https://www.kegerators.com/articles/CO2-Tank-Guide/
Compressed gases such as carbon dioxide, oxygen, and nitrous oxide are all gases at room temperature. But get them cold enough, and they become liquid. Get them colder still, and they will become solid - and more concentrated or dense. As these compounds increase in temperature, they also expand in volume. Your CO2 tank is the same way - the pressure increases the hotter the tank (and therefore the CO2 inside) gets.
CO2 expands rapidly as the tank's temperature increases, putting more and more pressure on the gas regulator which controls the CO2 output. The CO2 that the tank has been filled with is very cold (between -57 and -78 degrees degrees). At that temperature, the CO2 puts out only 100 PSI (pounds per square inch). At room temperature (70 degrees), the tank puts out about 850 PSI, and at hot temperatures (around 110 Degrees), the tank can put out a whopping 2000 PSI. If your tanks are ever in the position to be raised to that high of a temperature, the release valve will be triggered to prevent the tank from exploding. This can be quite startling, so it is wise to take steps to avoid this by storing your tank in a cool place, even while disconnected. This is why CO2 tanks are filled to only 34% of their volume. If the tank is filled more, it can trigger the safety and let all the gas out if it is exposed to high temperatures.
Keeping the fuel tank of liquid co2 with a flow valve that send the fuel to a secondary tank that gets super heated to allow for the gas to pressurize before letting it flow out a rocket nozzle.
]]>lots of pages to read
CO2 cooling for HEP experiments
https://cds.cern.ch/record/1158652/files/p328.pdf
Fundamental process and system design issues in CO2 vapor compression systems
http://citeseerx.ist.psu.edu/viewdoc/do … 1&type=pdf
It would have been nice to have a bit more information as to the rpm, blade characteristics ect....but we can get quite a bit from the heliocopter topic...I am wondering about plane use as well if we augment the wings with a bouyancy gas that can be added and heated to make it more or less bouyant.
]]>Welcome to newmars!
Interesting question and interesting concept.
I'm going to start by restating the question as I understand it to make sure I'm going about answering it in the right way.
You're designing a drone to fly over the surface of Mars which you'd like to power with compressed CO2. You want to figure out the most efficient way to use this energy source to maximize the range of the drone, and you've come up with two possible alternatives: First, using the compressed CO2 to power an engine to turn a propeller or second to use jets of compressed CO2 in a cold gas thruster, with the aim of maximizing flight time and therefore range. Both alternatives will run in tandem with a system of electric motors (and presumably batteries) familiar from drones on Earth.
I must admit that in reading your post I don't understand why you'd want to design a system using both compressed CO2 and electric propellers. I have limited exposure to principles of aeronautical engineering, but here's how I think about the issue: For any given drone design, you will have a certain amount of payload mass you can dedicate to energy storage/production. In order to maximize range and flight time you will want to maximize the number of newton-seconds you can get out of that mass. You will therefore look at your options, determine the efficiency of each, and dedicate 100% of that available mass to the most efficient one, providing for redundant systems where necessary.
I discussed the energy storage ability of compressed CO2 at length in this thread and much of what follows is based on information presented there.
One thing I want to push you on specifically is your choice to use CO2. I can see the appeal, maybe, if you want your drone to be a sort of hopper, which flies until the battery runs down, then lands to recharge (in this case, recharging by running the engines backwards to compress atmospheric gas), then taking off again. If this is your goal (much more complicated than a drone that flies until it runs out of power and then crashes!) then CO2 is the only gas you could potentially use (atmospheric separation would be crazy for this sort of mission imo).
Anyway, whatever your plans are I want to address the two scenarios you mentioned and then try to compare them to battery-electric and chemical-fueled engines.
The real problem with CO2 is that, compared to other gases like Nitrogen, it has an extremely low vapor pressure. Consequently, you can't pressurize it very much before it either liquifies or solidifies. This is made worse by the fact that Martian temperatures are much lower than Earth's, and there's no real way for an airborne drone to absorb thermal energy from the ground to vaporize CO2. For reference, at 230 K (typical Martian temperature), CO2's vapor pressure is 10 atmospheres; Nitrogen and Helium are far above their critical points and therefore cannot liquefy at any pressure, and for reference it is not unusual for bottles of compressed N2 or He to have pressures of 150 atm or above in regular commercial use. Cold gas thrusters using Nitrogen can see specific impulses as high as 75 s (for comparison, the SSME got 450 s). Isp scales in proportion to the inverse square root of the molar mass, so you might get up to 200 s with compressed Helium (which is, uh, pretty good actually?).
Anyway, to get back on track CO2 has both a lower possible pressure and a higher molecular mass than either of those gases; Accounting for molar mass alone you're looking at about 60 seconds, but the low vapor pressure really limits the possible expansion ratios and I'd be surprised if you could hit 20 s. That's 200 newton-seconds per kilogram of compressed CO2, which frankly is awful given that the gas itself is a pretty low density and requires comparatively heavy tanks to store.
