CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Application Serial No. 15/885,095 filed on January 31, 2018, the entire disclosure of which is hereby incorporated by reference.

BACKGROUND

[0002] The present disclosure relates generally to a vehicular fuel system for selectively separating an onboard fuel into octane-rich and cetane-rich components, and more particularly to such a system that promotes heat balance as part of such onboard fuel separation in such a way to reduce the size, weight and complexity associated with such fuel separation activities.

SUMMARY

[0003] Within the realm of internal combustion engines (ICEs) used for vehicular propulsion, it is the four-cycle variant (with its intake, compression, combustion and exhaust strokes) that is most commonly in use, where the combustion is typically achieved through either a spark ignition (SI) or compression ignition (Cl) mode of operation. In ST based modes, a mixture of air and fuel (typically octane-rich gasoline) is introduced into a combustion chamber for compression and subsequent ignition via spark plug. In CTbased engines, fuel (typically cetane-rich diesel fuel) is introduced into the combustion chamber where the air is already present in a highly compressed form such that the elevated temperature within the chamber that accompanies the increased pressure causes the fuel to auto-ignite. Of the two, the Cl mode tends to operate with greater efficiency, while the SI mode tends to operate with lower emissions.

[0004] Various engine concepts or configurations may mimic the relatively low emissions of an SI mode of operation while simultaneously satisfying the high efficiency operation of a Cl mode of operation. Such concepts go by various names, and include gasoline direct injection compression ignition (GDCI), homogenous charge compression ignition (HCCI), reactivity controlled compression ignition (RCCI), as well as others. In one form, a single fuel may be used, while in others, multiple fuels of differing reactivities, usually in the form of selective octane-enrichment or cetane-enrichment, may be introduced. While performing octane on demand (OOD) or cetane on demand (COD) as a way of fueling these engines is possible, such activities may be fraught with problems. For example, having the respective octane-enriched or cetane-enriched portions be in either pre-separated form involves the parallel use of at least two onboard storage tanks and associated delivery conduit. In addition, the time and complexity associated with vehicle refueling activity in this circumstance renders the possibility of operator error significant. Likewise, OOD or COD generation once the single market fuel is already onboard may require distillation or membrane-based permeation-evaporation (pervaporation) activities that are accompanied by significant increases in size, weight and overall complexity of the onboard fuel-reforming infrastructure. These difficulties are particularly acute as they relate to achieving a heat balance associated with the underlying fuel enrichment activities. As such, a simplified approach to integrating such infrastructure into an onboard fuel separation system is warranted.

[0005] According to one embodiment of the present disclosure, a vehicular propulsion system is disclosed. The propulsion system includes an ICE with a combustion chamber, as well as a fuel system for converting an onboard fuel into octane-rich and cetane-rich components. The fuel system includes a supply tank for containing the onboard fuel, fuel conduit in fluid communication with the supply tank, a separation unit, a heat exchanger and first and second product tanks. The separation unit includes one or more adsorbent- based chambers such that the separation unit may selectively receive and separate at least a portion of the onboard fuel into an adsorbate and a remainder. The heat exchanger works with the separation unit to selectively deliver residual thermal energy that results from operation of the ICE to at least one adsorbent-based chamber to heat and subsequently vaporize (that is to say, desorb) at least some of the adsorbate. In one form, a first of the product tanks may be used to contain the desorbate, while a second of the product tanks may contain the remainder. A controller may be used to determine whether the ICE is in a first operational condition such that the controller will direct the flow of a portion of the onboard fuel to the combustion chamber without first passing through the separation unit, or a second operational condition to direct the flow of a portion of the onboard fuel to the separation unit. [0006] According to another embodiment of the present disclosure, a fuel system is disclosed. The fuel system includes a supply tank for containing the onboard fuel, fuel conduit in fluid communication with the supply tank, a separation unit, a heat exchanger and first and second product tanks, while a controller cooperative with an ICE and fuel system is configured to determine whether the ICE is in a first operational condition or a second operational condition such that when the controller determines that the ICE is in the first operational condition, the controller is configured to direct the flow of a portion of the onboard fuel to the combustion chamber without first passing through the separation unit, and when the controller determines that the ICE is in the second operational condition, the controller is configured to direct the flow of a portion of the onboard fuel to the separation unit.

[0007] According to yet another embodiment of the present disclosure, a method of operating an internal combustion engine is disclosed. The method includes configuring a fuel system to have an onboard fuel supply tank, a separation unit, a heat exchanger, a first product tank and a second product tank, as well as fuel conduit. A controller provides directions to at least some of the other components so that the controller can ascertain an operational condition of the ICE and then direct the flow of a portion of the onboard fuel to either the combustion chamber of the engine or to the separation unit depending on the engine operational condition. In a first ascertained engine condition, the onboard fuel flow does not interact with the separation unit, instead going to the combustion chamber for immediate use by the engine. In a second ascertained engine condition, the onboard fuel flow interacts with the separation unit such that an adsorbent portion of the onboard fuel collects on a surface of at least one of a plurality of chambers of the separation unit.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0008] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

FIG. 1 shows a vehicle with a partial cutaway view of an engine in accordance with one or more embodiments shown or described; FIG. 2 shows a simplified cutaway view of a cylinder of the engine of FIG. 1 along with a controller in accordance with one or more embodiments shown or described;

FIG. 3 illustrates a simplified view of an onboard fuel separation system in accordance with one or more embodiments shown or described;

FIG. 4 illustrates an adsorption rate of a highly aromatic fuel compound on a particular adsorbent functional group that may be used in the onboard fuel separation system of FIG. 3; and

FIG. 5 illustrates an exemplary adsorbate flow rate under three separate time periods in accordance with one or more embodiments shown or described.

