LIQUID PUMP

BACKGROUND

Under certain circumstances, it may be desirable to introduce liquid into gaseous environments experiencing changes in pressure.

SUMMARY

Embodiments relate to architectures for pumps responsible for introducing liquid into cylinders reversibly configurable to perform gas compression or expansion. Particular embodiments maintain liquid flow rates in the face of the different pressure profiles (A-P) encountered during various portions of gas compression and gas expansion cycles. In some embodiments, the pump comprises multiple pumping elements per cylinder, at least one pumping element separable with a clutch and designed to spray/not spray during portions of compression/expansion cycles. Embodiments may employ phase difference(s) between the multiple pumping elements to introduce liquid in a desired manner. Mechanisms allowing adjustment in phase of multiple pumping elements, are also disclosed. The liquid may be introduced through sprayers arranged in rings in the cylinder, with rings (or partitions thereof) dedicated to spraying during different portions of compression and/or expansion. Embodiments may flow liquid to a gas compression/expansion cylinder via an intervening chamber of changeable volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 are plots showing pressure and water flow rate versus crank angle for gas compression and expansion cycles taking place respectively, within a cylinder.

FIG. 2 is a simplified view of a liquid pump according to an embodiment.

FIG. 3 is a simplified view of a liquid pump according to an embodiment.

FIG. 4 is a simplified view of a liquid pump according to an embodiment.

FIG. 5 is a simplified view of a liquid pump according to an embodiment, comprising multiple pumping elements operating in different phases.

FIG. 6 is a simplified view of a mechanism for a liquid pump according to an embodiment, that allows adjustment in phase.

FIGS. 7-7D show an embodiment configured to flow liquid to a gas compression/expansion cylinder via an intervening chamber having a changeable volume.

FIG. 8 shows an alternative embodiment of a chamber comprising a plurality of sprayers formed in a single integral piece.

FIG. 9 shows the pump for the particular chamber embodiment of FIG. 8.

FIG. 10 shows spray profiles in a compression runs utilizing four of the nine spray rings of the chamber of FIG. 8.

FIG. 11 plots efficiency across a range of pressure ratios (PRs) for optimized spray timings.

DESCRIPTION

Incorporated by reference in its entirety herein for all purposes, is U.S. Patent Publication No. 2011/0115223 (“the '223 Publication”). The '223 Publication discloses that gas may be compressed and/or expanded in the presence of a liquid heat exchange medium. That is, heat generated from the compression of gas is transferred across a gas-liquid boundary (e.g. fine droplets), such that the temperature experienced by the gas remains within a relatively small range over the course of the course of the compression cycle. This enhances the thermodynamic efficiency of the storage of energy by compression. During expansion, heat may be transferred across a gas-liquid boundary (e.g. fine droplets) to heat expanding gas, such that the temperature experienced by the gas remains within a relatively small range over the course of the expansion cycle. This enhances the thermodynamic efficiency of the recovery of energy by expansion.

A compressor and/or expander as described in the '223 Publication, may utilize a reciprocating or rotating moveable member for gas compression. An example of the former is a solid piston connected to a mechanical linkage comprising a piston rod and rotating shaft (e.g. crankshaft). An example of the latter is a rotating turbine, screw, or other structure connected to a mechanical linkage comprising a rotating shaft.

In certain embodiments as described in the '223 Publication, liquid may be introduced directly into the compression/expansion chamber for heat exchange. In certain embodiments, liquid may be introduced to gas in a mixing chamber upstream of the compression/expansion chamber.

The '223 Publication discloses that in certain embodiments, the same cylinder structure may be configurable to selectively perform gas expansion and gas compression. The number and type of liquid sprayers (nozzles) present in such a reversible cylinder structure will generally be fixed (e.g. sprayers will not easily be removable or their positions altered between compression and expansion cycles).

