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#26 2016-06-21 17:26:17

SpaceNut
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Re: Air breathing engines on Mars

elderflower I did a quick topic search on solar sterling and here are the topics that we have on Newmars.

Sterling engine+solar= neat powersource - EETimes article

Solar thermal power - Fathers Day gift

Solar thermal power

Some topic get good discussion while other get duplicated after a period of time as the originals are not sought out to continue in.....

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#27 2016-07-11 06:26:45

Antius
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From: Cumbria, UK
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Posts: 1,003

Re: Air breathing engines on Mars

A pulse-jet engine may be a good choice for an air-breathing silane engine on Mars.  On Earth, these engines are relatively inefficient, partly because they are effectively sea-level rocket engines with a poor expansion ratio.  On Mars, atmospheric pressure is low, so a pulse-jet could achieve a much better expansion ratio.  Also, as CO2 is the oxidiser and is 95% abundant in the Martian atmosphere, flame temperatures will be high, providing an additional boost to ISP.  As the external environment is close to zero pressure, the outlet from the combustion chamber could be a diverging nozzle, thereby reducing the potential for solid build-up.  The pulse jet could reach take-off speed by blasting compressed CO2 into the engine until dynamic pressure on the inlet is great enough to open the injection valves.

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#28 2016-07-11 08:24:38

GW Johnson
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From: McGregor, Texas USA
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Re: Air breathing engines on Mars

I dunno about pulsejet on Mars.  But I do know pulsejet,  and there's nothing about them that functions like a rocket,  other than thrust = jet momentum.  There's a whole lot more flow and combustion chemistry and physics going on in such a device than just thrust = jet momentum. 

Here on Earth,  the peak of the oscillating pressure-versus-time trace for the combustion chamber is only about 2 to 2.5 times the ambient atmospheric pressure,  on an absolute-pressure basis of calculation,  in the best designs,  less for the poor ones.  The min chamber pressure is around 70% ambient atmospheric in the best designs.  The thrust you get is directly proportional to average chamber pressure,  and to engine cross section area. 

That's more-or-less true whether you build a valved or valveless pulsejet tube.  Neither form's chamber pressure responds to inlet dynamic pressure;  that affects mixing of fuel and air,  but not the basic cycle pressure.  Most designs develop static thrust that is actually higher than thrust when moving. 

In the valved form,  the valves must be very lightweight,  and must mechanically vibrate open-and-closed at the same frequency as the engine oscillates.  Such valves have very short lifetimes,  usually measured in a few dozens of minutes.  They are subject to combustion backflow impact,  and would be fatally affected by any slagging at all,  which changes the mechanical frequency as well as destroys the sealing. 

The shape of the combustion chamber and exhaust tube strongly affects whether the engine will resonate at all.  It has to reflect the waveform effectively at the exit,  and it has to flow efficiently for exhaust pipe inflow as well as collimate the exhausting jet flow.  Slag would really upset all of this.  If any of this is not done right,  the engine will not run at all. 

The exact shape and size of the inlet is not as important,  as the inlet is nonresonant.  But the size of the inlet relative to the chamber needs to be in the correct range to achieve best performance,  as well as good combustion physics and flameholding.  If any of that last is wrong,  it will not run. 

The other critical factor is combustion chemistry rate,  and how that interacts with device size and frequency (in turn intimately linked).  Here on Earth,  really big ones the size of the V-1 Buzz Bomb engine can be made to run on gasoline.  Smaller ones like the hobbyists play with can only be made to run on properly-vaporized propane.  Those range from 3 to 10 inches combustion chamber diameter,  and from 100 to about 500 Hz frequency.  Really little ones (about 1 inch diameter,  1000 Hz stuff) can only be made to run on acetylene,  sometimes with raw oxygen injection added.  Getting this wrong means the pulsejet will not run at all.   

If that +2.5/0.7 x atmospheric pressure trace description holds on Mars with the silane fuels discussed here,  it means your pressure numbers and resulting thrust numbers are going to be very low for the size and mass of the equipment you have to build.  Precisely because that is such a thin atmosphere.  Pressures achievable would oscillate between around 15 and 4 mbar in a 6 mbar atmosphere,  all else equal. 

