×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

pre-ignition triggered by lubricating oil

pre-ignition triggered by lubricating oil

pre-ignition triggered by lubricating oil

(OP)
thread71-215499: Peak Cylinder Pressures

We are looking at a 90 Bar (1323 psi) pre-ignition pressure and a 5200 psi peak cylinder pressure.

I saw a post regarding pre-ignition triggered by lubricating oil getting pas the rings. Our current design has 4 rings -- oil wiper ring plus 3 compression rings.

I am interested in hearing from others that have addressed this issue.

Thanks,
Don ---

RE: pre-ignition triggered by lubricating oil

Not nearly enough info. How about a description of the engine, combustion principle, application/mission, & background info (i.e. where this started and how it got to this point)?
A representative cylinder pressure trace and related heat release info would be very informative as well.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: pre-ignition triggered by lubricating oil

(OP)

hemi says -- "Not nearly enough info. How about a description of the engine, combustion principle, application/mission, & background info (i.e. where this started and how it got to this point)?"

Thanks for your post hemi:

I am an engine designer in Southern California. We are in the early manufacturing stage of a new very high pressure multi-fuel compression ignition supercharged direct injection engine. The anticipated applications are wide spread -- transportation, power generation, and industrial applications.

The motivation for this engine is improved fuel economy, lower emissions, reduced manufacturing costs and low weight (high energy density).

My reason to post my question is to advance my insights into potential pre-ignition problems from lubrication oil migrating past the rings into the combustion chamber.

Thanks,
Don ---

RE: pre-ignition triggered by lubricating oil

If your combustion principle is compression ignition based, pre-ignition is not commonly considered to be an issue. Note that there do exist some estoric variations of compression ignition where this question becomes much more complex, e.g. HCCI.
There is a known issue with conventional diesel engines, when there is a mechanical failure of some kind leading to excessive amounts of lube oil being drawn into the combustion chamber, leading to engine runaway (since there is no external control to prevent the oil getting into the chamber once the failure has occurred, and no way to prevent ignition, since it occurs automatically due to compression. The engine will only stop when the oil supply has been used up, or more likely, it self-destructs or a quick thinking operator brakes it to a stop somehow or starves it for air by blocking the air intake.
Other than the above, assuming competent design and manufacturing of oil control features in the ring pack and intake valve seals, you shouldn't have to worry about lube oil interfering with normal combustion.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: pre-ignition triggered by lubricating oil

DonMurray-

With any recip piston engine some lube oil passes by the rings by design. If there were no oil film present on the cylinder wall surface as the compression rings passed by, the compression ring faces and bore surface would rapidly fail due to scuffing. The oil control rings are designed to produce a micro-thin film of oil on the bore surface as they slide up and down, which prevents the compression ring faces from scuffing. If the oil control rings are working properly, the oil film they create on the bore surface is just sufficient to prevent scuffing of the compression rings, but not so thick as to result in the oil film on the bore surface near the upper end to become hot enough to flash and auto-ignite due to compression heating.

What is key to preventing the oil film on the upper bore surface from flashing and auto-igniting is providing sufficient cooling of the cylinder liner such that the bore surface always remains just below the flash temp of the lube oil. However, this can be very difficult to achieve with a very high pressure CI engine.

RE: pre-ignition triggered by lubricating oil

(OP)
Thanks for your thoughts. We should be running up on the dyno in another month or two. I'll let you know how it all goes.

Thanks,
Don ---

RE: pre-ignition triggered by lubricating oil

hi there.

am puzzled by your question.
sounds like you are designing something very experimental.
designing a high output Diesel engine from scratch is an awesome task.
forgive my asking but this question is a little basic for such an involved project.
more info will get you a clear cut solution on this board.

I wish you well on your project.

M6

RE: pre-ignition triggered by lubricating oil

Don,

Try checking the SAE papers published by SWRI in 2012.

I have symphaty to the problems that you may be facing. Check your oil carry over at various load/speed and ensure that it is below 1 g/hr. Conduct also oil consumption test if you have to. Unless you go into ionic liquid based lubricants, it is really difficult to change the engine oil's autoignition temperature.

RE: pre-ignition triggered by lubricating oil

(OP)
Thanks to all of you for your insights.

I am trying to anticipate all potential issues before our first dyno runs. Because our pre-ignition pressure is so high, I was looking for your insights regarding experience with any pre-ignitions stemming from lubrication oil. While our design prevents any friction between the pistons and cylinder walls, we are using lots of oil to augment cooling.

Thanks for all your help,
Don ---

RE: pre-ignition triggered by lubricating oil

If your oil control rings are doing their job, the only lube oil that should be present in the working space is the oil film on the cylinder wall surface. Normally this oil film is extremely thin, and because it is in contact with the inner cylinder liner wall that is being aggressively cooled at its outer surface, the oil film is kept cool enough to prevent it from vaporizing, mixing with the intake air and combusting. Do some calculations to determine if the bore surface at the upper end is being cooled sufficiently to keep its temperature within the safe limit of your lube oil.

