Can someone explain how oil protects against LSPI?

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ZZman

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Wouldn't it be the proper computer/timing that would do the protecting or stopping of it?
 
I don't know that the exact mechanism is completely understood even now, but the chemical composition of oil can strongly affect uncontrolled ignition of the air/fuel charge through oil droplets and/or tiny solid particles from oil combustion in the cylinder. Since it is Low Speed Pre Ignition and tends to occur in high torque conditions, I can only assume that relatively low RPMs during periods of high stress on the engine basically give the unwanted ignition more time to occur in any given combustion cycle...and these DIT engines are generally pretty good at producing a lot of torque at low RPMs. I know, the whole thing seems weird...I doubt very much that anybody working on early mass market DI systems even remotely saw this coming.
 
Is it really protecting against it, or minimising what is causing it? I gather there would be no LSPI if there were no deposits whatsoever in the first place.
 
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Originally Posted By: ZZman
Wouldn't it be the proper computer/timing that would do the protecting or stopping of it?
Oil doesn't protect against LSPI. The oil and/or some components of the oil are possibly contributing to LSPI. They are trying to either get rid of or mitigate the components that do possibly contribute. In early testing, it looks like higher levels (1500 or above) of calcium MAY be a possible contributor. So, the manufacturer either lowers the calcium, or raises ,say, magnesium, moly, or ZDP, or some combination thereof, to mitigate this. This is all early on, so nothing is set in stone.
 
Originally Posted By: Garak
Is it really protecting against it, or minimising what is causing it? I gather there would be no LSPI if there were no deposits whatsoever in the first place.
My understanding is that there is no LSPI if there is no oil present in the chamber, but I can't prove that and I'd think it would be very hard to test without quickly seizing an engine. That would say that proper oil composition is minimizing the problem since oil is the cause of the problem.
 
Ok. Run Krytox pfpe in the experiment. Ill go ahead and blame the high static compression AND low octane fuel. They hoped a stratified charge would allow good ignitability ( a late puff of fuel rich mist near the sparker) but the lean boundary charge may be prone to pre-ig due to burn carryover from exh cycle in the ring land area - now rings are closer to the crowm. All speculation on my part here, but drawn from building hi comp engines in the late 70's
 
There seems to actually be no concrete answers. Additives, Base oils engine components who knows.
 
Now I have PTSD OVER LSPI, now what? There will be 1000s in here losing sleep not to mention millions of googling over it....lol Did we ever solve PS "piston slap"?
 
Originally Posted By: ARCOgraphite
Ok. Run Krytox pfpe in the experiment. Ill go ahead and blame the high static compression AND low octane fuel. They hoped a stratified charge would allow good ignitability ( a late puff of fuel rich mist near the sparker) but the lean boundary charge may be prone to pre-ig due to burn carryover from exh cycle in the ring land area - now rings are closer to the crowm. All speculation on my part here, but drawn from building hi comp engines in the late 70's
Strange that you should mention Krytox grease. When I was running oil consumption tests at Cummins back in the mid-90's, one technique that we used was to shut off all the oil going to the cylinder head of the test engine, to see how much oil was being lost through the ring pack alone. When we shut off the oil, we packed the rocker arm pivots, valve tips, and pushrod cups with Krytox grease, then ran the engine at idle for 100 hours to get a stable oil consumption reading. The natural gas C-series engine I was testing was shown to be using about half of its oil through the multi-lip valve stem seals. Switching to single-lip seals cured that problem.
 
Originally Posted By: CourierDriver
Now I have PTSD OVER LSPI, now what? There will be 1000s in here losing sleep not to mention millions of googling over it....lol Did we ever solve PS "piston slap"?
STBY!!! ;^)
 
Originally Posted By: ZZman
Guess this answers it https://www.oronite.com/products/lspi.asp
I tend not to believe much coming from a companies website. I am not saying it doesn't exist and the information isn't correct (not sure) but their main goal is to sell you a product. If it came from engineers I would tend to be more trusting. That said, Dexos and ILSAC GF-6 standards are telling me that there is something to this. Although it seems like there are a lot of variables to this problem that have yet to be fully vetted out. I have never heard of engine damage due to LSPI. Has anyone had this happen in real life? It just seems like there are a lot of variables and POTENTIAL for major problems but on all the boards I am on, haven't heard of any engines blowing up because of this.
 
http://papers.sae.org/2016-01-2277/
Quote:
Consistent with previous reports, the detergent system was found to have the largest impact on LSPI frequency. Furthermore, once a balanced detergent system was identified and its LSPI impact was minimized, the effect of other additives, ash-containing as well as ashless, became apparent. In order to develop a robust additive package that maintains performance in critical bench and engine tests while offering optimal LSPI protection, consideration must be given to the impact of all lubricant additives not simply the detergent type and treat rate.
 
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