GW

Last edited by GW Johnson (2016-07-11 08:47:02)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#29 2016-07-11 10:10:23

GW Johnson
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Re: Air breathing engines on Mars

Just following up about pulsejets ---

My best design recommendations for the valveless form of the pulsejet derive from work done cooperatively by Hiller Aircraft here in the US and SNECMA in France circa 1960,  based on earlier French work in the 1950-1960 time frame. 

I collated this immense body of work as best I could,  and turned it into usable design recommendations for the subcases not limited by fuel-air chemistry reaction rates.  Consequently,  to employ these design recommendations,  you must pay strict attention to the chamber diameter limits. 

That collation work is summarized and posted over at http://exrocketman.blogspot.com as “Recommended Broad Design Guidelines for Valveless Pulsejet Combustors”,  dated 5-20-2012,  under keyword “pulsejet”.  It’s a ways down;  use the date tool for year 2012,  and scroll down from there. 

The valved pulsejet is not as geometrically-sensitive as the valveless,  but all the valved designs have lower performance and more noise than any of the successful valveless designs.  If you can find the ancient thing,  there is a good report on the German version:  USN PQ-TM-4 (1948) ''The Aero-Resonator Power Plant of the V-1 Flying Bomb'' by G. Diedrich, translated by A. Kahane.  This is long-declassified intelligence information collected just after WW2.  It was part of something called “Project Squid” by the Navy.  That valved engine ran on gasoline,  but had very high fuel consumption. 

Over here in the 1950’s and 1960’s,  there were a couple of small valved pulsejets available to hobbyists.  These were known variously as Tigerjet,  Dynajet,  and similar brand names.  All featured a single reed valve instead of the bank of German flapper valves,  which was mechanically feasible only because of the small size.  I think these were propane-fueled devices,  of rather low performance. 

In the 1970’s,  there were a couple of modest-sized valveless pulsejets available as an alternative for launching sailplanes.  One of these was offered by Thermo-Jet.  I believe these were also propane-fueled.  Performance was better than the valved engines,  but lower than the best valveless designs of Hiller/SNECMA. 

The very best of the Hiller/SNECMA designs added an augmentor shroud to the exit and the inlet,  and bent the engine into a U-shaped tube,  since about 40% of the total jet momentum gets “spit” out of the inlet tube during the blowdown phase of the cycle.  The augmentor increased thrust by a factor of roughly 1.5,  and decreased thrust-specific fuel consumption (TSFC) by roughly a factor of 2. 

They were testing items of 9 or 10 inch diameter chamber,  several feet long,  operating about 100 Hertz,  for potential military aircraft applications.  Shrouded like that,  they achieved about 500 lb of thrust from a device massing about 30-40 lb,  and (at the most favorable power setting) a TSFC of just under 1 lbm/hour fuel per lb of thrust.  Typically,  they measured about 125 dB noise up close. The form of the successful augmentor shroud was very specific:  a rounded-lip entrance into a short divergent exit cone,  located just off the inlet or exit tube exit planes.  It was very definitely an unsteady-flow device. 

In contrast,  the German engine was about a foot diameter and about 11 feet long,  operating about 47 Hertz on gasoline.  It achieved a max static thrust of 1100 lb,  and got at best about TSFC = 8 at around 800 lb of thrust.  Its noise level was about 145 dB.  Hiller maintained that about the top 20 dB of that was valve clatter noise.  Valve lifetime averaged 45 minutes.  The flight time from sites in France to London was 40-43 minutes. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#30 2016-07-11 17:27:04

SpaceNut
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#31 2016-07-12 10:18:44

GW Johnson
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From: McGregor, Texas USA
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Re: Air breathing engines on Mars

Amazing.  The U-tube Lockwood designs I have characterized for you over at "exrocketman" appear in two of those sites whose links you gave.  The reversed-inlet designs I have characterized over there,  as well.  That pulsejet article I put on "exrocketman" is one of the two or three most widely read items I ever posted.  Lots of people play with this stuff. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#32 2016-07-25 14:56:35

Antius
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Re: Air breathing engines on Mars

Apologies for the late reply.

