Oil and detonation, old but interesting.

[Bill Chase]

Curious if any of you guys have seen a higher knock threshold with different oils in higher compression street/strip cars. This world probably be more applicable to a mpfi setup than it would be to a carb/tbi setup. Hoping this will stir some interesting conversation, trying to learn. Thanks guys!


https://www.enginelabs.com/engine-tech/ ... eed-knock/

[RDY4WAR]

What that article is referring to is low speed pre-ignition, an issue with reactive detergent chemistry in engine oil causing pre-ignition in direct injected engines. This is a phenomenon mostly unique to gasoline direct injection, turbo GDI in particular. The issue is from the inevitable oil transport past the rings into the chamber and highly reactive additive chemistry, particularly sodium and calcium based detergent additives, will ignite causing pre-ignition. It's more of an issue at low rpm and high load. Dexos 1 Gen 2 targeted this issue specifically. API SN Plus and SP ratings also test against LSPI.

The easy solution for major oil brands, and the additive companies, was to eliminate sodium based additives completely and reduce calcium concentrations to <1500 ppm. Detergent concentrations went from 2000-2500 ppm Ca to a blend of 1000-1500 ppm Ca and 500-1000 ppm Mg. This isn't the ideal way to tackle LSPI though. ZDDP and MoDTC (moly) are both great LSPI quenchers. However, since API limits the phosphorus and sulfur content of engine oil, they can't increase ZDDP and MoDTC so they have to go with the next best thing which is reducing calcium (CaCO3).

Driven DI series oils combine both the lower calcium concentrations and increased ZDDP and MoDTC concentrations. As a boutique oil, they aren't limited by API. Many other boutique oils, including Amsoil OE, XL, and SS series and High Performance Lubricants PCMO, also contain an anti-LSPI add pack. Note if you don't have gasoline direct injection, this won't make much (if any) difference.

Also to note... Calcium and magnesium detergents in engine oils don't really "deterge" per say, but actually function as acid neutralizers, and are something we're all familiar with. The core of these additives is calcium carbonate and magnesium carbonate, which are found in many over-the-counter antacids like Tums and Mylanta. The same way they neutralize acids in your stomach that cause heartburn and indigestion, they neutralize acids in the oil that cause oxidation and corrosion.

[Bill Chase]

Low rpm high load na compression engine on pump gas mpfi is what I was thinking when I posted this. See similar thing in these types of engines?

Like a typical 10.5-11 street engine, heavy car/ truck low stall etc. Torque builds with almost too much static compression pushing the boundaries of pump gas any correlation there?

[RDY4WAR]

Low rpm high load na compression engine on pump gas mpfi is what I was thinking when I posted this. See similar thing in these types of engines?

Like a typical 10.5-11 street engine, heavy car/ truck low stall etc. Torque builds with almost too much static compression pushing the boundaries of pump gas any correlation there?

No, because MPFI engines have fuel swirling around in the cylinder throughout the entire compression stroke which suppresses any reactive chemistry from the oil. The fuel also vaporizes during the compression stroke which has a cooling effect, further reducing pre-ignition and detonation from oil contamination. With GDI engines, the fuel isn't introduced to the cylinder until right before the spark so there's no fuel in the cylinder during the compression stroke to mask the oil. Without fuel, cylinder temps rise faster during the compression stroke creating the environment for igniting the oil around the top ring.

[Bill Chase]

Thanks. I really appreciate you taking the time to explain it to me.

Makes me wonder why the recent push for direct injection/higher compression from OEM/EPA. If they can do it with 50 year old mpfi technology? Do the di engines burn that much cleaner? Or are they just that much more fuel efficient?

[hoodeng]

An interesting side note to this topic was when Formula 1 were introducing performance additives in their engine oil packages,then letting the engine consume oil during the race, the amount consumed during the race was within the rules, so no infringement there,, the power addition they achieved? enough to get the practice banned.The additives? I'd love to know.

Cheers.

[Kevin Johnson]

An interesting side note to this topic was when Formula 1 were introducing performance additives in their engine oil packages,then letting the engine consume oil during the race, the amount consumed during the race was within the rules, so no infringement there,, the power addition they achieved? enough to get the practice banned.The additives? I'd love to know.

Cheers.

WAG nano particles of nickel to act as a combustion catalyst. It creates a deadly gas, however, so not something that I would suggest replicating.

[dannobee]

Well, that and the visible smoke coming from the tailpipe probably wasn't the best image that F1 wanted to promote.

[RDY4WAR]

Thanks. I really appreciate you taking the time to explain it to me.

Makes me wonder why the recent push for direct injection/higher compression from OEM/EPA. If they can do it with 50 year old mpfi technology? Do the di engines burn that much cleaner? Or are they just that much more fuel efficient?

Fuel economy is the main one, but it's defeating itself in a few ways. GDI engines regularly see more valve deposits as well as more fuel dilution and soot in the oil. Oil change intervals become shorter due to that dilution.

[In-Tech]

Many DI engines suffer from oil pre-ignition. It's a phenomena that exists world wide, even with low mileage. I have become involve'd to help provide a solution.

[hoodeng]

Well that's just it Dannobee, there was no smoke, that would have been an earlier telltale. Very clever these Formula one folk, if there is an edge to be gained they will find it. This is one reason i love F1, to a lot it is just roundy round with a predictable finish line,, under the surface,, a lot of guys working at the nano level.

I would love to see F1 have a few basic rules like, a capacity limit,declared fuel, a box drawn on the ground that the car must fit in and maybe a tyre rule, that it, the rest, they can go for it. I loved the eras of ground effects, blown diffusers, unlimited rpm! now we see things like adjustable toe in toe out, seemingly an incremental change,, keep it coming!

Cheers.