Care of LPG engines 3

[davidwilloughby]

For an engine that uses dual fuel -LPG or Petrol - it is wise to switch over to petrol just before shutting down the engine to help extend the life of the engine. Is this true?

 

[romke]

no it is not. there may be other reasons to do it however.one reason would be if the engine has to be restarted in extremely cold weather. it might be easier to start on petrol then on lpg under those circumstances. another reason might be that the engine has electronic fuel injection. althoug running on lpg it might be that the fuel lines are filled under a slight pressure, while the small amount of fuel is stationary. that might lead to oxidation of the fuel over time (gum and varnishbuilding) and therefore it would be wise to use the petrol occasionally to refresh the trapped amount in the fuel lines to prevent oxidation.

one other thing to bear in mind with dual fuel engines. they are usually run on lpg because of the lower cost, where only a limited amount of petrol is available for emergency purposes - when you run out of gas - literally. that limited amount of fuel cannot be stored indefinetely, over time the quality will deteriorate so if you really need it it might have gone "stale". it is better to use it up say every three months or so and replenish with a small amount of fresh petrol. you then will also be sure that you have the right variety (winter/summer or intermediate) so that your chances that the engine will actually start on petrol when needed are much better.

 

[IceStationZebra]

I know that LP is a lot harder on valves - but this isn't related to starting/stopping. Its more analagus to the lead reduction in gasoline.

I don't have personal experience with starting issues specifically but the only thing that I can envision (besides Romke's previsous post) is cylinder washing. The colder the weather the lower the tank pressure. Starting on LP in very cold air results in liquid fuel in the cylinder - which I would suspect washes the oil off resulting in a slight wear.

I suspect that this bit of wisdom was originally a recommendation for a specific system but morphed into a modern "truth."

ISZ

 

[turbocohen]

Yall make me laugh. OK, I gotta clear the air here, scuze the pun.

Cold starting is much easier on lpg if the fuel system is engineered for the fuel.. most lpg fuel systems are so poorly designed that it is a misnomer to call them "engineered". A few OEM's and just a few mfg's have worked out the cold starting issues using liquid phase injection that also tolerate hot restart as well. (not all liquid systems are the same, see the beginning of this paragraph).

LPG has a higher vapor pressure than any blend of gasoline and is much easier to atomise than winter blend gasoline at low temps. If the fuel is injected as a liquid then cold starts down to -40F are a breeze if the engine will turn over fast enough. Been there done that in alaska and canada numerous times. At -20 about 5% enrichment is about the max required with butane rich blends.

Cheers, Turbo

 

[IceStationZebra]

Turbo - I can't discount your experience but mine was with testing OEM LP systems for Hyster/Yale forklifts. I suspect your reference to the actual fuel blend is the reason. In Portland OR it hardly ever freezes so they probably don't put in a lot of butane.

I know that if we tried to start an LP truck at -10 deg F in the cold room we would be lucky if it would start, especially the GM 4.3's. If they didn't start right away you knew that the spark plugs were too wet. We would keep the tanks outside the cold room and install them just before starting so the tank pressure could atomize the fuel better. And these systems were engineered by us specifically for these trucks, using one injector per cylinder. We didn't have as much of a problem with the gas engines. Many of us believed that the LP systems should start easier in the cold, but that was not the case. - But like you said it depends on rpm's, fuel blend, ignition systems, fuel system, etc.

 

[Lou Scannon]

"In Portland OR it hardly ever freezes so they probably don't put in a lot of butane."
Ice, I'm not following your point here. You seem to be implying that butane is added to raise vapor pressure. Last time I checked, butane's vapor pressure curve was below propane's.

 

[reidh]

Hemi is correct, adding butane will decrease the vapor pressure of propane. At 20 C, butanes vapor pressure is about 25% that of propane.

-Reidh

 

[romke]

normally lpg consists of a blend of butane and propane. the amount of butane may vary depending on climate and season. you may also run the engine on pure butane or propane. in winterconditions propane (or a large amount of it) is to be preferred because it more readily vaporizes.

 

[turbocohen]

Icestation, Out of economic neccessity, low volume oem hardware has to meet global oem requirements while at the same time be cheap enough to make and integrate with a minimum of production line second ops. From hot high altitude to late summer arizona desert to january-february 5am northern alaska.. oem LPG fuel systems must operate as reliably as the gasoline system. This is seldom the case.

If hyster/yale gets serious about forklifts with 5000hr emissions durability I beleive they need to rethink fuel delivery technology and suggest deposit control additives.

Koreans use neat butane, most countries have nearly 95% propane mixtures and other points on the planet use whatever came out of the well or was left over from petroleum processing at the refinery.

