WO2016126695A1

WO2016126695A1 - Natural gas compression in a hybrid vehicle

Info

Publication number: WO2016126695A1
Application number: PCT/US2016/016152
Authority: WO
Inventors: Christopher L. HAGEN; Mathew S. Smith; Jeffrey G. WITWER
Original assignee: Onboard Dynamics, Inc.
Priority date: 2015-02-06
Filing date: 2016-02-02
Publication date: 2016-08-11

Abstract

This application concerns systems and methods for compressing natural gas within the drive system of a hybrid vehicle. In one implementation, the application features a method of compressing a gas within a drive system of a hybrid vehicle, the drive system comprising an internal combustion engine having a crank shaft and an electric motor. The method includes (a) placing a first cylinder of the internal combustion engine in a compression mode, (b) compressing a gas within the first cylinder, using the cylinder as a reciprocating compressor, and (c) powering the compression of the gas using electricity.

Description

NATURAL GAS COMPRESSION IN A HYBRID VEHICLE

FIELD

This application concerns systems and methods for compressing natural gas within an internal combustion engine of a hybrid vehicle.

BACKGROUND

Reciprocating internal combustion engines (ICEs) are utilized in Electric-Internal Combustion Engine (ICE) hybrid vehicles. Internal combustion engines configured to operate using

conventional motor fuels, such as gasoline or diesel, can be easily converted to run on natural gas. However, relatively few refueling stations exist that offer compressed natural gas for use in passenger and commercial vehicles. As a result, operators of natural gas-powered vehicles often must drive long distances to the nearest refueling station. This lack of natural gas refueling infrastructure has limited the adoption of natural gas-powered vehicles by the public and industry to those who operate on fixed routes and/or return to a central location where a refueling station can be located. Accordingly, improvements to systems and methods for refueling natural gas-powered vehicles are desirable.

Onboard compression systems and methods are disclosed in U.S. Patent Application No.

14/244,807, and its parent, International Patent Application No. PCT/US2014/019623, the full disclosures of which are incorporated herein by reference. These systems include a valve manifold block external to the engine, and a plurality of compression tanks in fluid communication with the valve manifold block. Onboard compression systems in which compression takes place within cylinders of the engine are described in U.S. Provisional Application 62/080880, filed November 17, 2014, the full disclosure of which is incorporated herein by reference. Generally, onboard compression utilizing the piston cylinder assemblies from an internal combustion engine (ICE) is benefitted by utilizing multiple cylinders from the ICE to achieve staged compression of gases, while utilizing other cylinders to power the compression process. This tends to limit the use of in- cylinder compression to larger engines, e.g., 6 cylinders or more.

SUMMARY

[001] Disclosed herein are representative systems and methods that can be used to compress natural gas, using the drive system of a hybrid vehicle, for storage onboard a vehicle. By taking advantage of the electric motor already contained in the vehicle to power compression, rather than relying upon one or more cylinders of the ICE being used in combustion mode, these systems and methods can be used with the relatively small (e.g., 4 cylinder) ICE's used in hybrid drive systems. In some embodiments, all cylinders of the ICE are used for compression during the compression process.

[002] In one aspect, the disclosure features a system for compressing a gas within a hybrid vehicle, the system comprising (a) an internal combustion engine comprising a crank shaft, a plurality of bimodal cylinders, and a plurality of pistons disposed in the cylinders and operably connected to the crank shaft; (b) an electric motor configured to turn the crank shaft when in a compression mode; (c) a check valve system configured to regulate gas flow into and out of the bimodal cylinders during compression of the gas within the bimodal cylinders; and (d) a control unit configured to operate the electric motor in the compression mode.

[003] In another aspect, the disclosure features a method of compressing a gas within a drive system of a hybrid vehicle, the drive system comprising an internal combustion engine having a crankshaft and an electric motor configured to drive the crankshaft. The method comprises (a) placing a first cylinder of the internal combustion engine in a compression mode, (b) compressing a gas within the first cylinder, using the cylinder as a reciprocating compressor, and (c) powering the compression of the gas using electricity. [004] In some implementations, compression is powered by using an electric motor directly or indirectly to turn the crankshaft. The electric motor may be powered, for example, by a battery and/or by an external AC source, e.g., household electricity.

