Low-speed pre-ignition (LSPI) Questions with Answers
Question 1: Which of the common OEM oil specs (from VW, Mercedes, BMW, etc) include some form of LSPI test, and how do the tests vary? We know it’s a focus of API and ILSAC, but LSPI testing is also part of some of the other major euro OEM approvals, and even some diesel specs. Although you often have to dig to see which ones have that test.
As an example: I’ll be using your Euro L 5w30 in my Explorer 2.3 TGDI at some point. It’s only API SN, so one would think it would not have been tested for LSPI. But it does carry the Dexos2 cert which, although being targeted primarily at diesels, actually contains an LSPI test. I only know this because I did a deep dive into the spec.
Pennzoil Answer 1: For most OEMs, they incorporate the ASTM D8291“Sequence IX Engine Test” methodology as a criterion to measure the ability of motor oil to protect against Low-Speed Pre-Ignition (LSPI). You are correct that certain OEMs (GM, PSA and BMW) do have their own internal SPI test. Unfortunately, we do not have all the details on how they test for Pre-Ignition. The tests are proprietary and based on their own specific engine designs.
We think that the methodologies are similar to the API Sequence IX test (with their inhouse specific engines) where the conditions are set to create opportunities for an LSPI event; in the API LSPI test (1), “the test consists of 4 iterations. Each iteration is 175,000 ignition cycles from each cylinder with the first 170,000 valid cycles evaluated for the number of pre-ignition events”.
Question 2: What is the cause(s) of LSPI and how does the new formulation address LSPI? What are the test(s) the new LSPI formula is measured against? How well does it perform on those test(s)?
Pennzoil Answer 2: There are many theories on what initiates an LSPI event. A good summary of the causal of LSPI comes from Afton Chemical (2, 3). The consensus from research has narrowed the cause of pre-ignition to two major factors: fuel droplets and combustion deposits accumulation in “downsized and turbocharged spark-ignited engines” (4).
LSPI is nothing new to the industry for downsized “boosted engines” (4). The industry agrees that conditions favorable to a pre-ignition occurs when the engine undergoes conditions of high-load, low-speed operating conditions, leading to a pre-ignition process referred to as LSPI, a “conventional knock” (5). The event is normally seen at high-load operations around “15-24 bar Brake Mean Effective Pressure (BMEP)” (5) and “at engine speeds around 2000 r/min or below” (6)
The current methodology to test protection against LSPI is the Sequence IX Engine test. This test simulates conditions to stimulate LSPI events and sees if the fuel or engine oil can minimize the effects of pre-ignition. Since the introduction of API SN Plus, oil manufacturers have demonstrated their ability to protect against LSPI. The new ILSAC GF-7 and API SQ has carried forward the same requirements for LSPI protection and now have included aged oil LSPI protection also.
Question 3: Can LSPI be created in the lab, and if so, how easy is it to produce? Do you think it is easy for LSPI to occur "in the wild", or do you believe its' occurrence is rare? How do the answers to these questions dictate how Pennzoil approaches LSPI mitigation in their oil formulations?
Pennzoil Answer 3: Even though pre-ignition knock is not an uncommon event, the conditions to stimulate LSPI are difficult to create in the lab. It requires a: Source for pre-ignition, such as an oil droplet, a deposit particle, a pre-ignition event, and temperature and pressure condition to generate autoignition (4). However, an additional condition of “end-gas autoignition outside of the preignition flame, leading to a high intensity pressure wave called a “Super-knock” is needed to cause potential engine damage.
From the oil formulation side, we have recognized that LSPI can be minimized by lowering the concentration of calcium in the detergent package and the addition of MoDTC and ZDTP (5). There is also research that says higher quality base oils have shown to reduce pre-ignition events due to their higher flashpoints. Since the introduction of API SN Plus, Pennzoil has altered our formulations to address the LSPI issue; including the new API SQ specification requiring LSPI protection in aged oil. We continue to monitor the needs of the industry and work to deliver the motor oil that will meet and exceed the industry’s specifications.
Question 4: What is the history of this problem that wasn't a problem, until recently? Seems like a thing with today's tightly managed, high strung, small displacement, forced induction engines. I haven't heard of it until this week, and consider myself a "car guy" in the know. Without giving up corporate strategies, of course, how should an oil company market their product's resistance to this issue?
Pennzoil Answer 4: Since the introduction of the CAFÉ (California Average Fuel Economy) standard, the requirement for fuel economy and emissions limits has led to the introduction of downsized Direct Injection and turbocharged engines to achieve the fuel economy and emission benefits. As mentioned in the previous answer, the issue of pre-ignition has been around for many years; we see it as ignition knock. However, in the drive for fuel economy, downsized direct injection and turbocharging has led to an increase in LSPI issues. As oil manufacturers, we work closely with engine manufacturers to address their concerns, as well as providing high-quality performance oils for the consumer and the OEMs.
Question 5: Why is different formulation of oil what’s mainly used to combat LSPI? How much does LSPI resistant oil really do before other factors like low quality fuel start causing it?
Pennzoil Answer 5: Again, there are many factors that lead to LSPI event; engine design, engine management, fuel and oil formulation (5). From the oil formulation standpoint, changes to the detergent package (lowering Calcium content, increasing Magnesium), addition of anti-wear additives like MoS2, or ZnDTP have positive effect in reducing LSPI events. Fuel type and fuel management can also be a factor (5). Thus, mitigating LSPI requires the industry to work together. Pennzoil is constantly working with our OEM partners, testing house, and additive suppliers to deliver products that meet the needs of the OEMs and our customers.
