Running an Engine on Raw Natural Gas 4

[AboveRedline]

Hey guys,

We have a customer who runs engines on raw natural gas from either gas wells or condensate wells, in all weather conditions. Cold start is sometimes an issue, as is liquid(?) build-up in the intake manifold. So I guess I can't treat it as a dry vapor. Do you have any hints which may help me with a manifold design?
thanks in advance.

 

[IRstuff]

Methane's boiling point is -162°C, there's no natural place, including inside an engine that's that cold. How do you know the natural gas is dry, though? Water obviously has a higher boiling point that's more in line with natural cold temperatures.

TTFN

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[AboveRedline]

I think the issues are due to the gas being unrefined; straight from the well. I'm wondering what may be in it.

 

[IRstuff]

If it's straight from a well, there could be all sorts of crap in it, including water, dirt, gunk, etc. It sounds more like a filtering problem than a manifold design problem.

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[bcs5274]

also the btu level of the gas might be too high for the engine and cause damage in the long or short term depending on how "rich" it may be. Type of engine can factor in also.

 

[rmw]

For the liquids you can get an industrial grade 'knock out pot'. Google "Wright Austin" for a start.

For the butanes, propanes, etc that may be in the raw gas, good luck. That is pretty much a roll of the dice. Some industrial plants bleed air, nitrogen or CO2 into rich gas in order to bring the BTU content down to something near pipeline grade natural gas.

rmw

 

[Lou Scannon]

I've seen engines that run on well gas, and their exhaust pipes look like a diesel's (worse, actually).

I forgot what I was going to say

 

[patprimmer]

If the manifold runs downhill continuously from the fuel introduction point to the inlet valve, puddles cannot form.

Smaller dia runners keep velocity up and tend to carry all components forward due to velocity.

Warming the manifold floor evaporates puddles.

Regards
Pat
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[daviwy]

Running an engine on raw gas is very tricky if it's not designed for it.
You really need a filter, seperator and some form of water / condy handling unit.
I think the issue you've got is called "wet gas", i.e. presence of condensate, water and other form of sludge in the gas.
There're a lot of issues you've got to think about when running wet gase

But first of all what do you mean when you say gas/condy well? Is the engine designed to take both gas and condensate? Does the engine have it's own seperation system? what inlet pressure do you get and what can the engine handle? What's the composition of the gas you're sending into the engine compared to it's intent design conditions?

Mechanical Operations Engineer
Oil, Gas & Power

 

[AboveRedline]

Thanks so much for all the replies. There is a separation system between the well and the engine, but it can't be perfect. Pat's suggestions are along the lines of what I was thinking. I think I'll keep the plenum small also, to bias towards good distribution instead of intake tuning via long straight runners. You're right davi, I should at least get an inlet pressure.
Does the randomness of the mixture components make these engines prone to detonation? If I make the runners too small in an uncontrooled gasoline application low speed detonation can be a problem.
Thanks for the input!

 

[Hoxton]

It is a lot more complicated than this!

1. Engine manufacturers do not want any liquids of any sort in the engine inlet, at worst, excess of liquid will cause the engine to "hydraulic" if a combustion chamber fills with liquid. Liquid is essentially not compressible, conrods can bend etc!

2. If this is gas from a gas well or an oil well then the composition of the fuel gas is indeterminate. Not only can the Lower Heating Value (Nett Calorific Value) vary but so can the Methane Number (MN) this is the factor which relates to the "knock value" of the gas. Pure methane is excellent and pure hydrogen is bad. The associated gases in well head gas often contain butane propane and other higher hydrocarbons. Preesence of these in the fuel gas can give rise to knocking (detonation) in the combustion chamber. This is similar to pinking in petrol engines. Knocking is explosion instead of burning of the fuel and the pressures / temperatures can result in engine damage - burnt piston and worse. Cure is reducing the power and / or changing the timing. This is ok if the fuel composition is known, but difficult with well head gas, where the gas composition can change by the hour or minute.

 

[patprimmer]

Unless it is a very high compression engine or there is a lot more liquid than a normal dose of fuel hydraulic lock is not really an issue. Of course if fuel can flow into the engine without the engine running and the liquid portion continues to accumulate, or if a truckload of extra flow is allowed to compensate for a VERY high water content it might be a problem. Normal a:f for hydrocarbons is in the ballpark of 15 parts of air by weight to 1 part of fuel by weight.

Before hydraulic lock becomes an issue you need about 2 parts of air by weight or less to one part of fuel by weight or other liquid with an SG n the range of 0.7 to 1.0.

If fuel octane is variable, you need to set compression and timing so it won't knock in the worst case scenario. You also need to control the a:f so that it will never be dangerously lean or so rich so as to misfire.

If it is electronically controlled, a knock sensor and a wide band oxygen sensor might help provide data to the ECU. Of course the ECU would need capability to be tuned to read and use this data.

Regards
Pat
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[AboveRedline]

Actually the customer is only looking for 30HP with 230 cid, at 2200 rpm. And they already have engines in the field, which have been successful enough to warrant a proprietary intake for their application.

 

[MiketheEngineer]

All the above considerations aside, my Dad used to tell a story that when he was a teenager in WWII, he and a buddy had an old Model A. They rigged up two fuel tanks - one with regular gas which was hard to get and the other with dry cleaning fluid which they stole from his buddy's dad.

The would fire up on regular gas and once the engine was warm - switch over to the dry cleaning fluid.

Worked for them...

 

[berkshire]

And the dry cleaning fluid was?
Benzine maybe?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[Duwe6]

You're getting "Drip" out of the well -- hexane, heptane, and possibly a tiny ammount of octane. Knew of some old-timers that would fuel their pickups using "Drip". They probably had to retard the timing a bunch, but am just guessing.

 

[patprimmer]

If the dry cleaning fluid was White Spirit, it is OK up to 3 or 4:1 CR. I guess that's all a tired worn out old A model effectively had.

Of course if they ever got a chlorinated hydrocarbon dry cleaning fluid, the results might have been somewhat disappointing at least. Best result would be it would not fire. Worst might be there was enough good fuel to keep it running while making a truckload of phosgene in the exhaust gas.

Regards
Pat
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[berkshire]

patprimmer
I am most likely showing my age here, but your post reminds me of the days in my youth, when we did fire drills with mini-max pump type fire extinguishers ( carbon tetracloride). Watching the resulting green and purple flames and clouds of black smoke coming off the flaming petrol, before it went out.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[rmw]

I grew up in a part of the country where there was a lot of natural gas production. The 'oil patch' guys were famous for running NG liquids in their vehicles. And, yes it did bang and knock, but not if not mixed too heavily into the gasoline. Occasionally you'd hear of someone who would get greedy and then have problems.

rmw

 

[mtrider16]

Interesting design problem. We have some integral engines/compressors in the field made by AJAX. If your getting liquid in the manifold it will be difficult to modulate your air/fuel to meet any type of emission requirements.

liquids from a well will consist of water, oil, and natural gas liquids. I'm not sure how I would design an manifold for it. Probably have a low spot that can catch the crap so it can eventually evaporate and be carried through the engine.

By itself methane is almost impossible to detonate, but we have detonation problems because of the higher level hydrocarbons. CH4 is methane, and then C2H6, C3H8 etc.

It is easy to regulate the fuel pressure down to what ever is desired but that pressure cut may cause lower temperatures and drop out liquids.

All the industrial engine manufacturers we buy from have a minimum fuel quality requirement. Without filtering or even some processing most well gas wouldn't pass muster.

Good Luck, David