs ● Flowcharts are continually being adjusted, refined, and detailed ● During process of creating flow charts, also brainstorming how to program safety measures in case something goes wrong 68
Controls Hardware Block Diagram 69
Communication Diagrams ● Customer requirement for avionics: RS422 ● DB9 connectors and serial cables acquired, transceiver being selected ● Packet design up to engine team Potential designs: ○ Standard 8 bit ASCII ○ 16/32 bit data (from engine) ○ Binary commands (from FC) ● Potential framing: ○ Escape character ○ Consistent overhead byte stuffing (COBS) ● Note: Logic Shifter unnecessary with current 3.3V Transceiver IC (Old 70 picture)
Communications Circuit 71 GIF demonstrating full duplex operation
Valve Circuit Not a GIF (But it works!) 72
Valve Circuit Changes / Implementations: ● TVS diode opens for transients 3x the operating voltage. ● Diode for kickback. ● IGBT to handle high power ● Optocoupler to isolate microcontroller from high DC and transients. ● Previous optocoupler was inverting output. New optocoupler is uninverting (high input = high output), rated for more power, and smaller. 73
Pressure Transducer and Thermocouple Circuits ● Pressure Transducer is read through ADC. It has an incorporated ASIC which auto-calibrates it, so a simple op-amp seemed sufficient. Alternately, the Op Amp IC could be removed and the ADC on the Teensy could use differential inputs, if there is sufficient room for the signal lines. ● 12 bit ADC on Teensy 3.6. Analog input LSB resolution is 3.3/10^12 = 0.8mV. Transducer accuracy is 0.25% of 4V full scale = within 10mV, so the ADC should be more than sufficient. 74 ● Thermocouple IC calibrates itself and sends data over SPI.
Sensors: Flight Configuration - Pressure transducers (x3) - 0 - 2000 psi range (x2) - 0 - 5000 psi range (x1) - 0.25% accuracy - 5V supply voltage - 8mA supply current - Metri-Pack 150 Connector - ~ $100 each - Thermocouples (x2) - K-type standard thermocouples - ~ $75 for 5 pack 75
Sensors: Test Stand Configuration - Flight configuration plus: - Primary Load Cell - PCB Piezotronics S-type Load Cell - 2000 lbf capacity - 2.4 kHz resonance frequency - Secondary Load Cell - TE Connectivity, 100 lbf capacity - Accelerometers (x2) - Considering Sparkfun breakout board - 3-axis, +/- 2,4,8,16g, up to 3200 Hz - Other options will be researched - Microphone - To be selected (or borrowed) - Not a critical measurement 76
Power Distribution 77
Battery Sizing ● 14.8 Li-Ion battery needs to be able to supply 7A, 114W, 14.4 Wh in worst case scenario. Example Components Voltage Current (A) Quantity Power (W) Time (V) ● Potential Battery Selection: ○ AA Power Corp Li-Ion Teensy 3.6 5 0.5 1 2.5 60 min ○ 14.8V working voltage, 4Ah, 59Wh TI LMV344 Op Amp 5 100u 1 500u 500 sec ○ 16.8V max, 11Vmin, 20A max ○ 5.51" x 2.0" x 1.7’, 17 oz. MAX31856MUD+ 5 1.2m 3 18m 500 sec Thermocouple IC ○ Has integrated balance PCM (easier for us) Honeywell MLH Series 5 4m 3 60m 500 sec Pressure Transducer Worst case scenario assumes: 1. The 24V regulator will be at maximum current N2 Solenoid Valve 24 0.4 2 19.2 250 sec draw the entire time. Worst case power is at low battery voltage (which should not be N2O Solenoid Valve 24 0.66 2 32 250 sec reached) and valves always on with 3.3/5 Regulators 5 ~0 2 0 500 sec maximum current draw (which will not be true), in which case an extra 2.7A of current LM2588 24V Regulator 11 (Worst 2.7 (Worst 2 60 500 sec is needed. case) case) 2. The valves will be at maximum current draw 7A Total 114W Total 14.4 Wh the whole time (in reality, they will only peak when turning on/off) 78
Battery Input Circuit ADC monitors battery voltage 79
Battery Input Circuit ● Normally powered by DC jack and brick charger with current sensing. If charger unavailable, unpopulated resistors can be added to charge the battery from a powers supply to the pins Vin+/Vin- (with careful supervision of battery’s PCM’s fuel gauge). ● When plug is inserted, pin 2 of DC jack is disconnected. Power PNP BJT Q3 is off and IGBT is off, disconnecting the load. LED is powered. ● When plug disconnects, pin 2 connects to pin 3. Q3’s gate is pulled to ground, opening the IGBT. ● We couldn’t find any p-type IGBTs and are open to a better solution for disconnecting the load during charging. 80
