SpaceX Raptor LRE Proposed Successor: Project LEET-1337 LRE

[Sarigolepas]

I think pressure out of the pre burners should be higher than the MC chamber...   Only a fraction of the flow, but higher pressure.

And it's a lot easier to extract work from high pressure and low temperature fluid than from low pressure high temperature fluid.

Yes, the pressure is higher in the preburner than the main combustion chamber, but in this case the main combustion chamber is the preburner, and it's a preburner 4 times hotter so you have 4 times more energy to spin the turbine.

So you actually have even more pressure than you might expect from the increase in temperature, because you removed the loss of pressure and other inefficiencies caused by having two combustion chambers in a row. You still lose some pressure between the combustion chamber and the throat though, because you added a turbine there.

[meekGee]

I think pressure out of the pre burners should be higher than the MC chamber...   Only a fraction of the flow, but higher pressure.

And it's a lot easier to extract work from high pressure and low temperature fluid than from low pressure high temperature fluid.

Yes, the pressure is higher in the preburner than the main combustion chamber, but in this case the main combustion chamber is the preburner, and it's a preburner 4 times hotter so you have 4 times more energy to spin the turbine.

So you actually have even more pressure than you might expect from the increase in temperature, because you removed the loss of pressure and other inefficiencies caused by having two combustion chambers in a row. You still lose some pressure between the combustion chamber and the throat though, because you added a turbine there.

I'm kinda imagining that if anyone tries this  the turbine will be on a parallel path, tapping to only a small fraction of the flow.  Still between MCC and nozzle, or MCC and throat.  Probably the former.  Shrug.  Not a rocket scientist obviously.

[InterestedEngineer]

chamber pressures temperatures are 3700K.

No turbine material can survive that.  Turbojet turbines achieve maybe half that temperature

A big advantage of FFSC is cooler turbines.  A turbine in the chamber or early in the exhaust would negate that advantage

[deltaV]

chamber pressures are 3700K.

You mean chamber temperatures.

[Sarigolepas]

I'm kinda imagining that if anyone tries this  the turbine will be on a parallel path, tapping to only a small fraction of the flow.  Still between MCC and nozzle, or MCC and throat.  Probably the former.  Shrug.  Not a rocket scientist obviously.

That's called a combustion tap-off cycle. That way you can allow the gases to cool down or expand before spinning the turbine so it doesn't melt.
But there is no advantage in chamber pressure, you lose some pressure by putting the turbine between the combustion chamber and the nozzle but you gain way more pressure because of all the additional energy you get back. We just don't know yet if it's possible to build a turbine that doesn't melt.

[Sarigolepas]

chamber pressures temperatures are 3700K.

No turbine material can survive that.  Turbojet turbines achieve maybe half that temperature

A big advantage of FFSC is cooler turbines.  A turbine in the chamber or early in the exhaust would negate that advantage

Gas turbines used in powerplants operate at 1700K so twice the temperature of Raptor turbopumps, just by adding cooling.
And those turbines are using air, not oxygen, so it's likely that they are limited by the flame temperature, not by what the turbine can handle.

Yes, full flow engines use all the flow to drive the turbopumps, which is why they get more power for the same temperature.
But that's the whole point, raptor already uses all the flow of the engine so the only way to get more power is to increase the temperature, hence why they need film-cooled turbines.

They will probably add film-cooled turbines to raptor and over time increase the turbopump temperature to something like 1700K. Once they made sure that it works they will start working on a new engine that won't be called raptor, meaning it will have a different combustion cycle. So a single combustion chamber must be it.

[redneck]

chamber pressures temperatures are 3700K.

No turbine material can survive that.  Turbojet turbines achieve maybe half that temperature

A big advantage of FFSC is cooler turbines.  A turbine in the chamber or early in the exhaust would negate that advantage

Gas turbines used in powerplants operate at 1700K so twice the temperature of Raptor turbopumps, just by adding cooling.
And those turbines are using air, not oxygen, so it's likely that they are limited by the flame temperature, not by what the turbine can handle.