DETAILED DESCRIPTION

[0009] In the present disclosure, an adsorption-based separation system may be used to split an onboard fuel into OOD or COD streams by taking advantage of one of two specific mechanisms: (1) employing differing functional groups that attract specific adsorbates (such as aromatics, cyclic and optional oxygenates) that are present in the onboard fuel supply; and (2) using a molecular sieve to selectively pass certain smaller (that is to say, linear) molecules while retaining larger (that is to say, branched) ones. Examples of the first type of adsorbent include activated carbon, silica, and alumina, as well as some types of zeolites and functionalized porous material in general, while examples of the second type include zeolites, metal organic frameworks and structured porous material. Within the present context, a fuel is deemed to be octane-rich when it has a concentration of iso-octane (2,2,4-trimethylpentane, C ₈ H _I8 ) or equivalent anti-knocking agent that is greater than that of the readily-available market fuel from which one or more separation activities have been employed. By way of example, a fuel would be considered to be octane-rich if it had a research octane number (RON) of greater than about 91-92 or an anti-knock index (AKI) of greater than about 85-87 for a so-called regular grade unleaded fuel, with respectively slightly higher values for mid-grade unleaded fuel and premium unleaded fuel. Within the present context, it will be understood that there are regional variations in the values of RON, AKI or other octane or cetane indicia, and that the ones expressly discussed in the previous sentence contemplate a United States market. Nevertheless, such values will be understood to be suitably adjusted to take into consideration these regional variations, and that all such values are deemed to be within the scope of the present disclosure within their respective region, country or related jurisdiction. As with octane, a fuel is deemed to be cetane-rich when it has a concentration of n-cetane (n-hexadecane, Ci ₆ H ₃₄ ) or components with equivalent ignition delay characteristics that is greater than that of readily-available market fuels. By way of example, a fuel would be considered to be cetane-rich if it had a cetane number (CN) of greater than about 40-45 (for most of the United States market, with suitable variations elsewhere).

[0010] Referring first to FIG. 1, a vehicle 100 includes a chassis 110 with a plurality of wheels 120. Chassis 110 may either be of body-on-frame or unibody construction, and both configurations are deemed to be within the scope of the present disclosure. The passenger compartment 130 is formed inside the chassis 110 and serves not only as a place to transport passengers and cargo, but also as a place from which a driver may operate vehicle 100. A guidance apparatus (which may include, among other things, steering wheel, accelerator, brakes or the like) 140 is used in cooperation with the chassis 110 and wheels 120 and other systems to control movement of the vehicle 100. An ICE 150 is situated within an engine compartment in or on the chassis 110 to provide propulsive power to the vehicle 100 while a controller 170 interacts with ICE 150 to provide instructions for the latter’s operation.

[0011] Referring next to FIG. 2, details associated with the structure and operation of a portion of the ICE 150 and the controller 170 are shown. The ICE 150 includes an engine block 151 with numerous cylinders 152, a crankshaft 153 rotatably movable within the block 151, numerous cams 154 responsive to movement of the crankshaft 153, a head 155 coupled to the engine block 151 to define numerous combustion chambers 156. The head 155 includes inlet valves 157 and exhaust valves 158 (only one of each is shown) that in one form may be spring-biased to move in response to the crankshaft 153 through a corresponding one of the cams 154 that are controlled by either a crankshaft-driven chain, crankshaft-actuated pushrods or pneumatic actuators (none of which are shown). An air inlet 159 and an exhaust gas outlet 160 are in selective fluid communication with each of the combustion chambers 156 through a fuel injector 161, while a piston 162 is received in each respective cylinder 152 and coupled to the crankshaft 153 through a connecting rod 163 so that the reciprocating movement of the piston 162 in response to an SI or Cl combustion taking place within the combustion chamber 156 is converted by the pivoting movement of the connecting rod 163 and crankshaft 153 to rotational movement of the crankshaft 153 for subsequent power delivery to the remainder of a powertrain that is made up of the ICE 150 and transmission, axles, differentials (none of which are shown) and wheels 120. Although ICE 150 is shown without a spark ignition device (such as a spark plug) in a manner consistent with the various Cl-based engine configurations (such as RCCI, HCCI or the like), it will be understood that in certain operating loads or conditions such as low loads, cold starts and associated warm-ups, such a spark ignition may be used (possibly in conjunction with some throttling) to increase the flame propagation combustion rate while keeping lower cylinder pressures.

[0012] In one form, ICE 150 is configured as a gasoline compression ignition (GCI) engine that can be operated with a gasoline-based fuel. In such case, the presently- disclosed fuel system may be used to achieve COD through operation on various fuels, including market gasoline, gasoline without an oxygenate or related anti-knock compound (also referred to as base gasoline) or gasoline with one of the many types of alkyls, aromatics or alcohols. In one non-limiting example, such fuel may have a boiling temperature in the range of ambient to about 200° C. Unlike an SI mode of operation where the fuel is substantially injected during the four-cycle operation’s inlet stroke, a GCI mode substantially injects the fuel during the compression stroke. In one form, the fuel and air are not fully mixed, which permits phasing of the combustion process to be controlled by the injection process. Moreover, the ignition delay permitted by gasoline- based fuels versus diesel-based fuels will allow for the partially premixed fuel and air to become more mixed during compression, which in turn will leave to improvements in combustion. Gasoline-based market fuels with some amount of fuel and air premixing helps ensure suitable fuel-air equivalence ratios for various engine loads and associated fuel injection timing scenarios. Thus, when configured as a GCI engine, ICE 150 using a fuel in the gasoline autoignition range (where for example, the RON is greater than about 60 and the CN is less than about 30) can provide relatively long ignition delay times compared to conventional diesel fuels. This in turn can lead to improved fuel-air mixing and related engine efficiency, along with lower soot and NOx formation; this latter improvement leads in turn to a simplified exhaust gas treatment system since the emphasis is now on oxidizing hydrocarbons and carbon monoxide in an oxygen-rich environment rather than trying to simultaneously control NOx and soot. Moreover, when operated as a GCI engine, ICE 150 requires lower fuel injection pressures than diesel-based Cl engines.

[0013] Furthermore, when configured as a GCI engine, ICE 150 may take advantage of gasoline-based market fuels that require lower amounts of processing; in one form, the fuel may be in the form of gasoline with an intermediate RON of between about 70 and 85. Such octane concentrations could then be adjusted via OOD or COD through the operation of the fuel system 200 that is discussed in more detail elsewhere in this disclosure.

[0014] Moreover, unlike HCCI modes of operation where the fuel and air is fully premixed prior to introduction into the combustion chamber 156, the GCI embodiment of ICE 150 will permit Cl operation under higher engine loads and compression ratios without concern over engine knocking. Furthermore, by permitting in-cycle control of the combustion phasing, an ICE 150 configured as a GCI can take advantage of fuel injection timing in order to make it easier to control the combustion process compared to an HCCI configuration where the combination of temperature and pressure inside the cylinder may not be precisely known.

