Day 29: WE HAVE IGNITION!

I spent the morning battling the leaky connection monster. After that war was finally won, I dragged everything out to the holding bay where we typically store the race team's tractor trailer (plenty of room) and gathered everyone who has been apart of the journey so far. The first test was with 91% IPA straight from the store. When I would run the fuel, there was a great flamethrower effect until I hit the nitrous. Then the flame went out... I tried a couple different combinations with the propane torch across the injector as my ignitor and I couldn't get the combination to burn. I then realized that my nitrous tank was almost empty and that very little liquid N2O was actually getting out of the injector. Coupled with the fact that there is only supposed to be a 100 psi drop across the injectors, the mixture was off balance. Since I can't dial back the pressure on  the N2O to anything less than about 400 psi, I let the gaseous nitrous flow and reduced the injector pressure to 45 psi to try to reduce the richness caused by the, now gaseous, nitrous flow. All this tinkering cause my crowd to dwindle.

I paired the correct flows with first fuel followed by oxidizer and IGNITION! The 10-15 foot flame roared to life with a thunder. The deep rumbling sound vibrated that whole building and then the masses poured back into the holding bay. There is no question about it. This is a real rocket.

After a couple tests of 91% IPA and 99% methanol (HEET fuel system cleaner), I had to get my nitrous tank refilled ASAP. I called around and it isn't as easy as I thought it was. All of the big companies like BOC and Praxair need either a letter from a race track or league documenting that you are using it for a racing application or they need to send a representative to your company to see that it is legitimate. Even though my company name is Advanced Engine Technologies....? I called around to a couple performance shop where I was finally able to find a company that would fill the tank today. The quote of $6 per pound was like hearing fingernails on a chalkboard. I did some research and found that price to be a little high of the average $5.50 per pound so I went to get it filled. Then the real tests began.

I tested 91% IPA, 99% IPA with some proprietary chemical that makes it turn yellow (Iso-HEET), and 99% methanol. There is no doubt that methanol burns the hottest. Methanol is on an completely different level compared to the more energy dense IPA. The biggest contrast was between the 91% and 99%. The 99% FAR surpassed the 91% in terms of intensity and burn rate. I expected a difference but not that big. The pictures help but the videos say it all.

99% IPA

99% IPA

91% IPA

91% IPA

99% Methanol

99% Methanol

99% Methanol

99% IPA

91% IPA

99% Methanol

99% Methanol Injection Pattern

Day 28: Stared work on the ignitors. Tomorrow will be injector hot tests!

Harbor Freight saved the day with the broken pipe. The EZ out extractor set took it out without an single problem!

Started work on the ignitors. They consist of a short circuit dipped in a nitro cellulose emulsifer of black powered.... which is just a fancy way of saying a ping pong ball melted in an acetone milkshake with black powder sprinkles. I tested a couple and they worked well enough. I think I will still wrap them in cotton and dip them in fuel for the tests.

I got the new solenoid installed as well and everything checked out with the control panel. As soon as I stop my leaky connections I will be able to start some testing!

Day 27: Things are coming together!

After three injector blanks and $30 of micro drill bits, I was finally able to get a plate drilled! The design called for 6 x 0.017" inch impinging fuel jets to be drilled and that was simply not going to happen. I wound up breaking the bit on the second to last hole. Being that I was so close, I drilled it out with a 0.023" bit with the intent of reducing the injector pressure drop.

I ran about 20 flow tests at varying pressures to verify the design...but before that I had to get my daily dose of adrenaline. It turns out that 300 psi max in the lines was no joke. At about 400 this finally gave out on me right into my chest. Like a bomb went off and punched me in the chest, I found myself stumbling around my rocket lab concussed from the BANG!

My ears were ringing for at least an hour. Luckily I had a back up hose and went right back to it getting the tests done... with ear protection on this time.

