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

1. A method for an internal combustion engine system comprising

at least one combustor,

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 system 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,

comprising providing an exhaust treatment device arranged to receive exhaust gases from the first expander, to process the received exhaust gases,

the method comprising determining the temperature in the exhaust treatment device, and adjusting the swallowing capacity of the first expander to control the temperature of the process in the exhaust treatment device.

2. A method according to claim 1 , wherein the internal combustion 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 processed exhaust gases are delivered to the second expander.

3. A method according to claim 1 , comprising increasing the temperature of the exhaust treatment device by increasing the swallowing capacity of the first expander, and decreasing the temperature of the exhaust treatment device by decreasing the swallowing capacity of the first expander.

4. A method according to claim 1 , wherein the first expander is arranged to receive the exhaust gases by means of an expander inlet valve, an expander variable valve actuation mechanism being arranged to actuate the expander inlet valve, wherein adjusting the swallowing capacity of the first expander comprises adjusting the expander variable valve actuation mechanism.

5. A method according to claim 3 , comprising increasing the swallowing capacity of the first expander by delaying a closing event of the expander inlet valve, and decreasing the swallowing capacity of the first expander by advancing the closing event of the expander inlet valve.

6. A method according to claim 3 , wherein the first expander is arranged to expel the exhaust gases by means of an expander exhaust valve, the expander variable valve actuation mechanism being arranged to actuate the expander exhaust valve, the method comprising controlling the expander variable valve actuation mechanism so as to adjust the expander exhaust valve to minimize the pressure difference across the expander exhaust valve at an opening event of the expander exhaust valve, and/or to minimize the pressure difference across the expander inlet valve at an opening event of the expander inlet valve.

7. A method according to claim 2 , comprising

adjusting the swallowing capacity of the second expander to control the temperature of the process in the exhaust treatment device.

8. A method according to claim 7 , comprising increasing the temperature of the exhaust treatment device by decreasing the swallowing capacity of the second expander, and decreasing the temperature of the exhaust treatment device by increasing the swallowing capacity of the second expander.

9. A method according to claim 7 , wherein adjusting the swallowing capacity of the first expander and/or the second expander is done in dependence on a rotational speed of the engine system and/or a requested torque for the engine system.

10. A method according to claim 7 , comprising increasing the temperature of the exhaust treatment device by increasing the swallowing capacity of the first expander and decreasing the swallowing capacity of the second expander, and decreasing the temperature of the exhaust treatment device by decreasing the swallowing capacity of the first expander and increasing the swallowing capacity of the second expander.

11. A method according to claim 10 , comprising determining a temperature of the exhaust gases and, with an increasing exhaust gas temperature, decreasing the swallowing capacity of the first expander and increasing the swallowing capacity of the second expander, and, with a decreasing exhaust gas temperature, increasing the swallowing capacity of the first expander and decreasing the swallowing capacity of the second expander.

12. A computer program comprising program code means for performing the steps of claim 1 when the program is run on a computer.

13. A computer readable medium carrying a computer program comprising program code means for performing the steps of claim 1 when the program is run on a computer.

14. A control unit arranged to perform the steps of claim 1 .

15. A method for an internal combustion engine system comprising

a combustor arranged to combust air and fuel,

an expander arranged to receive, expand and extract energy from exhaust gases from the combustor, and to expel the exhaust gases from the expander by means of an expander exhaust valve, and

wherein the system comprises a crankshaft, and the combustor comprises a piston arranged to reciprocate in a cylinder, and to drive the crankshaft,

wherein the expander is a piston expander arranged to drive the crankshaft with the extracted energy, and

providing an exhaust treatment device arranged to receive the expelled exhaust gases from the expander and to process the exhaust gases,

the method comprising determining the temperature in the exhaust treatment device, and controlling the expander exhaust valve to control the temperature of the process in the exhaust treatment device.

16. A method according to claim 15 , wherein the control of the expander exhaust valve comprises controlling the temperature of the process in the exhaust treatment device to be within the range of 300-450° C.