Chinese Engine Development

ZeEa5KPul · Sep 23, 2023

no_name said:
Would RDE work with rocket fuels and oxidizers, maybe replacing traditional liquid rocket engine in future?

Is RDE being investigated partly because of reducing improvement in turbine blade technology breakthroughs?

In theory a detonation engine could work with anything. In a traditional combustion chamber the fuel and oxidizer are deflagrated (burned), while in a detonation engine they are detonated (a supersonic shockwave as in an explosion). The advantage of a detonation engine is that much higher temperatures and pressures can be reached, which makes the engine more efficient. The disadvantage is obvious: you're trying to control an explosion and make it stable for hours on end.

no_name · Sep 24, 2023

ZeEa5KPul said:
In theory a detonation engine could work with anything. In a traditional combustion chamber the fuel and oxidizer are deflagrated (burned), while in a detonation engine they are detonated (a supersonic shockwave as in an explosion). The advantage of a detonation engine is that much higher temperatures and pressures can be reached, which makes the engine more efficient. The disadvantage is obvious: you're trying to control an explosion and make it stable for hours on end.

Even combining controllable mini nuclear fusion detonations in the far future?

latenlazy · Sep 24, 2023

no_name said:
Even combining controllable mini nuclear fusion detonations in the far future?

No the detonation is a combustion reaction.

Philister · Sep 24, 2023

taxiya said:
How is it cheaper than RDE? In what sense?

By PJ, do you mean pulse jet? PDE is the same thing as pulse jet. The process is, ingest air and fuel -> detonation -> purge. Only detonation phase produces thrust which is about 55% time of the full cycle. While RDE has 100% time producing thrust because there are many simultaneous detonations along the circular combustion chamber. In essense PDE is like an one stroke ICE, RDE is like a X stroke ICE where X is determined by number of the circules. The advantage of RDE is obvious, higher torque in ICE sense.

Yes, in a PDE the gas expand in the same direction of the flight which is more efficient than forcing gas to change directions, same princile as thrust lost of TVC nozzle, but PDE is more difficult to realize sustained combustion due to its working cycle, the realization machenism may be more complicated and expensive than RDE.

I think the reason that we are seeing many RDE research bing put into near real life test is because after decades research, most scientists have realized that RDE is more realistic than PDE.

No, PDE engines has been in test years ago, and it didn’t stop there,no doubt RDE is a more ideal solution and that’s why it caught so much attention here.
PDE I mentioned here is merely an improved PJ with no compressor, and the combustion chamber is much simpler than that of a RDE engine, though both must be 3D printed.
I don’t get it why you say PDE is even harder to sustain? Detonation could be exited by multiple means

taxiya · Sep 24, 2023

Philister said:
No, PDE engines has been in test years ago, and it didn’t stop there,no doubt RDE is a more ideal solution and that’s why it caught so much attention here.

I don't know what does the "No" refer to. I did not say PDE is something new or under studied, I said that "after decades research, scientists have chosen RDE over PDE for application" at least for the moment. Here is what I said.

I think the reason that we are seeing many RDE research bing put into near real life test is because after decades research, most scientists have realized that RDE is more realistic than PDE.

I did not make the assertion myself but quoted professional papers and reports, see the following link and my quote in the last paragraph.

Philister said:
PDE I mentioned here is merely an improved PJ with no compressor, and the combustion chamber is much simpler than that of a RDE engine, though both must be 3D printed.

PDE is simpler because it is only a straight pipe, but it has a more complicated ignition system, see below.

Philister said:
I don’t get it why you say PDE is even harder to sustain? Detonation could be exited by multiple means

The reason of my assessment is in second paragraph of the post that you just replied.

Here I can explain in another way. RDE detonation is self-sustained, there are multiple detonations in the channel, the new coming fuel air mixture got ignited by the hot gas of previouse detonation. PDE as its name suggests is pulse, there is only one combustion at any given time, the next detonation happens after the expanding gas is purged. PDE is not self-sustained, but relies on external means like a spark which is machenics and has to run on high frequency and perfectly synced with the pulsed combustion. This mechanical system makes it complicated and more difficult to realize. No matter what means you choose, the perfect syncing mechanics is always there, that is the harder part compared to RDE. Think about lighting a mach in a storm every second, it is not impossible but you know how hard that is.

If you don't believe me, here is a summary article from China Aviation Journal for more details. It is in Chinese, I will translate passages that are related to the comparison.

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旋转爆震发动机（RDE）的研究最早起源于20世纪60年代，最早由苏联学者提出。由于该类发动机其只需一次起爆，避免了脉冲爆震发动机（PDE）的很多固有难题，受到了很多国家的重视。
RDE only ignite once, therefor eliminates many inherent difficulties of PDE.

在RDE中，爆震波围绕两个同轴圆柱体间隙中的环形空间传播，空气燃料混合后被喷射出去，并被前一轮的燃烧所点燃，如果设计得当，原本不稳定的燃烧和点火过程将可自发维持下去。
In RDE fuel air mix is ignited by previouse combustion. Self-sustained.

