NASASpaceFlight.com Forum

General Discussion => Advanced Concepts => Topic started by: Jerry Fisher on 05/26/2021 09:11 pm

Title: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 05/26/2021 09:11 pm
   I infused PLA with KMnO4 and used it as a fuel core for rocket grade hydrogen peroxide. The PLA fuel core can be segmented, printed on a desk top 3D printer, and infused with KMnO4 at high temperature and pressure. The infusion takes less than an hour and results in the KMnO4 being evenly distributed throughout the PLA. I put together a small rocket engine using a 1/4 inch stainless steel mist nozzle as the HTP injector, a Soda Stream bottle for an oxidizer tank, a low pressure 12 V DC solenoid opening valve, a plastic one way valve, a graphite nozzle, and some CPVC piping glued together with CPVC cement. Primitive, but enough to demonstrate the catalytic reaction of HTP with PLA/KMnO4 fuel core. As long as I don't go over 100 psi chamber pressure and run longer than 10 seconds, it holds together long enough for the demonstration. I've written a paper on the HTP and PLA/KMnO4 hybrid rocket engine. I licensed the paper under the creative commons share alike copyright to engage in a dialog on this concept, if there is interest. Also, I've updated my website at www.fisherspacesystems.com. The website has a link to the paper as well as links to some engine test.

Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 06/29/2021 04:39 pm
  To simplify (i.e. get rid of the igniter) and to explore different fuel grain geometries, I changed the PLA fuel core from an annular design with a 20% infill to a five point star configuration. The typical "star chamber" fuel grain geometry has a rapid rise in thrust, levels off to an even thrust, and then decreases rapidly. With this fuel grain geometry, the surface area of the PLA/KMnO4 exposed to the oxidizer was increased from 57 cm2 to 90 cm2. I used the same geometry for three separate test. The only parameter I changed was the flow rate. Of the three test, only one ignited and that took ~11 seconds. So, it looks like it's back to the igniter. On the one that ignited, I did observe an even burn through the length of the fuel core. And, if my calculations are correct, the O/F ratio was very close to theoretical. Next month it's back to the glow wire igniter and more quantitative results on O/F ratio. Also, I'm adding another variable to the test.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 07/29/2021 05:54 pm
In the latest series of test, to shorten the ignition time, I blended ~85% hydrogen peroxide with ethanol using oxidizer to fuel ratios of 30 and 20. The first test base lined the series using just HTP/PLA/KMnO4 hybrid motor. The next test used an HTPE blend with a 30:1 ratio (i.e 1 ml of ethanol added to 30 ml of HTP). The third test used an HTPE blend with a 20:1 ratio (i.e. 1.5 ml of ethanol added to 30 ml of HTP). The HTP oxidizer was at 85% and the fuel grain, PLA infused with KMnO4, core was 2.3 cm in diameter, 15 cm long, and in the star configuration for all three test. Why would I add ethanol to 85% hydrogen peroxide?

Welllll! Several months ago I read a couple of articles on blended HTP as a mono-propellant for micro satellites (Ref). In the articles, the authors stated that ethanol was chosen because it was somewhat compatible with HTP and significantly increased the specific impulse. In theory (using the NASA CEA program), adding a small amount (O/F = 30) of ethanol not only doubled the specific impulse but, also doubled the combustion chamber temperature (from 380 C to 1178 C). This necessitates the use of a more robust catalyst. In a catalyst pack based on silver, the silver would melt away quickly (silver melts at ~961 C) and in a catalysts pack based on platinum, the platinum would wash out (platinum melts at ~1770 C). And they cost a lot, platinum more so than silver.

When I used the NASA CEA code to check on HTPE blend with the PLA/KMnO4 fuel, there was only a small increase (<1%) in specific impulse and combustion temperature. I was basically adding a hydrocarbon fuel to another hydrocarbon fuel. So, in theory, it didn't make sense. But, in practice, the HTPE blend showed significant melt of the PLA/KMnO4 over the straight HTP oxidizer. However, I didn't get an ignition. I may keep the HTPE blend at O/F=30 just because it may improve the O/F ratio of the HTP/PLA/KMnO4 hybrid rocket motor.

The HTPE blend got me thinking. What if I used an O/F ratio of 10 (i.e 3 ml of ethanol to 30 ml of HTP) with my mixed metal oxide (MMO) I've been working on for the last SEVEN YEARS (first batch was 07/25/2014) but couldn't get up to the auto-ignition temperature of ethanol?  So, I pulled my MMO off of the shelf, used it as the catalyst in a small rocket engine, and the results were awesome! On the first test, ignition occurred in about 9 sec and ran for another 9 sec at an initial flow rate of 1.7 ml/sec at 120 psia.