[0015] In another form, ICE 150 is configured as an SI engine that can be operated with a gasoline-based fuel. In this case, the presently-disclosed fuel system may be used to achieve OOD through operation on various fuels, including market gasoline, gasoline without an oxygenate or related anti-knock compound or gasoline with one of the many types of alkyls, aromatics or alcohols.

[0016] Controller 170 is used to receive data from sensors S and provide logic-based instructions to the various parts of the fuel system 200 that will be discussed in more detail later. As will be appreciated by those skilled in the art, controller 170 may be a singular unit such as shown notionally in FIGS. 1 and 2, or one of a distributed set of units throughout the vehicle 100, this latter configuration as shown notionally in FIG. 3. In one configuration, controller 170 may be configured to have a more discrete set of operational capabilities associated with a smaller number of component functions such as those associated solely with the operation of the fuel system 200. In such a configuration associated with only performing functions related to operation of the fuel system 200, the controller 170 may be configured as an application- specific integrated circuit (ASIC). In another configuration, controller 170 may have a more comprehensive capability such that it acts to control a larger number of components, such as the ICE 150, either in conjunction with or separately from the fuel system 200. In this configuration, the controller 170 may be embodied as one or more electronic control units (ECUs). It will be appreciated that ASICs, ECUs and their variants, regardless of the construction and range of functions performed by the controller 170, are deemed to be within the scope of the present disclosure.

[0017] In one form, controller 170 is provided with one or more input/output (I/O) 170A, microprocessor or central processing unit (CPU) 170B, read-only memory (ROM) 170C, random-access memory (RAM) 170D, which are respectively connected by a bus 170E to provide connectivity for a logic circuit for the receipt of signal-based data, as well as the sending of commands or related instructions to one or more of the components within ICE 150, one or more components within fuel system 200, as well as other components within vehicle 100 that are responsive to signal-based instructions. Various algorithms and related control logic may be stored in the ROM 170C or RAM 170D in manners known to those skilled in the art. Such control logic may be embodied in a preprogrammed algorithm or related program code that can be operated on by controller 170 such that its instructions may then be conveyed via I/O 170A to the fuel system 200. In one form of I/O 170A, signals from the various sensors S are exchanged with controller 170. Sensors may comprise pressure sensors, temperature sensors, optical sensors, acoustic sensors, infrared sensors, microwave sensors, timers or other sensors known in the art for receiving one or more parameters associated with the operation of ICE 150, fuel system 200 and related vehicular components. For example, one or more sensors S may be used to determine if a minimum threshold level of an octane-rich fuel component or a cetane-rich fuel component is present in the respective enriched product fuel tanks 250, 260. Although not shown, controller 170 may be coupled to other operability components for vehicle 100, including those associated with movement and stability control operations, while additional wiring such as that associated with a controller area network (CAN) bus (which may cooperate with or otherwise be formed as part of bus 170E) may also be included in situations where controller 170 is formed from various distributed units.

[0018] In situations where the controller 170 is configured to provide control to more than just the fuel system 200 (for example, to the operation of one or more of the ICE 150 or other systems within vehicle 100), other such signals from additional sensors S may also be signally provided to controller 170 for suitable processing by its control logic, including those where combustion data from the ICE 150 is provided for control over the mixing or related delivery of the fuel and air. Likewise, in a manner consistent with various modes of ICE 150 operation, controller 170 may be programmed with drivers for various components within ICE 150, including a fuel injector driver 170F, a spark plug driver (also referred to as a spark ignition driver, for SI modes of operation) 170G, engine valve control 170H and others that can be used to help provide the various forms of fuel introduction to the combustion chamber 156, including those associated with a multiple- late-injection, stratified-mixture, low-temperature combustion (LTC) process as a way to promote smooth operation and low NOx emissions of ICE 150 over a substantial entirety of its load-speed range. Within the present context, load-speed mapping of ICE 150 may be used to identify operating regions such as those used during cold starts and ICE 150 warm-up, low ICE 150 loads, medium ICE 150 loads and high ICE 150 loads, where correspondingly lower amounts of exhaust gas re-breathing takes place through manipulating the overlap of the intake valve 157 relative to the exhaust valve 158, possibly in conjunction with other approaches such as exhaust gas recirculation (EGR) to help provide one or more of combustion control, exhaust gas emission reductions, or other operability tailoring for ICE 150.

[0019] In addition to providing instructions for combustion control, emission reductions or the like, controller 170 interacts with conduit 210 and various actuators, valves and related components to control the operation of the delivery of market fuel from a fuel supply tank 220, preheater 230, separation unit 240, heat exchanger 243 and enriched product fuel tanks 250, 260 in order to effect the production of OOD or COD required to operate ICE 150 for a given set of load and related operating conditions. In one form of CAN, the controller 170 could manage the fuel flow from either the fuel supply tank 220 or one or both of the enriched product tanks 250, 260 to the combustion chamber 156 where the two fuels corresponding to OOD or COD are injected separately, or by blending prior to being introduced into the combustion chamber 156 at different ratios depending on load, speed and other optional parameters associated with operation of ICE 150.

[0020] In particular, controller 170 is useful in promoting customizable fuel injection and subsequent combustion strategies for various Cl engine configurations. For example, when used in conjunction with a GCI-based engine, the controller 170 may instruct the fuel to be injected in a staged manner late in the compression phase of the engine’s four cycle operation. In this way, the fuel charge may be thought of as having both locally stoichiometric and globally stratified properties. Significantly, because an octane-rich fuel (for example, gasoline) has a higher volatility and longer ignition delay relative to a cetane-rich fuel (for example, diesel), by introducing the octane-rich fuel into the combustion chamber 156 relatively late in the compression stroke and taking advantage of the fuel’s inherent ignition delay (which helps to promote additional fuel- air mixing), combustion does not commence until after the end of the injection. To achieve a desirable degree of stratification, multiple injections may be used. By operating under the LTC conditions that are associated with stratified fuel combustion, GCI engines can have significantly reduced NOx production and soot emissions while achieving diesel-like thermal efficiencies. Moreover, such an approach permits the vehicle 100 to use an onboard market fuel with a lower octane than would otherwise be used. This is beneficial in that such fuel requires a smaller amount of processing than conventional gasoline and diesel fuels; this in turn reduces the entire well-to-tank emissions of other undesirable substances, such as C0 ₂ .

