Engine component specialist Mahle says that its engineers are working to overcome challenges presented by high levels of low-speed torque in small engines. In particular, it says that ‘low speed pre-ignition’ can damage piston rings and other engine components.
Mahle notes that more than 50% of all vehicles sold in the US by 2025 are expected to have downsized engines, according to EPA (Environmental Protection Agency) and NHTSA (National Highway Traffic Safety Administration) reports.
Engineers at Mahle are developing solutions to help improve the performance and durability of components such as pistons and piston rings for this new generation of engines.
It says that modern turbocharged direct-injection gasoline engines are more fuel efficient and more powerful than conventional naturally aspirated engines. Power ratings in excess of 120-horsepower per litre are common. To maintain vehicle drivability, however, high torque at low speeds and good throttle response are required, especially as downsized engines find their way into larger vehicles such as SUVs and trucks that typically used V-8 engines.
Mahle maintains that high levels of low-speed torque have led to an increase in the occurrence of an abnormal combustion phenomenon called low-speed pre-ignition (LSPI). LSPI can generate extremely high combustion-chamber pressure which can result in damage to pistons, rings and other engine components, it says.
“LSPI has the potential to catastrophically damage individual components,” says Dr. Joachim Wagenblast, director of R&D for engine systems and components at Mahle USA, Inc.
“Mahle Group is at the forefront of research on LSPI-related problems,” Wagenblast adds. “Our development teams are focused on creating engine components and systems designed to withstand low-speed pre-ignition events, as well as assist in preventing their occurrence.”
Mahle research engineers in Farmington Hills and Stuttgart have been actively working on understanding and finding solutions to LSPI-related problems for several years. Lab-based ring testing helps with the understanding of LSPI occurrences and effects. The knowledge gained is being used to refine simulation techniques and enable Mahle to design more robust components. For example, incorporating a high-strength ring carrier in a piston’s first ring groove has been shown to avoid piston land breakage which is a common issue with LSPI, the company says.
Engine-based testing also is used to validate component designs and rank these designs based on robustness to LSPI events. Mahle uses a robustness test that induces LSPI on a turbocharged direct-injection engine. Low-speed pre-ignition can damage piston ring running surfaces and coatings that potentially affect long-term oil consumption, blowby and durability, and also increase OEM warranty costs.
“Having the ability to rank ring coatings has already proved useful in recommending technology to customers that experience LSPI in their engine development programs,” Wagenblast says.
Other Mahle engine test programs are looking to determine how Mahle components can help to reduce the likelihood of LSPI events by addressing triggers thought to be responsible for LSPI, such as oil droplets in the combustion chamber or high component surface temperatures.
“All this research is helping Mahle develop products to meet customer demands and enable engine manufacturers to further push the boundaries of performance and fuel economy,” Wagenblast says. “Today we are working with a number of engine manufacturers and car makers to develop next-generation piston and ring components that are expected to go into production within the next one to five years.”