With high cycle pressure CI engines, it can be very difficult to adequately cool the bore surface at the upper end of the cylinder, due to the very thick liner wall needed to handle the high pressure loads. If the lube oil is flashing off the bore surface due to excessive temperatures, the most obvious symptom will be ring/liner scuffing.

RE: pre-ignition triggered by lubricating oil

I recall (I think) having heard that in spark ignition engines GM had determined that preignition can start well before TDC, and maybe even before the compression stroke begins.

over on speedtalk there is a recent thread that has evolved from detonation to about a phenomenon ( in Direct Injection gasoline engines?) resembling pre-ignition by some folks ( well, maybe just one) who has experienced it under circumstances new to me, but I'm pretty much a summer soldier / arm chair athlete. References to research by SWRI has been offered.

Something about accumulation of "stuff" in the relatively cool interstitial spaces between rings over several combustion cycles, and in ring gaps if I'm following it correctly.

RE: pre-ignition triggered by lubricating oil

(OP)
Thanks for your input

RE: pre-ignition triggered by lubricating oil

Tmoose-

The accumulation of HC compounds in the crevice volumes around the ring grooves, quench areas between the piston deck and cylinder head, and spaces between the piston crown sides and cylinder wall above the top ring, have presented HC emissions problems for production SI auto engines. But typically these HC mixtures never become hot enough to combust due to the fact that they are in intimate contact with the relatively cool piston, head and liner surfaces.

SI auto engines deal with these HC compounds by burning them in the catalytic converter.

RE: pre-ignition triggered by lubricating oil

Hi Tbuelna,

That was and probably still is my take on gases in the far reaches of the combustion chamber of gasoline or diesel engines.

Here is a link to that lengthy impenetrable thread.
http://speedtalk.com/forum/viewtopic.php?f=15&t=38759

notchback is the one working on Low Speed PreIgnition with well monitored engine at SWRI

Nitro2 claims firsthand knowledge of some autoignition events originating in crevices the cool nether regions in extreme race engines.

A few others seem to have real info to offer.

RE: pre-ignition triggered by lubricating oil

Don,

The discussion at Speedtalk about preignition in highly supercharged or turbocharged GDI engines at low rpms concerns top ring land or between ring material triggering preignition in cylinders that are fully fueled. Since diesels are "dry" before the injection of fuel and since ignition occurs automatically with the injection, "preignition" is impossible in a normal, healthy engine despite the likely presence (IMHO) of similar ring space material.

RE: pre-ignition triggered by lubricating oil

BTW, it appears that low speed pre-ignition, LSPI as it is called in a number of papers, is a serious problem occurring under very high boost leading to very destructive detonation. Since the use of high boost at low speeds to make big low-end torque is an effective strategy to improve low speed responsiveness in "undersized" engines, LSPI is getting a lot of attention.

As I opined above, I think diesels are immune to this problem.

RE: pre-ignition triggered by lubricating oil

back in 2012, SWRI published a paper linking the engine oil temperature with gasoline knock rather than diesel one. I wont worry much about the effect of engine oil property in diesel engine.

RE: pre-ignition triggered by lubricating oil

Hmm, correlating oil temperature with knock is not surprising since in-chamber temperatures are causal to knock and causal to overall engine temperatures, coolant temperatures and oil temperatures. What seems to be implied is that oil temperatures are causal to knock even while controlling everything else. This I would like to read about. The inference that comes to mind is that the amount of oil getting into the chamber is related to oil temperature.

RE: pre-ignition triggered by lubricating oil

Lube oil will not combust unless it vaporizes, mixes with sufficient oxygen, and is heated to a high enough temperature. In most piston engines, there are only two ways lube oil can enter the combustion space: leakage past the intake valve guides, or leakage past the piston rings. Neither one is affected by oil temperature.

RE: pre-ignition triggered by lubricating oil

Tbuelna,

The condition that you described easily available before and during the spark ignition. Even Heywood's book discussed the hydrocarbon molecular structure and how it can affect knock tendency.

Oil can still get into the combustion chamber through the PCV breather and it is bad if the oil separator is not working well. The amount of oil in the blow by may also be caused by oil temperature, engine rpm and windage.

RE: pre-ignition triggered by lubricating oil

Another source of oil in the charge air of boosted engines is failure of the oil sealing system of the compressor/blower.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: pre-ignition triggered by lubricating oil

The examples of lube oil entering the combustion chamber from a faulty PCV system or a faulty turbocharger/supercharger are not normal conditions, so they are not relevant to the discussion.