[0021] In addition to a GCI engine, such instructions as provided by controller 170 are particularly beneficial for the multiple-late injection strategy used for the delivery of fuel in RCCI or related modes of operation of ICE 150, as such delivery is optimized when it coincides with various sequences in the compression stroke that can be measured by sensors S as they detect crank angle degree (CAD) values from the crankshaft 153 to help control when auto-ignition occurs. Within the present context, the position of the piston 162 within the cylinder 152 is typically described with reference to CAD before or after the top dead center (TDC) position of piston 162. The controller 170 may also base such delivery strategies on other ICE 150 operating parameters such as the previously- mentioned load and engine speed, as well as the number of times such injection is contemplated. For example, CAD from 0° to 180° corresponds to the power stroke, with 0° representing TDC and 180° representing bottom dead center (BDC). Likewise, CAD from 180° to 360° represents an exhaust stroke with the latter representing TDC. Moreover, CAD from 360° to 540° represents an intake stroke with BDC at the latter. Furthermore, CAD from 540° to 720° represents a compression stroke with TDC at the latter. By way of example, the controller 170— when used in a 6-cylinder engine— would have ignition taking place every 120° of crankshaft 153 rotation, that is to say three ignitions per every revolution of ICE 150. Thus, when ignition has taken place each of the six cylinders one time, the crankshaft 153 has rotated twice to traverse 720° of rotary movement. Likewise, if ICE 150 were configured as a 4-cylinder engine, the ignition would take place every 180° of crankshaft 153 rotation. In one form, one of the sensors S may be a crank sensor to monitor the position or rotational speed of the crankshaft 153. The data acquired from such a crank sensor is routed to the controller 170 for processing in order to determine fuel injection timing and other ICE 150 parameters, including ignition timing for those circumstances (such as cold startup, and the ensuing warm-up) where a spark ignition device is being used. Sensors S such as the crank sensor may be used in combination with other sensors S (such as those associated with valve 157, 158 position) to monitor the relationship between the valves 157, 158 and pistons 162 in ICE 150 configurations with variable valve timing. Such timing is useful in Cl modes of operation of ICE 50 in that it can close the exhaust valves 158 earlier in the exhaust stroke while closing the intake valves 157 earlier in the intake stroke; such operation as implemented by controller 170 can be used to adjust the effective compression ratio of ICE 150 in order to obtain the required temperature and pressure associated with Cl combustion. Likewise, when SI combustion is required, the controller 170 may instruct the valves 157, 158 to reduce the compression ratio consistent with SI operation. Likewise, the controller 170 may— depending on the need of ICE 150— provide auxiliary sparking for fuel preparation (such as the generation of free radicals in the air-fuel mixture). Sensed input (such as that from various locations within ICE 150, including CAD from the crankshaft 153, as well as those from driver-based input such as the accelerator of guidance apparatus 140) may be used to provide load indicia. Likewise, in addition to suitable adjustment of the valves 156, 157, balanced fuel delivery from each of the enriched product tanks 250, 260 with pressurizing forces provided by one or more fuel pumps 270 may be achieved by controller 170 depending on if ICE 150 is in a Cl mode or an SI mode of operation.

[0022] The controller 170 may be implemented using model predictive control schemes such as the supervisory model predictive control (SMPC) scheme or its variants, or such as multiple-input and multiple-output (MIMO) protocols, where inputs include numerous values associated with the various post-combustion exhaust gas treatment components discussed elsewhere in this disclosure, sensors S (such as exhaust gas temperature sensor, 0 ₂ sensor, NOx sensor, SOx sensor or the like), estimated values (such as from the lookup tables or calculated algorithmically) or the like. In that way, an output voltage associated with the one or more sensed values from sensors S is received by the controller 170 and then digitized and compared to a predetermined table, map, matrix or algorithmic value so that based on the differences, outputs indicative of a certain operational condition are generated. These outputs can be used for adjustment in the various components within the purview of the controller 170, such as the remaining components associated with fuel system 200.

[0023] As mentioned above, in one form, controller 170 may be preloaded with various parameters (such as atmospheric pressure, ambient air temperature and flow rate, exhaust gas temperature and flow rate or the like) into a lookup table that can be included in ROM 170C or RAM 170D. In another form, controller 170 may include one or more equation- or formula-based algorithms that permit the processor 170B to generate a suitable logic- based control signal based on inputs from various sensors, while in yet another form, controller 170 may include both lookup table and algorithm features to promote its monitoring and control functions. Regardless of which of these forms of data and computation interaction are employed, the controller 170— along with the associated sensors S and associated flow control conduit 210— cooperate such that as an operating load on the ICE 150 varies, a suitable adjustment of the market fuel that is present in the fuel supply tank 220 may be made to provide the amount of octane or cetane enrichment needed for such operating load by mixing the onboard market fuel with one or the other of the product fuels from the enriched product fuel tanks 250, 260. [0024] One parameter of ICE 150 that may be preloaded into or generated by controller 170 is the mean effective pressure (MEP). In one form, MEP may be used to correlate ICE 150 operating conditions to fuel needs and the various forms of multiple-late injection strategies discussed previously for various Cl engine configurations. MEP— including its variants indicated mean effective pressure (IMEP), brake mean effective pressure (BMEP) or friction mean effective pressure (FMEP)— provides a value of the ability of a particular ICE 150 to do work without regard to the number of cylinders 152 or related ICE 150 displacement. Moreover, it provides a measure of the pressure corresponding to the torque produced so that it may be thought of as the average pressure acting on a piston 162 during the different portions of its four cycles (inlet, compression, ignition and exhaust). In fact, MEP is a better parameter than torque to compare engines for design and output because of its independence from engine speed or size. Furthermore, MEP provides a better indicator than other metrics (such as horsepower) for engines in that the torque produced is a function of MEP and displacement only, while horsepower is a function of torque and rpm. Thus, for a given displacement, a higher maximum MEP means that more torque is being generated, while for a given torque, a higher maximum MEP means that it is being achieved from a smaller ICE 150. Likewise, higher maximum MEP may be correlated to higher stresses and temperatures in the ICE 150 which in turn provide an indication of either ICE 150 life or the degree of additional structural reinforcement in ICE 150. Significantly, extensive dynamometer testing, coupled with suitable analytical predictions, permit MEP to be well-known for modern engine designs. As such, for a naturally aspirated (that is to say, non-turbocharged) Cl engine, MEP values of about 7.0 bar to about 9.0 bar are typical at engine speeds that correspond to maximum torque (around 3000 rpm), while for their turbocharged counterparts, MEP values of about 10.0 bare to about 12.0 bar are typical. For naturally aspirated SI engines, MEP values of about 8.5 bar to about 10.5 bar are common, while for turbocharged SI engines, the MEP might be between about 12.5 bar and about 17.0 bar.

