Internal combustion engine system and a method for an internal combustion system

An internal combustion engine system comprising an internal combustion engine comprising at least one combustor, and a first expander arranged to receive exhaust gases from at least one of the at least one combustor, and to expand and extract energy from the exhaust gases, wherein the engine comprises a crankshaft, and the combustor comprises a piston arranged to reciprocate in a cylinder, and to drive the crankshaft, wherein the first expander is a piston expander arranged to drive the crankshaft with the extracted energy, wherein the engine comprises a second expander arranged to receive exhaust gases from the first expander, and to expand and extract energy from the exhaust gases, wherein the system comprises an exhaust treatment device arranged to receive exhaust gases from the first expander, to process the received exhaust gases, and to deliver the processed exhaust gases to the second expander, and, where the first expander is a piston expander, the first expander comprises an expander inlet valve and/or an expander exhaust valve, the engine further comprising an expander variable valve timing mechanism arranged to actuate the expander inlet valve and/or an expander variable valve timing mechanism arranged to actuate the expander exhaust valve,

• wherein the system further comprises a control unit configured to:
• receive a signal indicative of a temperature in the exhaust treatment device;
• and
• control the valve timing of the expander exhaust valve based on the temperature in the exhaust treatment device.