I used a 1/4" stainless steel mist nozzle with a 0.5 mm orifice as the injector, four porous ceramic cylinders (3 1/8" x 7/8") infused with my MMO and sintered at 600 C, a 1" CPVC pipe 1 3/4" long combustion chamber, and a graphite nozzle with a throat diameter of 3.4 mm (L*=101"). As shown in the video (https://rumble.com/vkhm09-htp-blended-with-ethanol-using-a-mmo-catalyst.html (https://rumble.com/vkhm09-htp-blended-with-ethanol-using-a-mmo-catalyst.html)), burn through occurred at the injector toward the end of the run. There was significant charring in the combustion chamber suggesting ignition but it was not visible on the video. I suspect the L* was to great (it was a miscalculation on my part) and will have to redo the experiment with a smaller L*. Three of the four cylinders were recovered and were still reactive to ~85% HTP. In a followup test, I reused the cylinders with a stainless steel mist nozzle with a 0.8 mm orifice (flow rate 5.4 ml/sec at 120 psia) but got no ignition. I've bounded the flow rate on the test and look forward to further experiments with my MMO.

I now have two rocket engines to experiment with, HTP/PLA/KMnO4 hybrid rocket engine and HTPE rocket engine :)

Ref:  J Lee and S Kwon, 2013, Evaluation of ethanol-blended hydrogen peroxide monopropellant on a 10 N class thruster, J. Propul. Power. AIAA Early Edition and J Huh, J Lee, D Seo, S Kang, and S Kwon, 2013, Fabrication of ethanol blended hydrogen peroxide 50 mN class MEMS thruster, PowerMEMS 2013, Journal of Physics: Conference Series 476 (2013) 012124
Title: Re: HTP/PLA/KMnO4 Hybird Rocket Engine
Post by: rubicondsrv on 07/30/2021 02:43 am
   I infused PLA with KMnO4 and used it as a fuel core for rocket grade hydrogen peroxide. The PLA fuel core can be segmented, printed on a desk top 3D printer, and infused with KMnO4 at high temperature and pressure. The infusion takes less than an hour and results in the KMnO4 being evenly distributed throughout the PLA. I put together a small rocket engine using a 1/4 inch stainless steel mist nozzle as the HTP injector, a Soda Stream bottle for an oxidizer tank, a low pressure 12 V DC solenoid opening valve, a plastic one way valve, a graphite nozzle, and some CPVC piping glued together with CPVC cement. Primitive, but enough to demonstrate the catalytic reaction of HTP with PLA/KMnO4 fuel core. As long as I don't go over 100 psi chamber pressure and run longer than 10 seconds, it holds together long enough for the demonstration. I've written a paper on the HTP and PLA/KMnO4 hybrid rocket engine. I licensed the paper under the creative commons share alike copyright to engage in a dialog on this concept, if there is interest. Also, I've updated my website at www.fisherspacesystems.com. The website has a link to the paper as well as links to some engine test.



so this is basically a hypergolic hybrid motor using HTP and a permanganate filled plastic fuel grain?   
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 08/02/2021 12:59 pm
   
Quote
so this is basically a hypergolic hybrid motor using HTP and a permanganate filled plastic fuel grain?   

Yes! It's as Simple as that. The infusion of potassium permanganate into polylactic acid, a thermoplastic polyester, makes the PLA hypergolic with HTP. Also, I surmise that KMnO4 reduces the melting temperature of the composite thus increasing the regression rate of the material. Using the "star chamber" fuel grain geometry, I've found that the O/F ratio is ~3, close to the theoretical value from the NASA CEA code. I'm cautiously optimistic that the characteristic velocity will be close to theory as well. In the next series of experiments, I'm inserting a pressure probe into the combustion chamber. With the pressure reading, I'll determine c* and compare it to theory.
Title: Re: HTP/PLA/KMnO4 Hybird Rocket Engine
Post by: rubicondsrv on 08/07/2021 02:23 am
it looks like the fuel grain is getting melted to the chamber,  you may want to try wrapping the fuel in some paper that has been soaked in a borax solution to both slow down the gasses leaking between the segments and allow the grain to be removed from the tube easily. this may also reduce the burn through problems.

 
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 08/09/2021 12:44 pm
Quote
you may want to try wrapping the fuel in some paper that has been soaked in a borax solution