[0025] Likewise, MEP values may be determined for various operating regimes for ICE 150. Such operating regimes may include low power or load (including, for example, engine idling conditions) that in one form corresponds to a MEP of up to about 1.0 bar, in another form of an MEP of up to about 2.0 bar. Likewise, such operating regimes may include normal (or medium) power or load that is one form corresponds to a MEP of between about 2.0 bar to about 5.0 bar, in another form of an MEP of between about 2.0 bar and about 6.0 bar, in another form of an MEP of between about 2.0 bar and about 7.0 bar. Moreover, such operating regimes may include a high power or load that is one form corresponds to a MEP of about 7.0 bar and above, in another form of an MEP of about 8.0 bar and above, in another form of an MEP of about 9.0 bar and above, and in another form of an MEP of about 10.0 bar and above.

[0026] As will be understood, these and other MEP values may be input into a suitably- mapped set of parameters that may be stored in a memory accessible location (such as the lookup tables mentioned previously) so that these values may be used to adjust various ICE 150 operating parameters, as well as for the controller 170 when acting in a diagnostic capacity. In such case, it may work in conjunction with some of the sensors S, including those that can be used to measure cylinder 152 volume (such as through crankshaft 153 angle or the like).

[0027] Referring next to FIG. 3, details associated with managing the heat balance associated with performing onboard COD and OOD operations while avoiding complicated system redundancy for fuel system 200 is shown. Significantly, by taking advantage of existing onboard fuel delivery and ICE 150 operating infrastructure, any on- vehicle cooling and heating needed to promote the various adsorbing and desorbing-based regenerating activities can be achieved without requiring additional equipment or efficiency-decreasing modes of operation of the ICE 150. The fuel system 200 includes a network of pipes, tubing or related flow channels— along with various valves to preferentially permit or inhibit the flow of the onboard fuel and its byproducts of fuels, depending on the need— that make up conduit 210. The fuel supply tank 220 is used as a main tank for the storage of the market fuel (for example, conventional or even low-grade gasoline). A preheater 230 is thermally coupled to the fuel being delivered from the fuel supply tank 220 through conduit 210 so that if the market fuel that is being delivered to either the combustion chamber 156 of ICE 150 or a separation unit 240 (either of which are fluidly coupled to the fuel supply tank 220 through the conduit 210) is in need of being heated, it can receive thermal energy from the preheater 230 that in one form may be an electric heater or in another form as a heat exchanger. [0028] Significantly, the fuel system 200 may operate using residual thermal energy from the vehicle 100, such as that from the waste heat of the combustion process that takes place within the combustion chamber 156 of ICE 150. This use of existing heat helps promote system compactness by reducing component redundancy. In particular, a batch like processing approach may be made to take place within the separation unit 240 where a pair of chambers 241, 242 are placed in thermal communication with a heat exchanger 243, all within a housing or related containment structure. Thus, upon receipt of market fuel from the fuel supply tank 220 through conduit 210 and optional preheater 230, the first of the chambers 241 is sized and shaped to fluidly receive an aromatic (that is to say, octane-rich) compound such that contact of the aromatic on the surface of chamber 241 results in the creation of an octane-rich adsorbate for OOD, such as by the preferential action of a suitable functional group contained within or formed on the surface of the adsorbent that makes up the chamber 241 as will be discussed in more detail later in this disclosure. The two-chamber construction of the separation unit 240 is such that while octane-rich adsorption is taking place in chamber 241, any adsorbent that was previously saturated in the other chamber 242 is regenerated by exposure of the adsorbate to elevated temperatures (such as from exhaust gas from ICE 150 or a hot coolant from a radiator- based cooling system or the like) through the heat exchanger 243. This addition of latent or waste heat and the subsequent vaporization of the octane-rich adsorbate causes the evaporated adsorbate to be desorbed and released— such as to an octane-rich product tank 260 for subsequent use in the combustion chamber 156. With a different choice in adsorbent in the chambers 241, 242, a cetane-rich adsorbate (rather than octane-rich adsorbate) can be formed in a comparable manner for COD through the use of a size- selective adsorbent. In one form, such OOD-specific and COD-specific activity may be achieved through multi-stage configurations of separation unit 240 where sequentially- placed units each with one or more of the chambers 241, 242 may be arranged, each configured with affinity-based or size-selective adsorbents. Thus, in one form, by the operation of the adsorbent that is configured to preferably retain aromatics or related functionality fuel components such as oxygenates or double bond-based alkyls, much of the octane-rich portion of the market fuel forms on the surface of the chamber 241 while much of the cetane-rich portion passes through to become a remainder that can be then conveyed (as shown) to a cetane-enriched product tank 250 or back (not shown) to the fuel supply tank 220. Within the present context, the terms“adsorb”,“adsorbate” and their variant includes those portions of the onboard fuel that interact by surface retention (rather than by bulk absorption) with the adsorbent that makes up the chambers 241, 242, while the terms“desorb”,“desorbate” and their variant includes those portions of the adsorbate that are subsequently liberated from the adsorbent as a result of some regenerating action. In one non-limiting form, such desorbing may take place by the application of a quantity of heat to the chambers 241, 242 sufficient to vaporize the adsorbate. Furthermore, it will be appreciated that unlike chemical reactions, adsorption is a physical phenomenon, although in certain circumstances the term chemi- sorption may be used. Likewise, within the present context, the remainder (also referred to as the filtrate) is the portion of the market fuel being exposed to the adsorbent in the chambers 241, 242 that does not get adsorbed, such as through one or both of the previous-discussed functional group (affinity- based) or molecular sieve (size-selective) operations.

