Pulsejet workflow simulation online

[Alex Eng]

If you need computer simulation of your pulsejet engine, valved or valveless, but don't know how to do it, we can offer you to do it online. And this is not a calculator!

Well, we got a need to create the cheapest attack drones, and the most mass-produced ones. We immediately discovered that a turbojet engine is too expensive for a large series, and it's impossible to find so much money, but with a piston engine the drone flies too slowly. In result, we decided to consider a pulsejet engine, according to the old German tradition.

Further, there will be a lot of words below, and we apologize in advance to all pulsejet specialists, but it is impossible to explain the problem briefly.

So, we started to figure out what's what, and almost immediately came to the conclusion that developing a project with a calculator, cutter and welding machines in own garage, that is, everything as you like here, is already a completely frivolous undertaking. At least, for our projects.

Then, we looked at what people do in terms of pulsejet calculations and modeling. It's a pitiful sight, if not to say horror. On the one hand, a bunch of scientists who write some murky programs just to write their clever articles only. On the other hand, some strange individuals who seemed to have done something, and even seemed good, but it's impossible to use and repeat it. Well, and the third ones have gone somewhere into the astral plane: they have taken up 3-D modeling for drawing very nice pictures. But it is completely unclear for what and where to do with all this, especially when for some reason they start modeling transverse vibrations of petals. And the most interesting thing is that no one has a hint of calculating thrust and fuel consumption, including by flight speed. Therefore, why they did all this remains a mystery to us. Of course, this is only our opinion, but it turned out that all these "achievements" are impossible to use in real practice, and accordingly, they are not worth a dime.

By the way, all this disgrace cannot be compared with the ideal order in turbojet and piston engines. There, you can buy or even just download free of charge 3-4 standard programs for each type, and they will not only model the entire work process for you, but also draw the engine itself, and then calculate all its characteristics. Nothing like this is even close to being observed for pulsejets, except for some murky calculators, because everybody knows pulsejet is extremely complicated thing, bla-bla-bla. Therefore, and everybody knows it still much better, the calculators are all that we can get. Unfortunately, they might be fine for own garage with cutters and welders, but we decided that we had slightly different goals and tasks. So we approached the matter from absolutely different side.

As a result, in a couple-triple of weeks we developed our own pulsejet mathematical model. Then, in a couple of months, we have moved further and already got a workable modeling program. For final debugging, it was posted on a specially created website, having developed an interface for the program.


This is our program, welcome!

The website has a fairly detailed description of how the mathematical model itself was made, and how the program works. Of course, this is only the beginning, we will continue to improve, deepen and add all this. But a certain fact can already be recorded: it seems, this is the first online program for calculating and modeling the pulsejet's working cycle, we have not found anything like this yet. And it is the exactly first such program, where it is possible to modeling both pulsejet engine types, valved and valveless.

The main features of the model and the program, briefly, so as not to take up the time of respected specialists in pulsejets, are the following:

1. Everything is online, for everyone. But there will be a special service for professionals.

2. You can simulate online the working cycle of all the main types of pulsejets - both valved and valveless.

3. The principle of the model and the program operation is in solving a large system of differential equations of the 1st and 2nd orders. Only the geometry is set, then, after the engine is started by supplying starting air, all the parameters are determined by the program itself. The program calculates the pulsating process in the engine, and these are cycles of self-oscillations of gas pressure, temperature and velocity, at the end of which the thrust, fuel consumption, and frequency are calculated. Moreover, if the engine has entered the self-oscillation mode, it is working, but if it cannot start and stalls, it is dead. You can check for yourself that this is never a calculator, which everyone likes so much .


Main engine dimensions - it is possible to use default sizes or to write in the own ones

4. Combustion chamber: for now, it is assumed that the gas is distributed uniformly in a certain volume there, i.e. the instantaneous pressure and temperature in the chamber are the same by volume. At any given time. This allows using a 0-dimensional thermodynamic model to describe the processes of gas-air filling, mixing, combustion and leaking. The combustion process is described as in liquid rocket engines. It means how much air has entered at a given moment in time over a short period, so much fuel has burned, but after an ignition delay time. Then we will clarify and improve all this, if necessary.

5. For resonant pipes (in valveless engine for the intake pipe too) the so-called "liquid piston" analogy is adopted (this is not our idea, the University of Cincinnati likes it too, by the way). This is when the dynamics of the movement of a certain mass of gas concentrated in the middle of the gas column is calculated. The addition of cold air during reverse flow is taken into account, it is especially important for the intake pipe in a valveless engine. Then we will replace all this with a 1-dimensional model of gas flow in a pipe, as in ICE models, but for now the "liquid piston" is more than enough for everything. Well, and for now, the calculation is only for the cylindrical pipes, a conical one will be added later (not all the features at once, only gradually).


The features of valveless engine - all the default parameters can be changed on your own

6. The program allows you to assemble and test the engines of different designs. For example, it can be a valved one with front and side inlets, a valveless one with several intake pipes, etc.

