Root Cause Analysis of Failed Diesel Engine Aluminum Pistons

Root cause analysis was performed to determine the cause of failure of numerous cast aluminum pistons used in high speed diesel engines over ~7 months. The analysis consisted of metallurgical and engine systems evaluations. The metallurgical evaluation of two of the initial failed pistons showed failure by exposure to incompletely atomized and combusted fuel droplets that melted and eroded the piston crown outer diameters. The initial suspected root cause of the uncombusted fuel droplets was the presence of fuel-tank biological growth. The tanks were cleaned and the engines restored to service, but there were additional piston failures after only a short time back on-line, including piston seizures that fractured the pistons and cylinder liners. A subsequent, much more detailed engine system evaluation showed that the true root cause explaining all the failures was incorrect fuel injection timing. Two key points to be taken from this analysis are: (1) determination of the true root cause in this case required continuous and close interaction among metallurgical and engine systems personnel throughout an extended analysis process; (2) getting to the true root cause may require tenacious ‘detective’ work to track down and eliminate all other potential causes.