[0029] The two-chamber construction of the separation unit 240 is conducive to the batch processing of octane-enriched or cetane-enriched fuel. In particular, the two chambers 241, 242 may be operated in a parallel manner such that while one is being used as an adsorbent to preferentially capture a thin film of octane-rich adsorbate, the other may be exposed to the latent heat from the operation of ICE 150 in order to regenerate the adsorbent by desorbing the previously-collected adsorbate, after which the roles of the two chambers 241, 242 are reversed through manipulation by controller 170 of valves (not shown) that make up part of conduit 210. In order to have a compact separation unit 240 that does not add much to the weight of vehicle 100, the adsorbent type is selected to give a high surface area-to-volume ratio by exploring the geometry and structure of the adsorbent particles and bed that makes up the two chambers 241, 242. In particular, higher surface area leads to higher adsorption capacity and smaller separation unit 240 size, which in turn promotes ease of system integration.

[0030] As mentioned previously, various forms of stratified combustion may lead to the types of LTC that are beneficial to low-NOc modes of operation of ICE 150. With regard to the use of OOD or COD for a Cl engine, the fuel may be formed as a hybrid of a main fuel (for example, gasoline or other low-cetane variant) and an igniter fuel (for example, diesel or other high-cetane variant), where the location, frequency and timing of introduction of each varies by concept or configuration such as those discussed previously. For example, in one concept, a single high-octane fuel is introduced via direct injection during a compression stroke. In such case, the injection of the fuel takes places at a time relatively retarded from conventional diesel injection timing to ensure adequate mixing. Since the overall combustion process is dominated by reactivity-controlled LTC, the resulting NOx and soot exhaust emissions tend to be very low. In another case, a single igniter fuel is introduced via direct injection during the compression stroke in order to promote cold-start and high-load operation where the overall combustion process is dominated by diffusion-controlled mixing of the fuel at or near the piston 162 TDC movement. In still another case, a dual injection regime introduces the main fuel via port fuel injection early in the compression stroke such that it is fully mixed with a fresh air charge during the intake stroke, after which the igniter fuel is introduced via direct injection as a way to control ignitability such that the overall combustion process is dominated by the spatially well-mixed high-octane fuel after the ignition of high-cetane fuel. As with the first case mentioned previously, such operation produces low NOx and soot emissions, due at least in part to an overall lean mixture. In yet another case, the main fuel is introduced via direct injection during the compression stroke, while the igniter fuel is introduced via direct injection near TDC to enable the ignition control; in this way, it provides a relatively robust mixture via improved thermal or spatial stratification. This in turn leads to low hydrocarbon, NOx and soot formation, at least for relatively low engine loads.

[0031] In one form, a so-called partial bypass may be used for intermittent circumstances (such as cold starts, or where one of the two high-octane or low-octane fuel tanks may be empty) such that a fraction of the market fuel from the fuel supply tank 220 is provided directly to the combustion chamber 156 without entering the separation unit 240. This partial bypass the operation of which may be established by controller 170 helps promote a continuous supply of fuel to ICE 150, and that such continuity is particularly useful under the intermittent operating conditions mentioned previously. In particular, the controller 170 may be used to manipulate various fuel delivery parameters, such as coolant temperature, exhaust gas temperature, level of separated fuels, delivery timing or the like for such transient operating situations. This helps promote wider operating ranges reactivity differences between the high-octane and high-cetane fuel components, especially with regard to reducing NOx or soot emissions over a much wider range, thereby reducing the likelihood of having to make a soot/NOx tradeoff.

[0032] Various fuel injection strategies can be utilized to enable optimum efficiency, reduced emissions and improved combustion robustness compared to conventional diesel- based cycles, including using EGR and reduced compression ratios. For example, EGR is used as a way to dilute the mixture and decrease the combustion temperature as part of a larger LTC strategy. Likewise, lowering the compression ratio can help reduce engine friction loss, heat loss and hydrocarbon emissions.

[0033] As mentioned previously, in one form, the adsorbents used for the chambers 241, 242 are configured as one or more functional groups presenting on the surface of the sorbent material such that they comprise affinity-based sorbents. In another form, the adsorbents may separate adsorbates by their molecular shape such that they comprise size- selective sorbents. For example, to target high-cetane fuel components, the design would focus on separating linear or slightly branched alkanes (which tend to be associated with high cetane fuels) from aromatics, cyclic and highly branched alkanes that tend to be present in high octane fuels. Stated another way, the solid sorbents can act in two mechanisms, where in a first, the adsorbent is selected to have functional groups that attract specific molecules such as aromatics, cyclic, (and oxygenates if present). The linear and slightly branched molecules (which may include cetane) are not adsorbed and pass through the pores of the chamber 241, 242. The second mechanism is based on the difference in the molecules sizes such that linear molecules (such as n-alkanes) may pass through the relatively porous material while other molecules which have a larger dynamic diameter are hindered from passing through most pores and accumulate in the adsorption- based chamber 241, 242. In this latter mechanism, a packed bed of size- selective sorbent is used for COD generation, as linear alkanes with high CN will go into smaller pores while the other components with larger molecular size will not, causing these other components to come out first as a raffinate. In such case, the preferentially adsorbed linear alkanes could then be desorbed using thermal energy such as discussed in the present disclosure in a manner similar to an affinity-based sorbent. In situations where the market fuel onboard the vehicle 100 is gasoline-based, the thermal regeneration such as available through the operation of heat exchanger 243 is particularly appropriate, as the separated stream of fuel will tend to have a relatively high volatility and associated low temperature boiling point. Examples of the first type of sorbents include: activated carbon, silica, and alumina based sorbents as well as some types of zeolites and functionalized porous material in general. Likewise, zeolites, metal organic frameworks and structured porous material may be made to act according to the second mechanism. As such, the chambers 241, 242 may— in addition to having batch processing capability through selective adsorbing and desorbing activities— be set up in stages (not shown) in the manner previously discussed such that a first stage preferentially provides affinity- based aromatic adsorption while a second stage acts like a size-selective molecular sieve. In one form, such staging may be made to take place sequentially, in either common or separate housings, in a manner suitable to ensure relatively small volumetric packaging needed to fit as unobtrusively as possible within vehicle 100. Regardless of the construction, such a multi-stage approach allows the first stage to adsorb octane while the second stage adsorbs cetane. Thus, whereas gasoline has relatively small aromatics with single benzene rings (such as benzene, toluene and xylene), diesel fuel has larger aromatics in the form of polycyclic (or polynuclear) aromatic hydrocarbons (PAHs) including naphthalene and its derivatives. It is recognized that there are some cetane-rich additives that have functional groups, thus, if some such additives are present, then affinity-based sorbents could be used as well for these components. As such— and depending on the needs associated with a particular market fuel— the adsorbents useful in the chambers 241, 242 may be selected with a high affinity for these components specifically, and that the order, placement and configuration of each of the chambers 241, 242 may be configured with the appropriate adsorbent depending on the construction of fuel system 200. Thus, different adsorbents can be used to adsorb the low boiling point straight alkanes as a way to produce a fuel with different specifications. For instance, to adsorb certain aromatics, the adsorbent that makes up the chambers 241, 242 can be mesoporous (2-50 nm diameter) activated carbon, which in turn can lead to an average recovery of about 80%. An example of the anticipated adsorption capacity of some aromatic components for activated carbon is listed in Table 1. Table 1

