Oil Composition, Direct Injection, & Low-Speed Knock

The advent of direct fuel injection and the required changes with respect to fuel delivery and engine calibration has forced automotive manufacturers to make serious changes in their fueling strategies. These changes are designed to extract the maximum amount of usable power without creating other operational challenges. Direct injection has not been terribly friendly to aftermarket changes, however, and a recent test session initiated at EFI University with the help of Lake Speed, Jr. and Driven Racing Oil investigated some of these challenges. It seems that low-speed spark knock has been a concern when turbocharged direct injection is used, so the two companies got together to flog the EFIU dyno and see what kind of data they could extract from the series of tests, which is still taking place.

The entire concept was spurred on by research performed by Oak Ridge National Laboratory; about two years ago Speed received a phone call which pushed him into action.

“They contacted us and asked for help with a project they were working on,” says Speed.

“They had identified an issue with direct injection turbocharged engines, which they called low-speed pre-ignition. As an engine guy, I said ‘you’re getting knock,’ and they explained that it wasn’t knock, it was more a detonation event so large that it could potentially break the piston in one event. They felt it was a common occurrence with DI vehicles around the world, and as a result all of the OEMs had put procedures in place to try to work around the issue.”

Workarounds are great, but not when they impact fuel economy and emissions – that’s when the government perks up its ears and starts to pay attention. Since the reason for using direct injection in the first place is to improve fuel economy and reduce harmful tailpipe emissions, it’s not helpful to the cause if these mega-knock occurrences are destroying engines.

How much does oil composition matter when it comes to low-speed knock events when using direct injection? Read on–you’re about to find out.

The Research Begins

The ORNL research had discovered that oil had the ability to increase the tendency for mega-knock – and potentially had the ability to decrease the mega-knock tendency. Their research had shown that the types and amounts of detergents in the oil seemed to have an effect on the tendency and the magnitude of these events. With the understanding that Speed – and Driven Racing Oil by extension – had the ability to create oils with specific formulations, they asked for help with their research.

Driven Racing Oil created a variety of oil formulations using various detergent packages and sent them to ORNL, whereupon the government boys did their thing, and ended up with more questions. By the 2016 SEMA Show, Speed had questions of his own related to the shared information from ORNL.

“So these turbocharged, direct-injection vehicles are having these issues with knock – essentially related to the detergents in the oil – and I couldn’t help but think back to the discussions I used to have with old-school engine guys I used to deal with who said to not run detergent oils in high-compression race engines because it can cause them to detonate,” says Speed.

“They knew that detergent oils tended to have knock issues, and non-detergent oils tended to not have knock issues.”

“In the end, you end up with this third chemical which is neither fuel nor oil, and the octane value of this third chemical is lower than the fuel or the oil, so it is what detonates,” – Lake Speed Jr., Driven Racing Oil

But without specific data on these theories, they were just conjecture. So he set out to do some research on the issue, and that’s where EFI University came into the picture. In discussion with EFIU’s founder, Ben Strader, Speed discovered that there were instances where a calibration was performed on a turbocharged direct injection vehicle, the car was all set and performing well, and within a week, boom – catastrophic failure.

So what happened? What if the engine was tuned on low-detergent break-in oil, and was then taken home and loaded up with standard detergent oil? Since the detergents had been shown by ORNL’s research to be a potential cause of the low-speed mega-knock issue, it was entirely plausible that these oils were unintentionally causing the problem.

EFIU had the facility, the measuring and testing equipment, and most importantly, the knowledge to assist with the testing processes Speed had in mind. EngineLabs is privy to the results of this ongoing testing, and we stress that at this point it’s just testing – but there are some interesting, quantifiable results so far.

Setting The Stage

There are several direct-injection engines – both turbocharged and naturally-aspirated – in use in performance applications today; from the LT1 Corvette/Camaro engine to the EcoBoost family of Ford engines and engines produced by other companies.

Perhaps the most visible is the naturally-aspirated LT1 engine found in the 2014-current Chevrolet Corvette Stingray and 2016-current Camaro SS. It is this engine selected as the test subject; Speed says the high-quality built-in knock sensor in this platform was the perfect choice to help them categorize the results of the testing.

