How do I calculate the movement of air in a valveless pulse jet engine?

[telepresence]

I'm trying to create a piece of software that can approximate the physics of a valveless pulse jet engine. What I need right now is to figure out the math behind the moving air. How would I calculate how the air from the combustion chamber after combustion (assumed for simplicity to be instantaneous) would move down the exhaust and intake pipes relative to the size of the pipes and the pressure of the air in the chamber? (Yes, I realize this needs calculus) As the gas leaves the combustion chamber, It forms a vacuum in its wake that eventually stops the flow of air and starts pulling it back. I need the equations for this. I also could use some explanation of how the size of an opening effects the amount of pressure placed on it when in this type of scenario (how much of the pressure is exerted on the openings to the exhaust and inlet tubes?

 

[RandomGuy88]

Are you just trying to approximate some particular quantity or are you trying to simulate the entire flow? Because simulating the entire flow is an extremely complex problem that will need a lot more than calculus. Ever hear of the Navier Stokes Equations? That is where you need to start if you are going to simulate a fluid.

 

[telepresence]

for right now I was going to be content with just a simple simulation that incorporated the heat cycle only. I was calculating the amount of energy given by combustion of a given amount of propane (based on the amount of fresh air in the chamber, somewhere between 2.15 and 9.6 [the flamability limits of propane] percent of the air) and then calculating how much that would heat the air. From that calculating the increase in pressure (since I'm assuming all of this is instant, I can also assume that the volume is constant. I know that will result in a much more powerful result than is actually possible, but it's a start).

Ever hear of the Navier Stokes Equations? That is where you need to start if you are going to simulate a fluid.

Thanks for the info, I'll look into it.

 

[telepresence]

does anyone know a conversion for pressure difference to acceleration in air?

 

[PJC01]

)

Calculating the movement of air in a valveless pulse jet engine involves understanding the principles of fluid dynamics and thermodynamics. The first step would be to gather all the necessary parameters such as the size and shape of the combustion chamber, exhaust and intake pipes, and the pressure of the air in the chamber.

To approximate the physics of the engine, you would need to use equations from fluid mechanics, such as the Bernoulli equation, which relates the pressure, velocity, and height of a fluid. This equation can be used to calculate the pressure difference between the combustion chamber and the exhaust/intake pipes.

You would also need to consider the effects of compressibility and heat transfer in the engine. The ideal gas law, which relates the pressure, volume, and temperature of a gas, can be used to approximate the changes in pressure and temperature as the gas moves through the engine.

To determine the movement of the air in the exhaust and intake pipes, you would need to use the continuity equation, which states that the mass flow rate of a fluid is constant at any point in a closed system. This equation can be used to calculate the velocity of the air as it moves through the pipes.

Furthermore, to understand the vacuum created by the gas leaving the combustion chamber, you would need to use the Navier-Stokes equations, which describe the motion of a fluid in terms of its velocity, pressure, and density. These equations take into account the effects of viscosity and can help determine the pressure distribution in the engine.

The size of the openings in the exhaust and intake pipes will also affect the pressure in the engine. This can be calculated using the concept of flow rate and the continuity equation. The larger the opening, the higher the flow rate and the lower the pressure.

In conclusion, calculating the movement of air in a valveless pulse jet engine requires a thorough understanding of fluid dynamics and thermodynamics. It involves using various equations and parameters to approximate the physics of the engine. It is a complex task that requires advanced mathematical skills and knowledge of these principles.