Vaporizer temperature, contaminants, and separate thermostats

Propane, Butane, LPG, GPL, C3H8, C4H10
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evranch
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Vaporizer temperature, contaminants, and separate thermostats

Post by evranch » Fri Feb 01, 2019 10:35 pm

I came across this chart on Century's website, where they recommend installing a thermostat in the return line from the vaporizer: https://centuryfuelproducts.com/parts/f ... re-control

It seems to imply that something happens to propane as the vaporizer temperature climbs above 60C. I know the mixture will lean out as the gas gets hotter, and thus lighter - I think this is the "mixture change" line across the chart. (Maybe this is part of the reason my warm-weather systems always run on the rich side, as I run vapour from the tank, which comes out cold?)

However, what do they mean by "temperature range where propane cracks to liquid" above 60C? Propane is not cracking to anything at these temperatures. Are they talking about contaminants dropping out?

I have heard that keeping the vaporizer temperature lower will help avoid fouling it, but why is this the case? When operated on liquid, doesn't the liquid always fully evaporate in the primary stage of the regulator/evaporator, leaving the contaminants behind? If they are not being left in the evaporator, where are they going to go?

Relevant to me as I'm running heating propane which is supposed to be dirtier. I run vapour propane from the tank on most of my lower-horsepower equipment to leave contaminants in the tank, but will be forced to run liquid through the evaporator for sustained cold-weather operation on my latest tractor conversion. I'm not sure if I should be installing this auxiliary thermostat or not, I've never heard of them before and they don't seem to be a part of older systems.

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BigBlockMopar
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Re: Vaporizer temperature, contaminants, and separate thermostats

Post by BigBlockMopar » Sat Feb 02, 2019 5:11 am

I think they indeed do mean to say the 'heavy' oil will seperate from the vapour.

This thermostat would be nice for a low performance setup where there is 'enough' time to compensate for changes in engine-load and fuel demand.
I'm not so sure the thermostat will/can change quick enough to compensate for a high fuel-demand in a car engine.


Every year orso I open up the vaporizer to check and remove some of the oil that's accumulated there.
The first time I did that, there was plenty of oil (about 1 or 2 table spoons full I guess), which also had started to detoriate the membrane and causing bubbles to appear on it.
The next time I opened it up there was much less drop-out.
To be honest my engine hardly ever really gets up to its 'proper/designed' operating temperature as the radiator is doing a very good job, my trips are short and the engine tune(timing) is 'right' so it runs cool enough by itself.
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'73 Dodge Dart - 360ci - 11.3:1cr
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IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

C3H8
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Re: Vaporizer temperature, contaminants, and separate thermostats

Post by C3H8 » Sat Feb 02, 2019 1:46 pm

All propane is contaminated to a small amount with heavy ends. Take the specification for automotive propane in Canada. It specifies HD5 as 90% propane, 5% Butane, and 5% of other products. The last 5% are typically the items referred to as heavy ends. They are the small amounts of oil and contaminants remaining in the final product which would require expensive refining to remove. The amounts of these heavy ends can depend on different factors. LPG from NG is typically cleaner and purer than LPG derived from oil. Secondly, refineries use scrubbers to clean heavy ends out of the LPG and when demand is high and they sometimes fail to clean the scrubbers often enough, increasing the amounts of heavy ends. Also some of the heavy ends in LPG come from the transfer points where compressors are used and small amounts of the lubrication oil in the compressor gets past the piston rings. The more transfers the more heavy ends. Example: Refinery to truck; truck to distributor; distributor to delivery truck; delivery truck to refueling station; refueling station to vehicle tank. Some of these are compressors and some electric pumps but you get the point.

The heavy ends remain suspended in the liquid LPG until it reaches a hot vaporizer. At this point the heavier ends fall out of the vapor slowly building up until they can restrict diaphragm movement. Decades ago Century reached the conclusion that vaporizers only needed to be about 60C (135F) to properly vaporize propane but still remain dense enough to keep some of the heavy ends suspended in the vapor. (Note: Some companies disagree with this claiming their vaporizers should not be used with thermostats). The theory is using a thermostat will allow the heavy ends to remain suspended entering the engine and burn up with the propane minimizing the build up of oil in the regulators. There is a great deal of validity to this however, a thermostat is not always required as some countries have very clean propane with minimal contaminants. In the prairies of Canada most propane comes from NG and when tested was 97% pure. However, in eastern and western Canada higher quantities of propane came from oil, and heavy ends were an issue. These areas needed constant maintenance to clean regulators. At one time in the Edmonton, Alberta area, a vaporizer could be contaminated in 6 months or less until the one of the refineries discovered a problem with it's scrubbing equipment and fixed it.

The bottom line is a vaporizer works just like the chimney on a refinery. It heats the liquid LPG and vaporizes it while the heavy ends remain a liquid or heavy mist. It becomes its own minnie refinery and the hotter the vapor the more likely the heavy ends will fall out.

The Century thermostat offers two advantages. If heavy ends are a problem. it helps reduce them, not eliminate them. The really better advantage is a uniform temperature of the vapor resulting in more uniform mixtures throughout engine operation. The downside is the need for extra cation in how the regulator is plumbed in. Australia has been in the news for really hot weather recently. Secondary thermostats may be a serious consideration there. Canada on the other hand has been experiencing some record lows. In Winnipeg this week we hit overnight lows of -40C real temps with windchill temperatures hitting -52C. That's 62 below F for the US readers. Anything that reduces water flow through our heaters is not good. In the event colder climates use a secondary thermostat the routing of the coolant lines to the regulator and the location of the thermostat are critical.