Such a fixed configuration, however, may present an issue with changing water flow rate and not changing the type or number of sprayers. In particular, as explained in connection with FIG. 1 below, the ΔP across sprayers will be different for compression and expansion. This situation is not ideal from an efficiency standpoint.

Incorporated by reference in its entirety herein for all purposes, is U.S. Patent Publication No. 2013/0098027 (“the '027 Publication”). The '027 Publication discloses certain architectures which may be used to introduce liquid for heat exchange with expanding gas or gas that is being compressed within a chamber.

Embodiments described herein, relate to pump architectures that are responsible for introducing liquid into cylinders that are reversibly configurable to perform gas compression or gas expansion. Particular embodiments maintain liquid flow rates in the face of the different pressure profiles (A-P) encountered during various phases of gas compression and gas expansion processes. In certain embodiments the pump comprises multiple pumping elements per cylinder, at least one pumping element separable with a clutch and designed to spray or not spray during the compression or expansion modes.

As further discussed below in connection with FIG. 5, in certain embodiments the multiple pumping elements may be operated by different cam sets in order to enhance efficiency.

Other embodiments may dispense with a clutch in favor of a split water pump having multiple stages (at least one of which having a phase adjustment device). Such a configuration may enhance efficiency.

Liquid may be introduced through sprayers arranged in rings in the cylinder. The rings (or partitions thereof) may be dedicated to spraying at different times.

FIG. 1 shows plots of pressure and water flow rate through nozzles, versus crank angle, for gas compression and expansion cycles taking place within a cylinder. FIG. 1 shows that the compression cycle experiences maximum benefit from the spraying of liquid for heat exchange at different times and at different points than the expansion cycle.

For example, FIG. 1 shows that for the compression cycle, the greatest change (increase) in pressure occurs at a crank angle of about 270°. In order to ensure a uniform of distribution of fine liquid droplets to absorb heat at this point of the compression cycle, the period of liquid spraying (shown as → in FIG. 1) should commence at some point earlier than the crank angle of 180°. This upper plot of FIG. 1 also shows how the flow rate of injected liquid water may change over time, in order to achieve desired heat exchange in compression.

Conversely, FIG. 1 shows that for the expansion cycle, the greatest change (decrease) in pressure occurs at a crank angle of about 90°. In order to ensure that a uniform distribution of fine liquid droplets is available in the cylinder to transfer heat at this point of the expansion cycle, the period of liquid spraying (shown as → in FIG. 1) should commence well before a crank angle of 90°. The lower plot of FIG. 1 also shows how the flow rate of injected liquid water may change over time, in order to achieve desired heat exchange in expansion.

To accommodate the different demands of liquid spraying encountered in compression versus expansion cycles, various pump architectures are described. FIG. 2 is a simplified view of a liquid pump according to one embodiment.

Specifically, liquid pump 200 comprises a first pumping element 202 and a second pumping element 204 driven by a pump drive mechanism 206. The first pumping element and the second pumping element are in fluid communication with manifolds 208 that surround rings of sprayers 210 arrayed to introduce liquid for heat exchange with gas within cylinder 212.

A moveable element 214 comprising a solid piston is disposed within the cylinder. The solid piston is coupled to a rotating crankshaft 216 by a piston rod 218. In this particular figure, the piston rod is shown connected directly to the crankshaft. Alternative configurations are possible, however, including the use of an intervening cross-head.

In compression, the crankshaft is placed in communication with a source of shaft torque to drive the piston to compress gas within the cylinder. In expansion, the crankshaft is rotated by gas expanding within the cylinder to drive the solid piston and the piston rod.

Second pumping element 204 is selectively disengageable from the pump drive mechanism by a clutch 220, in order to spray or not spray at particular times during the compression or expansion modes. In particular, in this particular embodiment the second pumping element 204 is in fluid communication with the top two rings only.

During compression, the second pumping element is disengaged from the pump drive mechanism by the clutch. Accordingly, spraying occurs in lower cylinder regions in a manner calculated to accomplish heat absorption with the greatest effect (see top plot of FIG. 1).