It is noted that the phrases "first cylinder", "second cylinder", "third cylinder", etc. in this section and in the claims do not refer to the location of the cylinders; instead, "first", "second", "third", etc. are merely used to provide antecedent basis and for clarity.

The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the

accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic plan view of a hybrid vehicle having an onboard natural gas compression system according to one embodiment of the invention. FIG. 1 A is a schematic showing the drive configuration of a Toyota SYNERGY® hybrid being used for in-cylinder compression.

FIG. 2 is a schematic diagram illustrating a first configuration for in-cylinder onboard compression.

FIGS 3 A-3E are various views of an engine assembly suitable for use in the system shown in FIG. 2. FIG. 3A is a cross-sectional view, taken along line A-A in FIG. 3C, of the engine during Stage 1 compression; FIG. 3B is a cross-sectional plan view of the engine during Stage 2 compression; FIG. 3C is a perspective cross-sectional view taken along a plane generally perpendicular to the plane of FIG. 3 A; FIG. 3D is a top down perspective view; and FIG. 3E is a diagrammatic bottom view of a portion of the cylinder head.

FIG. 4 is a schematic diagram illustrating a second configuration for in-cylinder onboard

compression.

FIG. 5 is a perspective view of an inlet check valve according to one implementation. FIG. 5A is a cross-sectional view of the valve in a closed position. DETAILED DESCRIPTION

There are many types of Electric-Internal Combustion Engine (ICE) hybrids, which, if retrofitted to operate on natural gas, can utilize the systems and methods described herein. The hybrid need only have a configuration in which an electric motor is coupled directly or indirectly to the crankshaft of the ICE.

The present disclosure features systems and methods for compressing a gas utilizing one or more cylinders of an ICE. This in-cylinder compression is effected by utilizing an electric motor of the hybrid, directly or indirectly, to turn the crankshaft of the ICE. Advantageously, this arrangement allows all cylinders of the ICE to be used in compression mode during compression, rather than some cylinders being run in combustion mode to power the cylinders that are being used for compression, as described in U.S. Provisional Application 62/080880.

Moreover, by utilizing the electric motor to power compression, the engine does not need to idle during the compression process, reducing emissions.

Referring to FIG. 1, a representative natural gas-powered hybrid vehicle 10 can comprise an engine compartment 12, a cabin portion 14, and a rear portion 16. As used herein, the terms "natural gas" and "gas" refer to a hydrocarbon gas, the primary component of which is methane gas having the chemical formula CH₄. The vehicle 10 can further include a natural gas compression system generally indicated at 18 configured to compress and store natural gas onboard the vehicle 10 for use as fuel. The natural gas compression system 18 includes a reciprocating internal combustion engine 20, a storage pressure tank 22 which may be located in the rear portion 16 of the vehicle 10 or elsewhere (e.g., the spare tire compartment), a gas storage conduit 24 providing fluid

communication between the engine 20 and storage tank 22, and a gas source conduit 26 providing fluid communication between the engine and a gas source 25 at a pressure lower than that of the gas in the storage tank 22.

The engine can be a spark-ignited internal combustion engine configured to operate using natural gas as fuel. In some embodiments, the engine can be specially designed to operate using natural gas as fuel, or can be retrofitted to operate using natural gas as fuel. The internal combustion engine 20 has been fitted with a modified cylinder head 28 to allow in-cylinder gas compression, as will be discussed in detail below. Control logic for controlling the various components of the natural gas compression system 18 can be implemented by an onboard computer, using suitable software, e.g., as disclosed in U.S. Patent Application No. 14/244,807, incorporated by reference above. The engine may be any ICE suitable for use in an Electric/ICE hybrid vehicle. As an example, the Toyota PRIUS® hybrid uses a 1.5-liter gasoline engine that is an inline 4-cylinder, chain-driven 4- valve (2 intake and 2 exhaust valves per cylinder) DOHC engine.