“We tested everything – synthetic oils with a lot of detergents, synthetic oils without a lot of detergents, and similar mineral-based oils,” says Ben Strader.

Chemistry At Work

Quick, short, somewhat informative lesson before we get any further: the detergents used in engine oil are metals, typically sodium, calcium, or magnesium depending upon the specific oil formulation. These oil-soluble bases are polar, which allows them to stick to the surfaces of particles found in the oil and do one of two things – prevent them from coagulating (smaller particles) or repel one another (larger particles).

“Mostly what we’ve been interested in is the knock; at what RPM, what load, when the engine knocks, when it doesn’t, and what happens if we move the spark timing or the injection event. That’s one thing with direct-injected engines – they become very sensitive to knocking because of the way the fuel is injected into the engine. If you just change the fuel pressure, to get the same amount of fuel into the engine you have to make a longer or shorter pulsewidth. So where that happens in the engine relative to where the piston is in the cylinder and how much splash is on the cylinder wall makes a big difference.”

Calibrator Seth Francis tickled the keys on the laptop during the entire testing process, monitoring each of the important parameters and setting up the tune to ensure the engine was repeatable and consistent.

During the course of the testing sessions, they made well over fifty dyno pulls. In order to maintain testing accuracy, they monitored everything from the room temperature to the oil temperature. The dyno pulls for the tests were started with a pre-set speed of 2,500 rpm; they start the test, begin data collection at 2,750 rpm, then ramp up engine speed by 600 rpm per second to the peak of 6,250 rpm. Strader talks a lot about normalizing test results, and this is done by making three pulls per test. There is a five-second delay between each pull, and the results of the first two pulls are ignored. By using Mainline DynoLog’s completely-automated dyno software, they can eliminate operator variables from the equation and standardize the results as much as possible. Although horsepower and torque figures are lower on the third pull than they are on the first, the pressures and temperatures are normalized, making the data more accurate.

“The GM software is tracking knock; you can see the number of knock events, how the PCM is pulling timing from the engine, so we have a metric where we can run the engine in a given environment, holding all of the other variables consistent, and then only change the oil chemistry to see what effects the oil chemistry has on the number of knock events and the magnitude of knock events,” says Speed.

Although some of the oils tested during this process were from Driven Racing Oil, not all of them were. The testing process was designed to determine whether there was a problem, and if so, what the case was–brand of oil didn’t matter for research purposes.

Oil Testing

With the background set, plans laid, and procedures established, they began testing. Interestingly, as datalogging began, an issue was immediately discovered that could have derailed the whole test.

“There was so much knock because of the poor 91 octane fuel we have here in Arizona,” says Strader.

“Even on a light tuneup, the low octane tables in the GM system were pulling 10 or 11 degrees of timing initially,” says Francis. “It was 70 horsepower down.”

To solve the issue, Speed suggested using Driven’s Defender + Booster to improve fuel quality; by adding it to the fuel they were able to spec out a fairly aggressive tuneup calibrated by Seth Francis. Without the octane booster, they were experiencing knock events which were significant enough that the testing would have been impossible to complete. Even with the octane booster, they were still recording some knock correction with the datalogging software, but were able to perform the testing anyway.

Driven’s Defender + Booster was used to stabilize the fuel system’s performance on the dyno. The less-than-optimal high-octane fuel found in Arizona almost derailed the test.

“Detergents are metals. Sodium, calcium, and magnesium are on the periodic table, and they are reactive,” says Speed. “Sodium and water can cause big booms, and we make water with every combustion event.”

He mentions the octane value of the oil, and says people tend to focus on that particular concept, but it’s in fact not important at all. Regardless of whether an engine is burning oil or not, there will always be oil present in the upper ring zone as that’s what keeps the rings lubricated.

The test engine wore a set of big-tube dyno headers but was otherwise untouched save for Francis’ ECU calibrations.

“It has nothing to do with the amount of oil in the combustion chamber, or if the engine is consuming oil or not. There’s going to be oil in the upper ring zone in every properly lubricated engine. It’s a question of whether the oil in the upper ring zone has a tendency to hold fuel, or not. If the fuel mixes with the oil, and the oil creates an emulsion, if you will, where it holds the fuel in the oil, that’s where things can begin to go bad,” says Speed.