By contrast, during expansion the second pumping element is engaged with the pump drive mechanism by the clutch. As a result of this configuration, additional spraying occurs at regions of the cylinder near TDC in a manner calculated to accomplish heat transfer with the greatest effect (see bottom plot of FIG. 1).

While the above discussion has focused upon the use of a clutch to accomplish water pumping in the manner desired, this is not required. Alternative embodiments could utilize other types of mechanisms for this purpose. Examples of such mechanisms can include but are not limited to reversing gears and phasers.

As FIG. 1 shows, liquid spraying may be performed during a different range of crank angles for compression and expansion processes. As the spray pulse is nearly symmetric, this could be accomplished by changing the phase of the pump relative to the compressor/expander crankshaft.

Such a phase change could be achieved using a planetary gear set as shown in FIG. 6. This system has an input shaft coupled to the main crankshaft, an output shaft coupled to the pump, and a control input which is arranged to change the phase between the main crank and the pump. This arrangement permits continuous variation of the phase, which further allows for optimizing efficiency over a range of operating conditions.

It is also possible to operate the pump by reversing the direction of rotation of the pump camshaft. A reversing gear may be arranged to reverse the pump camshaft direction relative to a particular crank angle and thus give one spray phase for compression and another for expansion. While such an arrangement does not allow for continuous adjustment of the phase, it may be less expensive than a planetary gear set.

It may be possible to operate not only the pump, but also the compressor/expander with either direction of shaft rotation. In such a case, the entire machine may be reversed without the need for additional gearing. For example, if the machine is connected to a three-phase motor/generator, electrically swapping a pair of electrical phases to that device will reverse its direction.

FIG. 5 shows an example of a pumping apparatus 500 comprising a plurality of piston pumps 502a-c that are actuated by different cams 504a-c. While rotation of each of the cams is synchronized relative to a crankshaft of the compression and/or expansion cylinder, each of the cams is configured to be in a different phase relative to the other.

Utilizing such ganged operation of multiple pumping elements in different phases, an overall pumping profile having a desired character can be achieved. Such a pumping profile can be integrated to result in pumping in the desired manner in one or more regions (e.g. rings) present within a compression and/or expansion cylinder.

It is noted that the shape of the cams dictates the timing of the events triggered by rotation thereof. Thus, the cam could be shaped such that a liquid injection event occurs quickly, over a relatively short span of the 360° rotation angle, with the remainder occupied by a liquid intake event. As discussed later on, such a configuration could serve to help reduce cavitation and avoid wear on the pump.

It is further noted that the return mechanism for the plunger/pistons can comprise a spring. Alternatively, the plunger/pistons of the pump could be coupled to opposing plungers and operate according to a desmodromic-type actuation scheme.

Returning back to FIG. 2, while that particular embodiment shows the pumping elements as being in fluid communication with manifolds that surround all sprayers of a particular ring, this is not required. Alternative embodiments could employ partitioning of the rings. Such an approach is shown in FIG. 3.

In particular, FIG. 3 shows an alternative embodiment of a pump 300 in which some of the sprayers 302 (“expansion” sprayers) on a ring are connected to the second pumping element 307, and the rest of the sprayers 304 (“compression” sprayers) on the ring are connected to the first pumping element 305.

A clutch 309 is used to selectively disengage the pumping elements from the pump drive mechanism. In particular, during compression, liquid is sprayed through “compression” sprayers by the first pumping element. During expansion, liquid is sprayed through “expansion” sprayers by the second pumping element.

In the specific embodiment shown in FIG. 3, depending upon the location of a particular ring within the cylinder, it may comprise a higher or lower proportion of compression or expansion sprayers. A ring closer to TDC is partitioned into a larger proportion of expander sprayers. A ring closer to BDC is partitioned into a smaller proportion of expander sprayers.

