Author Topic: Blue Origin's BE-4 Engine  (Read 124357 times)

Offline Nilof

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Re: Blue Origin's BE-4 Engine
« Reply #20 on: 03/18/2016 11:34 AM »
At ER=25, I would expect to see more like SL~310s

With 1950 psi chamber pressure, I'd say that this is rather unlikely. More likely around 300s, especially if they go for an O/F ratio closer to 3.8 to improve density instead of optimizing only for Isp which was the basis for the 3.3 O/F ratio above.

On the Vulcan configuration which gets lift-off thrust from solids anyway, the BE-4 will probably have a somewhat longer nozzle and thus have a roughly similar and possibly slightly higher Isp than the RD-180 at altitude, but on the other hand have noticeably lower Isp at launch pad due to the lower chamber pressure. On Blue's own flyback booster where they need a short nozzle for landing and where liftoff thrust would be bottlenecked by the engine, they will probably go for a rather low expansion ratio and low Isp.

With that said, for a first stage total thrust to keep gravity losses down is much more important than a <5% Isp increase. The BE-4 only really needs a decent specific impulse. If it has a small enough physical footprint and is cheap enough that you can fit more engine thrust at the bottom of the rocket for a similar production cost, that configuration is going to be superior regardless of whether or not the specific impulse is slightly higher.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline STS-200

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Re: Blue Origin's BE-4 Engine
« Reply #21 on: 03/18/2016 01:15 PM »

With 1950 psi chamber pressure, I'd say that this is rather unlikely. More likely around 300s, especially if they go for an O/F ratio closer to 3.8 to improve density instead of optimizing only for Isp which was the basis for the 3.3 O/F ratio above.

If you change the O/F, you'll get different results.
Based on 3.3 and an output about midway between frozen-flow and shifting equilibrium simulations, with an optimised nozzle contour and decent combustion efficiency, you'll get about what I said.

On the Vulcan configuration which gets lift-off thrust from solids anyway, the BE-4 will probably have a somewhat longer nozzle and thus have a roughly similar and possibly slightly higher Isp than the RD-180 at altitude, but on the other hand have noticeably lower Isp at launch pad due to the lower chamber pressure. On Blue's own flyback booster where they need a short nozzle for landing and where liftoff thrust would be bottlenecked by the engine, they will probably go for a rather low expansion ratio and low Isp.

With that said, for a first stage total thrust to keep gravity losses down is much more important than a <5% Isp increase. The BE-4 only really needs a decent specific impulse. If it has a small enough physical footprint and is cheap enough that you can fit more engine thrust at the bottom of the rocket for a similar production cost, that configuration is going to be superior regardless of whether or not the specific impulse is slightly higher.

Building two different expansion ratios of the same engine isn't entirely trivial and it throws away some of the operational/production efficiencies of a single design.
In general terms, you are quite right about Isp/vehicle T/W, however there are still a lot of other trade-offs - Steering & G-Loads, Dynamic pressure, landing burn requirements and overall vehicle cost to name but a few.
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Offline Apollo100

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Re: Blue Origin's BE-4 Engine
« Reply #22 on: 03/18/2016 09:23 PM »
The BE4 should have high T/W as it uses additive manufacturing which helps to keep weight down.

Huh?

Offline Danderman

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Re: Blue Origin's BE-4 Engine
« Reply #23 on: 03/19/2016 10:20 PM »
About 20 years ago, Robert Zubrin was promoting methane engines (ultimately for use on Mars). When asked why methane was so great, if no was using it, his response was that "no one uses methane for rocket engines because no one uses methane for rocket engines".

Offline R7

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Re: Blue Origin's BE-4 Engine
« Reply #24 on: 03/20/2016 06:24 PM »
At ER=25, I would expect to see more like SL~310s

With 1950 psi chamber pressure, I'd say that this is rather unlikely.

No it isn't. If the illustrations are close to the truth the area ratio is somewhere in 23-25 region. 16.77 is way too low to match.

Your analysis has 1 atm nozzle exit pressure, that is too high. All real booster engines are overexpanded at sea level, many have the exit pressure at about 0.6 atm. This improves overall performance during flight.

I did some SWAG analysis in 2014. Back then 130bar (1885 psi) Pc produced result close to the imagery and the few known facts. ~3% error, yay!
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Offline TrevorMonty

Re: Blue Origin's BE-4 Engine
« Reply #25 on: 03/20/2016 07:41 PM »
Can anybody guess at throttle range of BE4. Blue plan to do vertical lands so deep throttling it one primary design features.

Offline Steven Pietrobon

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Re: Blue Origin's BE-4 Engine
« Reply #26 on: 03/21/2016 08:01 AM »
Poster of BE-4 engine inside Atlas-V reception building. Taken from ULA OA-6 video.

http://youtube.com/watch?v=d2BvvTZlqLc
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Offline Nilof

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Re: Blue Origin's BE-4 Engine
« Reply #27 on: 03/24/2016 10:07 AM »
Can anybody guess at throttle range of BE4. Blue plan to do vertical lands so deep throttling it one primary design features.

