Analysis of scuffing from red deposits on piston crowns and top edges since the 2020 marine fuel changeover has led Chevron Marine Lubricants to conclude that VLSFOs have sped the decline of some engines already in need of of an overhaul
Some shipowners changing to very low-sulphur fuel oil (VLSFO) have reported build-ups of red deposits on piston crowns and top edges, sometimes combined with red iron burrs in scavenge ports, a report from Chevron Marine Lubricants said.
The company found that the red deposits have been associated with abnormal liner wear (or scuffing), particularly on older two-stroke marine engines, since the shipping industry was mandated to switch from higher-sulphur heavy fuel oils (HFOs) to lower-sulphur fuel blends.
The company said incidences of red deposits and scuffing that were relatively frequent in the early days of VLSFO operations have since declined significantly and that most VLSFO users would not have experienced the issue.
"While most users transitioned smoothly, these [deposits] can cause trouble for older engines," said Chevron Marine Lubricants senior engineer Luc Verbeeke.
“Newer ships do not have a problem using these fuels, [but] engines already closer to an overhaul did struggle sometimes,” Mr Verbeeke said.
Some cylinder units "that could have run for another six months or a year on HFO did not survive the tougher conditions with the new fuels,” he said.
Although VLSFO has been found to offer a typically higher energy value content than heavy fuel oil, thereby reducing overall fuel cost, its combustion density properties can result in harsher operating conditions and more stress on engine components, Chevron said.
The company said they undertook a laboratory-based analysis to determine causes of scuffing and found the red deposits were a mix of detergent residue and iron oxide. Ruling out detergent residues out as a source of engine wear – as the deposits were only found in individual cylinders rather than across engines – Chevron found that the VLSFO blends they linked to the deposits showed differences from other fuel blends in two fuel characteristics. The blends they analysed typically contained a lower calculated carbon aromaticity index (CCAI) and higher estimated cetane number (ECN).