Can I run CNG thru' a LPG vapouriser?

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CNG
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Can I run CNG thru' a LPG vapouriser?

#1 Post by CNG » Mon Jun 07, 2021 1:05 am

Yes, I realise that'd be very daft.. (Let us have five minutes silence for those that tried this at home...) what I mean is, if we use a high-pressure first stage to knock the 200Bar down to 6-7bar, is there any reason why we can't feed methane at 6-7Bar into any LPG vapouriser?

Reason I ask: I'm messing around with my godforsaken Necam system again. Thing is the dizzy on these things wants pressure at 0.8 Bar which is both babies-breath pressure and unusual. The low-pressure reducer is getting tired, and these are pig to rebuild, thus it's not only that the rebuild kit is hard to get, it's that I have problems with the strip-down. The low-pressure section never comes apart without near destroying the body.
Necam.jpg
Necam.jpg (16.24 KiB) Viewed 413 times
Piccy - [Best explain what you're looking at, left: dizzy, middle: high-pressure reducer, which feeds - right: low-pressure reducer]

It occurs to me, why not take the high pressure stage and feed that into a low pressure LPG vaporiser?

I've spend a good hour looking, it seems standard sequnetial reducer output at 2-7Bar. Carburetor reducers are 1Bar ish, but are vacuum dependent-feed. Is there a constant feed, low pressure reducer/ vapouriser on the market that gets down to, or allows adjsutment to 0.7Bar? I don't think there's any particular requirement for it to be CNG, I would imagine once it's knocked-down to LPG pressures, we can put methane thru' any LPG vapouriser... first of all, am I right about that, and do LPG vapourisers go down to 0.8 Bar?

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Re: Can I run CNG thru' a LPG vapouriser?

#2 Post by Gilbertd » Mon Jun 07, 2021 11:14 am

0.8 bar with respect to what? If absolute, that's a partial vacuum or if wrt atmospheric, it's 1.8 bar. The CNG equivalent to the OMVL R90E is the R91E which looks identical so I suspect the only difference is on the first, high pressure, stage.
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Re: Can I run CNG thru' a LPG vapouriser?

#3 Post by LPGC » Mon Jun 07, 2021 11:36 am

Only some LPG reducers will go down to 0.7 or 0.8 bar, I'd be looking at e.g Lovato and HL Propan MJcompact reducers.

But I'm not sure how well they would work if fed with vapour instead of being fed with liquid, would usually expect peak output flow ability to be very much reduced as is the case when LPg reducers are fed with vapour instead of fed with liquid. The inlet valve on LPG reducers only has to be narrow diameter like a jet, such narrow point of entry will be more restrictive for low density vapour than high density liquid... 1 litre of liquid LPG turns into 270 litres of LPG vapour at atmospheric pressure so around 135 litres of vapour at 1 bar.

Looking at your pic (and as you've said) the primary pressure reducer on your CNG setup is separate from the secondary unit. Although you've mentioned the difficulties involved with stripping the secondary it may be a good idea to strip a CNG version and LPG version to see if there are any differences particularly with the gas inlet control valve/jet. If in future there's a problem with some other component in a CNG secondary you could use an LPG version and only change the inlet to one from a CNG version.

Post crossed with Gilberts, had a customer here since I started this post... P38 Rangerover with old Romano sequential system and Bigas ECU, 2 reducers each feeding a separate rail of injectors, replacement 025 pressure sensor but 013 pressure sensor selected in software. I sorted the LPG, he has recently changed his waterpump, other engine problems and done lots of work on the car changing door locks etc, had new keys programmed... I advised him to join the Rangerover pub.
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CNG
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Re: Can I run CNG thru' a LPG vapouriser?

#4 Post by CNG » Mon Jun 07, 2021 12:12 pm

Thank you Simon, and Gilbert, yes, you're correct. I'm after 0.8 above atmospheric, thus 1.8 above vacuum. I've a OMVL 89 going spare here, but if I'm right, supply form one of those requires a fair amount of vacuum via the intake-tract, as my post with 2 x BLOS etc etc. Unless there's legitimate (and safe) way to doctor an 89, can't see how that'll fly.

