In the search for better fuel economy and reduced emission levels, OEMs have lowered engine capacity and introduced turbochargers to cater for the smaller engines. These engines provide higher power outputs and better efficiency, but they can develop Low Speed Pre-Ignition (LSPI).
LSPI is a premature combustion event, that happens prior to spark ignition in turbocharged and smaller petrol engines. It happens when engines operate at low speeds and high loads. It can lead to extremely high cylinder-pressures and can induce a heavy knock. These can be audible knocking noises and continued exposure to these conditions can cause an engine failure, including broken spark plugs and cracked pistons.
LSPI cannot be predicted and corrected by adjusting spark timing. As such, mitigating pre-ignition involves altering the design of the engine or lubricant to help avoid this emerging issue.
There are several theories to explain LSPI.
The most noticeable impact has been from the detergent chemistry. Oils with higher concentrations of calcium, that is used in many detergent systems, have been shown to increase the frequency of LSPI. The exact chemistry of the detergent is less important to LSPI than the calcium content. Conversely, magnesium-based detergents do not seem to promote LSPI.
In addition, there are other additives that can also help reduce LSPI events. This provides an opportunity to formulate to prevent LSPI performance, whilst maintaining the level of detergency needed to help keep engines clean and neutralise acids generated during the combustion cycle as well as meeting extended service intervals.
There are other additive and base oil components that can reduce LSPI. Molybdenum compounds have been shown to decrease LSPI when used at high levels. Base oils can also affect LSPI. Both the quality of the base stock (i.e. Group II versus Group III) and the viscosity can have secondary effects on LSPI.
The effect on LSPI from these other lubricant aspects are not as significant as the detergent system but can shift the LSPI frequency in oils that are more prone to LSPI.
New engine oil specifications include LSPI prevention. ILSAC GF-6 includes a Ford engine test to discriminate oils based on LSPI event prevention (reduction). Thus, all oils that make GF-6 claims will need to be formulated to address LSPI. GM’s dexos1™ Gen 2 specification addresses the issues LSPI and is recommended for all GM petrol engines.
The Penrite Enviro+ Engine Oil Range includes a range of products featuring the latest in Low Viscosity Full Synthetic engine oil technology including Low Speed Pre-Ignition (LSPI) protection that maximises fuel efficiency in modern engines and are suitable for a wide range of popular Petrol and Diesel vehicles.
For more information, Tech Talks or New Products visit https://www.penriteoil.com.au/
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