Yes, full flow engines use all the flow to drive the turbopumps, which is why they get more power for the same temperature.
But that's the whole point, raptor already uses all the flow of the engine so the only way to get more power is to increase the temperature, hence why they need film-cooled turbines.

They will probably add film-cooled turbines to raptor and over time increase the turbopump temperature to something like 1700K. Once they made sure that it works they will start working on a new engine that won't be called raptor, meaning it will have a different combustion cycle. So a single combustion chamber must be it.

You might check out the single rotor turbine engine patented by LANL. Go to liquid cooling instead of air and you’d be on the same page.

added later when back on the computer.
https://patents.google.com/patent/US6430917B1/en
https://selenianboondocks.com/2008/11/affordable-triprop-pumped-engine/

[Sarigolepas]

Speaking of much larger surface area to protect against heat, here are two 3d printed aerospike combustion chambers:

I'm sure 3d printing is the key to make complex parts like this possible and there is nothing that could prevent them from adding cooling channels to the turbine. They have already integrated many cooling channels into raptor 3 much higher in the engine, probably even around the turbopumps.

[warp99]

Film cooled turbine blades are typically laser drilled with thousands of small holes that the cooling air bleeds out of.  On a rocket engine that cooling role role would be taken by liquid methane propellant which would burn immediately after it was released through the cooling holes. 

What if that was made a feature instead of a bug so that the methane turbine replaced the injectors as the primary mixer for fuel and oxidiser.  The LOX turbopump would be similar to the present arrangement.  The methane turbopump would be constructed as a spinning sleeve inside the main combustion chamber so running coaxially with the oxygen turbopump.  The pump impellers would exhaust to integrated cooling channels and circulate through the chamber walls, throat and then the bell.  On return the liquid methane would be used to support the sleeve on the walls of the combustion chamber as a hydrodynamic bearing and would travel through the vanes of the turbopump to cool them while being injected into the combustion chamber to mix with the pumped LOX and ignite. 

The rotation speed of the turbine means that there would be good mixing of the propellants similar to a swirl injector.  The turbine blades would remain well cooled even though they are physically placed at the upper end of the combustion chamber.  The combustion chamber temperature local to the turbine section would be intermediate between the LOX inlet temperature of say 800K and the final combustion chamber temperature and combination of evaporative and film cooling would keep the blade temperature under 1300K and with reducing conditions.

[InterestedEngineer]

I'm trying to figure out why the power head is getting optimized here with all sorts of fancy ways of dealing with fragile turbopumps that throws away what was learned with Raptor's power head.

Is the powerhead really the limiting factor on current state of the art methalox engines?

From what Elon says, it's temperature of the combustion chamber that's the problem. It gets very melty.  The other big problem is startup and shutdown sequences for FFSC, but they appear to be very far along on working that out.

Thrust and exhaust velocity is proportional to chamber pressure and temperature (de Laval equation).  If you aren't increasing those, then you aren't increasing Isp or thrust.

The combustion chamber is already 99.5% efficient an knitting the molecules together on Raptor.  What further energy do you think you can extract from methalox?

[redneck]

I'm trying to figure out why the power head is getting optimized here with all sorts of fancy ways of dealing with fragile turbopumps that throws away what was learned with Raptor's power head.

Is the powerhead really the limiting factor on current state of the art methalox engines?

From what Elon says, it's temperature of the combustion chamber that's the problem. It gets very melty.  The other big problem is startup and shutdown sequences for FFSC, but they appear to be very far along on working that out.

Thrust and exhaust velocity is proportional to chamber pressure and temperature (de Laval equation).  If you aren't increasing those, then you aren't increasing Isp or thrust.

The combustion chamber is already 99.5% efficient an knitting the molecules together on Raptor.  What further energy do you think you can extract from methalox?