在RDE和PDE之间，过去十年的研究越来越多地指出RDE更适合近期发展成实用推进系统。与PDE相比，RDE只需很少的移动部件和更简单的操作即可有效地进行循环燃烧，而PDE需要在每次脉冲后对爆震室进行吹扫和重新喷射燃料混合空气。
Research in the past decade pointed out that RDE is closer to be realized as practical propulsion system. Compared to PDE, RDE has less moving parts and simpler operation to sustain continous combustion, while PDE has to purge and inject fule air mix between every pulse (detonation).

gelgoog · Sep 24, 2023

PDE is simple in theory but you have the transients (which make the engine both noisy and vibration prone), and to get adequate performance you need really high frequency of ignitions. Which isn't achieved in actual working engines. You have to evacuate the tube before the next ignition and that messes up things among other factors.

latenlazy · Sep 24, 2023

gelgoog said:
PDE is simple in theory but you have the transients (which make the engine both noisy and vibration prone), and to get adequate performance you need really high frequency of ignitions. Which isn't achieved in actual working engines. You have to evacuate the tube before the next ignition and that messes up things among other factors.

It also involves a lot more mechanical steps. RDEs have more complex gas, flow, and combustion dynamics but if you can figure those out it’s mechanically simpler.

Philister · Sep 24, 2023

taxiya said:
I don't know what does the "No" refer to. I did not say PDE is something new or under studied, I said that "after decades research, scientists have chosen RDE over PDE for application" at least for the moment. Here is what I said.

I think the reason that we are seeing many RDE research bing put into near real life test is because after decades research, most scientists have realized that RDE is more realistic than PDE.

I did not make the assertion myself but quoted professional papers and reports, see the following link and my quote in the last paragraph.

PDE is simpler because it is only a straight pipe, but it has a more complicated ignition system, see below.

The reason of my assessment is in second paragraph of the post that you just replied.

Here I can explain in another way. RDE detonation is self-sustained, there are multiple detonations in the channel, the new coming fuel air mixture got ignited by the hot gas of previouse detonation. PDE as its name suggests is pulse, there is only one combustion at any given time, the next detonation happens after the expanding gas is purged. PDE is not self-sustained, but relies on external means like a spark which is machenics and has to run on high frequency and perfectly synced with the pulsed combustion. This mechanical system makes it complicated and more difficult to realize. No matter what means you choose, the perfect syncing mechanics is always there, that is the harder part compared to RDE. Think about lighting a mach in a storm every second, it is not impossible but you know how hard that is.

If you don't believe me, here is a summary article from China Aviation Journal for more details. It is in Chinese, I will translate passages that are related to the comparison.

Please, Log in or Register to view URLs content!

旋转爆震发动机（RDE）的研究最早起源于20世纪60年代，最早由苏联学者提出。由于该类发动机其只需一次起爆，避免了脉冲爆震发动机（PDE）的很多固有难题，受到了很多国家的重视。
RDE only ignite once, therefor eliminates many inherent difficulties of PDE.

在RDE中，爆震波围绕两个同轴圆柱体间隙中的环形空间传播，空气燃料混合后被喷射出去，并被前一轮的燃烧所点燃，如果设计得当，原本不稳定的燃烧和点火过程将可自发维持下去。
In RDE fuel air mix is ignited by previouse combustion. Self-sustained.

在RDE和PDE之间，过去十年的研究越来越多地指出RDE更适合近期发展成实用推进系统。与PDE相比，RDE只需很少的移动部件和更简单的操作即可有效地进行循环燃烧，而PDE需要在每次脉冲后对爆震室进行吹扫和重新喷射燃料混合空气。
Research in the past decade pointed out that RDE is closer to be realized as practical propulsion system. Compared to PDE, RDE has less moving parts and simpler operation to sustain continous combustion, while PDE has to purge and inject fule air mix between every pulse (detonation).

Thank you very much , that explains everything.
But I still wonder , as a pulse jet lover: is it still that hard if the vehicle flies in a lower speed( less than 1 Mach) and the engine works in a low frequency?
I’ve seen a youtuber made a working PDE with a 3D printer (though worked a few seconds and low frequency, but it was a plastic one)

taxiya · Sep 25, 2023

Philister said:
But I still wonder , as a pulse jet lover: is it still that hard if the vehicle flies in a lower speed( less than 1 Mach) and the engine works in a low frequency?
I’ve seen a youtuber made a working PDE with a 3D printer (though worked a few seconds and low frequency, but it was a plastic one)

Let me first rephrase your question to be answerable, "is it hard for PJ or PDE in low frequency to be adequate for practical application such as aircraft in 10s tonnes?" The answer is no, not when that frequency is below some threshold which the researchers are still struggling with. Before that PJ or PDE will remain as proof of concept or toy.

One important thing to note is that RDE is not more ahead of PDE in becoming reality at this time in experiment, both of them have been put into proof of concept including this latest flight test. What I and many people here argued is that RDE has a better chance to reach practical level than PDE due to RDE's inherit advantage of self-sustainable combustion and continious thrust generation.

siegecrossbow · Sep 28, 2023

Ramjet control tech wins top prize!

Chinese Engine Development

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