Voltage Regulators for 5V, and 3.3V ● Dedicated 3.3V regulator for microcontroller. ● Normally closed push button to easily power cycle uC during testing. ● The other two LDOs’ enables are normally pulled down. 81
24V Regulator 82
24V Regulator ● Circuit has been tested in SPICE minus the input circuit on right. ● Step-by-step start-up: ○ Input from uC (V5) turns on power BJT Q3 which turns on IGBT Q4. ○ The current limiting thermistor causes the large inductors and capacitors to slowly reach line voltage and prevents a large transient spike. ○ Later, 3.3V input from uC (V4) turns on BJT Q1 / IGBT Q2, bypassing the thermistor, and also enables the IC, causing the voltage to charge up to 24V. ○ A TVS diode could also be added, but the spike in voltage/current lasts ~1ms (a long time for a TVS). 83
Follow-Up ● Next step is to produce a PCB for the engine control. ● Major concerns / questions: ○ What is the best method for heatsinking this board if only 2 layers are available? ○ If 4 layers are available, is separating digital and analog power and ground necessary? ○ What is the best way to disconnect the load during charging? ○ What is the best way to prevent transient spikes when connecting the battery to the large RCL circuit of the 24V regulator? ○ Vge is a concern on the IGBTs (will the current voltages be sufficient to overcome the large IGBT threshold?) 84
Test Plans 85
1 - Proof of Concept Tests - Mold Paraffin - Testing for ease of molding, and lack of bubbles/density - Testing multiple techniques - Pouring wax vs melting wax in mold - Concentric circles mold vs machining inside diameter - Spin molding vs vibration molding vs careful pouring - Wax cooling speed - https://www.lonestarcandlesupply.com/blog/heating-pouring-waxes/ - Metal vs PVC mold | Maybe the chamber is the mold - Hard paraffin vs less hard paraffin - Controlling Solenoid Valve - Valve operation and test circuit - Component hardiness - Proof of Concept 86
1 - Proof of Concept Tests - Serial Communication - Serially communicate with a computer USB-Serial or an Arduino - Match up and document baud rate, error handling - Does it work if we connect late - Disconnect in the middle, etc. - Base Tank Pressurization - Just moving N2O or N2 - Loading N2 tank - Testing how pressure loading works, do we need a pump? - Manually and electronically - Benchtop Insulation Test - Both “will it work” as well as “which works” test - Firing ablative insulation and testing time until breakthrough - Acceptance: Yes this works - Optimization: This took the longest to burn through - Oxy-acetylene torch testing 87
1 - Proof of Concept Tests - Prototype Engine - Set up nitrous/paraffin and try lighting it - For initial test, likely ignite with paper or a match or something similar - I just want to see fire Check Solenoid Pressure Chamber Orifice Valve Tank Valve Valve Gauge 2” Schedule 80 Pipe N 2 O 88
1 - Proof of Concept Tests - Strain Gauge Calibration - Use strain gauge to measure test chamber pressure - Calibrate using shop air or CO 2 - Pressure transducer on the other end of the chamber - Prototype Engine Pressure - Trying to measure pressure in engine by varying output orifice size and using choked flow assumption - Multiple tests, cap pipe with hole drilled in cap to build pressure - Time to reach pressure as well - Somewhat verification test, not proof of concept - Initial Sensor Workings - Be able to read sensors with control board microcontroller - We will be using a lot of sensors for this testing - Likely on a DAQ, but good time to get them working 89
2 - Verification Tests - Fuel Regression - Start with a quick variation of parameters test - Nitrous flow rate, Chamber pressure/Outlet size, Port diameter - Length/D P same in small scale and full scale - G * D P is constant (Reynolds #) - Post combustion chamber allows for full combustion, chemical kinetics >> transport properties - Nozzle Cold Fire - Running pressurized CO 2 or shop air through the nozzle to test thrust characteristics - Will need a load cell, as well as a pretty high mass flow rate to keep pressure in the chamber - Battery Charging/Discharging - Regulator Tests - Testing the regulator should happen around the same time as strain gauge calibration - N 2 or CO 2 - Verifying both pressure and mass flow rate, as well as some vibration 90
