Alcohol reforming system for internal combustion engine

An alcohol reforming system for an internal combustion engine includes a reformer in selective fluid communication with a fuel line via a reformer inlet line for receiving liquid fuel from the fuel line. The reformer reforms the alcohol in the alcohol-gasoline mixture of the fuel into a reformate mixture comprising hydrogen gas and gasoline. A buffer tank in fluid communication with the reformer receives the reformate mixture and disengages the hydrogen gas from the gasoline in the reformate mixture. The buffer tank includes a liquid fuel outlet in fluid communication with the fuel line for re-introducing the gasoline as a liquid into the fuel line, and a reformate gas outlet for delivering the reformate gas to a reformate line through which the reformate gas is delivered to the engine.

FIELD OF THE INVENTION

The present invention generally relates to an alcohol reforming system for an internal combustion engine and a method of reforming alcohol on-board a vehicle having an internal combustion engine.

BACKGROUND OF THE DISCLOSURE

Alcohol reformate is superior to the parent alcohol as a fuel for internal combustion engines. The superiority of alcohol reformate, particularly those formed from methanol and ethanol, is primarily due to the presence of hydrogen. Reformate burns faster than the starting alcohol and is more tolerant of dilution with air or exhaust. At part load, dilution benefits efficiency by reducing throttling losses and loss of heat of combustion to the coolant. In addition, the heat of combustion of reformate is greater than that of the starting alcohol. Both alcohols and reformate are high octane fuels which can tolerate high compression ratios.

SUMMARY OF THE DISCLOSURE

The present disclosure is concerned with the operation of vehicles fueled by gasoline-alcohol mixtures in which fuel reforming is conducted onboard the vehicle driven by exhaust heat. In one aspect, E85 or other alcohol-gasoline fuel blends pass through a reactor known as a “reformer” which is typically maintained at a temperature of about 300-350° C. with exhaust heat. A catalyst in the reformer catalyzes the transformation of the alcohol component of the fuel into a mixture of permanent gases according to equations 1 and 2 for ethanol and equation 3 for methanol.
CH3CH2OH→CH3CHO+H2(1)
CH3CHO→CH4+CO  (2)
CH3OH→CO+2H2(3)

The product contains a mixture of permanent gases known as “reformate” along with liquids, primarily gasoline along with some unreacted alcohol and acetaldehyde. Gasoline does not react at 300-350° C. The product is cooled by heat exchange and passes into a “buffer tank” which serves as a reservoir for the gaseous fuel while disengaging the liquids.

The hydrogen content of the reformate makes it an attractive motor fuel, since it enables dilute operation of the engine at part load (open throttle and/or with high levels of EGR). Thus, reformed alcohol vehicles operate on two fuels: reformate and liquid fuel. The latter is partially depleted of ethanol by reforming. The reformer and other subsystems need to provide a reliable supply of reformate and manage the composition of the liquid fuel stream. However, the value of reformate is greatest at part load. At high load (2000 rpm, 8.5 bar NMEP) the dilution tolerance provided by reformate does not improve efficiency in part because the amount of diluent (EGR or excess air) that can be used is limited and also because of the value of the charge cooling of liquid ethanol at high load.

In one aspect, an alcohol reforming system for an internal combustion engine generally comprises a fuel system configured to deliver liquid fuel comprising an alcohol-gasoline mixture to the internal combustion engine, the fuel system including a fuel line through which the liquid fuel is delivered to the engine; a reformer in selective fluid communication with the fuel line via a reformer inlet line for receiving liquid fuel from the fuel line, the reformer configured to reform the alcohol in the alcohol-gasoline mixture of the fuel into a reformate mixture comprising hydrogen gas and gasoline; and a buffer tank in fluid communication with the reformer via a reformer outlet line for receiving the reformate mixture, the buffer tank configured to disengage the hydrogen gas from the gasoline in the reformate mixture, wherein the buffer tank comprises a liquid fuel outlet in fluid communication with the fuel line for re-introducing the gasoline as a liquid into the fuel line, and a reformate gas outlet for delivering the reformate gas to a reformate line through which the reformate gas is delivered to the engine.