The stoichiometric flow rate is ~0.02 kg/s for a 5.7:1 O/F ratio. There is no surprise about the increased diameter increasing the flow rate to about double what I designed. Further investigation shows that at an injection pressure drop of 60 psi will give me a 2.5:1 O/F ratio which offers a fuel rich combustion that can reduce combustion temperatures by nearly 1000 K while producing an ISP just over 200 seconds. I'll take it! If worse comes to worst, I can drop to ~30 psi (10% chamber pressure and still push 4:1 O/F ratio.

I got a couple good pictures of the injection pattern. It stays nice and centered. I chose an injection normal for the central oxidizer and 45 degree impingment angle for the fuel.

You can see the diamond shape in the middle of the injector stream. That is from the middle stream getting impacted by the fuel stream from the outside.

Behind the scenes

And of course when I am finally done monkeying around, tragedy strikes when I am trying to be careful. My tank fell off the top of the rocket assembly. This should be an interesting set back.

Did both ends have to break off!? Should be interesting getting that out.

Sneak peek of all the systems! It's starting to look like rocket!

Day 26: 1 extra hour in each day is what I'm asking Santa for this year!

The 80/20 law is in full swing! 20% of the work got me 80% of the way there. Its getting down to the last couple pieces and now comes the hard part.

Drilling the injectors has proven to be more difficult than I anticipated. The oxidizer holes (inner ring) are 0.033 inches where as the fuel holes (outer ring) are 0.015 inches which is the smallest drill bit in the world. It is a #80 drill bit. I broke 2 of them before ordering one made of carbide. That broke too. I am convinced that it is simply not possible for me to drill these holes with the tools I have so I will be changing to a 6 hole pattern which will allow me to use 0.038 and 0.017 inch bits for the oxidizer and fuel, respectively. I am also going to start by drilling one small hole to start that way if I can't get the 17 thousandths bit to work I can go to a 4 injector set up.

The bottom left hole on the outer ring contains the offender!

This is the new injector plate.

Since I couldn't work on my injectors until I got a new plate finished, I started to test my electronic systems. I learned that not all nitrous solenoids are created equal. My fuel solenoid is not powerful enough to open against the 400 psi charge pressure. Should have figured that since car fuel pressure is only ~20-50 psi. So ordered a new one that is on the way now.

I  took the time to just sit down and learn everything there is to know about DC circuits and capacitor banks. Turns out that even though the steady-state requirements of my coolant pump is only 110 watts at 5 amps, the start-up surge can top 50 amps. Even if it is only for a split second, it still shuts my set-up-down. Geoff comes to save the day yet again with lawn mower battery that I can use to run the pump separate from the rest of the system until I can get a capacitor bank put together.

 Testing of the cooling system with the battery. Everything checks out.

 This is the man himself! This is Geoff helping me get my solenoid to seat properly.

 For some reason, our horizontal band saw has been taking FOREVER to cut so while I got the stock for the injector plate cut, I started to shape my next next rocket! This one will be 100 lbf and regeneratively cooled. More on that later!


Quick design notes for my capacitor bank (Warning: Hand-wavy math incoming):

The governing equation is Charge (Coulombs) = Capacitance (Farads) x's Voltage (Volts)

Capacitors in series have additive voltages. A common voltage is a 2.7 volts so I will need 5 of them to get higher than my 12 volt power supply. 2.7 x 5=13.5 volts maximum.

They need to all be able to store the same amount of total charge.

So the equations break down to:

Vt=V1+V2+V3+V4+V5
1/Ct=1/C1+1/C2+1/C3+1/C4+1/C5
Qt=Q1=Q2=Q3=Q4=Q5

It (amperage)=Ct*dV/dt
Stored work potential in the capacitor (joules) is W=1/2*Ct*V^2

So my pump needs 50 amps at 12 volts minimum. My PSU supplies 12.3 volts. Ebay has cheap capacitors that are 80 farads at 2.7 volts. Combining them in series gives me a maximum of 16 farads at 13.5 volts.

dV/dt is going to be limited by the rate at which my power supply can recharge the capacitor.