7. The valves are available in different design and geometry options, including RC plane engine circular and "adult" wedge grids. The program calculates the petal movement optionally in a quasi-static version, when the valve opening depends only by the pressure drop, or by dynamic version: with lift delays, petal rebounds and gas backflows. The petal temperature will also be calculated, but later.


The valve system allows to consider many different types of valves

8. At the end of each cycle, the thrust, air, fuel consumption and frequency are calculated as integral parameters. The user can set any number of cycles up to 10, but as a rule, in a workable engine, the difference between cycles in % (we took it as a calculation error) after the 7th cycle is minimal.


This is picture, how does engine start and work

9. The program is designed so that the user can choose which engine he needs. There are 3 basic engine options: a small valveless, a small valved and a large valved type Argus 014. For each of them, default parameters are set, which can be changed within the specified limits or left as it is. This principle greatly simplifies and speeds up the data entry for modeling any engines.

10. For advanced users, there will be a special, not very heavily paid version - with its own account, recording of calculation data, downloading of the results, with parametric modeling and other useful features. But a little later.


Output of the main parameters

11. The mathematical model and the program never provide 100% accuracy for all engines. We don't even want to explain why. However, the approximation that already exists, sometimes even very rough, and the dependencies that are already obtained, have already proven useful in practice. For us, in general, this is enough. But we are open to those who are ready to help and improve the model and the program.

12. And one more important thing. This is not an "open source" at all, which everyone likes so much. On the contrary, everything is completely closed, and it's impossible to see model algorithm in the source code of the website. This is our know-how, which we now offer for use, and only in the form that we consider necessary. Free and for everyone. But only for now. It will definitely get worse later, because not for everyone and not for free.

So, the very first tests already gave us interesting results. It is especially interesting for the valveless: there the main thrust is created, it turns out, by the intake pipe, and not by a long resonant one, as everyone is always sure. In addition, the frequency of a valveless engine is always lower than that of a valved engine of the same basic dimensions. We really did not know this until the model showed it. The valved engine is also interesting: if you expand the valve grid too much to make the minimum possible resistance, the engine does not want to work at all, because there is nowhere for the vacuum in the combustion chamber to come from. But everyone always knew that the more is the better, right?


Diagrams of the last calculated cycle

But, of course, there may still be inaccuracies and failures in the model and program, including with some combinations of sizes. We will be glad if someone reports them. Of particular interest are specific complete data on all sizes of the completed engines and their real parameters (strictly according to the list of input-output parameters of the program), because this will allow us to refine the model. Gradually, we will bring it to a better condition and improve it, but not all at once.

In short, if you are interested, we invite you to first read about the model and the program on the website, and then try it.

https://pulsejet-sim.com

It is very simple, you don’t have to specify anything at all, you can just press the default data confirmation buttons, and one of the 3 selected engines will work at once! Even on your mobil phone too! Well, and please do not forget about comments and advice. Although the program already works for some practical tasks, it is still in the process of being finalized, so any information will be useful.

Thank you for reading to the end and hope all this will be useful.

[tufty]

Interesting. Haven't looked into it too deeply, though.

To get a start on validation of the model, there's a certain amount of literature regarding specific designs, particularly the various SNECMA engines and the stuff out of JPL.

[Alex Eng]

Thank you. We understand that we have achieved qualitative more than quantitative compliance. This is usual situation for such works, and this is also not so bad, for a start. We just had to start with something. The model will gradually improve, step by step.

[Alex Eng]

Just in case anyone is interested, I'll add.

The program works on the phone too, just like on a big computer. The interface for this is made adaptive, and all calculations still happen on the server, not on the phone or on the computer.

This is how it looks on the phone:





Perhaps no one needs all this, but we decided that if we do it, then do it well. At least, we have not seen anything similar at the moment.

Perhaps we will also make some kind of sound generator that will work on the pressure curve diagram, that is, decompose this curve into components of Fourier series, after which the sound will be obtained. It is already clear that the sound of a valveless engine is not the same as that of a valved engine. But this will happen a little later, not all at once.

[Alex Eng]

Sound is already working .

Parametric studies will be possible very soon, we mean it is important, because it allows to choose correct engine geometry. For example, small valved engine can work with resonant pipe length in a range 300-1800 mm, but on 300 and on 1800 mm our program shows thrust is very low and specific fuel consumption is too high. Parametric studies help to find the length with maximum thrust and/or minimum specific fuel consumption (in general, this is different length).

So, we are sure that with help of our program, it is possible to decrease the studies with cutter and welding , and to get the engine parameters better.

[Alex Eng]

Just in case, for information.

The program is being debugged continuously, and this affects the calculation itself. For example, right now (04.04.2025) the program gives underestimated parameters , but everything will be OK again soon. The reason is in difficulties for our "electronic guys" to implement the possibility of parametric studies . In order to know for sure that the program is debugged and working well, you need to wait until all warnings like "Program in developing" go out.