Thanks! I'll put that in my tool box. I'm using PVC pond liner (14 mil) right now and it is working just fine. It's good to have backups.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 08/31/2021 08:24 pm
   Of the last five test in August 2021, the test on August 24 was the best. I increased the throat diameter to 5 mm, decreased the characteristic length to 33 in, increased the oxidizer tank pressure to 130 psig, increased the length of the fuel core to 16.5 cm, and added a pressure probe to the mixing chamber.  Ignition occurred in 1.5 to 2.0 sec. The chamber pressure rose to ~93 psig in 2.0 sec and was steady throughout the ignition. Burn time was ~5 sec. The video (https://rumble.com/vlx4qr-08-24-2021-htpeplakmno4-chamber-pressure.html (https://rumble.com/vlx4qr-08-24-2021-htpeplakmno4-chamber-pressure.html)) shows a net positive thrust greater than 14 N (3.2 lb) at ignition and held throughout the burn time. Shut down was instantaneous. The oxidizer to fuel ratio was ~2.3 (2.5 theoretical) and total mass flow rate was ~13.4 gm/sec resulting in a characteristic velocity of 1,163 m/sec with a c* efficiency of ~77%. I still plan on launching a class I HTPE hybrid before the end of the year. Next month I'll lock down the thrust and begin building the flight system.
Title: Re: HTP/PLA/KMnO4 Hybird Rocket Engine
Post by: rubicondsrv on 09/01/2021 12:43 am
   Of the last five test in August 2021, the test on August 24 was the best. I increased the throat diameter to 5 mm, decreased the characteristic length to 33 in, increased the oxidizer tank pressure to 130 psig, increased the length of the fuel core to 16.5 cm, and added a pressure probe to the mixing chamber.  Ignition occurred in 1.5 to 2.0 sec. The chamber pressure rose to ~93 psig in 2.0 sec and was steady throughout the ignition. Burn time was ~5 sec. The video (https://rumble.com/vlx4qr-08-24-2021-htpeplakmno4-chamber-pressure.html (https://rumble.com/vlx4qr-08-24-2021-htpeplakmno4-chamber-pressure.html)) shows a net positive thrust greater than 14 N (3.2 lb) at ignition and held throughout the burn time. Shut down was instantaneous. The oxidizer to fuel ratio was ~2.3 (2.5 theoretical) and total mass flow rate was ~13.4 gm/sec resulting in a characteristic velocity of 1,163 m/sec with a c* efficiency of ~77%. I still plan on launching a class I HTPE hybrid before the end of the year. Next month I'll lock down the thrust and begin building the flight system.

looks like you didn't have burn through problems this time either. did you have to add a heater for ignition this time?
Title: Re: HTP/PLA/KMnO4 Hybird Rocket Engine
Post by: libra on 09/01/2021 09:41 am
Just saying in passing - you should correct the thread title from HYBIRD to hybrid.

Interesting stuff, always been a fan of H2O2 as oxidizer.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 09/01/2021 01:37 pm
Quote
looks like you didn't have burn through problems this time either. did you have to add a heater for ignition this time?

No burn through. It was a nice even burn. I plan on doing a longitudinal cut down the fuel core to get a better look at the burn. I'll post some pictures. I used a high resistance wire to preheat the nozzle. I'm not sure I need it. I'll do some testing to see if I can get rid of the preheat. Also, I left the solenoid valve open after the burn to cool down the mixing chamber. There was little warping this time.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 09/01/2021 01:39 pm
Quote
you should correct the thread title from HYBIRD to hybrid.

Thanks! I must've looked at that thread 100 times and never caught that misspelling :-[
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: libra on 09/01/2021 06:21 pm
Glad to be of help ! It's a very minor issue, btw.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 10/05/2021 01:59 pm
   There were five test in September (four succeeded & one failed). I varied the length of the PLA/KMnO4 fuel core as follows: 16.5 cm, 15.0 cm, 13.5 cm, and 12.0 cm. All other parameters were the same. I used a blend of 55 ml of ~ 87% HTP and 2.1 ml of denatured ethanol (O/F = 26.2) as the oxidizer. The propellant tank was pressurized to 130 psig using CO2 gas as the pressurant. I used a 1/4" stainless steel mist nozzle with a 1.0 mm orifice as the injector and a graphite phenolic nozzle with an initial throat diameter of 5 mm. The objective was to determine what effect the length of the fuel core had on the operation of the engine and to select the best length to continue. The ignition oxidizer flux of ~14 gm/cm2-sec, the run-time oxidizer flux of ~6 gm/cm2-sec, the fuel core regression rate of ~0.2 mm/sec, and the characteristic velocity of ~1390 m/sec were consistent on three out of the four successful test. The deciding factor was the oxidizer to fuel ratio, the thrust, and the burn time. For the 15 cm fuel core the O/F ratio was 2.3, close to theoretical. Ignition occurred in one second and lasted for ~7 sec https://rumble.com/vnb0wz-htpepla-kmno4-class-i-engine.html (https://rumble.com/vnb0wz-htpepla-kmno4-class-i-engine.html). There was a net positive thrust of greater than 16.2 N at ignition and lasted throughout the burn. Based on these results, I've selected the 15 cm fuel core for the class I flight system.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: colbourne on 10/10/2021 07:47 am
I find this thread very interesting . Some friends of mine built a H2O2 /liquiid parafin motor from the Montreal Solaire plans. Due to not having H2O2 of higher enough concentration thrust was not high enough.
I experimented by making very light weight rockets, using aluminium dust mixed with wax, as the solid fuel,  and a bag of KMnO4 as the catalyst. Ignition was  with a sparkler. I used low grade H2O2 as obtained from gardening shops of 60% so was not expecting good results. My results were very chaotic and would not be suitable for a serious rocket. I was happy with just getting the wax to ignite.

Try adding metal powder to your fuel and you might get better thrust.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: edzieba on 10/13/2021 02:27 pm
Adding metal powder would interfere with the FDM propellant grain fabrication method, as hard substances in the feedstock erode the inside of the extrusion nozzle.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 10/14/2021 01:28 pm
Quote
Adding metal powder would interfere with the FDM propellant grain fabrication method, as hard substances in the feedstock erode the inside of the extrusion nozzle.

