Split cycle engine control

1. A split cycle internal combustion engine comprising:

a compression cylinder accommodating a compression piston;

a combustion cylinder accommodating a combustion piston;

a recuperator arranged to exchange heat between exhaust fluid from the combustion cylinder and working fluid being supplied from the compression cylinder to the combustion cylinder; and

a recuperator bypass passage selectively operable to enable at least some fluid to avoid flowing through the recuperator.

2. The split cycle internal combustion engine of claim 1 , further comprising a controller configured to control usage of the recuperator bypass passage based on an indication of at least one operating parameter of the engine.

3. The split cycle internal combustion engine of claim 2 , wherein said at least one operating parameter of the engine comprises a temperature of at least one of: (i) a material of the recuperator, and (ii) the working fluid to be supplied to the combustion cylinder.

4. The split cycle internal combustion engine of claim 2 , wherein in the event that the indication of the operating parameter exceeds a threshold criterion, the controller is configured to control operation of the recuperator bypass passage to reduce a temperature of the recuperator and/or a temperature of the working fluid to be supplied to the combustion cylinder.

5. The split cycle internal combustion engine of claim 4 , wherein controlling operation of the recuperator bypass passage to reduce a temperature of the recuperator comprises controlling operation of the recuperator bypass passage to reduce an average temperature of the fluid flowing through the recuperator.

6. The split cycle internal combustion engine of claim 4 , wherein controlling operation of the recuperator bypass passage to reduce a temperature of the recuperator comprises at least one of: (i) increasing the amount of exhaust fluid from the combustion cylinder which bypasses the recuperator, and (ii) decreasing the amount of working fluid from the compression cylinder which bypasses the recuperator.

7. The split cycle internal combustion engine of claim 4 , wherein controlling operation of the recuperator bypass passage to reduce a temperature of the working fluid to be supplied to the combustion cylinder comprises at least one of: (i) increasing the amount of exhaust fluid from the combustion cylinder which bypasses the recuperator, and (ii) increasing the amount of working fluid from the compression cylinder which bypasses the recuperator.

8. The split cycle internal combustion engine of claim 2 , wherein in the event that the indication of the operating parameter does not satisfy a threshold criterion, the controller is configured to control operation of the recuperator bypass passage to increase a temperature of the recuperator and/or a temperature of the working fluid to be supplied to the combustion cylinder.

9. The split cycle internal combustion engine of claim 8 , wherein controlling operation of the recuperator bypass passage to increase a temperature of the recuperator comprises controlling operation of the recuperator bypass passage to increase an average temperature of the fluid flowing through the recuperator.

10. The split cycle internal combustion engine of claim 8 , wherein controlling operation of the recuperator bypass passage to increase a temperature of the recuperator comprises at least one of: (i) decreasing the amount of exhaust fluid from the combustion cylinder which bypasses the recuperator, and (ii) increasing the amount of working fluid from the compression cylinder which bypasses the recuperator.

11. The split cycle internal combustion engine of claim 8 , wherein controlling operation of the recuperator bypass passage to increase a temperature of the working fluid to be supplied to the combustion cylinder comprises at least one of: (i) decreasing the amount of exhaust fluid from the combustion cylinder which bypasses the recuperator, and (ii) decreasing the amount of working fluid from the compression cylinder which bypasses the recuperator.

12. The split cycle internal combustion engine of claim 2 , wherein the controller is configured to control operation of the recuperator bypass passage to control an amount of heat exchange occurring in the recuperator based on the indication of at least one operating parameter of the engine.

13. The split cycle internal combustion engine of claim 2 , wherein the controller is configured to control operation of the recuperator bypass passage to reduce a temperature of a material of the recuperator in the event that the indicated parameter is a temperature which exceeds an upper threshold value.

14. The split cycle internal combustion engine of claim 2 , wherein the controller is configured to control operation of the recuperator bypass passage to reduce an amount of heat-induced damage inflicted on the recuperator.

15. The split cycle internal combustion engine of claim 14 , wherein controlling operation of the recuperator bypass passage based on the indication of the temperature comprises: in the event that the indicated temperature exceeds an upper threshold value, controlling operation of the recuperator bypass passage to reduce a temperature of the recuperator to reduce an amount of heat-induced damage inflicted on the recuperator.

16. The split cycle internal combustion engine of claim 1 , wherein the recuperator bypass passage comprises: (i) a first passage for working fluid supplied from the compression cylinder, and (ii) a second passage for exhaust fluid from the combustion cylinder; and

wherein the recuperator bypass passage comprises: a compressed fluid bypass passage for the working fluid supplied from the compression cylinder to bypass the first passage, and/or an exhaust fluid bypass passage for the exhaust fluid from the combustion cylinder to bypass the second passage.

17. The split cycle internal combustion engine of claim 1 , wherein the recuperator bypass passage is arranged to enable recuperator bypass on both sides of the recuperator.

18. The split cycle internal combustion engine of claim 2 , wherein the controller is configured to control opening and/or closing times of an exhaust valve of the combustion cylinder based on the obtained indication.

19. A split cycle internal combustion engine comprising:

a compression cylinder accommodating a compression piston;

a combustion cylinder accommodating a combustion piston;

a recuperator arranged to exchange heat between exhaust fluid from the combustion cylinder and working fluid being supplied from the compression cylinder to the combustion cylinder;

a turbine arranged to be driven by the exhaust fluid flowing from the combustion cylinder to the recuperator; and

a turbine bypass passage selectively operable to enable at least some of the exhaust fluid to flow to the recuperator without driving the turbine.

20. A method of operating a split cycle internal combustion engine, the split cycle internal combustion engine comprising:

a compression cylinder accommodating a compression piston;

a combustion cylinder accommodating a combustion piston;

a recuperator arranged to exchange heat between exhaust fluid from the combustion cylinder and working fluid being supplied from the compression cylinder to the combustion cylinder; and

a recuperator bypass passage selectively operable to enable at least some fluid to avoid flowing through the recuperator;

wherein the method comprises:

obtaining an indication of at least one of: (i) a temperature associated with the combustion cylinder, and (ii) a temperature associated with the recuperator; and

controlling use of the recuperator bypass passage based on the indicated temperature.