The traditional valved pulse-jet would appear to be useless for anything other than a short range missile.  Too slow to be useful on Earth anyhow.  The non-valved version, sounds like some sort of pulsed ram-jet engine.  I struggle to understand why engine dimensions would be quite so critically important.

With so little pressure on Mars, maybe a detonation rocket engine would work better?  Inject both fuel and oxidiser as micron sized droplet and ignite before significant phase transition has time to occur.  A powerful enough electric arc (1-10KJ) will trigger detonation in most combustible mixes.  At lower energy it takes time for the flame front to gradually accelerate as turbulence increases.  Turbulence tends to accelerate flame fronts.  To a certain extent the droplets themselves will promote turbulence.  Hydrogen ions have high molecular speed compared to any other excited molecule.  Ignition using a plasma torch with hydrogen as a carrier gas may be a more efficient detonation trigger than an electric arc in heavier gas.  These ignition systems are energy intensive but reliably give rise to dentonation.  Some kind of free piston internal combustion engine coupled with a linear electric generator could generate the required electric pulse whilst keeping weight down.  But the two systems must be perfectly aligned, with injection preceding the pulse by microseconds.

On Mars, liquid CO2 could be used as the oxidiser, with a mixture of silane and hydrogen as fuel.  The ignition source would most likely be a plasma-jet, discharging hydrogen rich plasma into the combustion chamber.  With so little air on Mars, the noise would hardly matter.  How could we pulse the injection?  Globe valve seats would fail very quickly due to excessive wear.  Maybe some kind of rotating ball valve, releasing propellants from a reservoir, which is in turn pressurised from something like a diesel injection pump?  We can do that if we are injecting liquids instead of gases, as volume flow rates are low.

Last edited by Antius (2016-07-25 15:13:47)

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#33 2016-07-25 20:22:36

SpaceNut
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Re: Air breathing engines on Mars

I found that we have a topic where the interest was using silane and hydrogen with co2 for good measure.....
Silane Hoppers - Use the CO2 man...
Got some cleanup to do of that topic and wow its from 2003

Burning silane

https://www.linkedin.com/pulse/what-sil … ert-morlan
AAEAAQAAAAAAAAW9AAAAJDhiYzdmNjk1LTZiMDYtNGU1Yy1hZGNhLTFiMGE1ODg0N2Y1NA.jpg

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#34 2020-12-11 18:42:26

SpaceNut
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Re: Air breathing engines on Mars

Would this be a good fuel for a boiler plant for power creation....

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#35 2022-09-19 16:40:27

Calliban
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From: Northern England, UK
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Re: Air breathing engines on Mars

This thread has the title 'Air breathing engines' but is really all about aircraft engines.  On Earth, gas turbines extract kinetic energy from expanding exhaust gases and this energy is used to drive the compressor.  If the combustion products are solid, this will not be possible.  But the engine could be designed such that a hydrocarbon-oxygen mixture drives a primary gas turbine, powering the compressor, with silane burned in some sort of bypass combustion chamber.

On Mars, the atmosphere is much thinner.  On Earth, most commercial jets fly at 10km, where air pressure is 25KPa and oxygen partial pressure is 5KPa.  On Mars at datum sea level, air pressure is 0.6KPa, but this is almost all CO2, which is reactive in an airbreathing engine.  However, the temperature of the Martian atmosphere is far beneath the critical point of CO2 (31°C).  This reduces the amount of compressor work needed to compress the CO2 to the pressures needed for the combustion chamber.  On Earth, this is about 5 bar.  But on Mars, with a pure CO2 atmosphere all of which is reactive with the fuel, it may be somewhat less.  However, the low atmospheric pressure means that the pressure ratio of the engine will be higher, implying the need for a much higher swept area per lb of thrust.  I think an air breathing jet engine for Mars could be workable.  But the compressor would need to be driven by a seperate fuel system that does not produce solud combustion products that shot blast the turbine.

