LSPI, GDI Issues Call for GF-5 Plus, the Interim Solution for GF-6
The implementation of the next ILSAC engine oil service category for passenger cars, ILSAC GF-6, has been delayed. This delay has pushed original equipment manufacturers (OEMs) that produce vehicles powered by gasoline direct injection engines (GDI) to look for an interim solution to the challenges presented by GDI technology. That solution? GF-5 Plus.
Why is GF-5 Plus Needed Now?GDI technology coupled with volumetric efficiency improvers such as turbochargers and superchargers, results in improved engine efficiency and decreased fuel usage. However, these technologies have resulted in a condition known as low-speed pre-ignition (LSPI). LSPI is a premature ignition of the air-fuel mixture in the combustion chamber. Other terms used for LSPI include super knock, mega knock and stochastic pre-ignition. Over the past seven years, vehicles have been increasingly experiencing LSPI. Vehicle manufacturers need a solution to the problem.
Why Gasoline Direct Injection?Historically, gasoline has been mixed or injected in the air flowing into the combustion chamber. While these methods have worked well over the past 100 years, it is not the most efficient means of fuel delivery. With GDI technology, gasoline is sprayed directly into the combustion chamber under high pressure, often 2,000 psi or greater, atomizing fuel molecules to become very fine droplets. This allows for improved mixing of fuel with the incoming charge of air. This improved mixing results in increased efficiency of the engine and decreases the total amount of fuel used in the combustion process. This translates to more power from a smaller-displacement engine and improved fuel economy for the vehicle.
Understanding LSPIThe low speed in LSPI — which refers to the engine, not the speed of the vehicle — occurs in the 1,200-2,700 rpm range. This low-speed pre-ignition is very violent and causes over pressurization of the combustion chamber that can lead to damage and failure of the piston, rings, valves and other internal components.
During LSPI testing, pressures as high as 1,595 psi were observed in the combustion chamber. Normal combustion in this test yields a maximum pressure of 623 psi. That is a spike of 256 percent in pressure.
Understanding How GDI and Turbocharging Increases the Likelihood of LSPIIn addition to GDI, turbocharging is another tool to improve engine efficiency and fuel usage. Turbocharging is sometimes referred to as a volumetric efficiency improver. Adding a volumetric efficiency improver packs more air into the cylinder, resulting in smaller engines making more power and torque. Frequently, turbocharging is coupled with GDI. By harnessing these two technologies, OEMs can use 6-cylinder engines where 8-cylinder engines were necessary in the past. Additionally, 4-cylinder engines using GDI and turbocharging have become the new normal for power and efficiency in many small to mid-size cars and SUVs. Frequently, the combination of these technologies is abbreviated TGDI (turbocharged gasoline direct injection). While there are many benefits to combining these technologies, it also creates the perfect storm for LSPI.
OEMs Asked Engine Oil Manufactures to Reduce LSPI by Optimizing Engine Oil FormulationsUsing a GF-5 Plus chemistry engine oil in any GDI or TGDI engine will reduce the likelihood of LSPI.
General Motors included a LSPI test in the dexos1:2015 specification, which is marketed as dexos1 Gen2. Other OEMs have issued new specifications including LSPI protection, as well.
Testing of engine oils for LSPI tendencies has shown that calcium-based detergents increase the likelihood of an LSPI event. The removal of all calcium-based detergent is neither economical nor practical. The approach of a hybrid detergent package is the most economical and practical solution. A typical hybrid detergent package may contain lower calcium while increasing the level of magnesium-based detergent. By taking this hybrid approach, engine oil manufacturers are able to achieve an economical solution to a complex problem.