The system also includes an electric motor/generator 11 that is coupled to the crankshaft 13 of the ICE and acts initially to start the engine and then primarily as a generator during driving and braking, sending power to a battery 15 through an inverter (not shown). This electric

motor/generator can be used during compression, when the vehicle is stationary, to drive the crankshaft and thus reciprocate the pistons to compress the gas as will be discussed below. As shown diagrammatically in FIG. 1 A, the system may further include a second electric

motor/converter 17 that is operatively coupled to a drive shaft 21 to turn the vehicles wheels when the vehicle is operating in electric mode.

The energy stored in the battery may not be sufficient to power the electric motor/generator throughout the compression process. Thus, it may be desirable or necessary to plug the battery in to an external AC source 23 (FIG. 1), e.g., household electricity or a plug-in hybrid recharging station. In the case of plug-in hybrids, the vehicle is outfitted with a plug/cable; other hybrids can be retrofitted to include an after market plug/cable.

The system preferably also includes a controller 27, e.g., an ECU or an onboard control system, capable of activating compression by closing the ignition circuit of the vehicle, for example using ignition system 29. The controller may also be configured to monitor the energy state of the battery and temporarily deactivate compression if the battery charge drops below a predetermined level, reactivating compression once the battery charge has regained the predetermined level. The controller could also be configured to deactivate some or all of the compression valves and activate the combustion valves (described further below) periodically, e.g., when the battery is running low. Some or all of the cylinders could then be run temporarily in combustion mode, e.g., in order to supply power for compression. The cylinders being operated in combustion mode could power simultaneous compression by turning the crankshaft with other cylinders operating in compression mode, or later compression by recharging the battery via the engine/generator.

In some cases, the size of the storage tank can be reduced and/or it can be provided in a space saving ("conformal") shape, by the use of "adsorbent" or "absorbent" storage media within the tank. Storage tanks containing these materials can also allow lower pressures to be used, e.g., 500 psi rather than 3600 psi. Adsorbent storage media allows for the storage of natural gas in the physically adsorbed state. Adsorbed natural gas (ANG) is conventionally stored in porous carbon materials at a gas pressure of 3.5 MPa (500 psi). The DOE storage target for ANG has been set at 150 V/V, i.e., 150 STP (101.325 KPa, 298K) liters of gas stored per liter of pressure vessel internal volume.

Some systems utilize a packed activated carbon bed as the adsorbent material. Other systems include activated carbon in other configurations, e.g., briquettes, pellets or other monolithic structures. For example, an adsorbent carbon monolith based on carbon fibers developed at the Oak Ridge National Laboratory (ORNL) utilizes a continuous carbon skeleton, which allows for the liberation of practically all of the adsorbed gas via low-voltage electrical stimulation. BlackPak, Inc. (www.blackpaktech.com) manufactures natural gas fuel tanks that include monoliths of nanoporous carbon with a target system-level energy density greater than 6 MJ/L at 500 psi pressure. Other adsorbents include metal-organic frameworks such as Ni₂(dobdc) and HKUST-1. The lower pressure required when these tanks are used may allow greater driving range with the degree of compression that can readily be obtained using the systems and methods described herein. Use of these tanks may also, in some cases, allow compression to be performed using the power stored in the battery, without needing to plug the battery in to an external AC source.

In the embodiment shown, the natural gas compression system 18 can be in fluid communication with a natural gas source (not shown), such as a municipal gas utility hookup. In some embodiments, the natural gas source can be coupled to the gas source conduit 26 of vehicle 10 by a gas supply nozzle. The natural gas compression system 18, which utilizes one or more bimodal cylinders of the engine 20, operated in a compressor mode, is configured to compress natural gas supplied by the natural gas source such that the gas flows into the storage pressure tank 22 at a predetermined final pressure. In some implementations, the gas can be sequentially compressed further in each of several bimodal cylinders as will be described below. In this manner, the natural gas can be compressed in one or multiple compression stages all within the engine 20.

