tommy -- Glad you like the Penberthy Model LL. Don't know about you, but I'm not much of a fabricator, so finding a reasonably priced, professionally engineered unit that I can use for something is always a real plus.
If you do get an LL, I'm curious to know how you are thinking you would set up your experiments -- equipment, processes, methods? Whatever you feel like sharing.
with the proper relationship between the piston and rod in a double acting cylinder it is possible for a compressor cylinder to output positive torque at the crankshaft while compressing air at the same time. By itself, this is not enough to achieve even a self runner, but I find it interesting.
This stuff can get real complicated, real fast! Even something on the surface appearing well-known like crank arms and pistons, can quickly reveal all sorts of hidden surprises. It takes a strong will to keep pushing forward, but that is what is needed. There is a reason why air cars are not on every street corner, this sort of progress is an uphill fight. One thing I have figured out with the air subject, is that it is all about energy efficiency. I mean to say accounting for each and every drop of that precious energy within the machine. Not simply one process that creates energy, but instead many smaller contributors of efficiency throughout the entire process of the machine. I am confident that is the point of view for this type of machine design. This is a completely different approach compared to designing an internal combustion engine, or an electric engine, or a wind generator for example. There are hundreds of examples of cranks and pistons, but one that comes to mind is Kiser's patent 248218 where he matches the power flow from steam pistons to air compressor pistons with various arrangements of levers. Kiser was an accomplished air car builder, but was secretive about the details because early in his work, he was ripped-off with a train air brake design.
This stuff can get real complicated, real fast! Even something on the surface appearing well-known like crank arms and pistons, can quickly reveal all sorts of hidden surprises. It takes a strong will to keep pushing forward, but that is what is needed. There is a reason why air cars are not on every street corner, this sort of progress is an uphill fight. One thing I have figured out with the air subject, is that it is all about energy efficiency. I mean to say accounting for each and every drop of that precious energy within the machine. Not simply one process that creates energy, but instead many smaller contributors of efficiency throughout the entire process of the machine. I am confident that is the point of view for this type of machine design. This is a completely different approach compared to designing an internal combustion engine, or an electric engine, or a wind generator for example.
I couldn't agree more.
We believe that Neal's engine was real and worked and the patent is an accurate enough representation of it or we wouldn't be discussing it. Given that much I have to ask myself why did he have so many compressor pistons? Why add the friction of all those moving parts and extra rotating mass? At least part of his solution has to lie in the physical aspects of the compressor. That's only logical. If there was no gain to be found there he would have been better off just using an injector and spared himself the trouble and expense of the compressor.
Maybe there should be a thread focusing on the construction of the compressor. Maybe. So far no one has said a word about the charts that were posted, but it's early yet I guess. I found the compressor cylinder pressures chart to be somewhat illuminating since it is the same thing, more or less, as the old time indicator cards. Just looking at the difference between an old compressor card and that chart gives me an idea where to look next.
Post by Uncle Buddy on Sept 3, 2018 8:50:00 GMT -8
Mac, it seems like the many pistons are needed because this is like a roots blower, it puts out low pressure, but unlike a blower it can't run at thousands of rpm, so size makes up for its low speed to get the needed volume. But try to put all that volume in one giant cylinder and you have other problems. So the load is balanced in small bites around the crankshaft. Also the many pulsations per rev would help instigate the needed sound wave to build pressure.
Why Neal Jr used certain terminology, he would have gotten the terms from his dad who was a good ole boy raised on a Texas cotton plantation whose occupation was making orthopedic shoes by hand. Who knows where he got his terms? Inventors invent terms too. Neal Jr by the way was a saloon owner, not a mechanic as far as I know, although he seemed conversant with mechanical topics.
