Convert wounded GM 6.0 into a compressor?

[strantor]

If something like that were encountered with my compressor or your Wisconsin, there is I think a solution. I can't remember the name or how it works exactly, but I've seen it employed on exhaust systems to change the exhaust pitch. I'm probably about to botch the explanation but I'll try; hopefully someone will know what I'm talking about and provide better info....

The "system" consists of a tee, branching off into a dead-end (capped off) section of exhaust pipe of a specific length to achieve the desired effect. Sound/pressure waves stay off down that pipe, bounce off the dead end, come back and cancel out the waves headed out the exit. If there was a certain resonant frequency that shook your house or neighbors, perhaps this could be tuned (by specific length dead end pipe) to cancel out that specific frequency.

 

[strantor]

Google fodder: "exhaust helmholtz resonator"

 

[Warpspeed]

Strantor, yes heard of that.
Its called a Helmholtz resonator, and it can kill a drone at a particular frequency. But it requires some fairly critical cut and try tuning.

How much power do I get at 1200 rpm ? Not sure exactly, still putting it all together. It drives a 2Kw treadmill motor used as a dc generator to recharge a 100v lithium battery. The generator is rated for 11 amps but I hope to run it slightly higher than that with some serious forced air cooling through the generator. Need to do some testing to determine engine loading (vacuum) and generator output, also optimize engine rpm and generator rpm. Early days yet with all that. Still need to get a natural gas carburetor for it, and the electronic speed governor finished. The speed governor and tachometer work off the ac frequency coming out of the alternator, the governor actuates a model radio control servo which opens the engine throttle. Many marine diesels have tachometers and no ignition obviously, so you can buy marine tachometers that will run from the alternator or by counting flywheel teeth.

Haha, nobody makes tachometers that work from a single cylinder ignition. Anyhow, this Wisconsin is rated 12Hp at 3,600 rpm and max torque is somewhere around 2,00 rpm. So at 1,200 rpm should be slightly more than one third of 12Hp. Probably about 4.5Hp ? That only has to drive a 50A (12v) alternator and a 2Hp treadmill motor. With luck should work out to be just about right.
I can juggle the pulley ratios around a bit if I have to. It will be set up for dual A belts, but currently only have a single pulley on the dc generator.

The acoustics are interesting. If you drive a sub woofeer and amplifier with an audio oscillator, the frequency can be lowered to around 21Hz to 20Hz and you can hear it drone and see the speaker cone moving. At 19Hz or below the sound disappears very abruptly. The human ear cutoff is extremely sharp. You can see the speaker cone still moving at 19HZ , but its completely silent !!!
So I figured if I can run my little put put at 1,200 rpm, or just below, and kill all the higher frequency harmonics in an outrageously large absorption muffler, it should be completely silent. And it actually does work, its truly amazing.

Its all a bit obscure and rather odd as projects go.
But that is what makes it really interesting.
Had to put up some pictures as sometimes people on the internet do not believe some of the things I say I have done <grin>.

 

[Warpspeed]

That's really cool! That "silent sound" effect is weird. My neighbor across the street has a diesel truck that isn't loud, but something about its idle frequency and the spot/angle he parks it at, makes my bedroom reverberate/resonate like someone tuned a huge subwoofer to an obnoxious bass frequency and forgot about it. It's loud as **** in my room and I snap awake when I hear it, as it indicates I've overslept. Step outside and you can hardly hear it.

I had to think about that for a while Strantor, and I think I may have have experienced a similar thing myself.

While we cannot hear sub audio frequencies directly, the below 20Hz shaking might cause parts of your bedroom to rattle at their own self resonant frequency at multiples of 20Hz. So your windows might rattle, the walls shake and so on. Pretty disturbing, and when you go outside hear nothing. Kind of like how to really annoy the neighbors by stealth, hahaha. While that might actually happen, they will probably never be able to figure out it was me causing it.

 

[strantor]

I had to think about that for a while Strantor, and I think I may have have experienced a similar thing myself.

While we cannot hear sub audio frequencies directly, the below 20Hz shaking might cause parts of your bedroom to rattle at their own self resonant frequency at multiples of 20Hz. So your windows might rattle, the walls shake and so on. Pretty disturbing, and when you go outside hear nothing. Kind of like how to really annoy the neighbors by stealth, hahaha. While that might actually happen, they will probably never be able to figure out it was me causing it.

A 4 stroke V8 idling at 600-800rpm would create a sound wave of 40-53Hz. Inside the audible range, and the truck is audible outside, just not loud. So I don't think sub-20hz frequencies are the culprit, but I do concur with your theory about the exhaust being at resonant frequency of my doors, walls & windows, which rattle creating sounds at new frequencies.

 

[strantor]

Need to do some testing to determine engine loading (vacuum) and generator output, also optimize engine rpm and generator rpm. Early days yet with all that. Still need to get a natural gas carburetor for it, and the electronic speed governor finished. The speed governor and tachometer work off the ac frequency coming out of the alternator, the governor actuates a model radio control servo which opens the engine throttle. Many marine diesels have tachometers and no ignition obviously, so you can buy marine tachometers that will run from the alternator or by counting flywheel teeth.

Haha, nobody makes tachometers that work from a single cylinder ignition.