300 watt power supply can supply 300 joules/second.
If the total joules of energy in my full charged capacitor is W=1/2*~16*12.3^2=1152 Joules
If the total energy in the capactiors can be kept above W=800 Joules (~300 joules less than the full charged one), solving for V=sqrt(2*W/Ct)=sqrt(2*800/16)=~10 volts shows that my psu can supply about 2 volts/second to the capacitor. So my dV/dt is 2 v/s.

The amperage that my ebay capacitor can supply amounts to
It (amperage)=Ct*dV/dt=16*2=32 amps psuedo-continously but it is ok if the voltage drops for a little while until the motor gets spooled up so I think it will work.... "in theory"

Day 25: The stand is coming together (sneak peek)

I think my entire stand weighs about 15 pounds and 10 of them have to be from the bolts alone! I just have to get my injector plate drilled up and plumbed up. I got the new power supply in for $11 shipped from ebay. That is what Ill spend the weekend getting that put together. It won't be too long before I get to test out how bulletproof that housing is!

Day 24: Flipped the switch and only silence

Spent a majority of my work time today getting the control panel all put together. I double checked everything and tested the connections. Everything checked out so I threw the switch only to find a gimpy psu fan pulsing at maybe 50 rpms... I took everything that I just put together apart before pulling the psu. I am positive there is a short somewhere in that vast array of resistors and capacitors and after spending about 3 hours searching, I have gave up and moved on to the thrust stand. It reminds me of something Geoff says, "If you can't fix it with a hammer, it's an electrical problem."

Looks pretty bulletproof to me!

Day 23: Just sat around playing with my nuts and bolts

Looking at my pictures, it seems like I didn't get anything finished! Bulletproof glass has proves to be exactly what I expected. Working with it is a nightmare but I am positive that it will be as safe as I thought it would be. It may be slow work but I keep telling myself that I only have to do it once!

Milling down the glass rails for your viewing pleasure. I figure I only get about 8 inches of window so why have 4 of those inches be the aluminum?! 

3/4" of lexan is bulletproof up to a 9 mm point blank round... and I don't doubt that at all after working with this stuff.

Day 22: Rethinking the injector design, fabricating the new injector plate, starting the bulletproof test enclosure

Finally got my capacitor in today but I have some stuff to rethink first. Firstly, that the store bought nozzle was a bad idea and no matter how much I work on it, it will stay so. Why you may ask? The most important part of a rocket's injection system is the flow rate. The suppliers of these nozzles do not have the same concern. They are more concerned with the spray patterns and distribution at given pressure differentials. My pressure differentials are arbitrary. Hand-wavy estimates between 10-30% of the combustion chamber pressure is the differential I need to overcome to prevent chugging and other oscillations. What -is- important is that my holes restrict the flow to a certain amount of flow no matter what the pressure differential is... That's why using a spray nozzle is a bad idea.

 So resetting with what I have learned thus far, I noticed that in testing the oxidizer flow I had to wait for the entire injection system to chill down to -40F before liquid made it out of the nozzles.  I feel a large part of the lag time comes from the bulk thermal mass that the nitrous has to interact with on its way into the chamber. So I will be moving the oxidizer to the inside of the injection pattern. I will also be thinning out the injector plate so that there is less too cool and it will also help me heat up the fuel a little bit quicker.

Apart from redesigning my entire injection system, the thrust stand is underway! I milled the main 1/8" steel plate to fit flush with the structure of the stand before starting to mount the top and bottom plates, also 10G steel with 10 1/4" steel bolts. Once I get my 1/4" lexan later today, I will cut and stack triple layers (3/4" total) on either side of the stand to complete the enclosure. In theory, it can take a 9mm bullet from any direction... hopefully we don't need to test that part out.