The advantage the constant-volume combustion type gas turbine engine

Enthalpy

That combustion at constant volume is more efficient should be clear, but the whole question is how to achieve this in a turbine, since nobody got convincing results.

Your design with doors front and aft is the first option people think of. More refined attempts were made without success. In particular, you could have a look at the throughput possible with doors. Because is means stopping the flow, people had arrived to let it oscilate instead, and use air's inertia to achieve the constant volume during a detonation.

qumf

to etudiant
thank for your reply.
I correct you a little. the chambers do not rotate. the doors at the both sides do rotate.
you can not say " the doors don't need to be closed completely at both sides". It need or not depands on expriment. But i think at the begining of combustion, the space can not completedly closed.
you also express you worry about something: heavy and heat. You can get result by search the topic to get my articles in other website. the chambers are arranged in a circle is relative to solve the issues. I also will explain my solution here later.

qumf

to Enthalpy:

though I will explain the feasibility of this kind of engine later in this web, now you also can search the topic to get my composition on other website.
Here i say a few words.
the chambers exhausts gas in turn , and afterwads through a special pipes system to get a steady output at last.

I know for a certain chamber, the input gas is intermittent. so I set the input pipe rotating (with front door), the input gas flow continuously. thus throughput can be bigger than you thought.

qumf

to etudiant and Enthalpy:
for example, you can find my article in website http://forum.keypublishing.com/ , then choose section: Modern Military Aviation ,then search " The jet propulsion with closed combustion type" ( Last post 10th October 2012 by qumf )

I also heard there are a few institutes developed the new jet engine to utilize the advantage of the constant volume combustion type in their laboratory. So far there are still some limits to launch in market.

One of the big differences between mine to theirs that I didn’t mention before: I set two doors at the ends of the combustion portion to realize the exchange of gas. The main function is to separate the gases (fresh and burnt gas) easily, then lead to series of benefit, such as increase the gas pressure higher, easy to control the flow and regulate the process, adjust the combustion condition
I learn the point from the internal combustion engines

StorminMatt

I have to admit that the idea of a constant volume combustion gas turbine is an intriguing one. And it's one I have thought of on several occasions myself. Unlike this particular design utilizing a rotary valve, my idea was basically the same as the one mentioned with a rotating combustion chamber similar to the chamber on a six shooter (which slides by ports that allow gasses to enter and leave). However, although this sort of engine would seem to hold promise in terms of improving the efficiency of the standard Brayton Cycle turbine, it's not without its downfalls.

One of the WONDERFUL things about gas turbines is the inherent reliability of current designs. They are a wonderfully simple engine with few moving parts. Size and weight are low for the power produced. And flow is steady. So vibrations that could possibly cause cyclic fatigue are minimal. All of these factors lead to a engine that is rugged, reliable, and just plain works. When you add things like rotating chambers and/or rotary valves, you increase size and weight, and suddenly increase the failure points manyfold. In the case of a rotating chamber, you need a way to both seal the chamber against flat surfaces and keep it cool. With rotating valves, you need a design that will seal as well. And you will need to use materials as well as a design that will be able to withstand REALLY high temperatures without deformation. Furthermore, in ANY constant volume turbine, airflow through the engine will inevitably be unsteady to a greater or lesser degree. This will require an overall more robust compressor and turbine design which can handle cyclic loads without suffering from fatigue damage. And finally, with unsteady flow, noise could be a concern.

Of course, if these issues could be dealt with, then a constant volume combustor has the potential to increase turbine efficiency (and reduce fuel consumption). But it might also be helpful to look at other ways the efficiency of a gas turbine could be improved without such drastic changes that could lead to lower reliability and increased mechanical complexity. Such improvements as finding materials for turbine blades that can withstand higher temperatures (although not easy in itself) might ultimately be more practical in the end.

qumf

to StorminMatt:

I know the constant-volume combustion type is very easy to cause some problem. my target is avoid these weakness. I hope you study the structure of my engine again. I also hope search my feasibility report from internet. I have mentioned the website before and you can find it easily. I would like to send you the report from my E-mail (qumf@163.com) if you need.
I also anaylise the feasiblity here later.
I have considered many years all what you are concerned. I can not throw the idea away easily since it has a big advatage.

qumf

then I reply to some of your concerns. The detailed can be searched by E-mail.
Firstly (many years ago) I ever thought of rotating chambers. at last I gave up the idea.
It seems it need only one outlet pipe. Really the pressure of the gas out off the chamber is variable. so one outlet pipe is not enough. The structure is still very complicated.
the mass of chamber is much bigger than two doors; rotating the chambers cost more energy.
Then I gave up the idea.

