http://aircaraccess.com/resonance.htm
Part 1
US Patent 2030759 was granted to Bob Neal after 2 or 3 rejections because the inventor took a working model to Washington Town and proved the damn thing worked. So let's talk about why it worked.
When the late Bob Neal's friend, Mr McDonald, heard about my research he drove to my town to meet me and then started sending me money to try and prove Neal’s device, which he said was a way of building up air pressure in a valve inside the tank so the compressor’s job would be only to keep the air moving instead of resisting the whole tank pressure. I worked hard and learned a lot about how not to do things, but didn’t have enough time and money to complete my education, so Mr McDonald’s whole contribution pretty much went to a partial education for me and we got nowhere of substance with proving Neal’s machine.
Once we had found Neal’s patent, one of the first things I did was to show it to my landlord, a retired mechanical engineer named Irwin. Irwin immediately said, “This will work, it is like a pulsejet. It has to be tuned very precisely or it won’t do anything.” He drew me a diagram of how waves or disturbances of odd quarter-wavelengths reflect and compound in a cylinder with one open end and one closed end, and likened the tailpipe of Neal’s equalizer to such a resonator. He explained how resonance could build up a very intense pressure and rarefaction wave in a resonator. He also understood why Neal used several compressor cylinders to one engine cylinder, instead of what’s done today with one or two cylinders laboring and providing a more steady flow.
Based on the word “pulsejet” I dove in and spent my milk money on photocopies at big libraries in Berkeley and San Francisco for a couple years, creating what is now the acoustic power section of the Pneumatic Options Research Library. I also strayed far afield of Irwin’s suggestion and got distracted by the large variety of acoustic power devices that seem to indicate that pressurizing fluids with waves is not only possible but done every day.
The resonance explanation for Neal’s device was always the best, but I didn’t really understand it, so therefore I couldn’t quite believe in it, and because of this and other reasons, I didn’t test it out properly in the workshop. Eventually I posted an in-tank injector on a web page I called “Neal Tank” and from then on everybody has been effectively distracted from really looking at Bob Neal’s patent, which I now believe is virtually complete as is.
For about the past three years, a machinist in the US has been working to get back to basics and build what Neal actually patented: a compression unit with seven compressor cylinders to one engine cylinder. In various experiments using a variety of equipment, none of which was ideal, he was able to prove that Neal’s concept is in fact real, and that it is a tuned resonant device. The machinist’s device was not built well enough but cost him a lot of time and energy, and he has now turned to trying to come up with his own simpler invention, since he is now well convinced that the principle is sound, in both senses of the word. I have decided to try and put his results out there, without revealing anything about who he is or what he is working on now. His statement to me is that he won’t build another 7 cylinder compressor because he’s burned out on dealing with the cost of fixing it when something goes wrong.
What he didn’t realize when he designed the machine is that it has to be very stout so that it can function as a typical brute force air squeezing machine until its rpm’s match the resonant frequency of its delivery pipe. So he broke underbuilt piston rods trying to get past the hard work of making 100 psi the old fashioned way, but several times he was able to get the machine into the power band or sweet spot where resonance kicked in and made a huge difference in how the compressing of air actually got done.
Neal’s patent states that the compressor only has to resist 15 psi so I’d never thought through it well enough to realize that the pipe has to have serious pressure in it, say 100 psi, before resonance is going to take over and get the air into a 200 psi tank. Since it’s a single-stage compressor, no more than 100-120 should be expected from the compressor, ever. But resonance is like water hammer, in a house where the plumber got unlucky with pipe lengths and a fast-flush toilet sets off resonance in a pipe length. It goes on with its thumping and jumping for quite a while with nothing but a single driving disturbance having set it off, and sounds like the pipe is going to break out of the wall. I don’t think that would happen if the water in the pipes weren’t under some pressure before the sudden disturbance took place in the line.
If you look at the patent, part number 49 is a resonator. It appears to have two closed ends with all the individual compressor discharge pipes entering it at evenly spaced intervals and the exit pipe to the tank (probably purposely) hidden from view. I am indebted to my machinist friend for helping me to understand the material he found on my own site. Until I was told that there had to be about 100 psi in the pipe already for there to be any hope of resonance generating pulses of 200 psi, I didn’t get it.
Part 2
Bob Neal’s compression unit had to be strong enough to function as a conventional single-stage compressor. It had cooling water, a water pump, and a fan. It was not a screwed-together gizmo, it was a custom engine block. It took Neal a long time to get it right, and once he got it right he was able to reproduce his results in a small working model which he took to the patent office and demonstrated: a working engine putting air into a 200 psi tank without having to resist the 200 psi to get it in. A new, cheap way to compress air.
