SPLIT CYCLE INTERNAL COMBUSTION ENGINE AND METHODS OF OPERATING A SPLIT CYCLE INTERNAL COMBUSTION ENGINE

1 . A split cycle internal combustion engine comprising:

a compression cylinder accommodating a compression piston configured to provide compressed working fluid;

a combustion cylinder accommodating a combustion piston, wherein the combustion cylinder is coupled to the compression cylinder to receive compressed working fluid therefrom, and wherein the combustion cylinder comprises: (i) an inlet valve configured to control intake of compressed working fluid into the combustion cylinder, and (ii) an outlet valve configured to control exhausting of fluid from the combustion cylinder; and

a controller configured to change the position during the engine cycle at which the inlet and/or outlet valves open to switch operation of the engine between an active mode and an engine braking mode, wherein the controller is configured to control at least one of:

the inlet valve to open at a position which is closer to a bottom dead centre, BDC, position when operating in the engine braking mode than when operating in the active mode; and

the outlet valve to open at a position which is closer to a top dead centre, TDC, position when operating in the engine braking mode than when operating in the active mode.

2 . The split cycle internal combustion engine of claim 1 , wherein the controller is configured to control the position at which the inlet valve opens and/or closes in the engine braking mode so that working fluid is being further compressed in the combustion cylinder for a majority of the movement of the combustion piston from its BDC position to its TDC position.

3 . The split cycle internal combustion engine of claim 1 , wherein the controller is configured to control the position at which the outlet valve opens and/or closes in the engine braking mode so that further compressed fluid is exhausted from the combustion cylinder.

4 . The split cycle internal combustion engine of claim 3 , wherein the controller is configured to control the outlet valve to open at a position before the TDC position in the engine braking mode.

5 . The split cycle internal combustion engine of claim 1 , wherein the controller is configured to change the position during the engine cycle at which the inlet and/or outlet valves close when switching operation between the active mode and the engine braking mode.

6 . The split cycle internal combustion engine of claim 1 , wherein the engine further comprises a fuel reservoir and is configured to inject fuel for combustion into the combustion cylinder; and

wherein the controller is configured to control injecting of fuel so that no fuel is injected when operating in the engine braking mode.

7 . The split cycle internal combustion engine of claim 1 , wherein the controller is configured to receive a demand signal for demand from the engine; and

wherein the controller is configured to control operation of the engine to be in either the active mode or the engine braking mode based on the demand signal.

8 . The split cycle internal combustion engine of claim 7 , wherein the controller is configured to control opening and/or closing positions for at least one of the inlet valve and the outlet valve based on the demand signal.

9 . The split cycle internal combustion engine of claim 1 , wherein the compression cylinder is coupled to the combustion cylinder via a recuperator; and

wherein the recuperator is arranged to provide a heat exchange between fluid which has been exhausted from the combustion cylinder and compressed working fluid travelling from the compression cylinder to the combustion cylinder.

10 . The split cycle internal combustion engine of claim 9 , wherein the engine comprises a recuperator bypass passage.

11 . The split cycle internal combustion engine of claim 10 , wherein the controller is configured to receive a signal indicative of a temperature of the recuperator and to control operation of the recuperator bypass passage based on said received signal.

12 . The split cycle internal combustion engine of claim 10 , wherein the recuperator bypass passage comprises at least one of:

a high-pressure bypass passage arranged to provide a flow path for compressed fluid from the compression cylinder to the combustion cylinder which avoids the recuperator; and

a low-pressure bypass passage arranged to provide a flow path for fluid exhausted from the combustion cylinder which avoids the recuperator.

13 . The split cycle internal combustion engine of claim 12 , wherein:

the controller is configured to control operation of the engine so that fluid flows through the high-pressure bypass passage in the event that a temperature associated with the recuperator drops below a threshold value; and/or

the controller is configured to control operation of the engine so that fluid flows through the low-pressure bypass passage in the event that a temperature and/or pressure associated with working fluid exceeds a threshold value.

14 . (canceled)

15 . (canceled)

16 . The split cycle internal combustion engine of claim 1 , wherein the engine further comprises a turbocharger having: (i) a turbine arranged to be driven by fluid exhausted from the combustion cylinder, and (ii) a compressor configured to force additional compressed fluid into the compression cylinder.

17 . The split cycle internal combustion engine of claim 16 , wherein the engine further comprises a turbine bypass passage arranged to provide a flow path for fluid exhausted from the combustion cylinder which avoids the turbine; and

wherein the controller is configured to control operation of the turbine bypass passage to provide a selected amount of compressed working fluid be provided to the compression cylinder.

18 . (canceled)

19 . The split cycle internal combustion engine of claim 1 , wherein the engine further comprises a compressed gas storage unit arranged to receive gas compressed by the engine.

20 . The split cycle internal combustion engine of claim 19 , wherein the compressed gas storage unit comprises one or more storage units arranged to receive compressed gas which has been compressed in the compression cylinder and/or further compressed gas which has been further compressed in the combustion cylinder.

21 . (canceled)

22 . (canceled)

23 . The split cycle internal combustion engine of claim 1 , further comprising one or more phase change materials configured to store excess energy from the engine when operating in the engine braking mode.

24 . A method of operating a split cycle internal combustion engine, wherein the split cycle internal combustion engine comprises:

a compression cylinder accommodating a compression piston configured to provide compressed working fluid; and

(ii) a combustion cylinder accommodating a combustion piston, wherein the combustion cylinder is coupled to the compression cylinder to receive compressed working fluid therefrom, and wherein the combustion cylinder comprises: (i) an inlet valve configured to control intake of compressed working fluid into the combustion cylinder, and (ii) an outlet valve configured to control exhausting of fluid from the combustion cylinder;

wherein the method comprises changing the position during the engine cycle at which the inlet and/or outlet valves open to switch operation of the engine between an active mode and an engine braking mode, and controlling at least one of:

the inlet valve to open at a position which is closer to a bottom dead centre, BDC, position when operating in the engine braking mode than when operating in the active mode; and

the outlet valve to open at a position which is closer to a top dead centre, TDC, position when operating in the engine braking mode than when operating in the active mode.

25 . A computer program product comprising computer program instructions configured to program a processor to control operation of a split cycle internal combustion engine to perform the method of claim 24 .