qumf

You ever mentioned, the size and weight is bigger on the new type than the constant pressure combustion type. You should agree, only for chamber, the size and weight is bigger, the new chamber can increase the pressure. in the current engine this part of pressure will be produced by the the part of compressor. We all know the compressor is very heavy because it has many blades and strong hubs. comparatively the chambers only need to bear the pressure.
of course, if the working frequence is low, the new design is not proper, the jet engine is heavy than the current engine definitely.
if the jet engine can work on the very high frequency, each course can be allocated well, I think the size and weight have not big difference. After all the the type of combustion can finish in tiny little time.

qumf

As you mentioned "fatigue damage". I also noticed it and try to decrease the risk. I adopt proper structure to improve their force condition.
for example, I arrange these chambers on a circle position. thus the force on one chamber can be borne by all chambers. the deformation will become uniform, the part is not easy to destroied.
I adopt double wall for some import parts and input high pressure gas between the walls. Thus the condition of the force the part bear change. The parts are not easy to be damaged.

qumf

As to the seal on the flat surface, I know it is difficult. I make the seal a little flexible and with proper contact surface so that it can adjust itself with chambers deformation.
Even though there is a little gas leak, as long as the composition is not serious, this part of gas will not canuse bad effect and will not influrence the efficiency.

qumf

StorminMatt, you also mentioned the heat and cool solution, here I just explain a little of the solutions.
In this engine the flow is more easy to control precise than the current engine because of the doule walls and branch pipes system. We can release a little air from the front door to form a layer of air on it to seperate from the gas can be burnt, thus it can avoid contact the very high temprature and protect itself. the idea can be used on the others parts if necessary.

oatlids

Qumf,
Have you taken a look at the wave rotor engine concepts?

qumf

Hi,oatlids
when I published the idea including the structure of the engine on other website. Somebody ever reminded me it is like wave rotor engine. I search the wave rotor engine from internet. I think they are different.
the structure are similar, part of principle are same. but the input and outlet systems are different totally. in my memory the structure of combustion portion inside the wave rotor engine is more complicated; the original input gas to chambers is not the mixed gas can be burnt immediately.
please point out if i have something understood wrong.

oatlids

Qumf,
I do not deal directly with wave rotor engines, but I do have my hand in constant-volume combustion type concepts. Constant-volume combustion is always the goal but is quite difficult to achieve. You will realize this as you move from theoretical to experimental work. I would look more towards isolating whether your ideas on achieving constant volume combustion is feasible. Constant volume combustion is very well-defined.

As far as the wave rotor engine, you may be able to find more research regarding it if you have a subscription to a journal or are affiliated with a university with access to such. AIAA is a common on in our industry. There are quite a few Chinese Universities that do propulsion research and have publication archives as well. The wave rotor engine if you read the descriptions online is more of a "pressure-gain" combustor. Constant-volume combustion is that hard to achieve. Pulse detonations engines are a more common approach to achieving constant-volume combustion.

Notes:
How do you plan on injecting the fuel and air in the rotating chambers? Moreover how do you plan to make it so that it can be considered pre-mixed?
Since you say that the flow is relatively stagnant at the time of combustion, how do you plan on ejecting the gas to the turbines for work extraction? If you were planning on relying pressure expansion to purge gases, the turbines now see a lower pressure than you estimated at time of combustion, does this combustion process still provide a benefit?
Since you don't have flame holding in your design, how do you plan on initiating the combustible mixture?

qumf

Thank you for the concerns. I try to answer your questions:

“How do you plan on injecting the fuel and air in the rotating chambers? Moreover how do you plan to make it so that it can be considered pre-mixed?”-----Do you know the old type internal combustion engine on gasline? I plan to use same principle to mix fuel to air.It uses carburettor. Of course I need to improve the structure to get much better effection. The fuel will be injected at many points.
"Since you say that the flow is relatively stagnant at the time of combustion, how do you plan on ejecting the gas to the turbines for work extraction? If you were planning on relying pressure expansion to purge gases, the turbines now see a lower pressure than you estimated at time of combustion, does this combustion process still provide a benefit?"----I can not understand the sentences well. I can say, the gas pressure just after combustion and it at the turbine can be much different because there is branch pipe system the two places. There are many times of combustion happen in turn, not at the same time. they support each other to push turbine. I suggest you read my article again.

"Since you don't have flame holding in your design, how do you plan on initiating the combustible mixture?"------because the front door is rotating, and it is thick comparatively, while working orderly, the flame is led from one chamber to the one neighborhood through a path inside the front door. To choose the proper position(occasion) in the front door can get the proper temperature of the flame.(it is not the most hot, but can initiate gas)