“LSPI is not a simple problem,” explained Thomas Briggs, Jr., manager of engine systems research and development at Southwest Research Institute (SWRI) in San Antonio, TX. Briggs led SWRI’s Pre-ignition Prevention Program team that includes industry partners (GM, Ford, Honda, Infineum International, Afton Chemical and others) that began investigating LSPI in 2011.
“When the fuel is injected directly into the combustion chamber, it dilutes the oil film lining the cylinder,” Briggs shared. “This fuel dilution reduces the surface tension and viscosity of the oil, causing an oil-fuel mixture to accumulate in the upper reaches of the piston top land crevice. The mechanical energy of the upstroke during compression pushes droplets into the combustion chamber, where they vaporize and can auto-ignite prior to spark ignition and subsequent engine damage.
“The team used high-speed video, crevice sampling and other specialized tools to better determine the source of the problem. Captured video showed that droplets of material were coming out of the piston crevice in the engine. Sometimes those droplets burned, leading to LSPI and strong engine knock. The video also showed that the material was a complex cocktail of fluids—fuel, lubricant, soot and other material. It’s clear to us now that resolving LSPI issues will require addressing lubricants, fuels, engine design and more.”