Sorry for not responding sooner. Why so many cylinders with Neal? The cylinders are "pullers" because they pull in outside air. They grab a fixed amount of air, could call that a "metered dose" of air. Neal writes the pistons push against only 15 psi, that is one atmosphere, which is going from intake pulled in at 14.7 psia and compressing to double that. Using adiabatic compression formula, (Simons), pv^1.4, gives a doubling of pressure is when volume is now down to 0.61 of original volume in that cylinder. If it was isothermal, the volume would be exactly 0.5, but since it is adiabatic the air heats up, and that gets the doubling of pressure sooner, when the volume has dropped to only 0.61 of original volume.
When this pressure is reached, the checkvalve leading into main pipe will begin to open. This valve will open because the resonating wave contained within the main pipe has low pressure excursions reaching down to the low pressure level of 2 atm absolute. That low wave pressure will allow the intake valve to open in spurts, but the cylinder air wants out, so the cylinder air will also be trying to push that valve open steady. This all occurs only until the cylinder pressure has fallen, that is why you could call the cylinder air a metered dose. How long will it take that cylinder air to bleed down, and for the valve to close? Not long because once the cylinder air pressure has fallen below 2 atm, the intake checkvalve will no longer be opening.
Of course the crankshaft is continuing to rotate, so the cylinder is being steadily compressed. This cylinder compression is happening at a much slower speed, or rate, than is the resonating wave in the main pipe. End result is that the resonating wave lower pressure excursions will continue to pop open that intake valve, always bleeding off the compressed air in that cylinder. The wave low pressure excursions are happening roughly every 6 ms. We don't know for sure, but I have assumed the crankshaft is moving at a synchronous rate to the wave, certainly the crankshaft would not turn any faster than this, which is 240 rpm. This comes from 240/60 =4, and 4 rotations per second will supply the crank with 4*42 = 168 Hz wave.
At 240 rpm, a given compressor cylinder complete compression stroke will happen in 240/60=4 revs per second, 1/2 rev is a compression stroke which = 1/8 = 0.125 second = 125 ms. So, I am saying the LONGEST possible time would be 125 ms for a compression stroke of a given cylinder.
For simple explanation at this time, we could say the compressor piston moves the same distance throughout the stroke, just to simplify right now. Now, we know that the intake valve will not first open until cylinder volume is down to 0.61 volume. This then leaves only 125*0.61 = 76 ms time left to drain the compressor cylinder into the main pipe.
Do you still have the list of the cylinder compressor order? Take a look at that list, the order is separated by crankshaft degrees, 8.57 each, including some blank spaces where there is 17.14 degrees separation, the total being 42 steps. If the crank is turning at 240 rpm, then each 8.57 degrees rotation step occurs at a 6 ms rate, that is 0.006 seconds. If we have 76 ms to drain a cylinder, then 76/6= 12 or 13 steps of 8.567 degrees on the list of cylinder firing order. Remember some of the steps are 17.15 degrees.
This is important because it shows the overlap on the firing order listing for a given cylinder, per the above estimate, the overlap is 12 or 13 steps, or could say the overlap is slightly less than 110 degrees of crankshaft rotation.
Now, go back to Neal's diagrams and notice the top branch is forked, and the bottom branch is forked. This fork is assigned as R or L in the firing order listing. Remember that a wave filter needs closed branches, however a wave filter needs only maybe 3 or 4 good branches, that would be 3-4 good branches at the top and also at the bottom since top and bottom are filtering different frequencies.
If one of the forks of a branch has a valve open, then that fork is not perfoming as needed, but Neal has built seven decks of branches, so if there are 3 or 4 good closed-end branches at any point of time, then it should all work successfully. Now, there is this period of time, 12-13 steps when a given branch fork will be opening and that fork will not be helping with the filter action.
So, what needs to be done is to study the firing order list, which shows when each cylinder intake valve opens, then add the amount of steps when that specific valve is open. Do this for all the 28 intake valves. Now the question is: Can we make a new list of compressor cylinder firing order which shows which branches are good? Good means both forks of a given branch have their ends closed? That is the question.