Perhaps a bigger problem for an aeroplane would be takeoff and landing.  The air on Mars is so thin that takeoff and landing speeds may be dangerous.  The engines would generate insufficient thrust at takeoff due to the very low flowrates entering the compressor at low speeds.  Rocket assist may be needed.  At landing, drag chutes would be needed to slow the plane from near sonic velocity.  Runways would presumably be much longer than on Earth.

Last edited by Calliban (2022-09-19 16:41:56)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#36 2022-09-19 21:01:10

SpaceNut
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Re: Air breathing engines on Mars

The page content has been moved https://wickmanspacecraft.com/marsjet/

https://wickmanspacecraft.com/space/  only highlights its development for the moon as gelled liquid oxygen and aluminum powder but for mars WSPC was the first company to successfully develop and test fire a rocket engine burning carbon dioxide and magnesium powder. This was soon followed by a jet engine breathing carbon dioxide that used magnesium powder for the fuel.

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#37 2022-09-19 21:26:50

tahanson43206
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Re: Air breathing engines on Mars

For SpaceNut re #36

Thanks for the link to Wickman ... I took a quick look, and found an update on the site showing 2020.

A more thorough visit to the site may reveal later updates.

(th)

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#38 2022-09-20 04:51:07

Calliban
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Re: Air breathing engines on Mars

High speed rail or hyperloop trains would be good applications for air breathing jet engines on Mars.  The air is too thin for aerodynamic lift to be applied safely.  But if we can build flat enough tracks, then an air breathing gas turbine would be just what is needed to propel a train to speeds exceeding 200mph.  With only 2/5 the gravity and close to zero air resistance, conventional rail would be 3x as energy efficient on Mars.  The only catch with a Mars gas turbine is that it would need to get up to high speed before it can provide useful thrust.  A cold gas CO2 thruster could provide the boost needed to speeds of 200mph.


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#39 2022-09-20 06:43:45

tahanson43206
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Re: Air breathing engines on Mars

For Calliban re #38

The discussion about air breathing engines on Mars has picked up a bit since you joined.

I'm wondering if the well known effect of magnetic repulsion of permanent magnets passing over aluminum might provide "lift" of a vehicle moving along tracks at the speeds you've suggested?

Can you (would you) provide a fuel cycle for the system you're thinking about?

Recently the idea of using magnesium as a reactant with Mars CO2 came back for discussion in another topic.

Is magnesium powder a reasonable stored energy source for a rail system on Mars?

If the answer is yes, can the product of the reaction (an oxide of magnesium?) be captured for rework?

Or must the reaction mass be allowed to fall on the roadbed to gain the maximum possible energy recovery?

If ** that ** IS the case, then is it feasible to send a slow speed fuel collection machine along the tracks between trains, to recover the spent fuel?

I'm trying to understand the life-cycle of such a system.

In other topics, electric rail lines have received some attention, and that concept seems like a viable extension of Earth-proven rail technology for Mars.

A third "electrified" rail would not be a danger to pedestrians on Mars, because there aren't going to be many pedestrians there.

(th)

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#40 2022-09-20 06:45:53

tahanson43206
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Re: Air breathing engines on Mars

I just went back to the top of the topic, and was amused to find ...

(By RobertDyck)

Yup, atmosphere breathing. There has been work on engines that burn in the CO2 atmosphere of Mars.
John Wickman did work in the 1980s on a jet engine for Mars. It uses powdered magnesium for fuel. Here is his website:
http://www.wickmanspacecraft.com/marsjet.html

So we are just repeating earlier discussion without having read it.

That happens often in this forum.

(th)

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#41 2022-09-20 14:46:31

GW Johnson
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Re: Air breathing engines on Mars

Well,  the problem is a huge amount of exhaust stream solids.  2Mg + CO2 = 2MgO + C.  Both the MgO and the C show up,  C as solid and MgO as viscous molten,  with the MgO very sticky adhering to everything it hits.  The only gases will be any unused CO2 and maybe some CO from inefficient operation. 