There's always more crazy ideas to explore.  https://selenianboondocks.com/2008/10/rollerthroat-pump/       This one has rollers in the throat to reduce the heat load there with some minor pumping action for reverse film cooling of the main chamber.

The Raptor is state of the art at this time. The question being if it will be  like the piston engine we see in cars that would have been recognizable from over a century ago? Or is the rotary engine trying to edge the pistons out?  Or is it the 50s piston engine in Warbirds about to be eclipsed by turbojets?

[Sarigolepas]

Film cooled turbine blades are typically laser drilled with thousands of small holes that the cooling air bleeds out of.  On a rocket engine that cooling role role would be taken by liquid methane propellant which would burn immediately after it was released through the cooling holes. 

What if that was made a feature instead of a bug so that the methane turbine replaced the injectors as the primary mixer for fuel and oxidiser.  The LOX turbopump would be similar to the present arrangement.  The methane turbopump would be constructed as a spinning sleeve inside the main combustion chamber so running coaxially with the oxygen turbopump.  The pump impellers would exhaust to integrated cooling channels and circulate through the chamber walls, throat and then the bell.  On return the liquid methane would be used to support the sleeve on the walls of the combustion chamber as a hydrodynamic bearing and would travel through the vanes of the turbopump to cool them while being injected into the combustion chamber to mix with the pumped LOX and ignite. 

The rotation speed of the turbine means that there would be good mixing of the propellants similar to a swirl injector.  The turbine blades would remain well cooled even though they are physically placed at the upper end of the combustion chamber.  The combustion chamber temperature local to the turbine section would be intermediate between the LOX inlet temperature of say 800K and the final combustion chamber temperature and combination of evaporative and film cooling would keep the blade temperature under 1300K and with reducing conditions.

That's pretty much how monopropellant turbopumps work, there is a catalyst on the turbine blades so the reaction happends when the monopropellant touches the turbine.

Propellant moves from the highest pressure to the lowest pressure, what makes a turbopump work is that despite the pressure being higher in the fuel injector than on the turbine blades those gases expand as they burn so the flow rate is higher on the turbine than in the injector, which means the turbine gets back more power than it has to give to inject fuel.

That principle would also work if fuel injection was done on the turbine, the small holes only cover a tiny percentage of the area of the turbine so as the fuel burns and expands the overall force on the turbine is increased even if the pressure is reduced.

[Sarigolepas]

I'm trying to figure out why the power head is getting optimized here with all sorts of fancy ways of dealing with fragile turbopumps that throws away what was learned with Raptor's power head.

Is the powerhead really the limiting factor on current state of the art methalox engines?

From what Elon says, it's temperature of the combustion chamber that's the problem. It gets very melty.  The other big problem is startup and shutdown sequences for FFSC, but they appear to be very far along on working that out.

Thrust and exhaust velocity is proportional to chamber pressure and temperature (de Laval equation).  If you aren't increasing those, then you aren't increasing Isp or thrust.

The combustion chamber is already 99.5% efficient an knitting the molecules together on Raptor.  What further energy do you think you can extract from methalox?

It gets melty because they use as little film cooling as possible in order to have a good combustion efficiency.
You don't gain anyting by adding more cooling than necessary to the main combustion chamber because it's already burning at close to stoichiometric ratio.

But on a turbine you have so much to gain by going from 800K to 3500K that a little combustion inefficiency is worth it. More pressure also means an higher nozzle expansion ratio so it might ends up more efficient overall anyways.

[CorvusCorax]

A big limiting factor on LRE is chemistry.

You can't make the combustion much hotter, because if you do the temperature exceeds the disassociation point of your combustion results ( its too hot for H2O and CO2 to remain molecules ) But since this recombination provides the energy for your engine, the only way to further increase exhaust velocity is to increase MCC pressure.

Anything that ups MCC pressure is fair game

[redneck]

A big limiting factor on LRE is chemistry.