Since no customer can be expected to store fuel in a warm location to allow cold start and numerous other reasons, the oem's I worked with went with a clean sheet pump pressurized approach. Anything from straight Butane (low vapor pressure) to ethane rich LP (high vp) is easy to accurately meter at or below temps resulting in zero vapor pressure if the fuel is boosted above tank pressure 4-5 bar regardless of temp/saturation pressure. This problem is a shortcoming for vapor systems (carb or injected) that depend on tank pressure.

Conventional cranking RPM's are ok for LP, late ignition systems optimized for gasoline engines are eh.. ok for LP but the plugs should be upgraded to Denso iridium for better cold starts.

Just my 0.02 dinars.

Regards, Turbo

 

[IceStationZebra]

Well, I can't claim to be a LP system specialist -- just stating my experience. My area of concern was not the engines directly.

As far as fuel goes - what I was trying to say was that we were taking "summer" fuel (whatever the blend happened to be) and were using it in artic conditions (<0deg F). That could be the reason why the LP engines had a harder time in the cold. Could have been some other reason that I don't know, but it did seem consistent for different brands of engines. We couldn't really explain it and I didn't investigate further because it wasn't my responsibility nor did I ever hear of any field complaints.

As for the fuel systems, I don't know what the specific requirements are, but it had to meet the latest american and euro off-road emissions regs that when into effect this year. I know that it was a big leap to verify the durability of the whole system including the exhaust. Also mainly due to the emissions regs the gasoline and lpg fuel systems had almost nothing in common besides having an ECM and spark plugs. All fuel injection (LP & gas) along with spark timing was computer controlled and unique to each major configuration. But they were also using the same fuel systems and software in all markets except Asia. I don't claim it was the most technically advanced option - but it was a far cry from the LP carb and one-size-fits-all distributor I think you are referring to which was used by virtually everyone in that market untill recently. (excluding diesels of course)

I am not aware of anyone in the forklift business using anything but vapor systems. If the necessary equipment takes up more space than a 2L bottle I don't know where they would fit them into a forklift, on some trucks you can't even see the ground when you look under the hood. And it would have to live with ham-fisted mechanics at the plants and rental houses who know "everthing" about forklifts and can fix them with only a hammer and screw driver. And it would probably end up near an exhaust manifold

I don't know if this is helping answer David's question, but a good discussion. ISZ

 

[turbocohen]

The amazing fact is that liquid metered systems are much more compact and easier to package than vapor systems. The pump module is mounted in or next to the tank and the fuel injectors (ideally bottom fed take up more space than gasoline injectors but in many applications are packageable.

Aint never hear of that thar winter blend LPG. Never designed for anything other than the entire range of vapor pressure typically found in LPG worldwide i.e. anything from straight butane to ethane rich propane. Any blend will work great in cold weather with the right technology.
Thats my story and I am sticking with it till the cows come home.

 

[IceStationZebra]

Here is a thread from the UK on David's question. Too many opinions to list.

http://groups.google.com/group/uk.r...284058866b2/a66eaec043e75829#a66eaec043e75829

 

[IceStationZebra]

Moooo

----------------Regarding seasonal fuel mixture-------------------

“Varieties of LPG bought and sold include mixes that are primarily propane, mixes that are primarily butane, and mixes including both propane and butane, depending on the season - in winter more propane, in summer more butane.”
Wikipedia and numerous other sites

“Commercially available LPG in the USA ranges from 49-99% propane by weight.”
Southwest Research Institute; Project 03.07065 Final Report

“In the United States, the propane industry has attempted to adopt an automotive propane standard known as HD5. [min. 90% propane] The standard is not universally observed. Because, the concentration of propane as high as virtually 100 %, to as low as 50 % in certain locations. Much of the remainder of the gas is butane and some other hydrocarbons.”
West Virginia University – Alternative Fuel Vehicle Training Program; Propane Review;

http://wps.com/LPG/WVU-review.html

“Propane is a premium product with better vapour producing qualities, but it costs more, yet contains less energy than general blend LPG.”
Rockgas Ltd.;

http://www.gas.co.nz/questions.htm

“But sometimes (propane) is mixed with butane, and not identified as other than propane. Coming home to northern states from AZ with a full tank of mostly butane -- which won't vaporize until it gets above 32F -- can cause a problem, since butane needs to be above freezing to vaporize. If it doesn't vaporize, your appliances won't work. If you fill up with Butane in Texas and drive home to Minnesota in winter months, you'll find none of your "propane" appliances will work.”
RVer’s Online;

http://www.rversonline.org/02Propane.html

(similar -

http://rvcentral.com/html/fuelandoil.htm)

I found two different vapor pressure sets of data. Not sure why they differ, but 50/50 LPG has only ~1/3rd the pressure of pure propane at 0deg F.
vapor pressure @ 0deg F
100% propane: 38psi (or 25psi?)
50% propane, 50% butane: 10psi (or 7.6psi?)