As is well known in the internal combustion art, the engine can include a cylinder block, a cylinder head, and a plurality of piston-cylinder assemblies. Each of the piston-cylinder assemblies can include a piston configured to travel in a cylinder defined by the cylinder block and the cylinder head. The pistons can be coupled to a crankshaft such that rotary motion of the crankshaft translates to linear motion of the piston in the cylinder. In this manner, the pistons can be configured to travel in the respective cylinders between a top dead center (TDC) position and a bottom dead center (BDC) position. As used herein, the term "top dead center" refers to a position of the piston in the cylinder in which the piston is farthest from the rotational axis of the crankshaft, and the term "bottom dead center" refers to a position in which the piston is closest to the rotational axis of the crankshaft. The operation of the piston-cylinder assemblies during combustion is well known and is described in U.S. Patent Application No. 14/244,807, incorporated by reference above.

In the systems described below, a plurality of the piston-cylinder assemblies are configured as bimodal piston-cylinder assemblies (referred to hereinafter as "bimodal cylinders"), which can be operated in either a combustion mode or a compression mode. In the combustion mode, a bimodal cylinder can burn a fuel-air mixture drawn in through an intake valve and exhaust the combustion gases through an exhaust valve in a standard four-cycle mode. The various stages of the four-cycle combustion mode can occur in accordance with the position of the bimodal cylinder in the firing order relative to the other standard piston-cylinder assemblies. While operating in the combustion mode, the compressor check valves can be in the closed position, thereby isolating the bimodal cylinder from the natural gas inlet.

In the compressor mode, the intake and exhaust valves of each bimodal cylinder can be deactivated (e.g., by collapsible cam lifters) such that they remain in the closed position, and the compressor check valves (described in detail below) can be activated. Natural gas from the natural gas source can then be drawn into the bimodal cylinder and compressed by the piston.

The bimodal cylinder can include a bimodal piston, and can be configured to compress natural gas in a two-cycle mode when operating in the compressor mode (i.e., natural gas is drawn into the cylinder on a downward stroke of the bimodal piston and compressed by the bimodal piston on an upward stroke). The operation of the bimodal cylinders and their compression check valve systems will be described in detail below.

Referring to FIG. 2, in a first implementation during refueling two of the bimodal cylinders of the engine are run in compressor mode. These cylinders operate 180 degrees out of phase with each other (i.e., when the piston of one cylinder is in the TDC position the adjacent cylinder is in the BDC position.) The other two cylinders may be standard (non-bimodal) cylinders, or may be bimodal cylinders that are not utilized for compression in this scenario. Because of the

configuration of the compressor check valve system, discussed further below, the interstage pressure (between the outlet of Stage 1 and inlet of Stage 2) automatically adjusts so that the mass pumped by Cylinder 1 will equal the mass pumped by Stage 2, keeping the mass flow rate relatively constant over time. This implementation can be useful, for example, if some cylinders need to be run periodically in combustion mode, as discussed above, to provide supplemental power for compression.

In this implementation, gas travels to a first bimodal cylinder via an inlet to the cylinder head, is compressed in the first cylinder, and is routed through a conduit internal to the head to a second bimodal cylinder in which the gas is further compressed. The compressed gas then is routed to the storage tank, as discussed above with reference to FIG. 1. Cooling may be provided at any point in the process. For example, cooling devices such as heat exchangers (not shown) could be added, e.g., internal or external to the head after Stage 1 and/or in the line after Stage 2. In alternate embodiments external lines could be provided between Stage 1 and Stage 2 and/or after Stage 2. In this case, in some implementations air, engine coolant, cooling from the vehicle's air conditioning circuit, or the like can be provided to the lines.

The system shown in FIG. 2 can produce a final pressure of 500 psi or more, e.g., 500 to 800 psi, which may be used, for example, for adsorbent filling. Higher pressures, e.g., up to 3600 psi in some instances, may be obtained by adding additional stages (e.g., utilizing additional bimodal cylinders), inlet pressure boosting, or post-cylinder intensification. In the case of boosted inlet pressure, a compressor (e.g., compressor 302, FIG. 1, which may be for example a belt driven compressor) may be interposed inline in between the inlet and engine. For post-cylinder intensification, a compressor may be interposed inline between the engine and storage tank (e.g., compressor 304, FIG. 1). Use of either or both of these techniques will reduce fill time, often without excessively increasing the energy required for refueling. Boosted inlet pressure will improve displacement and efficiency during Stage 1 compression, which will determine mass flow throughout the system. In some cases, with boosted inlet pressure fill times can be less than 20 minutes, e.g., 15 minutes or less.