I've used off the shelf PLA/Al and printed out fuel core segments. I tried to auto-ignite using my mixed metal oxide as a catalyst with HTP. I got a lot of hot gas but no ignition. I had to replace my nozzle. The PLA/Al must've eroded my nozzle and damaged it.

I have not tried PLA/Al infused with KMnO4. I did a CEA run (frozen composition) with 15% Al, 6% ethanol, 77% PLA, and 2% KMnO4 as fuel for 85% HTP. There was a 1.3% increase in c* (1485 vs 1504 m/sec) and the O/F ratio went from 2.75 to 2.5. So, theoretically, it may not be worth the trouble. However, I'm getting ready to change out my nozzle anyway so I'll make a batch and we'll see.

Others (ref) have used Al as a metal additive to increase the regression rate of PLA. However, the results were disappointing. The Al did not increase the regression rate over straight PLA.

Ref: Small-Scale Static Fire Tests of 3D Printing Hybrid Rocket Fuel Grains Produced from Di erent Materials, Mitchell McFarland and Elsa Antunes, College of Science and Engineering, James Cook University, 1 James Cook Drive, Townsville, QLD 4811, Australia
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: colbourne on 10/16/2021 10:52 am
The preferred catalyst if money is not a problem is using a silver coated material (with as much surface area as possible in a box), through which the HTP is forced.
If the KMnO4 is mixed with the fuel , I thought it would be to late to achieve efficient catalysation of the HTP.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 10/17/2021 07:50 pm
True! Silver screens are the preferred method for catalyzing HTP. However, the cost of this catalyst is only one of the disadvantages. Keep in mind, my immediate objective is to develop a hybrid rocket motor for a Class I (as defined by the FAA) rocket for which the total mass allotment is 1.5 kg (3.3 lb).

The silver (density = 10.5 gm/cm3) is deposited on screens made of brass, nickel, or stainless steel (density ~7.9 gm/cm3). The silver screens are alternated with stainless steel screens and loaded under high pressure in the catalyst bed. My engine would be ~1" in diameter and 3"-4" long. I haven't done the calculations, but you can imagine the weight of this catalyst.

Another disadvantage is the pressure drop across the bed. Bed pressure drops usually run from 75 to 125 psi. Since I currently pressurize my propellant tank to 130 psi, I would have to double my pressure to get the same operating conditions. The higher pressure requirement will impact system mass.

Also, to increase performance, I've added a small amount (O/F = 25) of ethanol to the HTP. This increased the decomposition temperature from 380 C to 1178 C. In a catalyst pack based on silver, the silver would melt away quickly (silver melts at ~961 C) and most likely, would not sustain the combustion (and a waste of good money).

Further more, Byeonguk A., et el, (ref) found that the PLA fuel inlet partially melted down in the gravity direction because the inlet surface was directly exposed to the hot decomposed gas (~741 C). Using HTPE, my inlet temperature will be ~1178 C. This could result in the PLA melting and plugging up the fuel core or nozzle throat leading to a catastrophic failure. This has happened once but, let's not talk about that.

Finally, a silver screen catalyst may sound simple but is actually quite complicated. There is a rigorous procedure to go through getting the silver screen activated, multiple acid baths and cleanings. Infusion of KMnO4 into PLA is much simpler.

As to your last point on efficient HTP decomposition, the mixing chamber or post combustion chamber takes care of that. I've found that a characteristic length of ~33" works well. The mixing chamber is just a 4.6 cm long CPVC pipe 1" in diameter cemented into two 1" CPVC couplings.

Sorry about the long post in response to your comment but, once I got started, I couldn't stop.
 
Ref: Byeonguk Ahn, Vikas Khandu Ghosale, and Sejin Kwon, Three-Dimensionally Printed
Polylactic Acid as Solid Fuel for Hydrogen Peroxide Hybrid Rockets, Journal of Propulsion
and Power, Technical Notes, Downloaded on November 30, 2020, http://arc.aiaa.org
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: colbourne on 10/18/2021 10:02 am
The Solaire plans used dry ice to pressurize the fuel and HTP. It also used a bag of KMnO4 before the combustion chamber. It sounds like you are making good progress. Have you managed to have any flights with this set up yet ?
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 10/20/2021 12:44 pm
Quote
Solaire plans used dry ice to pressurize the fuel and HTP

Thanks for the tip. I didn't realize the vapor pressure of dry ice was that high (~830 psi @ 20 C). I will be experimenting with it for the class II engine. I was going to use my porous ceramic mixed metal oxide (that I've been working on for SEVEN YEARS) with 70% HTP as the pressurizing subsystem but, dry ice seems a lot simpler. However, there are questions of mass and duration. Does it weigh less than the HTP subsystem and can it sustain a pressure for greater than 60 seconds of run time?

The flight system is a work in progress. I'm working on a lightweight air-frame for the class I engine. I used fiberglass panels but the mass is to great (~450 gm). Ordering some carbon fiber cloth to try that next. For flight control, I'm using an RC transmitter, receiver, and spare servos.

