Review article on low-speed preignition (LSPI) and super knock

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Let's express the displacement, torque, and BMEP in metric units as they are expressed for all modern engines because it's getting confusing here.

The 1,991 cc Mercedes-Benz M139 has two variants -- 480 Nâ‹…m and 500 Nâ‹…m.

BMEP (bar) = 40π × torque (N⋅m) / displacement (cc) = 125.664 × torque (N⋅m) / displacement (cc)

These engines have BMEP = 30.3 bar and 31.6 bar, respectively, which are way higher than any existing production engine as A_Harman said. The review article was saying that it's very difficult to go beyond 27.0 bar because of conventional knock as well as LSPI-induced super knock but these engines are going well beyond that.

Certainly the highest-octane gasoline is a must here but that will do nothing to prevent LSPI and super knock. Oil is the crucial factor in preventing LSPI because that's what seems to be causing LSPI and super knock in high-BMEP engines. Regardless of the official oil recommendation, I would avoid any oil that's not tested for LSPI. Unfortunately the LSPI test in API SN PLUS is not very strict and the more strict dexos1 Gen 2 spec does not have oils with HTHSV ⥠3.5 cP.

Nevertheless, ACEA 2018 is expected to be released in mid-2020 or later and new A6/B5 and G6 categories for TGDI engines that include LSPI protection and timing-chain-wear protection are expected. I bet M139 will spec A6/B5 or G6 and there will be probably a new Mercedes-Benz OEM oil spec that has LSPI and timing-chain-wear tests.

https://www.lubrizoladditives360.com/introducing-acea-2018-light-duty-oil-sequences/
 
Originally Posted by A_Harman
Originally Posted by 2015_PSD
Originally Posted by Gokhan
Originally Posted by 2015_PSD
In thinking about this a bit more, which engines are typically higher than 22 bar? My AMG is producing more than 2HP per cubic inch, so is BMEP higher than 22 bar the only reason for LSPI? I have not looked into what OEM/engine family suffers the most from LSPI, but it would mean they are producing much more than 2HP/2LB-FT per cubic inch if that is the root cause.
BMEP = 22 bar is actually already in the danger zone and you may be having occasional moderate LSPI + super knock events depending on the oil you are using.
I am running Castrol Edge Euro 0W-40 SN and it is a full SAPS oil. I have had zero LSPI events and this is why I tend to believe that LSPI is much more about engine design and management versus that of oil composition. From my point of view, using oil to compensate for LSPI is a band-aid to an underlying design issue. It will be interesting to see the new M139 Mercedes AMG 2.0L engine which makes 416 horsepower and 369 lb-ft of torque giving it a specific output of 208.9 horsepower per liter or 3.40 HP per cubic inch and how it handles LSPI.


369 ft*lbs/122 in^3 = 3 ft*lbs/in^3 => 452 psi BMEP at peak torque. That's a BMEP level that's reached even in very few diesels. If I had the money to buy an AMG Mercedes, I wouldn't be cheaping out on fuel, and would buy the highest octane stuff I could find.
My AMG is the 3.0 Twin Turbo and it sees either Chevron or Shell premium in every tank with a bottle of Gumout One and Done every 5K or so.

The new M139 is a different beast and if they build the 3.0L version, it should give nearly every V8 a run for its money.
 
Originally Posted by 2015_PSD
I am running Castrol Edge Euro 0W-40 SN and it is a full SAPS oil. I have had zero LSPI events and this is why I tend to believe that LSPI is much more about engine design and management versus that of oil composition. From my point of view, using oil to compensate for LSPI is a band-aid to an underlying design issue. It will be interesting to see the new M139 Mercedes AMG 2.0L engine which makes 416 horsepower and 369 lb-ft of torque giving it a specific output of 208.9 horsepower per liter or 3.40 HP per cubic inch and how it handles LSPI.

Originally Posted by BMWTurboDzl
I suspect it's because vehicles which are spec'd for A3/B4 are NOT designed with fuel economy in mind. IIRC from the article LSPI is a phenomenon which occurs under a boost, high load and low rpm operating environment.

Regarding the engine design, I don't think any major car manufacturer is inferior or superior to another -- they all use the state-of-the-art knowledge and tools available to everyone.

My understanding is that there are three main factors that influence LSPI and super knock, in addition to various others:

1. BMEP (torque per displacement multiplied by a constant): The higher the BMEP is, the more likely the LSPI and super knock are. BMEP = 25 bar seems to be where real trouble starts and BMEP > 27 bar is where preventing LSPI and super knock becomes very challenging. However, it looks like you can have LSPI and super knock with BMEP as little around 20 bar, depending on the size of the engine (see factor 2).

2. Available torque: The less the available torque, the more often you will max out or nearly max out the torque and reach or near the highest BMEP your engine is designed for, which could start LSPI and super knock. That's why you're a lot more likely to get LSPI and super knock with a 999 cc displacement and 170 Nâ‹…m torque PSA Opel (GM Ecotec) engine with BMEP = 21.4 bar than with a 1,991 cc displacement and 400 Nâ‹…m torque Mercedes-Benz OEM engine (M264 E20 DEH LA) with BMEP = 25.2 bar.

3. Oil: Most literature is supporting the conjecture that the oil is what is ultimately causing LSPI and super knock. Therefore, it's crucial for oils to go through stricter LSPI tests as the BMEP gets higher and the engine displacement gets smaller. OEMs are in the process of creating new oil specs that test both the fresh oil and used oil for LSPI and super knock.
 
ran my Honda 1.5T Civic on Edge 0/40 A3/B4 40k people here scoffed, never a LSPI or MPG penalty, when the level rose during our cold I drew it down..
car is a pleasure to own. son has it now.
 
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...and now I operate a couple legacy engines... Toyota 4.7L and 4.0L so I look for hi Ca. legacy motor oil like a 0/40 M1.
 
Great discussion. I am confident BITOG will gather up all the disparate information and get us to this best possible answers sooner if not later.

We have Red Line with lots of calcium, plus lots of moly & zinc, as quenchers.

We have most oil designs going to lower calcium, with typically greater magnesium.

I listened to the podcast linked on BITOG, wherein lubrizol guys had some recent detailed thoughts. They stated that incidence of LSPI was very infrequent, and by merely being sure to use a D1G2 and NOT a D1G1 oil, the likelyhood of incidence of LSPI was made even exponentially less likely. They further stated that spec'd oil ought to be used, not the thick 0W40 oils mentioned herein. Obviously many beg to differ.
 
Originally Posted by dblshock
ran my Honda 1.5T Civic on Edge 0/40 A3/B4 40k people here scoffed, never a LSPI or MPG penalty, when the level rose during our cold I drew it down..
car is a pleasure to own. son has it now.


I read your comments with great interest.

A friend who is also a delivery driver has a 2018 Civic Hatchback. He also accumulates miles on the odometer rapidly.

I will talk to him soon and try to get him to switch to a 0W40, M1 or Belgian Castrol or whatever.

I really would to hear some feedback from him following his switch and experiences. I know darn well this Honda 1.5L TGDI has great performance and fuel economy.
 
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