FIG. 4 is a simplified view of a liquid pump 400 according to another embodiment. The particular embodiment of FIG. 4 has a first (baseline) pumping element 402 that sprays during both compression and expansion.

The particular embodiment of FIG. 4 also has a second (adjustable) pumping element 404 that selectively adds to the baseline flow of heat exchange liquid. In particular, this second pumping element pumps more into upper rings during expansion, and pumps more into center rings during compression.

This adjustability characteristic of the second pumping element depending upon operational mode, may be achieved in a variety of ways. One approach is to change the position of a 3-way valve 406 as in FIG. 4.

Another approach is to change the phase of the spray. FIG. 6 shows an embodiment of a mechanism 600 that could be employed to change spray phase. Specifically, the mechanism could comprise a cam 602 in communication with a camshaft 604. Selective rotation of a planetary gear 606 by worm gear 608 (e.g. utilizing a stepper motor or other actuator) allows change in the position/phase of the cam lobe relative to the cam shaft.

Different embodiments may employ varying architectures. For example, particular embodiments may utilize a split water pump with at least two groups of stages. No clutch is used, but at least one of the stages has a phase adjustment device, to maximize efficiency.

Alternative liquid pumping architectures are possible. For example, certain embodiments could employ a configuration in which liquid is flowed to the gas compression/expansion cylinder via an intervening chamber having a changeable volume. One embodiment of such a pumping scheme is shown in FIGS. 7-7D.

Specifically, one embodiment of a pumping apparatus is shown in FIG. 7. Specifically, the pumping apparatus 700 comprises a constant flow pump 702 that is in fluid communication with a gas compression and/or expansion chamber 704 via intervening liquid chamber 706.

The intervening liquid chamber 706 is defined within stationary walls 708. The intervening liquid chamber 706 is also defined within a moveable wall 710 to define a changing volume. Here, the chamber wall 710 comprises a piston 712 that is in communication with a linkage 714 (here, a mechanical linkage in the form of a crankshaft).

In this embodiment, movement of the linkage and the corresponding location of the moveable wall 710 is coordinated with the pressure inside the gas compression/expansion chamber, to result in a substantially constant flow of liquid therein. In certain embodiments, this coordinated movement may be accomplished by providing a further mechanical linkage 716 between the crankshaft of the gas compression/expansion chamber, and the mechanical linkage 714 of the liquid chamber.

According to other embodiments, this coordinated movement can be accomplished without providing such a mechanical linkage. For example, in certain embodiments the linkage 714 may be operated based upon timed inputs received from a processor, e.g., according to a Phase Lock Loop (PLL), or Voltage Controlled Oscillation (VCO) or Proportional-Integral-Derivative (PID) control schemes.

Operation of the pumping apparatus of FIG. 7 is now described in connection with FIGS. 7A-7D. In particular, as shown in FIG. 7A as the piston of the gas compressor approaches TDC at the end of the compression stroke, the gas pressure in the gas chamber is high. Absent an increase in the pressure of the liquid being injected, the flow rate of the liquid would fall, adversely affecting the quality of the heat exchange occurring in the chamber.

Accordingly, FIG. 7A shows that at this time the available volume in the intervening liquid chamber would also fall. This would increase the liquid pressure at the time when gas pressure is increasing within the cylinder, maintaining flow rate and gas-liquid heat exchange.

Conversely, FIG. 7B shows that as the piston of the gas compressor recedes from TDC toward BDC during the intake stroke, the pressure of the gas in the compression chamber is lower. Thus during this portion of the compression cycle, the volume available to the liquid in the intervening chamber would increase. This would in turn reduce the liquid pressure at the time when gas pressure also falling within the cylinder, again maintaining liquid flow rate and consistent gas-liquid heat exchange within the chamber.

FIGS. 7C-7D show the situation during expansion and expansion cycle. At the beginning of the expansion stroke, the gas pressure within the cylinder is at its highest. In order to maintain liquid flow and hence the quality of gas-liquid heat exchange during this period, FIG. 7C shows that the volume available to the intervening liquid chamber is low.