RE: pre-ignition triggered by lubricating oil

Tbuelna,

I beg to differ. We have a full test data to link high oil carry over from PVC breather to increased knock tendency. Not all engines in the market have oil carry over of less than 1 g per hour

RE: pre-ignition triggered by lubricating oil

higher oil temps will result in thinner oil, therefore more carryover past the control ring and valve guide. (and turbocharger seals, if present)

not to mention the increased evaporation potential of any lighter hydrocarbons present in the oil.

In two strokes, preignition from oil reducing the effective octane of the fuel, is a major consideration.

RE: pre-ignition triggered by lubricating oil

I think the issue of the rate of oil getting past the oil ring being dependent on oil temperature, as normally measured, must consider the fact that the temperature of the oil at the ring is exactly the same as the cylinder wall and ring/ring land temperatures and not the temperature of the oil in the pan or at the temperature sender. So, the rate of oil getting past the ring may correlate better with coolant temp unless oil spray cooling of the piston and walls dominates these temperatures.

RE: pre-ignition triggered by lubricating oil

A tiny amount of lube oil is supposed to get past the oil control rings by design. The oil control rings are designed to leave a micro-thin film of lube oil on the cylinder wall during each down stroke. This oil film is just sufficient to provide boundary lubrication for the compression ring contacts, but also thin enough to prevent it from flashing off due to exposure to the heat of intake charge compression or combustion gasses.

RE: pre-ignition triggered by lubricating oil


Beside the point somewhat - but I have seen very old and worn diesel engines running on their own lubricating that has got past their rings.

RE: pre-ignition triggered by lubricating oil

And they can only stopped by loading them to the point of stalling, or blocking the air intake with something that can withstand up to 15psi.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: pre-ignition triggered by lubricating oil

While it might be possible in theory for a CI engine to continue idling simply from sufficient lube oil finding its way past the oil control rings and into the combustion chamber, in reality it is highly improbable. If the rings are worn enough to allow this level of lube oil blow-by, there would probably not be sufficient compression heating in the engine to produce ignition of the lube oil. Also, the lack of intake throttling in a CI engine would mean there is no negative pressure differential produced in the combustion space that would cause lube oil to be drawn into this volume.

RE: pre-ignition triggered by lubricating oil

The usual failure route for a diesel engine running away on its own lubricating oil is that the piston rings or turbo seals fail to the extent that there is excessive crankcase blowby (or the oil goes directly into the intake stream via a failed turbocharger), the crank blowby overwhelms the crankcase venting system and goes directly into the intake stream. When it gets to the point of raising the revs, the higher cylinder pressure and higher revs cause more blowby and away it goes until either someone stalls or strangles the engine or a rod goes through the block.

RE: pre-ignition triggered by lubricating oil

The seals that usually fail on a diesel engine turbo are those on the turbine side. And this would not result in lube oil entering the combustion spaces. A bit of blow-by into the crankcase due to worn compression rings would also not tend to force lube oil into the combustion spaces with a turbocharged CI diesel engine, since there would be a positive pressure delta between the cylinder volume and the crankcase volume at all times. It would require a low pressure within the intake to cause significant amounts of lube oil to migrate past the piston rings, and this would not happen with a turbocharged four stroke diesel engine.

The only diesel engines I know of that have "run-away" on their own are those that had crude mechanical fuel injection systems, where the fuel delivery was metered by a mechanical control that responded to engine speed.

RE: pre-ignition triggered by lubricating oil

"Usually" ... perhaps, but not always.

I'm most familiar with the VW diesels. It's not unusual to find oil in the intake system. A small amount doesn't do any harm. A lot of it, is a big problem.

Runaways as a result of an exploded turbo aren't common, but they are not unheard of. On the old mechanical-injection engines, switching off the key cuts off the fuel solenoid, and if the engine is running away on lube oil, that doesn't stop the engine. The problem is NOT failure of the fuel solenoid to shut off fuel delivery, because that's the same solenoid that shuts down the engine normally when you turn off the key every time, and if that didn't work, you would know it (and it would be exceptionally coincidental for the shutoff solenoid to fail at the same moment as the governor failed).

If the turbo explodes and the shaft breaks (it happens) it doesn't matter what condition the seals are in; oil being fed to the turbo is going to pour into the intake ...

RE: pre-ignition triggered by lubricating oil

There is a record of a diesel engine in an underground machine here in Aus where the turbo impeller failed, the nut that held the impeller on got taken downstream by the airflow and lodged itself into the intake shutoff valve, which prevented the engine from being shut off when it ran away on the lube oil coming from the destroyed turbo. One of those failures where everything lined up to create a dangerous situation - I think the operator ended up loading the engine up in some way to stall it out.

RE: pre-ignition triggered by lubricating oil

Gentlemen, good day,
I have to support those who have experienced a runaway on the older golf diesels, not pleasant. The order of failure would appear to be worn rings/pistons [bad maintenance] blow by would force engine oil back through the PCV system into the intake system and you had a runaway. As long as there was oil in the sump it would run of its own accord, until it would self destruct.
Golfpin

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources