Split cycle engine

1. A split cycle internal combustion engine comprising:

a compression cylinder accommodating a compression piston;

a combustion cylinder accommodating a combustion piston;

a crossover passage between the compression cylinder and the combustion cylinder arranged to provide compressed working fluid from the compression cylinder to the combustion cylinder;

an inlet valve for controlling a flow of compressed working fluid from the crossover passage into the combustion cylinder, wherein the inlet valve is operable to move between an open state and a closed state; and

a controller configured to receive an indication of an engine parameter, to determine based on the indication of the engine parameter a value for another engine parameter, and to control the value for the engine parameter so that the compressed working fluid flows into the combustion cylinder at a speed greater than a speed threshold;

wherein the engine is a recuperated split cycle internal combustion engine having a recuperator arranged to heat compressed working fluid as the compressed working fluid flows from the compression cylinder to the combustion cylinder through the crossover passage; and

wherein the recuperator is arranged to recover heat from fluid exhausted from the combustion cylinder and to use this recovered heat to heat the compressed working fluid as the compressed working fluid flows from the compression cylinder to the combustion cylinder through the crossover passage.

2. The split cycle internal combustion engine of claim 1 :

wherein the indication is at least one of: (i) a pressure and (ii) a temperature of compressed working fluid in the crossover passage; and

wherein, in response to determining, based on the received indication, that the pressure and/or the temperature of the compressed working fluid in the crossover passage is below an input threshold, the controller is configured to control the pressure and/or the temperature of the compressed working fluid so that the compressed working fluid flows into the combustion cylinder at a speed greater than the speed threshold.

3. The split cycle internal combustion engine of claim 2 , wherein controlling the pressure and/or the temperature comprises increasing at least one of the pressure and/or the temperature of the compressed working fluid so that the compressed working fluid flows into the combustion cylinder at a speed greater than the speed threshold.

4. The split cycle internal combustion engine of claim 2 , further comprising a coolant system arranged to regulate the temperature of the compressed working fluid supplied to the combustion cylinder.

5. The split cycle internal combustion engine of claim 4 , wherein controlling the pressure and/or the temperature comprises operating the coolant system to cool the compressed working fluid to be supplied to the combustion cylinder.

6. The split cycle internal combustion engine of claim 4 , wherein operating the coolant system comprises cooling the compressed working fluid in at least one of the compression cylinder and the crossover passage.

7. The split cycle internal combustion engine of claim 4 , wherein the coolant system comprises a coolant injector for injecting coolant into at least one of the compression cylinder and the crossover passage.

8. The split cycle internal combustion engine of claim 2 , wherein the indication is both pressure and temperature.

9. The split cycle internal combustion engine of claim 2 , wherein the controller is configured to control both the pressure and the temperature of the compressed working fluid.

10. The split cycle internal combustion engine of claim 2 , wherein the controller is configured to control the pressure and/or the temperature of the compressed working fluid so that a peak speed for the compressed working fluid flowing into the combustion cylinder is greater than the speed threshold.

11. The split cycle internal combustion engine of claim 2 , wherein the speed threshold is selected so that the flow of the compressed working fluid into the combustion cylinder provides a mixing of fuel with a leanness ratio greater than a leanness threshold.

12. The split cycle internal combustion engine of claim 1 :

wherein in the open state, the inlet valve defines an inlet cross-sectional area through which compressed working fluid flows into the combustion cylinder; and

wherein, the controller is configured to select the inlet cross-sectional area defined by the inlet valve so that the compressed working fluid flows into the combustion cylinder at a speed greater than the speed threshold.

13. The split cycle internal combustion engine of claim 12 , wherein the controller is configured to select the inlet cross-sectional area based on the received indication, which is at least one of: (i) a pressure and (ii) a temperature of compressed working fluid in the crossover passage.

14. The split cycle internal combustion engine of claim 13 , wherein the controller is configured to: determine the pressure and/or the temperature of compressed working fluid in the crossover passage based on the received indication, and select the inlet cross-sectional area based on the determined pressure and/or temperature.

15. The split cycle internal combustion engine of claim 13 , wherein selecting the inlet cross-sectional area defined by the inlet valve comprises:

in response to determining, based on the received indication, that at least one of: (i) the pressure, and (ii) the temperature of the compressed working fluid in the crossover passage is less than a first input threshold, selecting the inlet cross-sectional area to be a first area;

in response to determining, based on the received indication, that at least one of: (i) the pressure, and (ii) the temperature of the compressed working fluid in the crossover passage is greater than a second input threshold, controlling the inlet cross-sectional area to be a second area; and

wherein the first area is less than the second area.

16. The split cycle internal combustion engine of claim 12 , wherein the controller is configured to control an amount of movement of the inlet valve from the closed state to the open state to select the inlet cross-sectional area defined by the inlet valve.

17. The split cycle internal combustion engine of claim 16 , wherein the controller is configured to select the amount of movement of the inlet valve based on the received indication.

18. A method of operating a split cycle internal combustion engine comprising:

a compression cylinder accommodating a compression piston;

a combustion cylinder accommodating a combustion piston;

a crossover passage between the compression cylinder and the combustion cylinder arranged to provide compressed working fluid from the compression cylinder to the combustion cylinder; and

an inlet valve for controlling a flow of compressed working fluid from the crossover passage into the combustion cylinder, wherein the inlet valve is operable to move between an open state and a closed state;

wherein the method comprises:

receiving an indication of at least one of: (i) a pressure and (ii) a temperature of compressed working fluid in the crossover passage;

determining, based on the received indication, a pressure and/or a temperature of the compressed working fluid in the crossover passage;

in response to determining that the pressure and/or the temperature of the compressed working fluid in the crossover passage is below an input threshold, controlling the pressure and/or the temperature of the compressed working fluid so that the compressed working fluid flows into the combustion cylinder at a speed greater than a speed threshold;

wherein the engine is a recuperated split cycle internal combustion engine having a recuperator arranged to heat compressed working fluid as the compressed working fluid flows from the compression cylinder to the combustion cylinder through the crossover passage; and

wherein the recuperator is arranged to recover heat from fluid exhausted from the combustion cylinder and to use this recovered heat to heat the compressed working fluid as the compressed working fluid flows from the compression cylinder to the combustion cylinder through the crossover passage.

19. A non-transitory computer-readable storage medium storing instructions executable by one or more processors for performing the method of claim 18 .