Liquid effects in a gas engine fuel 2

[rostanlin]

I'm part of a Cause Root Analisys of a Piston/Cylider failure in a gas engine caterpillar G3600.
I would like to know how liquids within the gas fuel (drops or mist) affects the combustion and engine components in a gas engine. How I know that a mechanical failure (piston, cylinder, cylinder head, etc ) is associated with it?. There is any patterns of failure?

 

[Lou Scannon]

I assume you mean liquids other than water. Hydrocarbon liquids in a natural gas fuel pose two problems. The first is that they are probably "heavy ends", which will lower the methane number of the fuel considerably. Caterpillar has a methane number calculation formula which can determine the methane number, given the fuel composition.
The second problem with combustible liquids in gaseous fuel is that the fuel is being metered as a gas; any liquids that pass through the metering device are "unmetered" and could cause the engine to exceed its rated output. More likely, while total power may be properly controlled by the external control system, the liquids will be unevenly distributed among the cylinders, causing individual cylinders to exceed designed pressure and temperature limits. The risk of damage due to local overpowering is greatly exacerbated by the probable low methane number associated with the liquids.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[rostanlin]

Thanks,
It known that Caterpillar uses the methane number, LVH and specific gravity of the gas fuel as as a reference to calculate timing and AFR. But I am wondering what hydrocarbon liquids can cause in a specific moments (for example: a fuel gas scrubber does not work as it should or due to pressure drop in the gas regulator downstream of the fuel valve, hydrocarbon liquids are formed) in the combustion or/and a gas engine components. How I know that a failure in a piston/cylinder/cylinder head is due to the presence of liquids in the gas fuel. There is any pattern for it? What should I look for?

 

[Lou Scannon]

Sorry, I do not have first hand experience with failures specific to liquids present in the gas. I have had encounters with unexpected gas compositions, having unworkable methane numbers.

The common element in failures due to unacceptably low methane number, or overfuelling, are signs of stress in the power cylinder: melted/eroded/scuffed or completely destroyed pistons, undue bearing stress; undue head gasket stress (in the fire ring especially); indications of overtemperature in the combustion chamber or exhaust.
My experience with heavy duty engines is that normally the piston is the first component to show evidence of such overstress.

If you're seeing any of the above indications, and don't know the root cause but suspect liquids as you have suggested, you will need to find a way to rule them in or out. I think the following is attributed to Sherlock Holmes: "Rule out the impossible, and you're left with the probable".

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[IRstuff]

What exactly is the failure? I don't think that it's reasonable to pose a question asking for general failures, as there are many causes of all possible failures. A specific failure is possibly a more manageable question.

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[bcs5274]

detonation is your first indication, shown on panel/ecu or you can even hear it at times, these spikes in cylinder pressure and over temp of cylinder cause the damage

 

[rostanlin]

Link Top Cylinder View
Link Outside Cylinder View
Link Internal Cylinder View
Link Top Piston View

Thanks, for all your opinions and ideas,

Please feel free to view some pics of the piston/cylinder failure, as you can see, during the fail the cylinder lost the end of the cylinder. Besides, there is some scratches in the in the internal cylinder wall and there is some solid deposits upon the top of the piston. By the way, in this gas engine, each piston and the internal cylinder wall are lubricated and cooled by a oil jet.

Sometimes the operation technicians have heard detonation sounds and the Engine ECU (ADEM III) shows that the engine had been stalled by high detonation levels in various cylinders.

Particulary, I think the failure is associated with the lubrication system (because of the scratches), maybe the lubricator jet was broken by the cylinder end metal particules. But, what could break the end of the cylinder?
The maintenance technicians believes that the piston/cylinder failure is associated with liquids in the gas fuel.

What do you think?

 

[IRstuff]

Your picture shows a large crack in the piston, which would be the cause of the "scratching", since the piston is no longer round, assuming that the crack existed before someone beat the cr*p out of the backside of the piston. The fact that the crack is so clearly visible is an indication of a gross movement of material radially outward, which is why the scratching is only on one side of the crack.


Why is this thing so rusty?

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[rostanlin]

There are two reason the cylinder is so rusty. First, the picture was taken 10 days after the failure and the cylinder has been exposed to a humid and rainy enviroment. Second, the engine jacket water is cooled by non-treated water.

The scrarching are in both side of the piston and cylinder wall with aproximate 180° one from the other and a magnitude of each scratch is 50° of the wall... .We are going to separate the piston and the cylinder. As soon as I take them pics I will upload them and show to keep figuring out the reason of the failure.

which came first, the chicken or the egg... The piston crack or the cylinder end snapping ? ..because the metal particules could crash against the cranckshaft and shoot the piston (there is evidence of that in the counterweight of the crankshaft). what else could snap/crack the cylinder end(just after the piston stroke)?

 

[IRstuff]

I don't see what you mean by "the cylinder lost the end of the cylinder" in the pictures?

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[Lou Scannon]

The amount of corrosion on the top of the piston makes me wonder if the cylinder didn't have water accumulating inside, perhaps from a leaking seal between the water jacket and the cylinder (e.g. head gasket or liner O-ring. Along with corrosion, water in the cylinder is a very likely cause of hydraulicking. A mild hydraulicking event (as opposed to a severe one), might result in cracking the piston as depicted, rather than buckling the connecting rod or other more substantial mayhem.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[Tmoose]

Are the liners in the other cylinders as badly corroded?
Do you have the oil analyzed a few times a year?
How long was this engine is service?
Are there more engines in service like this one?

I think the "untreated water" may be a big part of the problem, especially if you mean no coolant additives.
Pages 35 and 36 here -

https://parts.cat.com/cda/files/3244668/7/SEBU6400-05-secure.pdf

On another automotive board a poster from Malaysia reports that because the weather is warm some repair shops use straight water in cooling systems.
The poster has first hand experience with failures that would never have happened in colder climates where cars are antifreeze/coolant.

When corrosion proceeds far enough the gasket sealing is lost and coolant can reach the combustion chamber and in some designs even the oil sump.
As others said, hydrolocking can crack a piston.
Water lubricated piston skirts will scuff and gall.
there are Many pages of piston damage and casuses here -

http://cleviteonengine.com/publications/DistressGuide.pdf