An engine assembly 100 that may be used in one implementation of the system shown

diagrammatically in FIG. 2 is shown in detail in FIGS. 3A-3E. Using engine assembly 100, four cylinders may be used in series for multi-stage compression. Engine assembly 100 includes a plurality of bimodal cylinders 102, e.g., four cylinders as is common in ICEs used in hybrids. As shown in FIG. 3E, which shows the head 112 of engine assembly 100 from below, the bimodal cylinders 102 include an intake channel 200 and an exhaust channel 202, which are used in conventional fashion when the cylinder is in combustion mode. As seen in FIG. 3D, a fuel rail 203 provides fuel from a fuel inlet 205 to the intake channels 200 (FIG. 3E) as is well known. The bimodal cylinders additionally include an inlet compression channel 204 and outlet compression channel 206, which are used when the cylinder is in compressor mode. Each of the bimodal cylinders 102 includes a compression check valve assembly 106 that includes an inlet check valve 108 and an outlet check valve 110 mounted within the respective intake and exhaust channels of head 112. The structures of the inlet and outlet check valves will be described in detail later with reference to FIGS. 7-7 A.

[005] As shown in FIGS. 3 A-3B, in this implementation a conduit 114 supplies gas to the inlet of first cylinder chamber 116. As piston 120 moves downward in cylinder chamber 116, the inlet check valve 108a of the first bimodal cylinder passively opens in response to reduced pressure within the cylinder chamber, thereby allowing gas to flow into the chamber, while the outlet check valve 110a remains in its normally closed position. As the piston 120 rises (Stage 1 compression), compressing the gas, the outlet check valve 110a passively opens when a pressure is reached that is sufficient to overcome the combination of the spring bias and the force exerted on the top surface of the check valve. Because the surface area of the top surface of the check valve is greater than the surface area of the bottom surface, the pressure inside the cylinder must be greater than the pressure outside for the valve to open. The compressed gas flows past the outlet check valve and through conduit 118 to the inlet check valve of the second bimodal cylinder. The reduction in pressure caused by downward movement of piston 121, causes the inlet check valve 108b to passively open, allowing the gas to enter the second cylinder chamber 122 (FIG. 3B). At this point, the piston 121 in the second cylinder is in BDC position (FIG. 3B) and the inlet check valve 108b of the second bimodal cylinder is in its open position, allowing gas to flow into chamber 122. As in the previous stage, the outlet check valve 110b of the second bimodal cylinder is initially in its biased-closed position. During Stage 2 compression, the outlet check valve 110b is forced upwards and thus open by the increasing pressure in cylinder chamber 122, allowing gas to flow to the next bimodal cylinder. This sequence is repeated for the remaining two cylinders, after which the gas, compressed to its final pressure, is routed to the storage tank via a high pressure gas line 24 (FIG. 1 ) [006] As shown in FIGS. 3A and 3B, the inlet check valve opens with a downward motion, while the outlet check valve is an upward-opening poppet valve. Both valves are biased to a normally closed position. The operation of these valves, in the manner described in the preceding paragraph, provides a substantially constant, regulated mass flow rate. The valves generally will not open until the correct pressure differential has been reached, and thus the timing of opening and closing of the valves will self-adjust as the pressure in the storage tank (and thus the backpressure experienced through the cylinders) increases.

[007] A second implementation is shown in FIG. 4. In this implementation, Stage 1 compression occurs simultaneously in two (or in some cases more) bimodal cylinders. Thus, in this case the two Stage 1 pistons are operated in phase with each other (for an inline cylinder engine - the pistons would be out of phase by 90 degrees for a V- cylinder engine), and the inlet check valves and outlet check valves of the two Stage 1 bimodal cylinders are operated together (both inlet valves are open when both outlet valves are closed and vice versa.) After compression, the compressed gas from all of the Stage 1 cylinders (Cylinders 3 and 4 in FIG. 4) flows to one or more Stage 2 cylinders (Cylinder 2 in FIG. 4.)