Conversely, as the piston continues to move toward BDC during the remainder of the expansion stroke, the available volume of the intervening chamber would increase, thereby reducing the liquid pressure to match the gas pressure. Liquid flow rate, and hence the quality of gas-liquid heat exchange during expansion, is thereby maintained.

The character in the change of volume available to the intervening liquid chamber over time, need not be symmetrical relative to high liquid pressure (e.g. the TDC position). In fact, the shape of the liquid pressure profile could be determined by factors such as cam shape (in the case of a mechanical linkage), or alternatively under the influence of some other factor (e.g. field strength in the case of an electro-mechanical linkage). Hydraulic linkages to control the location of the moveable wall of the intervening chamber are also possible.

In the particular embodiment of FIG. 7, under certain conditions the pump will act as a net consumer of energy (e.g. to introduce liquid into the compression/expansion chamber at higher pressures). However, it is further noted that at other portions of the cycle the pump may be able to recoup energy.

That is, during certain times the constant flow pump may be flowing liquid into the chamber, while the volume available in the liquid chamber is increasing. Under such circumstances, the energy is recovered from driving the linkage by the liquid entering the intervening chamber. Such energy can be harnessed by placing the linkage into communication with a generator or motor-generator.

Some embodiments are now described in the following clauses.

1. An apparatus comprising:

a first pumping element coupled to a pump drive mechanism and in fluid communication with a first liquid sprayer of a cylinder having a solid piston disposed therein, the first pumping element configured to spray a liquid into the cylinder during gas compression; and

a second pumping element coupled to the pump drive mechanism and in fluid communication with a second liquid sprayer of the cylinder, the second pumping element selectively coupled to the pump drive mechanism via a first clutch to spray the liquid into the cylinder during gas expansion.

2. An apparatus as in claim 1 wherein the first liquid sprayer is in communication with the first pumping element via a liquid manifold.

3. An apparatus as in clause 2 wherein the first liquid sprayer shares the manifold with a third liquid sprayer.

4. An apparatus as in clause 3 wherein the first liquid sprayer and the second liquid sprayer are arrayed as part of a first ring.

5. An apparatus as in clause 4 wherein:

the second liquid sprayer is arrayed as part of the first ring; and

the first ring is partitioned.

6. An apparatus as in clause 1 wherein the first liquid sprayer is arrayed as part of a first ring, and the second liquid sprayer is arrayed as part of a second ring.

7. An apparatus as in clause 1 wherein a gas flow valve is located near Top Dead Center (TDC) of the cylinder, and the second liquid sprayer is positioned closer to TDC than the first liquid sprayer.

8. An apparatus as in clause 1 wherein the second pumping element is selectively coupled to the pump drive mechanism via a second clutch to spray the liquid into the cylinder during the gas compression.

9. An apparatus as in clause 1 wherein the first pumping element comprises a mechanism to control a spray phase.

10. An apparatus as in clause 1 wherein the first pumping element comprises a first cam and the second pumping element comprises a second cam.

11. An apparatus comprising:

a second pumping element coupled to the pump drive mechanism and in fluid communication with a second liquid sprayer of the cylinder, the second pumping element selectively coupled to the pump drive mechanism via a phase adjustment mechanism to spray the liquid into the cylinder during gas expansion.

12. An apparatus as in clause 11 wherein the phase adjustment mechanism comprises a cam selectively moveable relative to a rotating camshaft via a planetary gear set.

13. An apparatus as in clause 12 wherein:

the second pumping element comprises a piston; and

the phase adjustment mechanism comprises the cam selectively moveable relative to the rotating camshaft via a gear system.

14. An apparatus as in clause 13 wherein the gear system comprises a worm gear and a planetary gear.

15. A method comprising:

causing a first pumping element of a pump to flow liquid to a first liquid sprayer of a cylinder having a solid piston disposed therein in communication with a crankshaft, the first pumping element configured to spray a liquid into the cylinder during gas compression; and

causing a second pumping element of the pump to flow liquid to a second liquid sprayer of the cylinder during gas expansion.