Depends on expansion ratio. If it's in the ~16 range it should be able to get down to ~20% at sea level before hitting flow sep. At ER = 25 flow sep happens around ~30% throttle. If they use an altitude compensating nozzle they might be able to get lower.

At ER=25, I would expect to see more like SL~310s

With 1950 psi chamber pressure, I'd say that this is rather unlikely.

No it isn't. If the illustrations are close to the truth the area ratio is somewhere in 23-25 region. 16.77 is way too low to match.

Your analysis has 1 atm nozzle exit pressure, that is too high. All real booster engines are overexpanded at sea level, many have the exit pressure at about 0.6 atm. This improves overall performance during flight.

I did some SWAG analysis in 2014. Back then 130bar (1885 psi) Pc produced result close to the imagery and the few known facts. ~3% error, yay!

The number that I disputed was the 310s+ specific impulse at ER = 25 which is rather optimistic, not the possibility of ER = 25.
« Last Edit: 03/24/2016 10:09 AM by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Dante80

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Re: Blue Origin's BE-4 Engine
« Reply #28 on: 08/09/2016 05:39 AM »
Regarding BE-4, here is what we know so far.

Propellants: LNG/LOX
Thrust: ~ 550,000 lbf
Chamber pressure: 1,950 psi
Cycle: ORSC (single shaft)
Isp:<311s SL, <338 vac. (for the booster variant in Vulcan)
TWR: <78
Re-usability: 25 complete missions, minimum.

The above design goals seem both tame and achievable. As we have seen with other engine designs (Merlin comes to mind) Blue should be able to uprate their engine a lot with the data they gain from flight experience.

Regarding Isp and TWR, the info we have on them comes from this:
http://arstechnica.com/science/2016/03/behind-the-curtain-ars-goes-inside-blue-origins-secretive-rocket-factory/2/
Quote
Like the smaller BE-3 upon which it is modeled, a main feature of the BE-4 is its reusability, and it’s being designed to fly a minimum of 25 missions.

Bezos explained his philosophy on how to build a successful reusable engine: “Our strategy is we like to choose a medium-performing version of a high-performance architecture.” Here’s what that means: The Russian RD-180 engine is a high-performing version of a high performance architecture. It uses the best materials and pushes the performance envelope. It is the Ferrari of engines. But that comes with a cost. When it fires, the RD-180 engines produces extremely high chamber pressures of up to 3,700 psi. By comparison, the BE-4 engine produces a chamber pressure of 1,950 psi.

Developing an elite engine like the RD-180 was a decade-plus project, on par in complexity to the space shuttle’s main engines. It required expensive materials. On the plus side, this provides a lower weight engine and a higher thrust-to-weight ratio. But the engine’s specific impulse isn’t all that much greater than the BE-4, which can be built more easily, and because it doesn't push performance limits can be reused
« Last Edit: 08/09/2016 05:40 AM by Dante80 »

Online guckyfan

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Re: Blue Origin's BE-4 Engine
« Reply #29 on: 08/09/2016 07:50 AM »
I saw the < sign. I now read the article. But I still cannot believe they are not aiming to be at least somewhat better than RD-180. Even with an initial value which can be improved upon later. After all they use methane instead of RP-1 which should allow for higher ISP, if not better T/W.

Offline Hobbes-22

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Re: Blue Origin's BE-4 Engine
« Reply #30 on: 08/09/2016 09:09 AM »
The BE4 should have high T/W as it uses additive manufacturing which helps to keep weight down.

Huh?

With AM, you can make large monolithic parts, where traditional manufacturing would need to split the part into manufacturable pieces, adding flanges and bolts to connect the parts. The printed part does not need those.
You might also be able to create (more efficient) part geometry that is impossible to do with traditional fabrication.

Offline Dante80

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Re: Blue Origin's BE-4 Engine
« Reply #31 on: 08/09/2016 10:13 AM »
I saw the < sign. I now read the article. But I still cannot believe they are not aiming to be at least somewhat better than RD-180. Even with an initial value which can be improved upon later. After all they use methane instead of RP-1 which should allow for higher ISP, if not better T/W.

Contrary to popular belief, it is not that easy to match RD-180 performance...with any hydrocarbon engine ( and especially if your goal is half the chamber pressure). Its not only the article though (which quotes Bezos, unless the reporter misrepresented him). The "Tobey comments" also seem to indicate the speculated performance goals above.

Quote
Comparing the two engine developments – Aerojet Rocketdyne pursuing the classic government funding route, while Blue Origin has a billionaire owner who can act lightning-fast – the two companies’ situations do not favor Aerojet Rocketdyne.

“Compare it to having two fiancées, two possible brides,” Tobey said of ULA’s approach to the two. “Blue Origin is a super-rich girl, and then there is this poor girl over here, Aerojet Rocketdyne. But we have to continue to go to planned rehearsal dinners, buy cakes and all the rest with both.

“We’re doing all the work on both, and the chance of Aerojet Rocketdyne beating the billionaire is pretty low. Basically we’re putting a whole lot more energy into BE-4 for Blue Origin.”

Using methane would be new for the U.S. space sector, imposing risks, but Tobey said the BE-4 engine is only 60 percent of the cost of the AR1, a clear advantage in today’s cost-driven market.