I'd not thought about how the lack of liquid might affect the valves, but I think you're right. I've CNG and LPG Necam varaints here, but not exact like-for-like models to compare. The only way I can see to check this out is to suck-and-see. It'll either work or it won't. For a moment I had the notion to take the high-pressure 'first stage' from my spare OMVL89 and cobble that in. But what with LPGC's words, I'm starting to think this all sounds like a Darwin award in the making. I'll keep looking. Now a gander at Lovato and HL Propan MJcompact etc

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Re: Can I run CNG thru' a LPG vapouriser?

#5 Post by CNG » Fri Jun 11, 2021 12:11 pm

I've found a Tomasetto Reducer AT12. It's a real-deal CNG reducer, and specc'ed to go down to 1.0-2.5Bar. And more detailed research has the dizzy requiring 0.9bar. Damned close. But I'm thinking that pressure set to minimum it's on the edge. If I cobble shortening an internal spring or summint, I might get it to go. Is this is prudent, or plain dim?

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Re: Can I run CNG thru' a LPG vapouriser?

#6 Post by LPGC » Fri Jun 11, 2021 1:03 pm

Don't know. Most of the Tomasetto LPG reducers (wide range of them but all very similar designs) allow a wide range of pressure adjustment, some as wide as 0.7>2.odd bar, but some will only adjust to as low as 1 bar. None of them seem to live very long if pressure is set higher than around 1.5 bar but that won't be a concern for you. Ideal pressure for a lot of them seems to be around 1.2 bar for best pressure stability under changing loads and temperatures. I'd expect the Koltec reducer to be more pressure stable for changing temperatures but I've never used a CNG version.
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Re: Can I run CNG thru' a LPG vapouriser?

#7 Post by CNG » Fri Jun 11, 2021 5:45 pm

Thank you Simon. I'm getting the idea you don't like Tomasetto reducers and it wouldn't be the first time I'd hard this from a pro. Well I'm having a go now, and the damned thing is truly awkward in its plumbing. Odd (for me anyway) 8mm coolant hoses that head in odd directions to my install and leave no space to put anything other than Oetiker clips to them - appears they don't have Jubilee clips or stock 10mm car accessory shop hose in Italy.

Rather than under any engine-bay I've ever seen, The thing's been designed by someone at a desk. But now I'm twisting on... I'll save the spittle-flecked rant for next time.

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Re: Can I run CNG thru' a LPG vapouriser?

#8 Post by CNG » Mon Jun 14, 2021 2:58 pm

Well, the thing's specc'ed to deliver 1.0Bar but I can't can't get down to below 1.4Bar. Which might or might not be quite low, but not low enough. Best part of a day wasted. Ho hum.

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Re: Can I run CNG thru' a LPG vapouriser?

#9 Post by LPGC » Mon Jun 14, 2021 6:34 pm

Is the 1.4 bar with gas being drawn off or have you just opened solenoids and measured static pressure without a constant small use of gas? Or in other words was the pressure reading with the engine running on LPG (er CNG)? Reducers often initially over-shoot the pressure setting before there's a small drain of gas.
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Re: Can I run CNG thru' a LPG vapouriser?

#10 Post by CNG » Tue Jun 15, 2021 8:02 am

Is the 1.4 bar with gas being drawn off or have you just opened solenoids and measured static pressure without a constant small use of gas?
Thanks for the suggestion. That thought did occur to me. It's too high static, engine not running, which is a b*stard. But then and all, I suspect the pressure drops considerably once running. The rub is, the engine won't fire-up with pressure that high. The stock Necam reducer is fine, but with dwindling parts, the object was to find a widely available, and thus easy to replace/service substitute.

If I run my stock reducer too high, I hear the Necam mushrooms 'squeal' which can 't be good. Whilst I've got plenty spare, at the price and rarity of those things, I'm reluctant to risk smoking a set without good reason. And they're tucked under, hence a 3-4 hour job to change.

I've wimped-out. Better to put this particular exercise down to experience.

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