-------------On cold temp starting issues--------------------
Ford 1999 F-250 bi-fuel is programmed not to use propane below 20deg F. No reason given.

“Engines powered by gaseous fuels are generally considered easier to start than gasoline engines in cold weather because gaseous fuels are already vaporized before inducted into engine. However, under very cold temperatures, cold-start difficulty occurs for propane. In extreme cold weather environments a supplemental electrically powered heater will likely be necessary.”
BAF Technologies; LPG 101

“Some argue that propane is a better fuel in cold climates because it does not have the low viscosity and waxing problems of diesel fuel and that spark machines are easier to start. In actual practice a diesel engine offers more reliable starting in cold weather, and in areas which have wide temperature swings diesel is also lower in maintenance. The problem with propane engines is vaporizing the liquid fuel and the load valve adjustments which are subject to temperature swings. Until a computerized propane carburetor is available, diesel is the preferred choice for reliability in cold weather.”
Polar Power, Inc.;

http://www.polarpowerinc.com/forms/gensetworksheet.htm

“Vapor injection offers better range and no difficulties with hot conditions, but cold-start emissions can be a problem if the gas liquefies in the fuel line. The liquid is much denser than the vapor, so the injectors allow much more mass of fuel into the combustion chamber than is required. This produces high CO and HC emissions.”
Center for Environmental Research and Technology - University of California, Riverside; Development of an Advanced, Low-Emitting Propane-Fueled Vehicle

“..after the engine was shut off, the fuel in the line could condense (if the vehicle was cooled to 40°F) to a liquid at 90 psi. Because the injectors were designed to pass vapor, not liquid, they would allow too much fuel into the combustion chamber during cold-starting.”
Center for Environmental Research and Technology - University of California, Riverside; Development of an Advanced, Low-Emitting Propane-Fueled Vehicle

“Propane and natural gas require from 50% to 100% higher temperature to ignite a charge as compared to gasoline. The ignition must be in good shape.”
Alternate Fuels Technologies, Inc.;

http://www.propanecarbs.com/questions.html

----------------Other ideas on starting on gas vs propane----------

http://groups.google.com/group/alt....a2207f20bc9/649aedee0f2a2b67#649aedee0f2a2b67

ISZ

 

[turbocohen]

Moo is right. LP (no not LPG) is not consistently the same throughout the USA or the world. The only way that LP can reliably be metered across the temperature range is to allow 0- 600psi storage pressures and -40F startup attempt with safe failure mode -30F startup within 5 sec and 120F hot shutdown. No excuses, bs, flung poo or politics.

The way to design an LP fuel system is to put thermocouples everywhere the system will be and assume the fuel will absorb more heat than desired while towing in the desert and then as fuel depletes the evap cooling result in 0 pressure while the tank has plenty of fuel.

Vialle has liquid phase LP down cold, problem is not the technology but the lack of fuel additives that allow the fuel systems to tolerate the slew of crap that precipitates. HD5 is a joke, so is HD10. Neither of them address a fuel system cleanup or keep clean requirement in their spec. The imperfect but more crap-in-the-fuel tolerant vapor systems are the state of the art for that reason.

Signed, Moo

 

[IceStationZebra]

Most people don't realize that LP is nowhere near as regulated as galoline or diesel. I know that there were lots of problems with some of the %$#@ LP that was being sold in a particular region of California.

The liquid phase design sounds like a better system for metering consistancy. I infer from your comments that the injectors get plugged with crud from the fuel? Do you also need a pressure regulator or is that built into the fuel pump?

ISZ

 

[turbocohen]

You need a pressure regulator at the end of the fuel return line after the injectors but avoid allowing it to vaporize before returning to the tank to minimize heat absorption. Yep metering consistincey is much improved, the trick is to use an injector that operates across the temperature and pressure range while facilitating het vapor purge and the only one on the market that demonstrates all of the above is the Siemens Deka II LP spec injector. When I worked with them we came up with some additional improvements but the decision was they were not worth it due to the LP industry's arrogance. By that I mean that the upper brass claimed that our fuel injectors failed.. not the case. They could last 400,000 KM and frequently did but they could fail in 20 minutes if enough of the hydrocarbon based plastics formed or sulphur deposited on the >0.5 micron finish of the needle valve.
Yes there are other ways to make a leak proof valve but remember it has to HAS TO be able to operate 1/2 a billion cycles until failure in alaska, AZ, Alps, etc and integrate with reliable oem ECU's. No easy task with reasonably additized fuel but impossible with much of the LP sold as motorfuel.

Regards, Turbo