If you are looking at something with no moving parts,  your machinery might survive.  If you have any sort of valves or moving machinery,  it will not.  Plus,  solids do not expand with pressure drop.  It will be very hard (almost impossible) to expand such streams to any significantly higher velocity than what they actually burned at.  Which has to be quite low,  or you won't burn at all.

Sorry.  That's just the physical chemistry of it.  I actually did burn a lot of magnesium with air.  I know what I am talking about.  Aluminum will behave a lot like mag,  its just less reactive,  meaning it is a bit harder to ignite and burn successfully.  Silane,  aluminum,  mag,  doesn't matter.  All are grossly similar in CO2.

GW

Last edited by GW Johnson (2022-09-20 14:51:42)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#42 2023-04-22 22:24:00

RGClark
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Re: Air breathing engines on Mars

GW Johnson wrote:

Well,  the problem is a huge amount of exhaust stream solids.  2Mg + CO2 = 2MgO + C.  Both the MgO and the C show up,  C as solid and MgO as viscous molten,  with the MgO very sticky adhering to everything it hits.  The only gases will be any unused CO2 and maybe some CO from inefficient operation. 

GW

Thanks for that. Could this be used as an energy source on Earth? There is intensive research on energy sources now of course. And also research on removing CO2 from air. If there are extensive deposits of pure magnesium, unoxidized, available could this be used with CO2 to produce energy?

This could provide even further energy if we then burned the carbon produced, though of course that wouldn’t help with the CO2 problem. So the question is whether mining of magnesium would make this worthwhile financially.

Nice article here on doing the reaction:

The General Chemistry Demo Lab
Reaction Of Magnesium Metal With Carbon Dioxide.
http://www.ilpi.com/genchem/demo/co2mg/index.htm

  Bob Clark

Last edited by RGClark (2023-04-22 22:24:48)


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      “Anything worth doing is worth doing for a billion dollars.”

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#43 2023-04-23 00:50:50

kbd512
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Re: Air breathing engines on Mars

Jet engines don't work very well when they ingest volcanic ash here on Earth.  Apart from being sand-blasted, the hot sticky molten solids adhere to their internals.  The engine might survive one flight, but it won't be operable for the next.

So long as we're talking about exotic fuels, how about Sulfur-hexafluoride and Lithium?

The combustion products occupy less volume than the fuel and oxidizer, they're easy to store, and they produce a lot of heat.

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#44 2023-04-23 06:47:25

tahanson43206
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Re: Air breathing engines on Mars

Having just re-read the topic from the top, thanks for kbd512 post #43, here is a snip from one of GW's posts:

The closest thing I know to a practical piston engine system independent of atmospheric oxygen was attempted for submarines decades ago.  Diesel fuel plus hydrogen peroxide actually did work from storable liquids while submerged.  It's somewhat similar to the propulsion of the torpedoes,  but more suited to a reusable vehicle.  There were great difficulties with it,  and it was superseded by atomic power in submarines,  then forgotten.
Given some sort of fuel that could replace the diesel,  and some way to make hydrogen peroxide on Mars,  that technology might lead to practical internal combustion or gas turbine power plants on Mars.  The storable liquids are pressurized at around 1 atm,  like here.  Hydrogen peroxide decomposes to oxygen and steam.  Steam is the diluent gas that reduces stream temperatures to something you can confine with cooled steel.
It can be done,  but needs some development before we take it to Mars and count on it at the risk of lives.
GW
GW Johnson
McGregor,  Texas

While the topic (created by RobertDyck) is about "air breathing engines", the snippet above is about liquids for energy storage.

In the past on this forum, members have invested considerable time and thought evaluating options for gas state fuel and oxidizer systems for Mars.

I'll take a look to see if we have a topic for liquid energy storage systems for Mars.

It's fun seeing RobertDyck's original topic back in view again.

(th)

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