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The advantage the constant-volume combustion type gas turbine engine

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qumf
#19
Jan8-13, 09:06 AM
P: 38
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
#20
Jan9-13, 08:59 AM
P: 38
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
#21
Jan18-13, 09:34 AM
P: 38
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
#22
Feb22-13, 03:35 AM
P: 6
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
#23
Feb24-13, 08:27 AM
P: 38
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
#24
Feb24-13, 08:39 AM
P: 38
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
#25
Feb24-13, 08:54 AM
P: 38
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
#26
Feb24-13, 09:11 AM
P: 38
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
#27
Feb24-13, 09:16 AM
P: 38
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
#28
Feb24-13, 09:33 AM
P: 38
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
#29
Mar15-13, 03:11 PM
P: 2
Qumf,
Have you taken a look at the wave rotor engine concepts?
qumf
#30
Mar18-13, 08:01 AM
P: 38
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
#31
Mar21-13, 01:51 PM
P: 2
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
#32
Mar24-13, 03:18 AM
P: 38
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)
qumf
#33
Sep16-13, 07:19 PM
P: 38
Continue to discuss the feasibillity,
Now I discuss the the structure and function of exhaust system, that including the branch pipes, general pipe and turbine.

The branch pipe, general pipe,the turbine install behind the chambers.

The function of branch pipes behind the chambers:

because I need energy to drive the compressor(blower) in front of the chambers, the common way is to install a turbine to receive the energy of the exhaust gas from the chambers. So I set a turbine.
When the burnt gas will go through the turbine, we need to keep the speed and pressure stable. It’s good to utilize the kinetic energy efficiently from the gas and is benificial for turbine to bear the load.
for a certain exhaust branch pipe, the gas spout intermittently, so the condition of gas inside a branch pipe is changable. I have to arrange these flows to cooperate to get a comparable stable current.
So I set a group of output branch pipes after the chambers. each branch pipe is corresponding to a chamber. then these branch pipes merge one general pipe. the turbine wheel is installed within the general pipe.
several pairs of chambers spout gas alternately and cooperate, we also can add a space behind branch pipes as buffer storage and to regulate gases before turbine, when the gases encounters the turbine, the condition is relatively stable.
These branch pipes have a certain volume space. when the gas rush out off the chambers, A certain volume of buffer storage can reduce the fluctuation.depending on the branch pipes, at last in the general pipe the flow can become comparable stable.
When the working course turns to exchange tha gas ,(ie,the fresh gas enters the chambers),the speed of gases in the corresponding branch pipes is the highest and the pressure is lowest at the end of the spouting course, the Momentum of the burnt gas cause the negative pressure inside the corresponding chambers, it can suck the fresh gas into chambers afterward.
Without the branch pipes, when gas spouts out, the current will influence the gas flow in the other branch pipes, such as the course of exchange gas . Installing the branch pipes; the course will help each other by the effect of suction.
The quantity, the shape and the size of the branch pipes should be studied carefully, They are relative to the functions I state upper. it is nessesary to do some experiments to while building the engine.
The shape of the branch pipe to genaral pipe should be designed carefully in order that the flows can cooperate well, the energy loss and flow resistance should be as possible as small.
qumf
#34
Jan22-14, 08:29 AM
P: 38
I try to calculate the temperature before the turbine:
Pls see below figure 4: the figure show how I find their relationship of the main parameters in different course. (Sometimes I call constant-volume combustion type as closed combustion type)

Normally the pressure after compression is pretty high, if other things do not change, we make the pressure by combustion lower , the efficiency reduce a little, meanwhile the temperature before turbine reduce much,
I make a example: Set the temperature of outside air: 300K, k=1.4, set the pressure after compression/before compression α=7, the pressure after combustion/before combustion β=7.5, thus the temperature turbine 2206K; theory efficiency: η=60.2%; k=1.4, α=7, β=7, the temperature turbine 2100K, η=59.6%; k=1.4, α=7, β=6.5, the temperature turbine 1992K, η=58.9%; k=1.4, α=7, β=6, the temperature turbine1881K, η=58.2%;
Actually changing β is by change the volume proportion of fresh gas in each time or the concentration of fuel a little. In this example, η is reduced by 3%, the temperature before turbine decrease by 400K.

α and β all contribute to η. usually we expect the temperature before turbine not very high because of reliabity and life, thus in order to ensure a certain η, we need to increase α.
High temperature normally means high efficiency,but if it is too high, it will cause a series problem, it will influence the life and reliabity of the engine. Because the restriction, sometimes we have to make concession on efficiency.
This example just reminds the relation. The data to some parameters may not be so precise; Some modulus will change a little from in normal case to a very high temperature. Here I assume them unvaried for convenient study . Anyway it is a good enough reference for us.
The method also is used to calculate the temperature of each work course.
Attached Thumbnails
figure4.JPG  
qumf
#35
Jan25-14, 08:41 AM
P: 38
I have to compensate a little.
There is a sentence in the upper derivation "I set the pressure before turbine same as it after compressor. You can the same description appear in #9 floor. You can refer to it.


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