This is needed because (from the wave filter's point of view), what is needed is 3 or 4 good branches at top and at bottom. I think we have them, but I have not confirmed this by taking the time to work through it. What is needed is a new listing showing the good branches, in order, with reference to the crank rotation step of 8.57 degrees. When the branch becomes good, and when that branch ceases to be good, during the rotation of the crankshaft.
Back to the original question, why so many compressor cylinders? Because the cylinder needs to have only a certain metered dose, so that it will peter-out and have it's pressure drained away. It also requires some time period for the pressure to build up in the first place. This is because that branch supplying the air does not assist with the wave filter, it screws-up the wave filter action, when it's inkake valve is open. We want that screwing-up action to be evenly distributed along the branches, not to be concentrated in one location of the seven decks.
Also, I do not think the compressor piston rings are very tight. The crank arm has a slide arrangement that IMO would not survive high rpm speeds. These cylinders are more like a blower, high air movement but only minimal pressure increase.
"The cylinders are "pullers" because they pull in outside air."
That is how I initially interpreted the statement as well. But when discussing the later "Model 39," Mr. Neal describes "where the two pullers were" and how they had a little larger throw than those in the earlier "V" style engine. That seems to suggest he was referring to the two power cylinders rather than the compression cylinders.
I would add, though, it may simply be that Mr. Neal generally referred of all the pistons in his father's engines as "pullers", as most of them were used to pull in air, without making any distinction as to their precise function.
Also, more to add, about the branch forks, it may be that if only one fork is open while other fork is closed, then that branch does not assist with the filter actions, but at least will not degrade the filter action, just out of the picture so to speak, with the two end's effects cancelling each other. However, if both fork ends were open, then that would degrade the filter performance. This leads to a need to create a list of cylinders firing order showing the times when both ends of a fork are open, this would be helpful to see in a list. I think these firing lists were things that Neal would have created to get this machine figured out.
I can't offer an opinion about how the equalizer works, but from the work I've been doing I think he probably heard the term 'pullers' from his dad talking about the compressor pistons and just used it for all the pistons. Technically correct, the engine pistons are both pullers and pushers while the compressor pistons are primarily pullers. The term describing the direction of force exerted by the piston through the compressor connecting rods to the crank.
The quantity of pistons not only spreads the load into smaller bites, the pistons assist each other with some powering the crank while others draw power from the crank to do the compression work. The result is a lower torque drain from the engine pistons.
I found this description of Neal's firing order, written a few years ago. It would be extremely helpful if someone would check this and independently confirm the firing order, only thing needed is to look at Neal's patent drawing of the compressor crank arms and the crankshaft. Firing Order.doc (34.5 KB)
You are a good bit ahead of me in your analysis but I have been pondering the possible crankshaft pin locations (throws) just as you have pointed out. The crankshaft drawing leaves a lot of possibilities. I'll try to make a spreadsheet to see what can be done for the best firing order.
Neal's patent statement about the pistons working against 15 psi also leaves differing possibilities. If you believe as I do right now that the bottom of the compressor pistons are fed high(er) pressure air to be re-compressed then that changes the mass of the discharge air and when the valves open. Also the check valve spring pressures affect the air discharge timing.
It's a rats nest of variables.
On the other hand, have you considered that according to his son, he intended to put this motor in his car and use the stock drive train? Doesn't that do away with the notion of a constant low rpm? Could he have simply wanted the discharge to begin at the front and increase in mass and velocity as it moved toward the equalizer?
Ha, did you ever stomp on the end of a ketchup pack when you were a kid?
Could he have simply wanted the discharge to begin at the front and increase in mass and velocity as it moved toward the equalizer?Ha, did you ever stomp on the end of a ketchup pack when you were a kid?
Yes, agree with your thought. Then, when that is carried further we see that the ketchup pack needs to be stomped on multiple times, not just one shot. Since we have air, there will be reflections, repeatable areas of higher and lower pressure. This then leads to when is it best to do the stomp, to conserve energy. This is what leads to the talk of acoustic resonance, waves, etc. The whole line of thought begins with exactly what you have said.