PyroJoes Recipe for Beginners

[metiz]

Thanks for the scale down. Just to be clear, no expanded tail right?

I was referring to the sound level btw. Maddox and the likes stand next to bigger engines than this without issue it seems

[PyroJoe]

No expanded tail.
The sound, I can't explain it.
Will take overnight to create illustrations, will post them up tomorrow. Nothing fancy, just basic stuff.

[PyroJoe]

Again this is my own explanation, not completely accurate, but should provide a general idea of how the valveless engines can be improved.

I will use the basic tank model that Viv used before, it has inspired me to think and consider the many factors involved. This example will use two ports on either side of the tank. The blue line represents normal air pressure, above normal pressure will display above this blue line, pressure dropping below the blue line represents pressure below normal.

[PyroJoe]

Here the fuel and air are present and the mixture ignited, pressure is created.

[PyroJoe]

The blow down is occurring, the pressure is falling. The force of the pressure is creating a mass flow.

A couple of things to note here is the acceleration velocity near the ports are relatively high, as the exhaust plume spreads ever wider, the velocity is reduced.

Not far from the ports the velocity has already begun to drop.

One of my favorite videos:
http://www.youtube.com/watch?v=q1LQ94pj ... plpp_video

[PyroJoe]

Blow down has exhausted and the pressure has dropped to normal.

[PyroJoe]

A Helmholtz volume will drop below normal pressure and create a partial vacuum, or "below ambient" pressure.
Shown here in purple.

[PyroJoe]

The low pressure produces a small return flow into the chamber.

[PyroJoe]

The return flow will create a small positive pressure once the volume has been over filled passed normal. The Helmholtz volume (resonator cavity) will continue to oscillate, but the re compression represents the end of one cycle for this example.

[PyroJoe]

Add straight pipe to create a pulse jet.

[PyroJoe]

The fuel and air are present and the mixture ignited, pressure is created.

[PyroJoe]

The blow down is occurring, the pressure is falling, but the tail pipe has considerable trapped mass that has to be accelerated, and has helped to sustain, (or contain) the pressure better on the tail side of the chamber. The velocity of the trapped mass in the tail is considerable.

The intake with minimum trapped mass, is allowing the pressure to leak past. The green represents the pressure that the intake quickly releases. The pressure continues to be slightly elevated in the tail nearest to the CC

For me the intake leak has been a tough one to address. One improvement is in aerodynamic valving (will explain that one later). It helps reduce the leak but far from resolved it. Intake leak along with non blended bodies has made the valveless engines appear weak in performance.

[PyroJoe]

Blow down has exhausted and the pressure has mostly dropped to normal. The truth is there is alot of wiggle above and below ambient, but eventually most of it passes through. Note the trapped tail mass is still in motion at considerable velocity after blowdown.

[PyroJoe]

Helmholtz volume with a portion of the tail will drop below normal pressure and create the low pressure.

[metiz]

C-c-c-combo breaker! Very illustrative explanation, reminds me of NUDiS graphs. I'm well aware of the changes in pressure and velocities in the engine throughout the cycle.

When you mentioned Helmholtz volume and the "springiness" of air, isn't that more due to the Kadency effect (at least at the tailpipe section?) Afterall, the Helmholtz resonator would not exist without good 'ol Kadency

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