Keep those tips and comments coming.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Reuben on 10/22/2021 02:46 am
How would the co2 be vaporised? with liquids they can be ran through some sort of cooling jacket for the engine but this obviously can't be done with ice. or would it be stored above boiling temperature and just at pressure, where it could sublimate when more pressurant is needed, and the tank pressure is reduced?
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 10/22/2021 02:10 pm
Quote
How would the co2 be vaporised?

I did a quick search on sublimation rate of dry ice. Most research is done for the packing and transportation industries at room temperature and atmospheric pressure. Very little research at 830 psi and room temperature. I looked at the Clapeyron-Clausius Equation but it contains an experimental coefficient. So, no matter what equation you use, some research is required.

I plan on putting some dry ice in a stainless steel container, letting it come up to pressure, and measuring the change in pressure as I release the vapor through a stainless steel orifice. The diameter of the orifice will depend on how much gas I need to keep my tank pressurized. Once I have the coefficient, I can scale up to larger systems. There are additives such as ammonia to increase the sublimation rate if required. 
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: aceshigh on 10/22/2021 07:08 pm
Quote
How would the co2 be vaporised?

I did a quick search on sublimation rate of dry ice. Most research is done for the packing and transportation industries at room temperature and atmospheric pressure. Very little research at 830 psi and room temperature. I looked at the Clapeyron-Clausius Equation but it contains an experimental coefficient. So, no matter what equation you use, some research is required.

I plan on putting some dry ice in a stainless steel container, letting it come up to pressure, and measuring the change in pressure as I release the vapor through a stainless steel orifice. The diameter of the orifice will depend on how much gas I need to keep my tank pressurized. Once I have the coefficient, I can scale up to larger systems. There are additives such as ammonia to increase the sublimation rate if required.

BASE: we have some good news and bad news for you

The bad news is that the rocket and the ship that would save you had a problem. They wonīt be able to take off before you die from hunger and thirst OR lack of oxygen

Stranded astronaut: damn... and what is the good news?

BASE: we discovered the problem with your ship. A simple cable got disconnected. We will be sending the solution to your computer. Then you can return home. But beware, your velocity will be higher than normal on reentry, but donīt worry, the cookie tiles are much better than old ceramic tiles. Haha, of course, unless one of them is missing. You didnīt eat any, have you?

Stranded Astronaut: well, at least from HUNGER I wonīt be dying.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 11/03/2021 03:04 pm
   There were two test in October. I eliminated the glow wire for ignition and decreased the cross sectional area of the 15 cm PLA/KMnO4 fuel cell to increase the oxidizer flux. All other parameters were the same. I used a blend of 55 ml of ~ 85% HTP and 1.7 ml of denatured ethanol (O/F = 37.4) as the oxidizer. I used a 1/4" stainless steel mist nozzle with a 1.0 mm orifice as the injector and a graphite phenolic nozzle with an initial throat diameter of 5 mm. The objective was to determine what effect the increased flux had on the operation of the engine and if auto ignition would occur without the glow wire.

   The ignition oxidizer flux was ~14 gm/cm2-sec and was the same for both test. Ignition occurred in ~1.9 sec for the low flux fuel core and ~1.5 sec for the high flux fuel core. The ignition times are about the same as with a glow wire igniter. Eliminating the igniter simplifies the system.

   The run-time oxidizer flux was ~5.4 gm/cm2-sec for the low flux fuel core and 9.1 gm/cm2-sec for the high flux fuel core. The fuel core regression rate and O/F ratio was approximately the same in both test.  The deciding factor was the chamber pressure and the characteristic velocity.  The propellant tank was pressurized to 130 psig using CO2 gas as the pressurant in both test. The low flux test had a higher chamber pressure with corresponding higher characteristic velocity with a c* efficiency of ~91%. Based on these results and despite the longer ignition time, I've selected the low flux 15 cm fuel core for the class I flight system. https://rumble.com/voo0fx-plakmno4-high-flux-test.html (https://rumble.com/voo0fx-plakmno4-high-flux-test.html)
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Reuben on 11/04/2021 12:55 am
Do you know what the effect of a longer residence time of the HTP on the ignition delay? perhaps prior to ignition, the HTP injection pressure could be lowered to allow it longer to catalyse whilst not wasting all that isn't combusted. otherwise watching that video was very satisfying the combustion looked very very consistent- awesome build!
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 11/04/2021 01:52 pm
Quote
Do you know what the effect of a longer residence time of the HTP on the ignition delay?

I'm not sure there would be an advantage here. Lowering the propellant tank pressure to below 120 psig introduces oscillations in the combustion chamber. I need at least a 30 psig pressure drop across the 12V NC solenoid valve, the check valve, and the injector nozzle to dampen out the oscillation. Also, the lower chamber pressure results in a lower thrust and characteristic velocity. Finally, the mechanics of starting out with a lower tank pressure then ramping up to a higher pressure would add more mass to the class I flight system. This may be feasible in a class II system but not in a class I system. Thanks for the comment.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: CameronD on 11/05/2021 12:24 am
Quote
Do you know what the effect of a longer residence time of the HTP on the ignition delay?