Of both engines, he said: “They are never going to outperform the RD-180."

http://spacenews.com/ula-intends-to-lower-its-costs-and-raise-its-cool-to-compete-with-spacex/
« Last Edit: 08/09/2016 10:18 AM by Dante80 »

Offline pippin

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Re: Blue Origin's BE-4 Engine
« Reply #32 on: 08/09/2016 01:14 PM »
I think people underappreciate how good RD-180 is. I'm not sure the US (except maybe for AJR due to the license) has the technology to build an engine with similar performance let alone a relative newcomer like BO.
And the difference in ISP between methane and kerosene isn't very big. Actually, almost all methane engine designs proposed so far had lower ISP than high-ISP kerosene engines, probably due to less experience with the fuel. I'm not sure the high-pressure combustion behavior is as well understood as for kerosene and hydrogen
« Last Edit: 08/09/2016 01:17 PM by pippin »

Online Robotbeat

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Re: Blue Origin's BE-4 Engine
« Reply #33 on: 08/09/2016 01:34 PM »
I dislike "performance." If you mean Isp, say Isp. If you mean T/W ratio, say T/W ratio.

On the latter, Merlin 1D kicks RD180's butt all over town. Merlin 1D with recent thrust upgrades gets T/W of 200.
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Offline baldusi

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Re: Blue Origin's BE-4 Engine
« Reply #34 on: 08/09/2016 01:48 PM »
I dislike "performance." If you mean Isp, say Isp. If you mean T/W ratio, say T/W ratio.

On the latter, Merlin 1D kicks RD180's butt all over town. Merlin 1D with recent thrust upgrades gets T/W of 200.
Well, Merlin 1D is sort of an outlier in the T/W business. Before it, the RD-180 was up there as the best T/W (don't believe the NK-33 numbers published elsewhere, they don't include the TVC). But you can't forget the fact that the RD-170 was commissioned by 1985. And the RD-180 was flying by 2000, with Russian manufacturing technology of the 80s. In fact, the thing I find most impressive is that people says that the tolerances on that engine are ridiculously loose.

Offline Jim

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Re: Blue Origin's BE-4 Engine
« Reply #35 on: 08/09/2016 01:58 PM »
I dislike "performance." If you mean Isp, say Isp. If you mean T/W ratio, say T/W ratio.

On the latter, Merlin 1D kicks RD180's butt all over town. Merlin 1D with recent thrust upgrades gets T/W of 200.

Not a really relevant parameter for comparison. Try installed T/W.  Compare Atlas V thrust section to F9 thrust section.  Installation wise, I bet RD-180 kick Merlins butt all over town.  Atlas V/RD-180 had no need for 9 feed lines.
« Last Edit: 08/09/2016 02:00 PM by Jim »

Offline ugordan

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Re: Blue Origin's BE-4 Engine
« Reply #36 on: 08/09/2016 02:02 PM »
In fact, the thing I find most impressive is that people says that the tolerances on that engine are ridiculously loose.

Yet several years ago there were people on here calling RD-180 a "ticking time bomb". Whether it was due to its ox-rich staged combustion cycle, a distrust toward its country of origin and their manufacturing practices and whether it was coming from experts in the field or forum "experts", I don't know, but it was pretty amusing.

Offline rpapo

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Re: Blue Origin's BE-4 Engine
« Reply #37 on: 08/09/2016 02:10 PM »
Not a really relevant parameter for comparison. Try installed T/W.  Compare Atlas V thrust section to F9 thrust section.  Installation wise, I bet RD-180 kick Merlins butt all over town.  Atlas V/RD-180 had no need for 9 feed lines.
But they can't throttle down to what is effectively less than 10% thrust either.  Yes, I appreciate the KISS principle in rocket design, but they could never have pulled off the booster landings with only one or two very powerful engines.
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Re: Blue Origin's BE-4 Engine
« Reply #38 on: 08/09/2016 02:15 PM »
I dislike "performance." If you mean Isp, say Isp. If you mean T/W ratio, say T/W ratio.

On the latter, Merlin 1D kicks RD180's butt all over town. Merlin 1D with recent thrust upgrades gets T/W of 200.

Not a really relevant parameter for comparison. Try installed T/W.  Compare Atlas V thrust section to F9 thrust section.  Installation wise, I bet RD-180 kick Merlins butt all over town.  Atlas V/RD-180 had no need for 9 feed lines.
I'd take that wager.
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Offline Jim

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Re: Blue Origin's BE-4 Engine
« Reply #39 on: 08/09/2016 02:21 PM »
Not a really relevant parameter for comparison. Try installed T/W.  Compare Atlas V thrust section to F9 thrust section.  Installation wise, I bet RD-180 kick Merlins butt all over town.  Atlas V/RD-180 had no need for 9 feed lines.
But they can't throttle down to what is effectively less than 10% thrust either.  Yes, I appreciate the KISS principle in rocket design, but they could never have pulled off the booster landings with only one or two very powerful engines.

Neither can Merlin.  But what does throttling or landing have to do with the BE-4?

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