Well, the parametric study means to calculate 10 cycles from start many times with different amount (10-20 points) of 1 chosen parameter. For example, the test of such parametric study of a small pulsejet is below, 2 upper lines - by resonant pipe length, 2 bottom lines - by air-fuel ratio lambda. I.e. all these diagrams are the result of the calculation of about 100-200 cycles . Of course, all this is just testing result, our electronic guys still did not finish approximation of the diagrams, all this work is in process now...





By the way, the possibility of parametric studies, like some other special functions, is provided in the version for professional users only. But at the beginning, all the functions of the program will be completely free.

We hope for your understanding .

[Alex Eng]

... right now (04.04.2025) the program gives underestimated parameters , but everything will be OK again soon.
We hope for your understanding .

The electronics have fixed the problem - you can use the program again . There was some error when transmitting data to the server and back, somewhere one of the parameters in meters was converted to mm, for some reason...

[Alex Eng]

Now the parametric study gives the following view of diagrams:



This is small valved engine with 40 mm resonant pipe diameter. You can see, how to choose the pipe length. There is maximum thrust on about 1000 mm, but minimum specific fuel consumption is on less length, about 900 mm.

Of course, we need accurate experimental data to adjust our model, but even now the model and program can be useful for some applications.

Please try it - we need your opinion and advice.

[Alex Eng]

Interesting question - have you ever seen a pulse jet engine indicator diagram? We are 100% sure - never!

But now we can tell you: now you have it, and it is a real pulse jet engine indicator diagram! On top is the Argus V-1 , on the bottom is the small pulse jet engine .




So, here you can see that the pulse jet engine operates on the Lenoir cycle . Because it is close to 3 processes at once: 1) intake with constant pressure p, 2) compression-combustion with constant volume v=V/m, then 3) expansion as an adiabatic process.

Of course, all these are very specific questions, but even now we can make the following preliminary very funny conclusions :
1) all the scientists who previously studied the pulsejet, but did not get its indicator diagram, did not study the engine, the purpose of their study was not the engine, their research was not about the engine,
2) all the scientists who previously studied the pulsejet, but did not get its altitude-speed characteristics, did not study the aircraft engine, the purpose of their study was not the aircraft engine, their research was not about aircraft and not about aviation at all.

But now you can try it yourself and get all this for your own pulse jet engine .

[Alex Eng]

To get a start on validation of the model, there's a certain amount of literature regarding specific designs, particularly the various SNECMA engines and the stuff out of JPL.

Well... No. Exactly no . Because we are 100% sure everyone should mind their own business only. And no one should mind someone else's business. If it were the other way around, no model would have appeared.

We did the bare minimum of checks that we thought were necessary for its validation, and the results generally suit us for conducting the research we need. But if someone finds a significant discrepancy or mistake, we are ready to help him to correct the program according to his task if he provides us with all the data on his engine - strictly according to the list of those that are used in our program when entering the initial data.

Therefore, concerning the offer "if you go to, I don't know where and if you take something I don't know what" (it is not necessary for me, but I saw it there ) - no, it doesn't work like this on 100%.

[Alex Eng]

Well, in a month we have made great progress in our program. It is now called Pulsejet-Sim, a sort of brand name now .

So, what has been done:
1. Separation into amateur and professional levels.
2. The "Amateur" level is a random visitor without registration, he has limited functions of the program. He can calculate any engine, but it is not allowed to save results, it is not allowed to save its engine projects and it is not allowed to conduct parametric studies (except for one test along the length of the resonance pipe). Thus, amateurs can only watch (but what they want else? ).
3. The "Professional" level is for real users, students, engineers, scientist, researchers, designers . A simple registration is required, after which all functions of the program are available absolutely free of charge. Namely:
- you can develop your engine projects and save them for subsequent research,
- you can save all enter and calculation data and download them in Excel,
- you can save any diagrams,
- you can conduct all parametric studies,
- you can collect any diagrams together (a very cool function).

We think it is even more than enough .

By the way, not to offend the amateurs - they can also get all this, but only by themselves and manually, so they will need a lot of time . It's like driving on a highway or on a narrow road nearby. The only difference is that everything is free for us (for now ).

But what does "collect" mean? Here is a thing like this for Solar engine as example:



On the diagram: the pressure and temperature in the combustion chamber, the velocities in the pipe and at the inlet and the lift of the valve petal. Real researchers can already see at once the processes caused by a delay in valve closing using this assembled diagram .

By the way, the rectangles above the diagrams are a very cool thing. If you click on one, you can remove the curve from the diagram. And on the parametric study diagram there are two such rectangles - one removes points from the diagram, and the second removes the approximation curve.

And here is an assembly of diagrams of the parametric study of the Solar engine along the length of the resonance tube. Hope, it is interesting too.



In short, now in our Pulsejet-Sim, we offer you the most complete SaaS - Software as a Service . Unfortunately, this is not cutting or welding. But this is exactly what needs to be done before cutting and welding. .