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 ---
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
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
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
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
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
Thanks,
Don ---
RE: pre-ignition triggered by lubricating oil
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
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
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
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
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
RE: pre-ignition triggered by lubricating oil
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
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://
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
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
As I opined above, I think diesels are immune to this problem.
RE: pre-ignition triggered by lubricating oil
RE: pre-ignition triggered by lubricating oil
RE: pre-ignition triggered by lubricating oil
RE: pre-ignition triggered by lubricating oil
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
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: pre-ignition triggered by lubricating oil
RE: pre-ignition triggered by lubricating oil
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
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
RE: pre-ignition triggered by lubricating oil
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
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: pre-ignition triggered by lubricating oil
RE: pre-ignition triggered by lubricating oil
RE: pre-ignition triggered by lubricating oil
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
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
RE: pre-ignition triggered by lubricating oil
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