Natural Gas Engines in Cold Weather

cjjmw

New member
Hi all,

Do small engines running on Natural Gas need anything special for cold weather operation?

Will an air cooled engine have any issues on NG like it would on gasoline, or will it run completely normal if it's -10F outside? I.E. running lean, carb icing etc.
 

Gary K

Subscriber
Re: natural gas engines in cold weather

If the natural gas is like propane gas, when it gets down to -30 degree's, it won't give off many vapors.

I found that out years ago when I woke up in the morning and it was cold in the house, and the furnace wasn't running. I lit one burner on my gas stove, and it had very small flames, so I knew why the furnace wasn't running.

Anyway, I ran hot water into a pail, then went outside, and poured it on the propane tank. When I got back into the house, the furnace was already running,

I went to the NAPA store and purchased a KAT'S MAGNUM MAGNETIC HEATER, 300 watts. The magnetic heater will stick to any iron or steel material, such as oil pans.

When winter arrives, I place the magnetic heater towards the bottom of my propane tank, and laid out an extension cord, so all I need to do, is plug it in when they forecast temperatures -25 to -30 below zero.

The magnetic heater is small in comparison to the propane tank, so there's no worry of over heating it. It will heat a small area, creating propane bubbles.
 

Kimbra Dean

Subscriber
Re: natural gas engines in cold weather

Water will accumulate in the oil. You need to make sure the engine runs warm enough to evaporate the water out of the oil.
 

cornbinder89

Active member
Re: natural gas engines in cold weather

Natural gas doesn't liquifie at normal temps and pressures, and since it is not supplied from a tank, none of the above LP problems apply to NG.
Carb ice is caused by the moisture in the air freezing when the air pressure drops in the carb, so will happen with any fuel that is carb'd. Carb ice is more of a problem from around 32 deg F to the 6o deg F and air hold more moisture at those temps.
So oil viscosity will be an issue just like any engine as will cranking speed. You'll need enough vacuum to open the regulator, but there should be no special running problems.
NG pressure supplied by the pipeline doesn't drop with temp, it is a constant.
As to mixture, the colder the air the more dense, so as with any carb's fuel it will run SLIGHTLY leaner as the temp drops and the air is more dense, shouldn't make enough of a difference to require any changes to the reg setting.
 

cjjmw

New member
Re: natural gas engines in cold weather

Natural gas doesn't liquifie at normal temps and pressures, and since it is not supplied from a tank, none of the above LP problems apply to NG.
Carb ice is caused by the moisture in the air freezing when the air pressure drops in the carb, so will happen with any fuel that is carb'd. Carb ice is more of a problem from around 32 deg F to the 6o deg F and air hold more moisture at those temps.
So oil viscosity will be an issue just like any engine as will cranking speed. You'll need enough vacuum to open the regulator, but there should be no special running problems.
NG pressure supplied by the pipeline doesn't drop with temp, it is a constant.
As to mixture, the colder the air the more dense, so as with any carb's fuel it will run SLIGHTLY leaner as the temp drops and the air is more dense, shouldn't make enough of a difference to require any changes to the reg setting.

Is it correct that there's no need for a choke when burning fuels like NG and LPG?
 

cornbinder89

Active member
Re: natural gas engines in cold weather

That is correct, a choke is used with liquid fuel to get more liquid to air in the intake stream with the hope that enough will vaporize to get the engine to fire, then heat takes over and vaporizes the liquid and the choke is not needed.
With vapor fuel, esp NG which will not turn liquid (at sane temps and pressures anyway) a choke is counter-productive. You may need to press a primer button on the reg if the engine will not draw enough vacuum itself to open the regulator. This can be a problem on governed engines where they crank at wide open throttle, made worse by slow cranking speeds in the cold.
NG and Propane need a smaller spark plug gap than gasoline to ignite so be sure to check the gap spec's when running dry fuel for the setting for dry fuel.
NG will stay vapor well below -100 deg f IIRC and doesn't liquife until very high pressures. so none of LP's problems will effect running NG. Propane liquifes at -44 deg f at atmospheric pressure and the tank pressure drops with the temp. At -44 or below you could pour it in a gasoline tank (and if the rubber in the fuel pump didn't crack) burn it like gasoline! NG stays gas and since in most cases the gas is supplied by a pipeline not a tank, the pressure stays more or less constant on the supply.
In some areas, "propane" or more exact LP (liquified petroleum gas) is a mixture of propane and butane and butane liquifies at a much higher temp and this can cause lower tank pressure than pure propane. None of this matters if burning NG however.
 

cjjmw

New member
Re: natural gas engines in cold weather

That is correct, a choke is used with liquid fuel to get more liquid to air in the intake stream with the hope that enough will vaporize to get the engine to fire, then heat takes over and vaporizes the liquid and the choke is not needed.
With vapor fuel, esp NG which will not turn liquid (at sane temps and pressures anyway) a choke is counter-productive. You may need to press a primer button on the reg if the engine will not draw enough vacuum itself to open the regulator. This can be a problem on governed engines where they crank at wide open throttle, made worse by slow cranking speeds in the cold.
NG and Propane need a smaller spark plug gap than gasoline to ignite so be sure to check the gap spec's when running dry fuel for the setting for dry fuel.
NG will stay vapor well below -100 deg f IIRC and doesn't liquife until very high pressures. so none of LP's problems will effect running NG. Propane liquifes at -44 deg f at atmospheric pressure and the tank pressure drops with the temp. At -44 or below you could pour it in a gasoline tank (and if the rubber in the fuel pump didn't crack) burn it like gasoline! NG stays gas and since in most cases the gas is supplied by a pipeline not a tank, the pressure stays more or less constant on the supply.
In some areas, "propane" or more exact LP (liquified petroleum gas) is a mixture of propane and butane and butane liquifies at a much higher temp and this can cause lower tank pressure than pure propane. None of this matters if burning NG however.
Thank you for taking the time to respond.

Do I need to do anything with ignition timing when converting from gasoline to natural gas on an engine that runs at a fixed rpm? I.E. 1800 rpm or 3600 rpm on generators?
 

len k

Subscriber
Re: natural gas engines in cold weather

Carbs ice because as liquid gasoline turns to a vapor it cools , just like Freon.
Can condense humidity and ice up, just like cold coil in a refrigerator.

Vapor fuels are already a vapor so no carb icing.
Propane however does cool were ever it turns from liquid to vapor ( in tank, or heated vaporizer)

Nat gas is mostly methane.
Typically never a liquid, need very cold or very high pressure to do it, $$$$.
-- @ atmospheric pressure < -257 deg F
-- @ room temp, likely few thousand psi ... (even @ cold -121 deg F, need 625 psi)
.
 
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cornbinder89

Active member
Re: natural gas engines in cold weather

Timing will likely need to be advanced a bit if running NG only. Look to the engine Mfg for recommendations on plug gap and timing running dry fuel.

---------- Post added at 01:29:38 PM ---------- Previous post was at 01:27:09 PM ----------

Carbs ice because as liquid gasoline turns to a vapor it cools , just like Freon.
Can condense humidity and ice up, just like cold coil in a refrigerator.

Vapor fuels are already a vapor so no carb icing.
Propane however does cool were ever it turns from liquid to vapor ( in tank, or heated vaporizer)

Nat gas is mostly methane.
Typically never a liquid, need very cold or very high pressure to do it, $$$$.
-- @ atmospheric pressure < -257 deg F
-- @ room temp, likely few thousand psi ... (even @ cold -121 deg F, need 625 psi)
.
Air alone can cool and frost at the throttle plate. so it is possible to get carb ice on a dry fueled engine. Ever noticed frost on a valve stem when deflating a tire?
 

cjjmw

New member
Re: natural gas engines in cold weather

Timing will likely need to be advanced a bit if running NG only. Look to the engine Mfg for recommendations on plug gap and timing running dry fuel.

---------- Post added at 01:29:38 PM ---------- Previous post was at 01:27:09 PM ----------


Air alone can cool and frost at the throttle plate. so it is possible to get carb ice on a dry fueled engine. Ever noticed frost on a valve stem when deflating a tire?
I believe this is why many, if not most fuel injected cars still have heated butterfly valves for the throttle. There's no fuel anywhere near it.
 

len k

Subscriber
Re: natural gas engines in cold weather

Seen frost on tire valve stem , but that's cooling from expansion of higher pressure air, typically ~ 30 psi.

Wouldn't have expected noticable amount from VAPOR fuels as they are only ~ 7-12 inch WC max pressures ( < 1/4 psi) at inlet to demand reg, so not much expansion cooling from that.

Likely more pressure drop and expansion cooling from combustion air expanding across throttle butterfly to engine vacuum. Never noticed frost from that but never looked for it either. .... interesting idea though.
 

cornbinder89

Active member
Re: natural gas engines in cold weather

Just saying it can happen with dry fuel, or just with air alone. Primarily with light load/ mostly closed throttle.
Doesn't need the evaporation of a liquid fuel to form, although that tends to make it worse.
 

len k

Subscriber
Re: natural gas engines in cold weather

On cars carb is mounted directly on hot intake mainfold, so it's usually warm when I look at it. On Onan RV NHE types carb is mounted a relatively long ways from engine block, so doesn't warm up. I have seen gasoline carbs sweat heavily on a cool humid day. Haven't run it in below freezing weather to check for icing, but air box does have a lever for winter operation. It mixes in some warm air that has passed over hot exhaust manifold. Haven't looked at my Onan JB gen's propane carb in humid cool weather.
 

cornbinder89

Active member
Re: natural gas engines in cold weather

My Saab with port injection has coolant that runs around the throttle body to prevent ice, and all it meters is air, the fuel is added at the port.
 

len k

Subscriber
Re: natural gas engines in cold weather

After going for a walk, it finally occurred to me that air expansion cooling could be responsible carb sweating/icing I saw on my gasoline carb, 7NHM. Cornbinder's comment seems to confirm it, although preheating cold air would help vaporize gasoline for lower emissions

Seem to remember mostly ONLY my carb sweated (not so much the intake). I just ASSUMED it was gasoline phase change cooling, even though it bothered me that liquid would likely vaporize further down stream in intake manifold.

Been cool and humid here lately, good conditions to run my gasoline 7NHM tomorrow and take a closer look at what is sweating more...... carb or intake,

If air is close to 100% humidity won't take much additional temp drop to make it condense. And if slightly above freezing not much extra to make it ice up.
 

cornbinder89

Active member
Re: natural gas engines in cold weather

The liquid to vapor phase change of gasoline does absorb heat, so you are not wrong about that, it is just that it is not required for carb ice to occur. The gasoline is introduced into the air stream where the pressure lower than atmospheric pressure and will compound the problem.
 

len k

Subscriber
Re: natural gas engines in cold weather

Agreed....... back in the day we flushed solvents like trichloroethane 1,1,1 thru our rate gyros for cleaning. One tube connected to bottle of fresh solvent, other tube to a flask under vacuum that collected used solvent. I touched the flask it was COLD. I figured out solvent under vacuum was evaporating and cooling it.

Thought about it a bit and realized all liquids ( including solvents, gasoline, and water) likely behave the same, just as Freon and refrigeration gases do, just to different degrees.
.
 
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cornbinder89

Active member
Re: natural gas engines in cold weather

Yes, all substances to one degree or another absorb heat when making a phase change up and release when changing down, doesn't matter what the substance, how much they absorb or release changes with the substance but they all do it.
Water is used as a refrigerant in steam systems and can cool to the 40's deg F.
 

len k

Subscriber
Re: natural gas engines in cold weather

Water cooling to ~ 40 degs .......Yes, to dry out absorbed humidity from a car/house AC after you open the system have to pull a fairly hard vacuum to get it to boil off at room temps (or less) and be removed. Should work with solid water (ice) even, just slower.

There are some solid metals that evaporate at room temp, under a strong vacuum ...cadmium I think it is.
Also a couple other soft metals too.
.
 
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Re: natural gas engines in cold weather

Hey Guys
A couple of comments here not worth much.When changing semi truck tires you screw out the valve core, stand back and the stem will frost shut then thaw and shoot ice bullets, with enough velocity to be dangerous. In the late fifties I was a bit on the young side, a customer came into the shop and wanted me to help him build an air cond. system in his vehicle, he was going to use the gasoline from the fuel tank under high pressure through an orfice for the refrigerent and then send the gas back to the tank, at that time I was not interested in air conditioning, had never rode in a car with a.c. May have missed the boat.
Have A Good One
Jimmy
 
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