Low Speed Pre-ignition (LSPI), Oxidation and Wear
Published September 2, 2013
Challenges for Gasoline Direct Injection Turbo-charged (GDI-T) Engine Technology
Applying GDI plus turbo-supercharger (turbocharger) intake air boosting technology to the typical light duty passenger vehicle is being adopted by light-vehicle engine builders globally. GDI and turbocharging are enabling technologies that allow engines to operate at low speed and high loads for optimal fuel efficiency. The direct spraying of fuel into the cylinder improves cooling from combustion allowing higher The ratio of the volume of combustion space at bottom dead center to that at top dead center in an internal combustion engine. and in engine torque as delivered by the turbo charger. The higher torque from the turbo charger allows smaller engines (3 and 4 cylinders to generate equivalent torque, power and performance of previous larger engines (6 and 8 cylinders). The greater power is also delivered with improved efficiency since the smaller engine has less The resistance to motion of one object over another. Friction depends on the smoothness of the contacting surfaces, as well as the force with which they are pressed together. due to fewer pistons, bearing and less weight of older larger engines. However, often with new technology comes unintended consequences that need to be addressed. GDI engines with turbocharging (GDI-T) increase soot-like particles in the oil that can increase engine wear. Higher thermal loads increase engine oil stress from A reaction occurring when oxygen attacks petroleum fluids. Oxidation is accelerated by heat, light, metal catalysts, and the presence of water, acids, or solid contaminants. Oxidation leads to increased viscosity and deposit formation. and nitration. Pre-ignition at low engine speeds (Low-Speed Pre-Ignition. Uncontrolled combustion that takes place in the combustion chamber prior to spark in gasoline direct injection (GDI) engines.) can lead to mechanical damage to engine pistons and connecting rods. Vehicles with high technology GDI-T engines need a matching high performance engine lubricant for maximum protection against premature failure.
Watch: Low Speed, Pri-Ignition
Recent research illustrates how important the GDI plus turbo practice is becoming in Europe, with implications for other world regions. GDI penetration will reach 65% to 67% of new European gasoline-engine light vehicles by 2018. The larger-vehicle segments (D, E, and F) will have GDI as standard equipment by 2018. The smaller-vehicle segments (B and C), which are more cost-sensitive, will experience a more gradual penetration. The vast majority of Europe’s GDI cars will also be turbocharged (an estimated penetration of 90% to 92% by 2018). GDI system annual unit volume in Europe will triple between 2010 and 2018–welcome news for suppliers operating in this space.
The GDI/turbo combination is already present in the North American and Japanese markets. Forecasts for new car sales in North America show GDI technology will reach 60% to 65% market penetration by 2018 similar to the levels in Europe.
GDI technology will penetrate all other global markets.
Watch: What is LSPI?
The cost is substantially higher than a naturally aspirated engine with port injection. European CO2 Mobile sources - Pollutant exhaust gases created by the combustion of fuel. Water and CO2 are not included in this category, but CO, NOx, and hydrocarbons are and are thus subject to legislative control. All three are emitted by gasoline engines, while diesel engines also emit particulates that are regulated. Stationary sources - The release of sulfur oxides and particulates from power stations that can be influenced by fuel composition. Local authorities control the sulfur content of heavy fuel oils used in such applications. regulations have seen OEMs adopt GDI-t engines across all major manufacturers from Peugeot to Porsche. Japanese buyers like high-tech engines and pay high gasoline prices. Several of Japan’s OEMs have begun including GDI engines in their product line along with their HEV powertrains to improve their fleet fuel economy. Conversely, North American buyers are more value-driven and enjoy lower gasoline prices, so their adoption of costly higher-tech/fuel-saving powertrain features tend to be slower. However, GM and Ford have aggressively implemented GDI engines across their product line.
Original equipment manufacturers (OEMs) are trying to solve the unique technical challenges of GDI. For example, the kinetics and gas flow dynamics in the combustion chamber yield rich spots of incomplete combustion so that carbon particulate formation and engine-out particulate emissions are higher than for port-injected gasoline engines. As regulated particulate emissions limits tighten toward zero, the excess particulate problem must be addressed. Regeneratingsoot traps in the exhaust path–standard practice with highway diesel engines in key industrial countries–is one possibility.
Another challenge related to GDI soot formation is that carbon particulates can hide in crevices and get washed down cylinder walls or enter the crankcase via The passage of unburned fuel and combustion gases past the piston rings of internal combustion engines, resulting in fuel dilution and contamination of the crankcase oil., causing problems with lube oil.
The active surfaces of these carbon particles readily absorb key additives in lube oil that minimize oxidation and wear, compromising lube performance. These carbonaceous particles also tend to be abrasive increasing wear on critical engine parts such as cams and valve lifters. Such suspended carbon particles can reach 1% to 3% of the total lube oil mass. Lube oil blenders and lube additive suppliers, such as Lubrizol, are developing measures to offset these GDI side effects.
Some GDI engines also have an unwelcome tendency toward pre-ignition, or spontaneous combustion before normal spark ignition, especially at lower speeds coupled with higher loads and high cylinder pressures. This unwanted phenomenon is called Uncontrolled combustion that takes place in the combustion chamber prior to spark in gasoline direct injection (GDI) engines. Also known as LSPI. (LSPI). Combustion events occurring before they are wanted or expected can hammer the mechanical internals of gasoline engines (evident with severe knocking), because pistons and connecting rods are rising when this downward combustion “bang” occurs. In the worst case, ongoing pre-ignition can lead to broken piston rings, damaged ring lands and/or bent connecting rods. The mechanism of GDI pre-ignition is not yet fully understood. Multiple parallel strategies to mitigate GDI pre-ignition involve lube oil/lube additives, engine mapping (spark ignition and fuel injection event timing) and mechanical changes.
Low speed pre-ignition (LSPI) can in severe cases lead to engine damage such as a broken piston as shown above.
The engine operating area where LSPI occurs is very close to where fuel economy, performance and drivability are optimally balanced. Operating at relatively low RPM and constant load, such as highway cruising, the engine can slip into the LSPI zone where potential engine damage may occur.
Low speed pre-ignition occurs very close to the engine’s optimum operating area where fuel economy, performance and drivability are balanced.
The thermal stresses in GDI/turbo engines with high specific power ratings (hp/liter) are formidable, so dedicated external lube oil coolers are recommended. Also, many OEMs arrange a jet of lube oil to continuously hit and cool the underside of each piston The top of the piston in an internal combustion engine above the fire ring. The crown is exposed to direct flame impingement.. This heat stress could lead to thermal breakdown and in extreme cases, coking of lube oils if not properly managed. Lubrizol additives can help lube oil better cope with the thermal demands of high-output GDI/turbo engines.