My answer to' what is the compression racial of a PJ Engine

[55dcyinely]

The pulsejet uses Barometric pressure the (Lenoir cycle) which unlike external compressive drive such as the Otto cycle's piston, or the Brayton cycle's of the compression turbine, Pulse Jets engine relays on compression from acoustic resonance and barometric pressure. This limits the maximum (pre-combustion) pressure ratio, to perhaps 1.2 to 1.
The standard value for the atmospheric pressure at sea level in SI units is 101 325 pascals.(Lenoir Cycle, uses mathematical equations difficult to comprehend let a lone to understand.)
Valveless pulsejets come in a number of shapes and sizes, with different designs being suited for different functions. A typical valveless engine will have one or more intake tubes, a combustion chamber section, and one or more exhaust tube sections.
While the fuel-air mixture burns, most of the expanding gas is forced out of the exhaust pipe of the engine. Because the intake tube(s) also expel gas during the exhaust cycle of the engine, most valveless engines have the intakes facing backwards so that the thrust adds to the overall thrust, rather than reducing it.
The combustion creates two pressure wave fronts, “acoustic resonance” one traveling down the longer exhaust tube and one down the short intake tube. By properly 'tuning' the system (by designing the engine dimensions properly), a resonating combustion process can be achieved.
barometric pressure.


That's my thought.

[Rocket Man]

The pulsejet uses Barometric pressure the (Lenoir cycle) which unlike external compressive drive such as the Otto cycle's piston, or the Brayton cycle's of the compression turbine, Pulse Jets engine relays on compression from acoustic resonance and barometric pressure. This limits the maximum (pre-combustion) pressure ratio, to perhaps 1.2 to 1.
That's my thought.

The Germans had it right, best compression ratio is 2 to 1. Hobby engines use a compression ratio of 4 to 1 this doubles the exhaust velocity for the same size engine so you have a faster flying model airplane.

You can do the same thing with valveless PJ engines the higher the compression ratio the higher the exhaust gas velocity, fuel burns more efficient but the engine is harder to start.

If your going to put a PJ engine on a bicycle or Go-Kart you don't need high velocity exhaust gas because who is crazy enough to ride it 200 mph.

If you change the exhaust gas velocity from 200 mph to 100 mph take off power doubles so the vehicle will pick up speed twice as fast as before but reach full speed at 100 mph not taking into account wind resistance and other things.

[55dcyinely]

Hi Rocket Man
That's great! I couldn't remember where that information came from but I did remember reading it. At first you read everything you can about what interests you (in this case PJ's)
and soon forget where to find it.

[ganuganu]

can we say that if we make tail expansions(cones) in valveless pj the compression ratio can be increased.

[Rocket Man]

can we say that if we make tail expansions(cones) in valveless pj the compression ratio can be increased.

No. Compression ratio is a comparrison of the combustion chamber cross sectional area compaired to the exhaust pipe cross sectional area. A cone on the exhaust pipe does not make the cross sectional area of the exhaust pipe larger. But the cone has an advantage, the engine can have a 4 to 1 compression ratio making the engine more fuel efficient and giving the engine more take off power.

If you double the cross section area of the tail pipe end that doubles the pushing power of the engine. That also reduces exhaust gas velocity by half.

I have done some experementing with this but so far I don't have a lot of useful information. The cone acts like a longer exhaust pipe which changes the way the engine runs. If your going to add a cone you need to cut the tail pipe shorter. I have not experemented with this enough to come up with math formulas to calculate how much the tail pipe should be cut off for a given cone shape.

[PyroJoe]

I offer this question:
Would we ever see any significant pressure wave produced by a engine working on the Lenoir cycle?

[55dcyinely]

I offer this question:
Would we ever see any significant pressure wave produced by a engine working on the Lenoir cycle?

PyroJoe
Good Question! "That would be a real quandering" For all intent and propose Rocket Man, confirmed my Answer/Question.
Thanks