2 - Verification Tests - Miniature Nozzle Hotfire - Thrust proportional to port diameter for scaling - This connected with the coldfire test will verify the nozzle - The hotfire also allows us to verify choked flow and thrust and mass flow rate - Injector flow testing - w/CO 2 & N 2 O - Ambient & at pressure - Flow rate, pressure drop tests - Verifying atomization visually to characterize precombustion chamber length - Proof Pressure Tests - Burst Pressure Test - Plug the nozzle end (Cap without hole in it) - Pressurize with shop air/CO 2 to working pressure - Sensor Verification - Basic sensor calibration, will be done mostly alongside the rest of these tests as we use the sensors 91
2 - Verification Tests - Acoustics - Can try small scale tests - Unsure of scaling right now - Easy enough to record using a microphone - Fuel Grain Tensile Test - Stress test fuel grain - What happens when it heats up - Do we need to support the fuel grain at all - Redundant controller test - Chamber Pressure Test - Making sure that we’re aware of all of the factors affecting chamber pressure - We know we can hit it using different parameters, but will that scale up to the rocket - IE scaling the regression rate/nozzle/mass flow rate, what is the chamber pressure - May be a side effect of some other tests. 92
3 - Optimization Tests - Fuel Grain Manufacturing - Can we line the mold with something - Is there a way to automate manufacturing - How consistent are the fuel grains - Pre-Combustion Chamber - We only have a rule of thumb here, and a previous MSD project optimization - Looking at changing the - Injector Designs - Ease of Assembly/Repeatability & Reproducibility - Nozzle Geometry 93
4 - Integration Tests - Controlling Solenoids - w/ fluids with microcontroller - Igniter Tests - Controlling the ignition from the controller completely, no human intervention - Battery lifecycle w/ solenoid valves, microcontroller - Run it until it’s dead - Leak test - General Assembly - Microcontroller thinking off of sensor data - Trying to model this using MATLAB or some other microcontroller to fake inputs before integrating everything together 94
5 - System Tests - Day of operation - Prop loading/offloading - Arming/disarming - Quick Fire - Full Hot Fire - Leak tests (periodically) 95
Engine Mounting Test Stand Update Fixture Engine - Aluminum I -beams mounted to aluminum plate - Aluminum plate is already in bunker and secured to floor - Linear bearing/tracks - Allow for only axial translation - Each bearing is rated up to 720 lbf dynamic loading - Engine mounting fixture - Needs to hold engine level and straight - Sensor wires can be secured to fixture - Next Steps - Tank mounting Fixed Aluminum Linear I -beams - Force place/load cell mounting Plate Tracks (x2) (x2) - Review design for ease of assembly & cost 96
Test Stand Update - Determined that large oxidizer tank can fit upright in bunker - Bunker weatherproofed for winter & generator is being cleaned up - Next Steps: - Design fixture to hold tanks - Send design to EHS (by January 15th) - Source materials needed (some already procured) 97
Test Space Update - Have been recently granted shared-access to a BME lab in Institute Hall - Will use space to work on molding paraffin - Depending on scale of small-scale testing may be able to use fume hood - Also have a blast room in the machine shop - Can do larger scale testing in here (not bunker large) - This is in the event that BME lab is not equipped for small scale tests - Entire team is now certified for: - Lab Safety Training - Gas Cylinder Training 98
Testing Next Steps - Start with paraffin molding, as little else can continue without that - Assemble test combustion chamber and start calibrating gauges - Acquire Nitrous Oxide 99
Project Summary 100
Recommend
More recommend