Sorry for the essay and wordy post.

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Re: Vaporizer temperature, contaminants, and separate thermostats

Post by Tom68 » Sat Feb 02, 2019 4:21 pm

C3H8 wrote:
Sat Feb 02, 2019 1:46 pm


Sorry for the essay and wordy post.
Thanks for going to the trouble.

Appears our Gas in Oz must be pretty clean, rebuilt my kit (300A and Model E) a couple of years ago after more than 20 years of use (suvived 2 cars and 3 engines) everything was reasonably clean and functional, coolant side was a bit clogged up but no serious corrosion.

I've always plumbed for full coolant flow, not teed into heater lines as is quite common over here, 165 and 180 degree thermostats for engine temp with at least a 1/8" bleed hole and keep factory coolant bypass.

Have some pics of used kit somewhere, may post up later.

evranch
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Re: Vaporizer temperature, contaminants, and separate thermostats

Post by evranch » Sat Feb 02, 2019 6:48 pm

Yes, I appreciate the essay too. I personally would always rather learn why than how, because that is how I can learn how to do it myself and teach others someday. Propane is such a niche right now that knowledge like this is likely concentrated in only a few people in the entire world.

From what I know of organic chemistry, I would think higher temperatures would be more likely to volatilize the heavy oils, unless the issue is that by heating the propane too hot, those oils lose their solubility in the vapour stream and drop out. Liquid propane is certainly an excellent solvent, but I'm not sure if it can keep things like the heavy ends in solution as a warm-ish gas? It's been a long time since I studied this stuff. If that is the case, you would think in cold climates you would intentionally want them to drop out in the vaporizer, rather than make their way through the regulator and mixer, slowly gunking up the entire system.

As a side question, you mentioned lubricating oils for compressors being dissolved in the propane. I have a piston-type transfer pump here with O-ring seals, and it pumps liquid OK but squeaks pretty bad when purging it out with vapour at the end of a transfer, as the O-rings dry out. Do you know what oil to dress the O-rings with? Anything I have applied was immediately dissolved by liquid propane.

In any case, I agree that here in Canada hotter tends to be better, especially in the winter. I will not install the thermostat. I can't get this tractor to come up to operating temperature right now even without the added demand of the mixer - I have been chugging around testing on vapour while trying to decide how to plumb it into the block, and whether I should put my circulating heater in the same loop to get extra heat. My plan right now is to plumb it simply, with the heater in another loop, start the motor on vapour withdrawal and then switch to liquid once the coolant has warmed up. It will start and idle at -20C no problem on vapour, but bogs once I put it under load.

Off topic, I feel for you guys in MB, it's cold enough in SK but you guys have it something awful. It's already cold enough here to write off doing much. My shop is one of the worst prairie traditions - an unheated tin can quonset - and I decided to stop working today as it was too cold for metal. Tried to just drill and tap a set-screw into a hub this afternoon and things went like this:
- tap will not cut at all. Torch the hub and warm the tap up a bit.
- tap goes through, hub cools down, now the whole thing is seized.
- heat everything up again, but not the tap handle. Who heats a tap handle? Break the tap handle in half trying to get the tap out, the frame was pot metal and got brittle in the cold.
- extract the tap very carefully with a quality crescent wrench. Preheat the wrench after the tap handle incident.
- install a 1/4" grade 5 bolt. Bolt torques off with barely any force on it, flush with the hub of course. Thumb taps against the edge of the pulley, feels like I hit it with a sledge. Call it off, I'm going inside.

storm
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Re: Vaporizer temperature, contaminants, and separate thermostats

Post by storm » Sat Feb 02, 2019 10:55 pm

I have a couple of different systems running atm my 2 main systems are a 350 Holden in a Toyota Troopcarrier and an Ecotec V6 in a 1996 VS Holden Commodore wagon.

Anyway the Ecotec is setup to run the factory thermostat (albeit with the wiggle valve removed) of 195 degrees F and the coolants lines T'd off the heater lines. This works extremely well and the only time I had any difficulty with it was when the top radiator hose come off a few years ago (even posted on this forum about it).

The V8 in the troopy was originally setup with the original 195 thermostat, reg lines t'd off the heater lines and the reg has had alot of difficulty over the years. I rebuilt the reg changed the thermostat to a 160 and the end result the reg needed alot of attention. I then fitted a Davies Craig Electric Water Pump (EWP) set to have the engine operating at 195 while keeping both the original water pump operational and the 160 thermostat to assist with engine warmup. I have not had an issue with the reg since fitting he EWP.

The V8 taught me that engine temp does not matter much but coolant flow does. If you put a thermostat after the reg you will block coolant flow. For my next conversion I am considering fitting a auxiliary EWP just for the reg to increase coolant flow through it.
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BigBlockMopar
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Re: Vaporizer temperature, contaminants, and separate thermostats

Post by BigBlockMopar » Sun Mar 17, 2019 3:48 pm

Recently I've been looking into digitally manage the vaporiser (outlet) temp and use a modern heater valve for this purpose.

With the Megasquirt ECU in my car, I can install a temp-sensor in the vapourhose and control a heater valve with that to maintain a steady temp(range).
My goal is to be able to keep the vapourfuel temp as low as possible (within reason).
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

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