Question 6: Is LSPI a phenomenon that has only been observed in direct-injection gasoline engines? It seems the finer, higher-pressure mist when combined with the added heat of adiabatic compression from forced induction would be conducive to rogue ignition events.
Pennzoil Answer 6: LSPI is a pre-ignition event that can occur in port injected and/or direct injection engines. It is true that the Super-Knock (catastrophic event) is seen recently in turbocharged, direct-injection engines under very specific conditions; due to unburnt fuel droplets or a combustion deposit that are placed in conditions that leads to “the formation of propagating flames from pre-ignition hotspots” (4) prior to the timed ignition event. Below is an example of a possible pathway for LSPI (5)
Question 7: How does LSPI differ from "normal" pre-ignition and detonation/knock?
Pennzoil Answer 7: Pre-ignition does not guarantee a super-knock, but a super-knock is initiated by an LSPI event. The difference is that a super-knock starts with a pre-ignition event followed by an “autoignition outside of this flame, leading to developing detonation and subsequent pressure oscillation of high intensity”
Question 8: We know that oil is a contributing factor to LSPI events, but how much does oil actually influence these events compared engine design/calibration choices? Is oil the main contributing factor? Or can engine design choices on the small turbo charged engine like piston design/ring pack design be the main cause of LSPI?
Pennzoil Answer 8: It is difficult to point to which factors contribute most to the causal effects of LSPI. We recognize that the introduction of turbocharged, direct injection gasoline engines has led to the increase in LSPI issues in passenger car engines. Research has also shown that engine design, fuel spray pattern, injector location and ECU programming can also give opportunities for LSPI events (6)
Question 9: In comparison of API SN+, SP and incoming SQ, what changes in the formulation have taken place to combat LSPI and what is the overall reduction goal in LSPI with SQ over SP?
Pennzoil Answer 9: Since the introduction of API SN Plus, API implemented the Sequence IX Engine Test to measure the ability of engine oil to minimize LSPI. We recognize that formulation changes are necessary, such as: Reduction of Calcium and shifting to a magnesium based detergent package, incorporating MoS2 and ZnDTP to certain levels to minimize ash content while helping to quench LSPI. Base oil quality seems to also have positive benefits to minimize LSPI. The challenge for formulators is to balance the formulation for complete protection of cleanliness, wear, oxidative stability and extreme temperature performance.
The new API SQ added a new aged oil LSPI test the specification. This new test addresses the concerns that, as the oil ages, it may loose the ability to protect against LSPI. This new specification addresses this issue and ensure the consumer and OEMs that the oil will protect against LSPI during the entire drain interval.
Question 10: How do Euro formulas differ to combat LSPI?
Pennzoil Answer 10: European engines are also challenged with LSPI in their smaller, turbocharged engines. Depending on engine type and model, they may have specifications that will require LSPI protection. European formulation may also include other API engine tests in their specifications, such as wear and cleanliness protection. As mentioned earlier, certain OEMs like BMW may include their own internal LSPI test in order to receive their approvals for use.
Question 11: Is LSPI made worse by the US still hanging on to low octane fuels?
Pennzoil Answer 11: There is some data (5) that states fuel composition and physical properties can lead to LSPI frequencies. Some data suggests that increased RON and higher autoignition temp fuel can help to suppress LSPI events. Data also suggest that minimized wall wetting will help to minimize LSPI events. Again, LSPI requires a combination of conditions to line up that will lead to a pre-ignition event.
Question 12: If an engine has an LSPI event, while exclusively using Pennzoil, will Pennzoil warranty the engine? If not why? Can a motor oil completely mitigate LSPI, assuming the engine is sound?
Pennzoil Answer 12: Manufacturers have oil recommendations and drain intervals for specific vehicles and engine types. The new API SQ requires that these oils must pass the LSPI and aged LSPI tests, including all other API engine tests. Thus, OEMs would typically be the first contact for any warranty claims. Pennzoil stands behind the performance of our oil and meeting the specifications set by the OEMs and industry tests. If you have any questions concerning the performance of our oil from Pennzoil products, ranging from Pennzoil Conventional to Pennzoil Platinum, consumers can call our Technical Information Center at 1-800-Best Oil (237-8645).
Question 13: Is LSPI occurring because the oil is getting past the rings on the piston? I would think a tiny tiny tiny amount if any remains on the cylinder walls in a good engine?
Pennzoil Answer 13: All engines are designed to allow a tiny bit of engine oils to pass the rings and lubricate the cylinder. It is when it combines with some unburnt fuel that can lead to a pre-ignition event. As previously mentioned, not all pre-ignitions will lead to a super-knock. The diagram below shows one pathway through which a pre-ignition event can occur. (4, 5). Thus, a combination of events must take place for LSPI to initiate.
1. Sequence IX Engine Test
2. LSPI_API_SN_Plus_White_Paper_Infographic_02-14-18.pdf
3. New Hardware New Challenges GDI Engines and LSPI
4. Fuel property effects on low-speed pre-ignition - ScienceDirect
5. Low-speed pre-ignition and super-knock in boosted spark-ignition engines: A review - ScienceDirect
6. Low Speed Pre-Ignition (LSPI) Durability – A Study of LSPI in Fresh and Aged Engine Oils
