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LSPI engine knocking – when does it occur and how can it be prevented?

05 May 2023

Reducing emission standards presents many challenges for automakers. One way to comply is through so-called engine downsizing, which involves the use of smaller power units with the same output. Unfortunately, the result is often LSPI engine knocking, which can seriously damage the engine. 

Internal combustion cars and the Euro 7 standard 

The approach to automobiles, and in particular to the use of energy to power cars, has been changing significantly recently. Numerous green solutions are appearing on the market, including advanced electric cars, hydrogen fuel cells or even solar-powered vehicles. Internal combustion vehicles, which were virtually the only option for many decades, are slowly disappearing – but it will be a long time before they are completely replaced. However, the process is gaining momentum due to increasingly stringent emission standards, forcing automakers to adjust the parameters of the vehicles they offer. 

One of the most important regulations in this regard in the European market is the Euro standard, which is updated every few years by gradual reduction of emission limits. A transition to the seventh version of the standard is planned for the next few years: the new Euro 7 standards will introduce, among other things, limits on nitrogen oxides and additional requirements related to particulate emissions, monitoring of exhaust gas production or informing the manufacturer of any exceedances or failures. Internal combustion vehicles after 2025 will need to comply with the new limits, but such compliance comes with some design challenges.  

Many manufacturers are opting for increasing the efficiency of the combustion unit, i.e. replacing existing engines with smaller, more powerful systems offering similar power output. 

Why is engine downsizing applied? 

The stringent requirements that automotive manufacturers must meet make reducing emissions one of the key goals in vehicle design. How to reduce a car's combustion? A big help in this field are modern technologies that allow so-called downsizing, i.e. reducing the size of drive units while maintaining the same or similar power output. This technique involves reducing the engine's displacement and improving the process of filling the cylinders using, among other things, turbochargers. Using split-dose direct fuel injection for this, it is possible to achieve much higher engine efficiency, as well as considerable power and high torque at low rev ranges. This, of course, results in lower fuel consumption and thus lower exhaust emissions. 

What is LSPI engine knocking? 

Although downsizing engines is a very effective method of reducing emissions, the use of such solutions comes with certain risks. One of them is the phenomenon of engine knocking (LSPI – low-speed pre-ignition), which involves the premature ignition of the fuel-air mixture at low speed. 

During LSPI, the car's combustion takes place in a knocking manner. In practice, this involves the fuel mixture dissolved in the oil film to evaporate from the cylinder face and piston crown and undergo combustion. This in turn leads to ignition of the fuel-air mixture during the compression stroke. As a result, the pressure in the cylinder rises very quickly, sometimes exceeding 100 bar. The engine is thus exposed to very high loads – far higher than those that occur during normal combustion. This situation can lead to damage to pistons, cylinder walls, sealing rings or connecting rods. Sometimes the engine cover also fails. 

How to prevent LSPI from occurring? 

In order to protect the engine from knocking, the most important thing is to ensure the proper operating conditions of the drive unit. One of the most important issues is the use of engine oils of the right quality and viscosity class. Products with the right parameters guarantee less oxidation, reduction of changes in bond structures and slower evaporation of the lubricant. 

In particular, it is worth betting on oils with a synthetic base – oils with a large amount of calcium and sodium additives should definitely be avoided. 

In order to prevent LSPI, it is also important to ensure that the periods between oil changes are optimally short. Delaying oil changes for too long can contribute to oil aging and the collection of carbon deposits on piston bottoms, and small, detachable particles can promote engine knocking. 

Solutions to support combustion reduction from Knauf Automotive 

Downsizing engines is not the only way to reduce combustion – adjustment of the design of the car is also an important instrument here. In this case, the most important role is played by the weight of individual parts. More and more manufacturers are opting for components made of plastic, which significantly reduces the weight of the entire vehicle. Within the Knauf Automotive range, you can find a number of different components made of EPS and EPP, which combine strength with low weight. This makes it possible to ensure both fuel efficiency, as well as driving comfort and optimal conditions both for the driver and the passengers. 

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