I'm not sure there would be an advantage here. Lowering the propellant tank pressure to below 120 psig introduces oscillations in the combustion chamber. I need at least a 30 psig pressure drop across the 12V NC solenoid valve, the check valve, and the injector nozzle to dampen out the oscillation. Also, the lower chamber pressure results in a lower thrust and characteristic velocity. Finally, the mechanics of starting out with a lower tank pressure then ramping up to a higher pressure would add more mass to the class I flight system. This may be feasible in a class II system but not in a class I system. Thanks for the comment.

How about keeping tank pressure the same and using a slowly-opening ball valve instead of the solenoid?  Wouldn't that have the same/similar effect??

Impressive work, BTW!
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: edzieba on 11/05/2021 07:13 am
Or printing a flow-restrictor as part of the combustion chamber that rapidly burns away just after ignition.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 11/05/2021 01:13 pm
Quote
...a slowly-opening ball valve instead of the solenoid?

Yes. It would have a similar effect but, the ball valve weighs ~3 times as much as a solenoid valve (345 gm vs 102 gm). I will be using a ball valve on the class II engine. The ball valve I have is rated at 150 psig. I will be testing at higher pressure and throttling up after ignition on the class II engine.

Quote
Or printing a flow restrictor....

Good idea! I could print a PLA flow restrictor and place it at the end of the mixing chamber. After ignition, the orifice diameter will increase and the graphite nozzle throat diameter would take over. The PLA flow restrictor would not add much mass to the system. I would start with an orifice diameter of 4 mm (vs 5mm nozzle throat diameter) and work my way to smaller orifice diameters. I'll have to be careful and not plug the nozzle with PLA melt. That has happened before with resulting explosion.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Reuben on 11/08/2021 05:31 am
Quote
Do you know what the effect of a longer residence time of the HTP on the ignition delay?

I'm not sure there would be an advantage here. Lowering the propellant tank pressure to below 120 psig introduces oscillations in the combustion chamber. I need at least a 30 psig pressure drop across the 12V NC solenoid valve, the check valve, and the injector nozzle to dampen out the oscillation. Also, the lower chamber pressure results in a lower thrust and characteristic velocity. Finally, the mechanics of starting out with a lower tank pressure then ramping up to a higher pressure would add more mass to the class I flight system. This may be feasible in a class II system but not in a class I system. Thanks for the comment.
I am aware that a 30% pressure decrease is healthy for the negation of oscillation between the fuel tank and the combustion chamber, however that oscillation only arises ad a product of combustion, and would not begin until ignition had occurred, and chamber pressure could be raised again. The point you brought up about weight however does sound prohibitive.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 12/08/2021 01:29 pm
This month I showed that the class I engine performance was consistent, reliable, and ignition occurs in ~ 1.1 sec. The parameters were the same for each of the three test: propellant tank pressure, 130 psig; HTPE blend O/F ratio, 27.5, initial HTPE flow rate, 14.8 ml/sec; mass flow rate for HTP and ethanol, 19.7 gm/sec and 0.4 gm/sec, respectively; cross sectional area for the fuel cores,  ~1.1 cm2 ; and the ignition "oxidizer" flux, ~ 17.6 gm/cm2 /sec. All three test used the same batch of distilled HTP with 2.0 ml of ethanol.

The results were about the same across all three test. The average: ignition, 1.1 sec; mass flow rate, 12.4 gm/sec; chamber pressure, 105 psia; characteristic velocity, 1280 m/sec; efficiency, 86%, thrust, 16.5 N; regression rate, 0.23 mm/sec; O/F ratio, 3.0. Link to Nov 10, 2021 test https://rumble.com/vqb7of-htppla-hybrid-reliability-test.html (https://rumble.com/vqb7of-htppla-hybrid-reliability-test.html). Read more in the November end of month report.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: CameronD on 12/09/2021 12:23 am
This month I showed that the class I engine performance was consistent, reliable, and ignition occurs in ~ 1.1 sec. The parameters were the same for each of the three test: propellant tank pressure, 130 psig; HTPE blend O/F ratio, 27.5, initial HTPE flow rate, 14.8 ml/sec; mass flow rate for HTP and ethanol, 19.7 gm/sec and 0.4 gm/sec, respectively; cross sectional area for the fuel cores,  ~1.1 cm2 ; and the ignition "oxidizer" flux, ~ 17.6 gm/cm2 /sec. All three test used the same batch of distilled HTP with 2.0 ml of ethanol.

The results were about the same across all three test. The average: ignition, 1.1 sec; mass flow rate, 12.4 gm/sec; chamber pressure, 105 psia; characteristic velocity, 1280 m/sec; efficiency, 86%, thrust, 16.5 N; regression rate, 0.23 mm/sec; O/F ratio, 3.0. Link to Nov 10, 2021 test https://rumble.com/vqb7of-htppla-hybrid-reliability-test.html (https://rumble.com/vqb7of-htppla-hybrid-reliability-test.html). Read more in the November end of month report.

