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 From : tom perkins Date : 2003-07-10 19:09:09 Subject : Re:Ugly idea for design principle (long one, sorry) Niclas wrote : >I have into the subject before, so some of this may be old stuff. > >I have a few ideas based on the following assumptions: >1) The more fresh charge that can be inhaled each cycle, the better for thrust >2) The higher the frequency of operation, the better for thrust >3) The higher compression during combustion, the better for thrust and specific fuel consumption. > > >So what do I suggest to solve all this? >Point 1: >Well, to solve that one is a bigger combustion chamber needed but that also requires bigger intake, or does it really? >Point 2: >The faster you can filll the combustion chamber and the higherpressure that is achieved during combustion, the faster is those parts of the cycle and operation frequency is raised. >Point 3: >The smaller the holes out from the combustion chamber is, the bigger will the pressure during combustion reach > >So what is that I really propose? >My suggestion is to add more intakes at several places around the combustion chamber so the distance the fresh charge need to travel to fill the chamber is less and thus shortens that time. The total intake area is kept the same OR even lower than for a normal pjet. > >That also allows for a bigger chamber to be filled in the same time OR less than for anormal pjet. > >So we may both increase operation frequency and the combustion chamber size but keep intake hole area down. > >That increases the combustion chamber volume to entry/exit areas proportion, which means more fresh charge to be combusted while less slips out and thus raising the pressure achieved which improve sthe burn rate, thrust and specific fuel consumption. > >But if exhaust is kept at the same size (or even smaller) it will take longer time for exhaust gases to leave combustion chamber and that is the part where we might loose a bit on frequency of operation. > >So in total operation frequency is kept about the same but thrust and/or specific fuel consumption is gained. > >Here you have a weird rough drawing of how this principle engine could be designed: >http://w1.910.telia.com/~u91018394/pulsejet_hedgehog_design_idea.zip >NOTE: The intakes/exhausts shouldn't be in line as drawn (was easier to draw it this way though). And also note that I have no idea of proportions between differenet parts. > >In the bottom of the drawing I have added something to show that the exhaust gases going out from a intake can be lead back into the exhaust via a opening to free air so augmentation is achieved. > >So, what do you guys think? It sure is ugly but could it work as proposed? > >After reading the SAE paper recently discussed on the valved pjet forum I have realised that the intake I propose is of resistive aerodynamic type and not of reactive aerodynamic type. Maybe the two type is possible to combine by having tuned pie lengths on the parts pointing forwardly (right in the drawing)? >That would prevent exausts to leave forwardly and only go backwards where it performs good work. > >From the same paper I also realised that I abrupt wall in the front is good for the reflecting back the rarefaction wave that sucks in fresh air in the exhaust tube. > >I also realise that it is that rarefaction wave that makes augmentation worthful. The augmentor volume is filled from the front (where the pjet and augmentor meets and air is let in) and backwards so no power is lossed but a volume of "high" density air is filled in a tube and then accelerated by next cycle. We get the mass we want to propel and at the same time doesn't suck to much up backwards into the exhaust (the suction costs energy and also works less good when travelling compared to static mode). > >Earlier (before it have reached the front of the engine) the same rarefaction wave, which is the result from the compression wave (caused by combustion) travelling backwards and reflected at the opening, travels frontwards and causes the sucking in of new fuel air charge. But when travelling frontwards, its magnitude is lost if there are openings, such as the one I have proposed in the bottom of my drawing, that draws in air into exhaust tube. That must be bad for the size of fresh charge that can be drawn in. > >So the poropsol at the bottom of my drawing might be a bad thing. So what do you think? /Niclas What do I think; a great deal of thought went into this and it wasn't wasted. When I have more to say, I will. Thanks, TDP, ml, msl, & pfpp

 Ugly idea for design principle (long one, sorry) (2003-07-10 18:32:12) Re:Ugly idea for design principle (long one, sorry) ( 2003-07-10 19:09:09)