Sorry, this definitely not something I should still be thinking about 4 days later, but this little detail won't stop nagging me; I hope you'll excuse me dragging my own thread off topic.

Do I understand correctly that the alternator is there only as a speed reference to your governor? Or are you using its output for other things as well? I ask because alternators are pitifully inefficient and I assume that efficiency would be something at the top of the list of priorities for this. Could you not use the DC generator as a speed reference? Is your governor something off-the-shelf that is designed to read alternator ripple frequency? Could it accept a different type of frequency input? If you can't use the back-EMF of the DC generator as reference directly, it should be trivial to convert that to a frequency signal using a signal conditioning IC or an Arduino or something. Or even just mount an inductive sensor on the flywheel.

 

[KennyG]

This is all getting very interesting but complicated. I think it's close to the "try it or forget it stage". I really like the idea of running it as a IC 4 cylinder with a 4 cylinder compressor but I think that would work better with a carb engine, so you could easily build a custom intake to separately feed the banks.

As a point of reference, does anyone remember the spark plug/air chuck adapters. Back in the day, we carried one of these in all the tractors. If we got a flat tire, we would pull a spark plug, put in the air adapter and pump up the flat tire. I tried not to think about the gas vapor in the tire.

I also remember when someone bought a used 6 cylinder Chevy and brought it to my Dad because he thought it was rough at idle. My Dad quickly found one cylinder was not putting out power, then found the valves were adjusted shut. Adjusting the valves didn't fix it so he pulled the head and found the piston and rod missing (and the cylinder wall badly scored.) If I recall, the crankshaft journal was bare, but it still ran OK.

 

[strantor]

This is all getting very interesting but complicated. I think it's close to the "try it or forget it stage".

agreed. I've talked through this enough to believe it's worth moving forward, and it's been added to the project queue. I've got a CNC mill refurb and PTO generator to finish first.

 

[Warpspeed]

Sorry, this definitely not something I should still be thinking about 4 days later, but this little detail won't stop nagging me; I hope you'll excuse me dragging my own thread off topic.

Do I understand correctly that the alternator is there only as a speed reference to your governor? Or are you using its output for other things as well? I ask because alternators are pitifully inefficient and I assume that efficiency would be something at the top of the list of priorities for this. Could you not use the DC generator as a speed reference? Is your governor something off-the-shelf that is designed to read alternator ripple frequency? Could it accept a different type of frequency input? If you can't use the back-EMF of the DC generator as reference directly, it should be trivial to convert that to a frequency signal using a signal conditioning IC or an Arduino or something. Or even just mount an inductive sensor on the flywheel.

What I am trying to do here is charge a 100v lithium iron battery from natural gas, and do it as silently as possible.
Eventually this will all happen automatically if the battery voltage falls below some critical level. I can just set this up in my garage and forget about it, no refueling required.

Now very small "silent" gasoline generators have been around for quite some time and would be a simple low cost solution, except for one thing. No electric start on the smaller ones, and no easy way to add electric start for fully automatic operation. The larger ones with electric start are incredibly noisy, and definitely not what I want.

So I decided to resurrect a big old 12Hp Wisconsin, toss out the magneto and rope start, and fit a 12v lead acid starting battery, a 12v car starter motor, a Bosch electronic ignition, and of course a smallish 12v alternator. All that is just to start and run the engine. Cheap, simple, accessible, and very easy to fix. Now to charge the battery there is a separate 100v dc brush type generator. At the moment this is just a rather small treadmill motor, and that may do the job. Or I may fit something a bit larger later on if there turns out to be enough grunt from the Wisconsin.

Now there needs to be a speed governor of some kind, and as I am a retired electronic engineer, that part of it is quite straightforward. The original ignition points only open and close at 10Hz when the engine is doing 1,200 rpm which is rather slow for a nice tight speed control loop. As the alternator is already providing a frequency reference for the marine tachometer (in the usual marine way) I decided to use the same alternator output frequency for my engine speed governor.

The way this works, there is an oscillator on the governor circuit board that is controlled by a slider potentiometer, which I use to set the desired target engine running speed. A thousand engine rpm corresponding to roughly 3.2Khz. That is pulley ratio dependent, but it measures fairly close to that.

The alternator output frequency is compared to the set speed reference oscillator in a phase/frequency comparator chip, and that controls the position of a model control servo that opens and closes the throttle. I still need to buy a natural gas carburetor for this, the gasoline carburetor that is on it now will not be used.
I have only just received the blank circuit boards back from China last Sunday, and have not done anything with that yet. Its all pretty simple and straightforward electronically, and I don't anticipate any problems.

The automatic start/stop and voltage regulation will be a completely separate part of this project that I have not really thought very much about at this stage. That will almost certainly use a microcontroller of some type, but I just want to get all the mechanical part going first before looking into software.

 

[mapper]

Don't know anybody here has ever been around a compressor built from a V8 engine. I worked for a while at a construction site building modular pumping stations for the Alaskan pipeline. They had one serving the site, it was the loudest most obnoxious thing ever. It would rev all out for a few seconds then drop back to an idle - about once a minute! Sounded like a hot rodder blipping the throttle incessantly. Unless your looking for a huge volume of air this is not for you, especially if you want quite operation.