Looks good, Jerry!  Seems fairly stable in your video so you might be onto something with this.  Keep up the great work!
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 01/11/2022 08:20 pm
This month I made a wooden mold for the fuselage. I wrapped some Saran Wrap around the mold and hand laid up the carbon fabric in two layers. The carbon fabric fuselage has a mass of ~ 290 gm.

For the nose cone, I cut a styrofoam block into a rough shape of a nose cone and then sanded down the edges until I reached a tapered shape. I attached the nose cone to the forward strut. The forward strut is made of PLA and is secured to the fuselage by three small screws. When inserted into the fuselage, the propellant tank rest against the forward strut, pushing on the forward strut during take off.

The aft strut centers the rocket engine and supports the fin assembly. The aft strut is also made of PLA and is secured to the fuselage by three small screws. I made three fins using the thinnest wall setting on the 3D printer. I glued some K'Nex pieces to the fins to hold everything together.

I made some plumbing modifications to the propellant tank, solenoid valve, check valve, injector, and rocket engine assembly reducing its mass to ~ 575 gm.

Next will be the cockpit struts and cockpit. The total flight system mass is an estimated 1.3 kg (includes the fuel and oxidizer), well below the 1.5 kg class I requirement. Read more in the December, 2021 EOM report.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 02/02/2022 03:27 pm
This month I worked on the forward and aft struts for the cockpit, the paraglider box, the battery pack, and the placement of the RC receiver and the servos. I inserted the oxidizer tank and fuel grain (pictured below) into the carbon fabric fuselage. Everything fits and is ready for static testing. The mass is ~1.3 kg including the oxidizer and fuel. Read more in the January 2022 end of month report.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 03/08/2022 02:29 pm
This month, in an attempt to increase the thrust of the class I engine, I increased the O/F ratio by shortening the fuel grain from 15 cm to 12.5 cm. This reduced the contact surface area of the fuel grain and caused the rocket engine to run oxidizer rich. Also, it reduced the mass of the rocket engine by about 20 gm. Ignition occurred around 0.9 sec. I observed a net positive thrust of greater than 19.1 N at ignition and a c* efficiency of over 100%. https://rumble.com/vwtclh-htppla-hybrid-oxidizer-rich.html (https://rumble.com/vwtclh-htppla-hybrid-oxidizer-rich.html)

Quote
Try adding metal powder to your fuel and you might get better thrust.

Also this month, as suggested by colbourne (reply #14), I printed a 15 cm PLA/Al fuel core using off the shelf aluminized PLA with an aluminum content of ~ 13%. I infused the PLA/Al fuel core with KMnO4 and assembled a rocket engine based on the PLA/Al/KMnO4 fuel core. All other parameters were the same.  Ignition occurred in ~ 1.3 sec and burn time was ~ 5.8 sec. The c* was 1,477 m/s with a c* efficiency of 96%. This too looks promising.  If ignition time is reduced by running the engine oxidizer rich as noted above, it may be worth pursuing. Also, using a finer grain of Al with the PLA may improve performance. https://rumble.com/vwtcy9-htpplaal-hybrid.html (https://rumble.com/vwtcy9-htpplaal-hybrid.html)
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 04/06/2022 02:13 pm
This month, I mounted a static engine test stand, a load cell to measure thrust, and a test article with a blast shield around the oxidizer tank to my rocket engine test stand. To run a static engine test, I need to pressurize the oxidizer tank to 140 psig and turn off the fill valve. Adding a blast shield around the oxidizer tank makes it safer and is part of my KISSES principle of "Keeping it Safe". Over the next month or two I'll be testing fuel grain lengths of 11.5, 12.5, and 13.5 cm to narrow done the ideal fuel grain lengths for best overall performance.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 05/03/2022 06:20 pm
This month, I did a static engine test of the flight system. A video of the test is at https://rumble.com/v13dqgl-mki-viper-static-engine-test.html (https://rumble.com/v13dqgl-mki-viper-static-engine-test.html). The thrust ramped up from ~15 N to around 20 N over a 7 sec burn time. The longer than usual burn time is attributed to ignition occurring in ~0.3 sec and thus leaving more oxidizer to fuel the engine. This was due to a small amount of HTPE leaking into the fuel grain during initialization of the receiver, a preheating event. 

The center of mass (CM) is below the cockpit area and ~ 2 cm off the thrust vector. The off axis thrust will cause the Viper to rotate after leaving the guide rail. Due to the low thrust at ignition, the liftoff velocity will not be enough to correct the rotation of the MkI Viper using the elevators and the vertical stabilizer. I will rearrange the masses inside the fuselage and bring the CM closer to the line of thrust. Also, I believe I can increase the thrust by increasing the initial nozzle throat diameter from 5 to 6 mm.

Also, during my first test (with a 12.5 cm fuel grain) on the static engine test stand, I forgot to put a one kilogram mass on the rocket and it took off. I definitely need a pretest checklist. The liftoff was pretty cool. A video of the test is available at https://rumble.com/v13dp0n-liftoff.html (https://rumble.com/v13dp0n-liftoff.html).
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: CameronD on 05/04/2022 12:41 am
Also, during my first test (with a 12.5 cm fuel grain) on the static engine test stand, I forgot to put a one kilogram mass on the rocket and it took off. I definitely need a pretest checklist. The liftoff was pretty cool. A video of the test is available at https://rumble.com/v13dp0n-liftoff.html (https://rumble.com/v13dp0n-liftoff.html).