[008] This configuration results in compression of a larger volume of gas at once, thereby reducing refueling time, as well as allowing for more efficient compression which will minimize the energy required for refueling. In some implementations 10 GGE fill times can be less than 45 minutes, e.g., less than 30 minutes or even less than 20 minutes.

[009] Gas can be supplied to the two Stage 1 cylinders using an external gas line system or using internal conduits disposed within the head 112.

[010] Many types of check valves may be utilized as the inlet check valve. As discussed above, the inlet check valve is configured to be biased towards a normally closed position, and to open downwardly in response to reduced cylinder pressure. In order for the inlet check valve to function in the manner discussed above, the valve is generally shaped such that its cylinder facing surface has a larger area than the upper, head facing, surface. This causes the valve to remain closed until the pressure on the inside of the cylinder is less than the pressure outside the cylinder. Preferred check valves also include elements that control seating velocity on closing and on maximum opening, to preserve the life of the valve. An example of a suitable check valve 400 is shown in FIGS. 5-5A. Referring to FIG. 5A, the check valve 400 is in many respects of conventional poppet valve construction, but further includes a plurality of small diameter pins 402, spaced equally around the circumference of the valve, that are used as snubbers to dissipate velocity on maximum opening of the valve. These pins are dimensioned to only slow the last 1 to 20% of the valve stroke. The valve also includes one larger diameter pin 404 located at the proximal end of the valve stem 406, which is used as a snubber to control seating velocity on closing. The pin 404 acts direction on the valve stem 406 and is dimensioned to only slow the last 1 to 20% of valve stroke. A plurality of large diameter pins 408 are positioned at equal spacing around the valve to lock the valve in a closed position.

[011] Many types of upwardly (away from the cylinder chamber, in use in the systems disclosed herein) opening poppet valves may be used as the outlet check valves. Suitable outlet check valves include, for example, those described in U.S. Patent No. 8,151,747. In order for the check valve to function in the manner discussed above, the valve is generally shaped such that its cylinder facing surface is smaller than the opposing head facing surface area. Preferably, the outlet check valve includes a high force locking mechanism to prevent unintended opening during compression and combustion. Such mechanisms are well known in the valve art.

[012] Both the inlet check valve and outlet check valves are configured to be locked in their closed position when bimodal cylinder is operated in the combustion mode. The check valve system may be placed in the locked out condition using a control device, for example selected from the group consisting of microprocessors, internal mechanics, hydraulic controllers, pneumatic controllers, and mechanical controllers. In some implementations, an external three way solenoid valve may be used to switch the check valve system between refueling and compression modes. [013] Operation of the natural gas compression system can proceed in the following manner. If all of the piston-cylinder assemblies of the engine are operating in the combustion mode, the engine can first be turned off. A user can then connect the natural gas source to a natural gas input on the vehicle such that gas flows from the natural gas source to the gas source conduit of the engine block at the pressure of the natural gas source. The user can then engage the natural gas compression system 18 by, for example, activating a switch or other mechanism in the cab of the vehicle. The computer can then prepare the bimodal cylinders to operate in the compressor mode. The engine can then be restarted with the bimodal cylinders operating in the compressor mode as discussed and compressed gas being delivered to the storage tank in the vehicle. The final pressure of the compressed gas can be, for example, about 250 bar (3600 psi), corresponding to the standard pressure for storage of compressed natural gas in the United States.

Other Embodiments

Other embodiments are within the scope of the present disclosure.

For example, while natural gas is discussed above, in alternative embodiments the systems and methods disclosed herein can also be compatible with various other hydrocarbon gases including propane and butane, or non-hydrocarbon gases or gas mixtures, such as hydrogen, oxygen or air, to name a few.

While several multi-cylinder compression implementations are shown above, the methods described herein can be implemented in many different combinations of cylinders used for one or more compression stages.

In addition, the compressor check valves in the in-cylinder embodiments described above need not be in the head, but may instead be in a different location, e.g., a cylinder wall or within a piston assembly.

Moreover, the check valves discussed above can be replaced by other valve systems, e.g., by an electric or hydraulic fully flexible valve train. As will be clear from the various embodiments described above, the in-cylinder compression concepts described herein can be applied to a wide variety of hybrid vehicle drive systems.

In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.

