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Propane and Natural Gas Fuel Delivery and Tuning Discussion about the care and feeding of Propane and Natural Gas Engines.

Propane and Natural Gas Fuel Delivery and Tuning

Natural Gas Engines in Cold Weather


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  #71  
Old 11-28-2018, 02:40:33 PM
cjjmw cjjmw is offline
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by cornbinder89 View Post
That will work. You'll need a lockoff valve designed for low pressure (high volume) gas service.
I have to admit I am not a fan of using diodes to isolate critical circuits that would cause serious harm if the diode shorted. I know that with the proper selection of the diode the risk is minimal. I have just been around a few failures that put me off it.
A double pole start button would be a way around it, or another relay to provide a positive block in the starter circuit .
I've seen some really high cap NG valves that used a small hyd pump to open against a stiff spring and a large dump valve to slam the valve shut. Opened slow and would shut in a hurry if need be. Used Skydrol for operating fluid. Don't think you are running anything that big, are you? I don't think you said how big an engine you are going to run off this.
I could use a double pole switch for the start, not a big deal.

The engine size is small, 18HP. These are also temporary units connected via a hose with a quick disconnect.
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  #72  
Old 11-28-2018, 10:47:10 PM
cornbinder89 cornbinder89 is offline
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by cjjmw View Post
I could use a double pole switch for the start, not a big deal.

The engine size is small, 18HP. These are also temporary units connected via a hose with a quick disconnect.
Your way will work also, I was just stating my preference. When working with gases, it is best to try and think out every way a failure can happen and what the unintended results would be.
Everything can fail, a double pole switch can short internally, but is less likely to do so than a diode that is subject to inductive load voltage spikes.
I once had a relay with a short between the control coil and one of the load terminals, it cause all kinds of problems that weren't obvious because of how the relay was being used.
Just look for the likely failures and try and build in failsafes.
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  #73  
Old 12-02-2018, 01:29:18 AM
dkamp dkamp is offline
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Default Re: Natural Gas Engines in Cold Weather

Actually, if you've got a hydraulically opened, spring closed lockoff, you can just tap off the engine's oil gallery...
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  #74  
Old 12-02-2018, 12:00:55 PM
cjjmw cjjmw is offline
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by dkamp View Post
Actually, if you've got a hydraulically opened, spring closed lockoff, you can just tap off the engine's oil gallery...
I haven't seen one, but it sure doesn't sound like a cheap item.

---------- Post added at 11:00:55 AM ---------- Previous post was at 10:59:52 AM ----------

Also, how would you start it unless it opens at a very low pressure?
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  #75  
Old 12-02-2018, 06:12:38 PM
cornbinder89 cornbinder89 is offline
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Default Re: Natural Gas Engines in Cold Weather

Yeah, many reasons not to go that route. The one I worked on was for a large NG fired boiler. They wanted a slow open and fast shut for that application.
An oil pressure lock-off would take a fair bit of cranking to open the gas valve. Electric over vacuum or pure vacuum would be quicker to act.
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  #76  
Old 12-05-2018, 11:06:26 AM
dkamp dkamp is offline
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by cjjmw View Post
Also, how would you start it unless it opens at a very low pressure?
It would be very low pressure... 2psi or so, and it would take a few turns of the crank... but it takes at least one full rotation of any cylinder to have fuel, and in order to present vacuum, it requires those turns anyway. Added bonus is that it'd shut down if you ever had an oil pressure loss... with no additional critical circuitry required.

Vacuum and electric are more common.
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  #77  
Old 12-05-2018, 11:27:44 AM
cjjmw cjjmw is offline
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by dkamp View Post
It would be very low pressure... 2psi or so, and it would take a few turns of the crank... but it takes at least one full rotation of any cylinder to have fuel, and in order to present vacuum, it requires those turns anyway. Added bonus is that it'd shut down if you ever had an oil pressure loss... with no additional critical circuitry required.

Vacuum and electric are more common.
Can you recommend a 3/4" or 1" gas valve equipped as such?
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  #78  
Old 12-06-2018, 12:17:27 AM
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Default Re: Natural Gas Engines in Cold Weather

I have this one mounted in the main line that feeds all three of my generators:

https://www.propanecarbs.com/impco/f...y-shutoff.html

It's on the low-pressure side of the gas line... it is NOT intended for the high-pressure side of your fuel supply... so it goes downstream of your 11" w.c. regulator, but BEFORE your fuel controller/zero governor/negative pressure regulator.

Even though my system is all propane, it is same plumbing plan as your NG, in that fuel gas comes to the machine from a final-stage 11" w.c. regulator, and this type of lockoff goes right after that regulator.

I see a 1/2" NPT version of similar, and a 90-degree turn type also, but all the rest of the lockoffs, including the vacuum lockoffs I see are for high-pressure side operation- they are not suitable for your NG system.

Century shows this one:
https://centuryfuelproducts.com/part...solenoid-valve

I'm actually surprised that all the vacuum lockoffs are high-pressure only... that is curious.

It was either Century or Zenith on the hydraulically-piloted lockoff operated by engine oil pressure... was a Government contract... part of "LongLines"... cold-war microwave link... really cool stuff.
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  #79  
Old 12-06-2018, 09:07:00 AM
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Default Re: Natural Gas Engines in Cold Weather

Where's it best to vent the demand regulator?

All of the conversion kits I see just have it exposed but it seems like it would actually do better if it was vented into the air filter housing of the engine. No?

That way it sees the same pressure the carburetor inlet sees?
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  #80  
Old 12-07-2018, 01:47:02 AM
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Default Re: Natural Gas Engines in Cold Weather

No, it needs to be vented to atmosphere external to the engine... totally ambient...

And just in case someone's wondering... no fuel gas vents through the vent- the vent's purpose is to allow the demand regulator's diaphragm to modulate properly. If it was sealed in a cavity, the pressure inside the cavity would prevent the diaphragm from moving in response to demand vacuum... on a cold day, pressure in the cavity would 'lock off' the fuel supply, and on a warm day, pressure would be so low, that it'd flow fuel with no engine operation.

If you look at the Garretson KN, you'll see that one of the features is a 'primer' button. This is generally used to purge air from a propane line when an exchangeable bottle is used... everytime you remove the fuel hose, propane in the hose wanders out, and air wanders in... when you reattach the tank, air in that hose has to get pulled out... and it takes lots of cranking to get it started up. Press the PRIME button for a little bit, and all the air will be purged out. Well, if you look closer, you'll see that the vent is not far from that purge button... and the purge button simply presses on the diaphragm.

The fuel controller works on the principle that air pressure inside the VENTURI of the carb (the part where it's narrow... where a liquid fuel's main jet would normally be found) is LOWER than ambient pressure.

Realize that a carbeurator works because the pressure drop inside the venturi LIFTS fuel up from the carbeurator bowl, because ATMOSPHERIC pressure is in the bowl, pushing DOWN on the fuel level. If you were to plug off the carbeurator's vent... or connect it to some other partial-vacuum location, then the fuel draw from the bowl would be incorrect, and worse yet, unstable... so your fuel mix would be likewise errant.

The fuel controller (zero governor, negative pressure regulator) takes place of the liquid fuel's float bowl level... and the needle and seat... in one simple component.

And as an aside note... the 'power valve'... the large adjustable valve between the fuel controller and the venturi feedpoint... has NO control of the mixture at ANY point other than full throttle. It simply limits fuel at full throttle. At any other speed, it's the fuel controller's gain adjustment, which is essentially linear, based on the difference between ambient atmospheric pressure, and the demand pressure signal it senses in the venturi.
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