Well, there can be no arguing with actual results.. Well done, Jerry!
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 06/07/2022 02:41 pm
Quote
Well, there can be no arguing with actual results.. Well done, Jerry!

Thanks! Although it was an accidental launch, I got some useful data. That contraption had a mass of 1.9kg. As such, there was a net positive thrust greater than 19N and it sure was pretty. The throat diameter eroded to 6 mm.

As a result of the previous test, I increased the initial throat diameter from 5 to 6 mm which resulted in a slight increase in mass flow rate. I measured the thrust at 19.1 N and it looked pretty steady rumble.com/v17imbi-20-n-thrust-in-may-2022.html (http://rumble.com/v17imbi-20-n-thrust-in-may-2022.html).  The characteristic velocity was calculated to be ~1662 m/sec with an efficiency of 104% (theory @ 1593 m/sec).

Also, I've been working on the flight system. I have rearranged the mass some with the purpose of moving the CM more in line with the thrust vector. Next month, I plan to test for consistency and reliability and launch the Mark I Viper.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: colbourne on 06/18/2022 05:24 am
If the lift off thrust is a bit low, you could use a simple catapult to assist with take off. When ignition has started pull a cord (or use a servo) to release a hold down wire. Use a spring or rubber bungee.
I am avidly following your progress , as I was experimenting with HTP, but in a much more primitive rocket.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 07/04/2022 04:57 pm
     This is the first launch of the Mark I Viper https://rumble.com/v1b3jsn-mk-i-viper-first-launch.html (https://rumble.com/v1b3jsn-mk-i-viper-first-launch.html). The Mk I Viper cleared the rail guide at 2 m/sec and it was under thrust for ~ 7 seconds. I used 50 ml of unstabilized ~ 90% HTP plus 2 ml of ethanol for the oxidizer and PLA infused with KMnO4 for the fuel. Ignition occurred in ~ 0.3 seconds. The mass flow rate was about 13.29 gm/sec resulting in a total propellant mass of ~ 93.0 gm for the 7.0 seconds of thrust.

Quote
use a simple catapult to assist with take off.

    I expected the Mk I viper to clear the rail guide at 4 m/sec. As such, I didn't have the aerodynamic control I needed to correct the trajectory.  I may have to use a catapult but I have a few things to try first. To prevent it from pitching forward, I'll shift the center of mass more in line with the thrust vector. Also, I'll increase the thrust to give me more aerodynamic control. Read all about it in the Jun EOM report.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 08/02/2022 09:10 pm
   This month I had two flight test and one static test. All three test were an attempt to get a higher thrust. In the flight tests, I increased the throat diameter of the graphite phenolic nozzle to 6.7 mm. The first flight test blew the nozzle and failed to clear the rail guide. The second flight test cleared the rail guide and then blew out the nozzle https://rumble.com/v1eiis1-july-2022-mk-i-viper-flight-test.html (https://rumble.com/v1eiis1-july-2022-mk-i-viper-flight-test.html). I surmised that hot gases were leaking around the o-ring seal melting the PLA thus weakening the bond between the PLA adapter and CPVC coupling.

   In the static test, I increased the flow rate to ~ 23 ml/sec but keep all other parameters the same. Once again, the nozzle blew out immediately on ignition https://rumble.com/v1ein45-class-i-rocket-engine-static-test-july-19-2022.html (https://rumble.com/v1ein45-class-i-rocket-engine-static-test-july-19-2022.html). Test results show a pressure spike of ~ 140 psig in the mixing chamber and a peak thrust of ~ 33 N. The high pressure spike in the mixing chamber exceeded the design limit of 100 psia. It appears the thrust is there. I just have to tame it a little. I plan to introduce a variable orifice

Quote
Or printing a flow-restrictor as part of the combustion chamber that rapidly burns away just after ignition.

(ref: edzieba reply #28) at the end of the fuel grain to reduce the initial flow rate thus allowing the mixing chamber time to stabilize.
Title: Re: HTP/PLA/KMnO4 Hybrid Rocket Engine
Post by: Jerry Fisher on 09/02/2022 04:40 pm
   I spent most of the month identifying failure modes such as nozzle blow outs, pinhole leaks, and loose connections. Having resolved the problems, I had a successful test toward the end of the month with a flow rate of ~ 23 ml/sec. The thrust reached a peak of ~ 35 N and then declined ~ 24 N. Overall performance was pretty lousy with the c* and Ceff efficiency at 74% and 66% respectively. However, my O/F ratio was ~7.5, way to high. As such, next month will be spent improving the characteristic velocity and thrust coefficient. Aug 24 test. https://rumble.com/v1idcxo-htppla-test-on-august-24-2022.html (https://rumble.com/v1idcxo-htppla-test-on-august-24-2022.html)