The delivery pipe or resonator, part no. 49 in the patent, had to be the right length so that the frequency of the wavelength generated by the pulsations from the compressor would trigger resonance in the pipe. If not then the compressor would just stall, because the tank was pre-charged with 200 psi, and a single-stage compressor cannot put air into a 200 psi tank by any conventional means.
Resonance in compressor discharge piping is common, and the usual idea is to get rid of it since it is a sound wave, and causes vibration in equipment. So what I’m talking about here is not that exotic. Creating resonance in compressor discharge pipes is done every day, by accident.
Everything including a column of air has a frequency at which it wants to vibrate, its natural resonant frequency. Pulsing the air into a discharge pipe at this frequency or one of its harmonics can cause pressure to build up on account of wave reflection. The forward wave, headed downstream, is driven by incoming pulses or disturbances from the compressor pistons. It bounces off a closed end in the pipe, a sudden turn, a restriction, that sort of thing, and while air continues to flow through the pipe in one net direction, the disturbance or wave reflects back upstream, traveling against the air flow at the speed of sound. The forward and backward waves tend to cancel each other out or disrupt each other unless the discharge pipe is the right length to function as a tuned resonator, and then all hell breaks loose.
The amplitude of a disturbance in a pipe whose air would be 100 psi if it weren’t moving varies because of the wave or disturbance. The peak of the wave is over 100 psi and to make up for it, the pressure wave is followed by a rarefaction wave of pressure less than 100 psi. If the waves fit perfectly into the pipe because of the pipe being a tuned length with the pulses entering it, the forward and backward waves will match each other and add to each others’ amplitude. The amplitude is the distance above and below static pressure (100 psi) that is reached. With this process going on, a standing wave is the result of the forward and reverse wave adding to each others’ pressure changes.
The seven pairs of compressor discharge pipes in Neal’s machine entered pipe no. 49 at pressure antinodes, that is the spot in a standing wave where pressure changes are the most intense. At the trough or lowest point of each pressure wave, the air from the compressor could easily enter the pipe at around zero gauge pressure or a little more. Then inside the tank at the entrance to the equalizer, the first of a pair of check valves is positioned also at a pressure antinode where the seven successive pulses per crankshaft cycle in turn feed a high pressure wave into the equalizer, the space between the check valves. The pressure builds up in the equalizer with each successive pulse and after seven pulses, pressure in the equalizer is almost 200 psi, and something happens inside the tank. A blast of air leaves out the far end of the tank going to the engine. This is also in phase with the compressor cylinders, so the compressor is essentially generating the 7th harmonic of the fundamental wave generated inside the tank by the pulses of 200 psi air leaving the tank for the engine.
The air in the tank is also vibrating, and the tailpipe of the equalizer is another resonator. The sudden cyclical lowering of pressure in the tank generates another intense standing wave in the tank which assists the built-up air in the equalizer into the tank, in a sudden blast. Everything has to be tuned and position correctly and that’s why it took Bob Neal a long time to figure this out. He probably got the idea when he got his first flush toilet and asked his plumber why the pipe was drumming on his walls. He probably went to a local university professor to flesh out a series of experiments he could perform to test his idea.
Part 3
My machinist friend built a seven-cylinder compressor and ran it with a drill motor. He chose a pipe length for his discharge resonator based on wavelength calculators available online. He did not put his double check valve equalizer in a tank, and that was a stroke of intuition that would have increased my knowledge and saved my backer a lot of money if I’d tried doing it that way instead of first building expensive flanged tanks sealed by big o-rings. He ran it till it stalled, broke piston rods, and eventually burned up the drill motor, but not before getting results that made him a believer.
The compressor was balky and hard to run because it was homemade and working against full resistance of building pressure. Actually I believe the second check valve was replaced by a solid cap because the pipe was used as the tank. I’ll have to check my notes. The compressor got hot, like any compressor would. It stalled and stumbled and complained.
Finally after many tries and repairs, the machinist got the machine up to the rpm at which resonance kicked in. At this point, the functioning of the compressor smoothed out. It ran very cool. Pressure built up in the equalizer ABOVE the pressure being made upstream in the compressor. The end of the pipe where the equalizer was got VERY HOT.
He proved that we can compress air in the pipe, in the tank, instead of the compressor. There IS another way to compress air.
That makes all the frivoulous fluff about “when will MDI make me an air car” irrelevant. In fact if I believed in conspiracies, I’d say that maybe Negre was hired to pretend he was going to put an air car in every driveway so no one else would bother. While we sit on our duffs watching cable tv shows and You Tubes about new technology, new technology is not out in our three-car garages building itself.
I am working on a new page about this concept if anyone cares to see it. It has animation created by me and borrowed from other websites trying to show how resonance in piping works.
http://aircaraccess.com/resonance.htm