Claims

We claim:

1. A method of compressing a gas within a drive system of a hybrid vehicle, the drive system comprising an internal combustion engine having a crank shaft and an electric motor, the method comprising:

placing a first cylinder of the internal combustion engine in a compression mode, compressing a gas within the first cylinder, using the cylinder as a reciprocating compressor, and

powering the compression of the gas using electricity.

2. The method of claim 1 wherein compression is powered by using an electric motor directly or indirectly to turn the crankshaft.

3. The method of claim 2 wherein the electric motor is operably coupled directly to the crankshaft.

4. The method of claim 2 wherein the electric motor is powered by a battery.

5. The method of claim 4 wherein, during compressing, the battery is recharged by an external AC source.

6. The method of claim 1 further comprising connecting the vehicle to an external AC source prior to or during the compressing step.

7. The method of claim 1 further comprising utilizing an ignition switch of the vehicle to actuate the compressing step.

8. The method of claim 1, further comprising controlling the flow rate and timing of gas into and out of the first cylinder using a check valve system.

9. The method of claim 1, further comprising:

routing the compressed gas through an outlet of the first cylinder to an inlet of a second cylinder, and

further compressing the compressed gas in the second cylinder.

10. The method of claim 9, wherein the compressed gas is routed directly from an outlet of first cylinder to an inlet of the second cylinder.

11. The method of claim 9, further comprising controlling flow of the gas between the outlet of the first cylinder and the inlet of the second cylinder.

12. The method of claim 11, wherein controlling flow comprises utilizing a check valve system to regulate flow in response to pressure differentials within the cylinders.

13. The method of claim 1, wherein a first portion of the gas is compressed in the first cylinder, the method further comprising:

compressing a second portion of the gas in a second cylinder during compression of the first portion;

routing the compressed gases from the first and second cylinders to a third cylinder; and further compressing the gas received from the first and second cylinders in the third cylinder.

14. The method of claim 1 further comprising delivering the compressed gas from the cylinder to a storage tank in fluid communication with the cylinder.

15. The method of claim 1 further comprising delivering the gas to the cylinder directly through a head of the internal combustion engine.

16. The method of claim 1 wherein the gas comprises natural gas.

17. The method of claim 1 further comprising boosting pressure of gas delivered to the first cylinder using an onboard booster compressor.

18. The method of claim 1 further comprising running one or more other cylinders of the internal combustion engine in combustion mode while the first cylinder is being used as a reciprocating compressor.

19. The method of claim 13 further comprising switching one or more of the first, second and third cylinders from the compression mode to a combustion mode and operating the cylinders for combustion, with the vehicle stationary, to provide power for further compression.

20. The method of claim 19 further comprising, after operating the cylinders for combustion, switching them back to the compression mode and operating the cylinders in compression mode.

21. A system for compressing a gas within a hybrid vehicle, the system comprising:

an internal combustion engine comprising a crank shaft, a plurality of bimodal cylinders, and a plurality of pistons disposed in the cylinders and operably connected to the crank shaft;

an electric motor configured to turn the crank shaft when in a compression mode; and a control unit configured to operate the electric motor in the compression mode.

22. The system of claim 21 further comprising a battery in electrical communication with the electric motor.

23. The system of claim 22 further comprising a plug, in electrical communication with the battery, the plug being configured to connect the battery to a source of AC power.

24. The system of claim 21 wherein the control unit is configured to close an ignition circuit of the vehicle in order to actuate the electric motor in the compression mode.

25. The system of claim 22 wherein the control unit is configured to monitor the level of charge of the battery and activate or deactivate the electric motor at a predetermined level of battery charge.

26. The system of claim 21 further comprising a check valve system configured to regulate gas flow into and out of the bimodal cylinders during compression of the gas within the bimodal cylinders.

27. The system of claim 21 further comprising a storage tank, configured to receive gas compressed in the cylinders.

28. The system of claim 21 further comprising an inlet pressure boosting compressor disposed upstream of the cylinders.

29. The system of claim 27 further comprising a post-compressing pressure boosting compressor disposed between the cylinders and storage tank.

30. The system of claim 27 wherein the storage tank comprises an adsorbent tank or an absorbent tank.