[0034] Other natural adsorbents (for example, coconut shell) may also be used for separating the desired components. In another form, the adsorbent bed of the chambers 241, 242 may be made up of more than one adsorbent in order to preferentially promote the adsorption of a desired species. Regardless of the adsorbent bed choice, the performance is optimized on various factors, including the adsorbent's capacity and selectivity, the concentration ratio of the market fuel (which provides indicia of the aromatics fractions), and how fast the regeneration and desorption-based removal proceeds.

[0035] The selection of the ICE 150 and its associated fuel is dependent at least in part on the properties of the fuel and the solid sorbent contained within the chambers 241, 242; such properties may include the relative fractions in the market fuel, boiling temperatures and sorbent separation mechanisms. For example, using an affinity-based sorbent may be used to produce an OOD adsorbate for low boiling-point fuels such as gasoline, while a size-selective sorbent may be used to produce a COD adsorbate for such low boiling-point fuels. In configurations where the separation unit 240 is arranged to have sequentially- placed units each with one or more of the chambers 241, 242 with affinity-based or size- selective adsorbents as discussed previously, it will be appreciated that the order of such separation may be affinity-based first and size-selective second, or size-selective first and affinity-based second, depending on the need.

[0036] Thus, for a compact and cost-effective vehicular propulsion system, a smaller fraction of fuel associated with the production of the octane-rich or cetane -rich fuel components may be routed through a longer path within conduit 210 while the larger remaining or unseparated fraction may be made to pass through a shorter path. In this way, the length of the flowpath defined by the fuel system 200 components not used to perform such fuel enrichment may be kept relatively short, especially in view of the fact that the volume of high octane or high cetane fraction fuel components needed in OOD or COD operation is relatively small compared to the remaining fraction of the market fuel that is being supplied to the separation unit 240 or the ICE 150. In one form, the amount of time that ICE 150 is operated under high load is relatively small compared to total operating time. As such, a more compact, low-cost fuel system 200 may be realized when the octane-rich or cetane -rich stream is routed through the longer path (which in one form may involve the separation of between about 20% to 30% of the market fuel as an octane- rich or cetane -rich fuel stream). It is noted that the general use of fuels for certain engine configurations may not be available for all fuel forms at all fueling stations. For example, naphtha (that is to say, the light fuel fraction that results from distillation and boiling that takes place in the gasoline range from about ambient temperature to about 160° C) typically has only between about one and ten percent aromatics. Thus, in situations where an additional CN boost for a particular COD use is required, these aromatic components that represent the smaller fraction could be separated out, such as through the use of an affinity-based sorbent, as a way to ensure lower combustion temperature and associated lower NOx generation.

[0037] Likewise, in one form, the boiling range of the separated fuel stream is within a range that is compatible of heat exchange values that can be provided by the operation of the ICE 150. Thus, when such a stream has relatively high volatility— such as the case when separating gasoline fractions— then the heat available onboard from the operation of ICE 150 is enough to regenerate the sorbent. As such, using a gasoline-based market fuel for GCI or SI modes of operation of ICE 150 may be employed so long as the boiling range of the adsorbate or remainder is compatible with the thermal environment being generated in the heat exchanger 243.

[0038] In using the heat exchanger 243, the controller 170 may instruct the switching between fuel and fresh air flow between the two chambers 241, 242 through one of three different techniques. In a first technique, a sensor S is connected to the exit of the first chamber 241 such that when the inlet and outlet liquid streams have an equal aromatic content as detected by sensor S (which in turn provides indicia of saturation in that no additional changes in the aromatic concentration are occurring), the controller 170 in response to such an acquired signal switches the market fuel that is being delivered from the fuel supply tank 220 to the second chamber 242. In a second technique, a timer is connected to the controller 170 to allow it to open and close at certain time intervals (for example every 15 minutes) where the time intervals depend on the absorbent size and rate of the adsorption. In a third technique, sensor S may be a temperature sensor such that once the temperature at the respective chamber 241, 242 is no longer increasing (which in turn provides indicia of no further heat release due to adsorption), the controller 170 switches the fuel flow from the first chamber 241 to the second chamber 242.

[0039] To regenerate the saturated one of the chambers 241, 242, the heat source being provided by the exhaust gas or hot coolant is allowed to enter the heat exchanger 243. As a result of the increase in temperature, at least a portion of the adsorbed aromatics that are on the exposed one of the chambers 241, 242 is released as a vapor to be delivered to the combustion chamber 156 if the driving cycle warrants it, or otherwise stored in the low cetane (that is to say, high-octane) product tank 260 where in one form it can be condensed by an air stream and in another form by market fuel resident within the fuel supply tank 220 such that the market fuel may serve as the condensing medium. Although not shown, this latter form of condensing may be made to take place through appropriate routing of the vaporized desorbate through a portion of conduit 210. In one form, any such condensed liquid may be placed in selective (rather than constant) fluid communication with the desorbed vapor because there may be some modes of operation of ICE 150 (such as that mentioned previously in conjunction with certain driving cycles) where it is desirable to have the desorbed octane or cetane be sent directly to the combustion chamber 156 for use.