You can't make the combustion much hotter, because if you do the temperature exceeds the disassociation point of your combustion results ( its too hot for H2O and CO2 to remain molecules ) But since this recombination provides the energy for your engine, the only way to further increase exhaust velocity is to increase MCC pressure.

Anything that ups MCC pressure is fair game

Part of the concept seems to be that will all the extra power available, pressure can be increased considerably. I can't remember the formulas anymore. I think it would be something like triple the temp would allow triple the power which could increase pump pressures by sqrt3 or about 1.7 times pressure. which would increase power to the turbine which would again increase......

Right at the moment quite annoyed that Hill and Peterson is still in storage years later.

[Sarigolepas]

Part of the concept seems to be that will all the extra power available, pressure can be increased considerably. I can't remember the formulas anymore. I think it would be something like triple the temp would allow triple the power which could increase pump pressures by sqrt3 or about 1.7 times pressure. which would increase power to the turbine which would again increase......

Right at the moment quite annoyed that Hill and Peterson is still in storage years later.

Using basic hydraulics (power = pressure*volumetric flow) for a given fuel injector size, 3 times the energy per kg of fuel, so 3 times the pressure and 1.7 times the flow, so 5 times the turbopump power for a rocket engine that is only 70% more powerful but has a much smaller combustion chamber.

That's interesting, the volumetric flow of the injectors increase with the quare root of the pressure while the volumetric flow of the combustion chamber increases proportionnally to the pressure. So rocket engines with higher chamber pressure need bigger injectors to keep up with the combustion chamber. That probably makes deep throttling very difficult.

Now for a given combustion chamber size, 3 times the energy per kg of fuel so 3 times the pressure for 3 times the flow. So 9 times more turbopump power for a rocket engine that is 3 times more powerful.

[Sarigolepas]

I asked Tim Dodd on discord and he doesn't seem to believe in film-cooling for the turbine. I still hope he asked Elon about this during his interview. Especially since we know that raptor 3 has cooling channels at least on the outside of the turbopump.

[Sarigolepas]

It worked:

Answer at 46:25
Seems like the video was cut, maybe an issue with ITAR?

[IKM]

RE: We can all agree that the LEET engine is a methalox engine, so why does it need a new name?

Not sure that is the long term plan ...... fuel production is the real issue further down the track, in this case methalox, generations of the Raptor Engine and Mars all fit together.
However Raptor was conceived to burn hydrogen and oxygen propellants.

In 2012, Raptor became a methane-fueled rocket engine, because of the presence of underground water and carbon dioxide in Mars atmosphere, methane, a simple hydrocarbon, that could be synthesized on Mars using the Sabatier reaction. NASA found in-situ resource production on Mars to be viable for oxygen, water, and methane production.

So anything that comes out of LEET-1337 that can be used/modified for Raptor "methalox" Engnes, is a bonus, but lets not lose sight on the bigger more ambigious plans, beyond Mars, and alternative propellants.

[r8ix]

RE: We can all agree that the LEET engine is a methalox engine, so why does it need a new name?

Not sure that is the long term plan ...... fuel production is the real issue further down the track, in this case methalox, generations of the Raptor Engine and Mars all fit together.
However Raptor was conceived to burn hydrogen and oxygen propellants.

In 2012, Raptor became a methane-fueled rocket engine, because of the presence of underground water and carbon dioxide in Mars atmosphere, methane, a simple hydrocarbon, that could be synthesized on Mars using the Sabatier reaction. NASA found in-situ resource production on Mars to be viable for oxygen, water, and methane production.

So anything that comes out of LEET-1337 that can be used/modified for Raptor "methalox" Engnes, is a bonus, but lets not lose sight on the bigger more ambigious plans, beyond Mars, and alternative propellants.

There are other reasons, such as rocket structure, propellant handling, and so forth, that make methane preferable to hydrogen, especially for a lo-cost, rapidly reusable rocket system.