16. A method as in clause 15 wherein the first pumping element and the second pumping element are in communication with the crankshaft.

17. A method as in clause 16 wherein the second pumping element is in selective communication with the crankshaft via a clutch.

18. A method as in clause 16 wherein a phase of the second pumping element is adjustable relative to a phase of the first pumping element.

19. A method as in clause 18 wherein the phase of the second pumping element is adjustable by rotation of a cam relative to a camshaft via a planetary gear set.

20. A method as in clause 15 wherein the first pumping element is also configured to spray into the cylinder during gas expansion.

21. A method as in clause 15 wherein the second pumping element is also configured to spray into the cylinder during gas compression.

22. An apparatus comprising:

a liquid flow pumping element in liquid communication with a gas chamber receiving a reciprocating member, via an intervening liquid chamber having a changeable volume, wherein the intervening liquid chamber is configured to maintain a substantially constant pressure of liquid injected into the gas chamber.

23. An apparatus as in clause 22 wherein the changeable volume of the intervening liquid chamber is determined by movement of a piston in communication with a linkage.

24. An apparatus as in clause 23 wherein the linkage is in physical communication with the reciprocating element within the gas chamber.

25. An apparatus as in clause 23 wherein the linkage is in communication with a motor or a motor-generator.

26. An apparatus as in clause 22 wherein the changeable volume of the intervening liquid chamber is determined by movement of an elastic membrane.

27. An apparatus as in clause 22 wherein the flow pumping element comprises a rotary pump.

It is noted that the above description relates to only certain embodiments, variations of which are possible. For example, FIG. 8 shows an alternative embodiment of a chamber, this time comprising a plurality of sprayers formed in a single integral piece.

In particular, the chamber of FIG. 8 includes seven (7) spray rings with forty-five (45) nozzle locations each. The piston is not shown in this view for clarity of illustration.

Converting the cylinder into a single piece containing seven (7) rows, provides the benefit of greater mechanical integrity, and reduces the cost of fabrication. It also allows for tighter radial clearances between the piston and cylinder wall, reducing the geometric dead volume in the cylinder. Each plenum is separated internally by o-rings, so their pressures are independent.

This embodiment also features the spray rings bunched together near TDC. This configuration allows each ring to spend more time uncovered by the piston during the cycle.

Locating spray rings near TDC also concentrates spray delivery in the portion of the chamber where heat exchange will have its greatest effect. That is, on compression the greatest temperature increase is expected to occur proximate to TDC as the gas is compressed to its output pressure, while on expansion the greatest temperature drop is also expected to occur proximate to TDC as the gas undergoes initial expansion from its inlet pressure.

The pump for the particular embodiment of FIG. 8 is shown in FIG. 9. This pump features twelve (12) plungers capable of 122.7 g/rev total water flow (1.23 kg/s@600 RPM). In this particular embodiment, the plungers are not in contact with a seal, but in other embodiments a wiping seal could be used.

The pump includes several features designed to improve performance. For example compliance and length of the spray lines is reduced in order to achieve the sharpest possible spray pulse shape.

The embodiment of FIG. 9 also features decoupled opposing plungers. In particular, the plunger design was switched to a spring-actuated plunger return, allowing motion of each plunger to be controlled independently. This was particularly relevant to reducing the intensity of the fill stroke to reduce cavitation by avoiding relative pressures below the vapor pressure of water, a situation which can give rise to cavitation and wear.

The profiles of the pump cams were changed to make the plunger fill strokes less aggressive (i.e., occurring over a larger crank angle range) in an effort to reduce cavitation. On injection, more aggressive (i.e., occurring over a smaller crank angle range) cam profiles were optimized to achieve the desired step-profile for spray injection, thereby allowing concentrated spray “on demand” at certain portions of the cycle.