When they can work, propeller-based systems are inherently more efficient ways to generate impulse than rocket-based systems because they move more mass at slower speeds. Ideal conditions for propellers are slow travel speeds through a dense medium (Think boats). Whatever the travel speed, Mars's atmosphere is not a dense medium and the design of a propeller that will work in it is nontrivial. Presumably what you want is a very large one with a low speed of rotation. Frankly I have nothing to contribute here. What I'm trying to get at is that there's no good way to make an apples-to-apples comparison between a cold gas thruster and a propeller system. If the propeller works it will presumably be better, but that's a tautologically true and therefore useless statement.
]]>We have a topic on the Mars Helicopter which is riding with the 2020 mission.
Hopefully this will give you some more data for how to make what you want to do possible.
To go with compressed mars air this topic will have data for you.
Then again Airplanes on Mars
I hope these will help...
]]>The original idea posted by Louis sounds similar to NASA's Extreme Access Flyers project. I haven't found much recent information about it (I tried to reference an article from 2015 but apparently users are no longer allowed to post links), but I do know that Embry-Riddle Aeronautical University (ERAU) in Daytona Beach, Florida is still working with NASA on the project. More specifically, the Engineering Physics Propulsion Lab (EPPL) has been designing systems for UAV propulsion on Mars using compressed CO2.
Also, kind of related, I was wondering if you guys had any advice for me. I am a graduate student at ERAU beginning my thesis designing an optimal control system for a Martian drone that uses both propellers and compressed CO2. However, after doing some initial research of my own (which is how I found this topic actually), I find myself trying to decide between two options for such a system:
1.) Having a compressed air engine that the CO2 is fed into that can power the propellers in tandem with an electric motor and will recharge the batteries as the compressed air engine runs, just like a hybrid car works,
2.) Simply having both propellers and cold gas thrusters that work together to produce thrust and attitude correction.
Do you have any thoughts on either system? The goal is to maximize flight time (or flight distance I suppose, but one would assume that the two are closely related).
Hope the information above helps!
]]>Thanks! I'll look for that as i begin moving through the paper. (th)
I suspect that the helium is used as a heat transfer agent in closed loops in liquefying the gas for storage and/or in reheating it in the rocket.
A carbon dioxide thermal rocket that utilizes an
indigenous resource in raw form for Mars exploration
D-R Yu∗, X-W Lv, J Qin,W Bao, and Z-L Yao
School of Energy Science and Engineering, Harbin Institute of Technology, Harbin, People’s Republic of China
The manuscript was received on 11 May 2009 and was accepted after revision for publication on 21 September 2009.
DOI: 10.1243/09544100JAERO617
Abstract: A CO2 thermal rocket that utilizes an indigenous resource directly for propulsion in
Mars is proposed. The cycle of the proposed novel CO2 thermal rocket combines a CO2 power
cycle with a cryogenic cycle, which is driven by solar energy. Filling CO2 after every hop enables
the concept hopper with the CO2 thermal rocket to visit several regions of the planet. The energy
available for consumption in the processes of the proposed CO2 thermal rocket is analysed; the
simulation results obtained by applying the first law of thermodynamics show that the performance of the cycle of the CO2 thermal rocket is improved by properly designing such a system for
the recovery of freezing CO2 cold energy and waste heat during the cryogenic cycle. Furthermore,
the effect of thermodynamic parameters on the performance of the cycle of the CO2 thermal
rocket is evaluated through parametric analysis; the results show that environmental temperature, nozzle inlet temperature, helium mass flowrate, etc. are the factors affecting thrust-specific
power consumption.
Keywords: carbon dioxide thermal rocket, in situ resources utilization, energy recovery, Mars
exploration
1 INTRODUCTION
I am (at this point) wondering why helium is mentioned. The paper is supposed to be about carbon dioxide. (th)
]]>The researchers appear to have built a working prototype, and the distance covered may be as much as a 100 meters.
There is a graph showing ISP achievable with various levels of heating, and the levels appear to be comparable to CO / O combustion, which is also discussed.
(th)
pg 3 shows the heating
This is the satelite use
https://arc.aiaa.org/doi/pdf/10.2514/6.2014-3759
Cold Gas Propulsion System Conceptual Design for the SAMSON NanoSatellite
pg 3 shows the heating
This is the satelite use
https://arc.aiaa.org/doi/pdf/10.2514/6.2014-3759
Cold Gas Propulsion System Conceptual Design for the SAMSON NanoSatellite
Thanks for #36 ... interesting extension of PVC discussion into the hopper topic
***
Following the lead reported above, I am now investigating heated CO2 propulsion ...
Mr. Google came up with the paper at the link below:
https://digitalcommons.usu.edu/cgi/view … t=smallsat
This paper discusses the topic of heating CO2 in a tank to make it fully in gaseous phase, before it is allowed to escape to a regulator and on to an output nozzle.
The application is (apparently) limited to satellite positioning, but I'll go back to study it to see if there is any chance the technique could be adapted for the hopper. I am skeptical this technique would provide sufficient thrust to allow a hopper to complete the proposed 1 kilometer in 30 minutes delivery mission, but am definitely motivated to see if it would perform better than cold gas by itself, as described by the MIT student paper (Nothnagel).
(th)
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