[0040] With particular regard to the partial bypass mentioned previously, in certain operational conditions of ICE 150 (often referred to as a first operational condition), it may be necessary for reliable operation to use an SI mode of operation, as at startup or other scenarios there are no exhaust gases or hot radiator fluid available to heat the adsorption cycle, or where there are no high-cetane or high-octane fuels present in the enriched product tanks 250, 260. Furthermore, the partial bypass avoids otherwise undesirable latency periods associated with sudden driving conditions associated with speed or load, as well as those related to weather conditions. In such a partial bypass operational condition, the controller 170 may instruct a fraction of the market fuel from the fuel supply tank 220 to be supplied directly to the combustion chamber 156, without entering the separation unit 240. This fraction can be controlled and manipulated via different methods such as temperature of the coolant or exhaust gas, level of separated fuels, time or other variables. Two examples are presented o highlight the benefits associated with partial bypass operation.

[0041] First, during startup of ICE 150 when no heat is available to operate adsorption cycle and no fuel fractions are available, the controller 170 works together so that fuel flow may partially come from the two enriched product tanks 250, 260, while the main fuel portion comes from the fuel supply tank 220. If either of the two enriched product tanks 250, 260 is empty at any time (such as that associated with unexpected driving cycle conditions, lack of heating needed for desorption or insufficient air cooling), the controller 170 may instruct one or more fuel pumps 270 (only one of which is shown) to pressurize the market fuel being delivered from the fuel supply tank 220 directly to the combustion chamber 156 as a way to at least partially bypass the separation unit 240 to compensate for the shortage in the cetane-enriched product tank 250 or the octane-enriched product tank 260.

[0042] Significantly, the fuel system 200 is designed to avoid using supplemental equipment, instead utilizing components that are already operating for other purposes, such as a fan (not shown) that moves ambient air for cooling during the adsorption step, and the fuel pump 270 (although even equipment like this may be reduced, simplified or eliminated in situations where common rail fuel injection may be used). In one form, the fuel injection pressures generated by the fuel system 200 may be up to about 500 bar for gasoline direct injection, and up to about 2500 bar for common rail diesel injection where this higher injection pressure is used to expand the operating region of diesel-based Cl engines in that it facilitates premixed Cl combustion. In so doing, this latter pressure increase for diesel fuel-based engines may offset the needed robustness of construction and reductions in compression ratio and fuel ignition delay. As mentioned previously, the fuel system 200 takes significant advantage of latent heat associated with normal ICE 150 operation.

[0043] Referring next to FIG. 4, an example is provided to demonstrate the applicability of the proposed method and system with particular emphasis on small adsorbent size and fast adsorption rate g for three different temperatures of 150° C, 180° C and 210° C for a 1000 cc zeolite adsorbent sample with a Y-based framework; this size was chosen because it was deemed to be compatible with vehicular-based applications. In particular, thee employed adsorbent is zeolite NaY with a geometric volume of a-cages (0.294 cc/g) and b-cages (0.054 cc/g). The adsorption capacity of various aromatic molecules that are present in a commercially-available gasoline-based market fuel for this type of adsorbent is shown in Table 2.

Table 2

[0044] Despite the fact that adsorption of aromatics using Y-based zeolites tends to be a relatively slow process, there is no need to wait for full equilibrium as many of the aromatic species contained within the market fuel reach a saturation level much more quickly. For example, toluene is adsorbed and reaches equilibrium within 20 minutes, with substantially complete equilibrium occurring after about 1.0 to 1.7 hours. Moreover as shown, the adsorption rate g increases with temperature. This permits the adsorbate rate over the adsorption cycle to be easily estimated. Significantly, it demonstrates that various enriched fuel components can be produced in a timely manner using adsoprtion-based equipment that can meet the relatively small volumetric requirements needed for placement within a vehicular package.

[0045] Referring next to FIG. 5, the amount of octane-enriched fuel that can be separated onboard by fuel system 200 that uses the zeolite-based adsorbent with the properties set forth in previously-discussed Table 2 and following Table 3 in the reactant chambers 241, 242 is shown. By way of one example, vehicle 100 may be configured as a passenger vehicle that consumes 6 liters of fuel per 100 kilometers averaging consumption over city and the highway distances and running at an average speed of 70 kilometers/hour; in such case, gasoline demand may be typically 4.5 liters/hour. [0046] By way of another example, vehicle 100 may be configured as a compact vehicle that consumes 1.6 liters/hour of 95 RON gasoline that includes 30% aromatics consumed at the rate of 0.48 liters/hour. More particularly, the aromatic molecules include toluene (0.192 liters/hour), xylene (0.192 liters/hour), benzene (0.048 liters/hour) and mesitylene (0.048 liters/hour). The adsorbate amount is shown for three notional cycle times of 10 minutes, 20 minutes and 100 minutes for a 1000 cc Y-based zeolite adsorber. When this fuel stream passes through the adsorbent bed that is formed on each of the reactant chambers 241, 242, aromatic molecules separate and attract to the adsorbent particles at different rates depending on the molecule shape, size or the like.

[0047] After only 10 minutes of operation, 6% of the regular gasoline separates as high- octane gasoline with a 119 RON. Likewise, after only 20 minutes, 12% of the regular gasoline separates into the 119 RON gasoline, whereas complete equilibrium is attained after 160 minutes. The results indicate that adsorption-based OOD can be employed for onboard applications in terms of the system size and operation time.

Table 3

[0048] Having described the subject matter of the present disclosure in detail and by reference to specific embodiments, it is noted that the various details disclosed in the present disclosure should not be taken to imply that these details relate to elements that are essential components of the various described embodiments, even in cases where a particular element is illustrated in each of the drawings that accompany the present description. Further, it will be apparent that modifications and variations are possible without departing from the scope of the present disclosure, including, but not limited to, embodiments defined in the appended claims. More specifically, although some aspects of the present disclosure may be identified as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.

[0049] It is noted that one or more of the following claims utilize the term“wherein” as a transitional phrase. For the purposes of defining features discussed in the present disclosure, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term“comprising.”

[0050] It is noted that terms like“preferably”,“generally” and“typically” are not utilized in the present disclosure to limit the scope of the claims or to imply that certain features are critical, essential, or even important to the disclosed structures or functions. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the disclosed subject matter. Likewise, it is noted that the terms“substantially” and“approximately” and their variants are utilized to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement or other representation. As such, use of these terms represents the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0051] It will be apparent to those skilled in the art that various modifications and variations can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various described embodiments provided such modification and variations come within the scope of the appended claims and their equivalents.