One or more factors may be considered in determining an optimum spray profile under particular circumstances. Examples of such factors can include but are not limited to, flow rate across the nozzle, droplet size, injection velocity, and structure (e.g., 3-D shape) of the resulting spray plume.

Pump chamber refill considerations may also play a role. For example, injection over a minority of crank angle can leave the remaining majority of the cycle available for liquid intake into the pump chamber. Such an approach can lessen pressure differentials arising in the pump, reducing cavitation and wear.

FIG. 10 plots (normalized) pressure across the nozzles of the seven spray rings shown in FIG. 8, versus crank angle for various compression runs. The spray profiles detailed in FIG. 10 show some of the spray rings (e.g., rings 1-5) in fluid communication with multiple cam lobes of the pump—as in the configuration previously illustrated in connection with FIG. 5. Other of the spray rings (e.g., rings 6-7) are in fluid communication with only one respective cam lobe of the pump.

It is further noted that the pump embodiment of FIG. 9 features plungers of different sizes in communication with the various spray rings. For example, plungers of larger diameters may achieve a higher flow rate supplying spray rings at a lower pressure (e.g., further away from TDC). Conversely, smaller diameter pump plungers (capable of exerting more concentrated forces) may be used to supply the highest pressure spray rings located near TDC.

FIG. 10 further illustrates another aspect of cam design in the embodiment of the liquid flow pump of FIG. 8. That is, the cam lobes may be shaped to substantially reduce an amount of liquid that is flowed to a spray ring when the piston is overlapping.

Specifically, occlusion of the spray ring by the piston will prevent small droplet formation, instead resulting in the introduction of bulk water offering a small gas-liquid interface and poor heat exchange properties. And, this introduction of such bulk water consumes power, serving as a drag on efficiency.

Accordingly, the spray profiles of FIG. 10 show low pressures across the nozzles at crank angles when the piston is located at or near the spray ring. For example, FIG. 10 shows the pressure across a nozzle of ring 7, dropping at a crank angle of about 290° as the piston passes by (shown by the vertical line). This result is accomplished by the shape of lobe 11.

Spray ring 1 located much nearer to TDC, also experiences a drop in pressure owing to the shape of lobes 5 and 6. Here the pressure begins to drop as the piston approaches, before it actually reaches the spray ring (shown by the solid vertical line). Such a pressure profile can avoid or reduce a volume of liquid that is sprayed while the exhaust valve is open to flow compressed gas from the cylinder.

In one embodiment the mechanical connection between the pump of FIG. 10 and the drive train of the compression/expander piston, is a spline coupling with 34 gear teeth. This corresponds to each spline position being offset by 10.6°.

In order to study performance effects of sweeping spray timing, the following five spline positions were tested (in addition to the nominal 0° offset): −42.4°; −31.8°; −21.2°; −10.6°; and +10.6°. The timing was thus advanced to the point where the start of the spray corresponded to the low pressure valve closing event. The timing was also retarded by one position from nominal to investigate the effect on high PR conditions.

Compression Power One Way (CPOW) efficiency was then calculated using the maximum One Way Efficiency (OWE) for any spline position for each pressure ratio (PR). The resulting difference in OWE across the range of PRs is shown in FIG. 11.

By adjusting the spline offset, it is possible to improve OWE across the entire compression process. Thus in this example, a phaser configured to vary the injection timing across the compression event, could provide an improvement in CPOW by 0.6%.

In certain embodiments, actuation of the pump valves relative to the drivetrain may be accomplished utilizing a Variable Cam Phaser (VCP) structure available from Delphi Automotive PLC, of Gillingham, U.K. That VCP allows a cam lobe (lift event) timing to crank shaft timing to be changed, while the engine is operating, based on the parameters of the engine.

The cam lobe angular position, or phase relationship, is controlled by the internal vane mechanism of the VCP. Commands from a control module can adjust the position of the valve.

LIQUID PUMP

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