It’s perhaps this one single quote that really tells the tale of their entire testing session. Based on the information shared with them from the ORNL testing, and backed up by the discoveries they made during the EFIU test sessions, all indications point to particular detergents acting as the root of the problem.

Where we talk above about sodium being highly reactive is where they received their first clues.

“In the end, you end up with this third chemical which is neither fuel nor oil, and the octane value of this third chemical is lower than the fuel or the oil, so it is what detonates,” says Speed.

“And that’s the challenge, because when it detonates, it all burns off and then it’s gone. For example, we could run the engine in a certain way to kind of load up the ring zone with this fuel/oil/soup combination, and then make a power run. In that first power run, you’d see several knock events, especially higher magnitude knock events. Then you could instantly make a second run, and the number and magnitude of knock events would diminish. By the third run, they are all gone. The engine was consuming and burning off all of the soup of unburnt fuel and oxidized oil that was reacting together because of the detergent holding the fuel in suspension.”

“What we saw was that with the factory ECU tuning there was definitely a noticeable difference in the knock levels of the engine when running high Sodium and Calcium levels in a mineral based oil as seen in the top graph on the yellow line. The bottom graph shows the same engine calibration, but with a synthetic blend using only Calcium and at moderate levels. We also found ways to mitigate the amount of knock present by modifying the calibration with regards to injection timing and fuel pressure settings. Changing spark advance or retard had little effect at controlling the knock. It is also apparent, at least from the current state of processing the data, that the reactionary phenomenon is aggravated at lower engine temperatures. This is due to the viscosity index of the oil making it thicker and therefore more difficult for the rings to remove all of it from the cylinder wall, so more oil is exposed to the direct impingement of fuel splashing off the top of the piston and contacting the oil directly,” says Ben Strader.

Fuel Atomization

Fuel Blend Matters

One interesting aside that Speed shared with the EFIU team: on any given day, there are up to 47 different active specifications used across the United States. These are designed to maximize performance for the given region where they are produced: high elevation/low humidity, low elevation/high humidity, etc. So the next time your tuner wants you to datalog your car before he makes changes to it, we’d have to say it’s a critical thing to do!

Another interesting point Speed brought up during the conversation was the difference between the way a carburetor atomizes fuel extremely effectively and direct-injection does not. Think about the difference in time—measured in degrees of crankshaft rotation—from the first time that a droplet of fuel sees air to the time the spark ignites in a single-plane carburetor manifold configuration. The fuel is leaving the carburetor long before the intake valve opens, and because there is constant vacuum in the intake manifold, the fuel doesn’t wait for the valve in the cylinder where it ends up to actually open. Conversely, the fuel in a direct-injection engine does not see any air until the exhaust valve closes and it’s injected into the cylinder.

“Therein lies the difference in the amount of time that the fuel has to atomize in terms of how much fuel is being completely combusted,” says Speed.

“The harder you run the engine, the hotter it becomes, and now you have more heat energy to make that happen. That’s why we’re thinking of this as low-speed preignition—because this tends to happen more in a cold engine that’s just been started up, or one that has been idling for a long time.

(Click to enlarge) Test results from various oil blends they tested on the dyno; as you can see, the blend with the highest sodium count also had the highest number of knock events.

In Conclusion

There is no conclusion just yet as the testing is ongoing at this time. Speed does say that they have discovered that the third chemical—which comes to life as part of the combustion process—is the one which is causing the issue.

“By the time we know that it exists, it burns itself out and it’s gone,” he says.

“We have pressure, heat, and metal, and we really believe that there is a catalytic reaction that is occurring while the engine is running that’s creating these things. It’s unique to direct injection engines because the fuel is being injected into the combustion chamber. There is fuel that’s not atomized getting over into the cylinder wall, which is how it’s mixing with the oil.”

It’s fascinating research, don’t you agree? We’re eagerly awaiting the next round of information to come forth from the testing sessions.

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About the author

Jason Reiss

Jason draws on over 15 years of experience in the automotive publishing industry, and collaborates with many of the industry's movers and shakers to create compelling technical articles and high-quality race coverage.
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