In another aspect, a method of reforming alcohol on-board a vehicle having an internal combustion engine generally comprises delivering liquid fuel comprising an alcohol-gasoline mixture to the internal combustion engine, wherein the liquid fuel is delivered via a fuel line; selectively diverting a portion of the liquid fuel in the fuel line to a reformer via a reformer inlet line; reforming the alcohol in the alcohol-gasoline mixture of the fuel into a reformate mixture comprising hydrogen gas and gasoline using the reformer; delivering the reformate mixture to a buffer tank via a reformer outlet line; disengaging the hydrogen gas from the gasoline in the buffer tank; re-introducing the gasoline from the buffer tank as a liquid into the fuel line at a pre-selected flow rate; and delivering the reformate gas from the buffer tank to a reformate line through which the reformate gas is delivered to the engine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, an alcohol reforming system for an internal combustion engine power system is generally indicated at reference numeral10. In general, the reforming system10comprises a reformer12for reforming liquid fuel F comprising an alcohol-gasoline blend (or mixture) into a reformate mixture RM including reformate gas R and vaporized liquid. A fuel system14delivers the liquid fuel F to the reformer12and an internal combustion engine E. From the reformer12, the reformate gas R may comprise hydrogen (H2), carbon monoxide (CO), and methane gas CH4, and the vaporized liquid may comprise gasoline, unreformed alcohol, and acetaldehyde. As explained below, the vaporized liquid will be condensed after the reformate mixture RM exits the reformer12. This vaporized liquid may also be referred to herein as fuel F, since it primarily includes gasoline. A buffer tank, generally indicated at16, receives the reformate mixture RM and disengages (i.e., separates) the reformate R from the condensed fuel F (or liquid condensate or liquid fuel). A fuel re-introduction system, generally indicated at20, re-introduces the condensed fuel F into the fuel system14, as explained in detail below.

Referring still toFIG. 1, the fuel system14comprises a fuel tank22for storing a quantity of the gasoline-alcohol blend (or mixture) fuel F on-board the vehicle. In one embodiment the fuel F comprises ethanol-gasoline blend, such as E85 (i.e., 85% ethanol and 15% gasoline), or E20, or E50, or any other percentage of ethanol blended with gasoline. Many of these fuels F are presently commercially available at fuel stations. A first pump24is in fluid communication with the interior of the tank22for introducing the fuel F into a fuel line26(e.g., conduit, pipe, tubing) of the fuel system14. The fuel line26fluidly connects the components of the fuel system14, as explained hereinafter. The first pump24may be a low pressure pump, as is generally used in modern, commercial vehicles. In one example, the pressure in the fuel system line26immediately downstream of the first pump24is limited by a relief valve30set to open at a pressure at least about two bar below the pressure setpoint of the buffer tank16. In another embodiment, an actuated valve (not shown) controlled by a pressure sensor can also be employed for this purpose.

Downstream of the first pump24is a first heat exchanger32which is also in fluid communication with a reformer outlet line34that delivers the reformate mixture RM from the reformer12to the buffer tank16. At the first heat exchanger32, the liquid fuel F from the fuel tank22cools the reformate mixture RM from the reformer12, and in turn, the fuel is heated by the reformate mixture. An example of a suitable heat exchanger is a flat-type brazed heat exchanger with 2 ft2of heat exchanger area, such as a heat exchanger commercially available from McMaster Carr, having product number 35115K61.

After flowing through the first heat exchanger32, the fuel F flows through a check valve36and into a reservoir chamber40. As shown inFIG. 1, the fuel re-introduction system is fluidly connected to the fuel system line26at a fuel re-introduction location FL that is intermediate the fuel system check valve36and the reservoir chamber40. The check valve36inhibits backflow of fuel F (from both the fuel tank22and the buffer tank16) in the fuel system line26toward the fuel tank22. The reservoir chamber40maintains a suitable volume of fuel F intermediate the fuel re-introduction location FL and a second fuel pump42. That is, the reservoir chamber40is downstream of the fuel re-introduction location FL and upstream of the second fuel pump42. The reservoir chamber40may be a container having an increased volume compared to the fuel line26, or the reservoir chamber may be a suitable length of tubing, having a suitable volume, between the fuel re-introduction location FL and a second fuel pump42. In one example, the volume capacity of the reservoir chamber40may be the volume of fuel F used by the engine E at mid-load in about 1 second. The reservoir chamber40may include a mixer (e.g., a static mixer) to homogenize the fuel F from the fuel tank22and the fuel F from the buffer tank16. As can be understood, the fuel from the buffer tank16is depleted of alcohol because it has passed through the reformer12.

The second fuel pump42may be a high pressure pump, and in particular, may be a direct injection fuel pump. The fuel pump42provides the pressure required to drive the fuel F through the reformer12and also delivers fuel to fuel injectors46via a fuel rail (not shown). From the fuel line26, the fuel F is diverted and enters a reformer inlet line48(e.g., pipe, conduit, tubing) that delivers the fuel to the reformer12. The supply of fuel F into the inlet reformer line48and to the reformer12is controlled by a control valve50, which is itself controlled by a controller52. The controller52may comprises a processor (e.g., a microprocessor), a memory including a set of instructions for controlling the processor. Alternatively, control can be suitably provided by the engine control module (ECM). Methods of controlling the control valve50, and therefore, controlling the flow rate of fuel F into the reformer12using the controller52are set forth below. After flowing through the valve50, the fuel F flows through a second heat exchanger54, where it is heated by reformate mixture RM flowing out of the reformer12via the reformer outlet line34(e.g., pipe, conduit, tubing). In one embodiment, the second heat exchanger54functions as a vaporizer, whereby the fuel F is vaporized before entering the reformer12. The second heat exchanger54may be similar or identical to the first heat exchanger32(i.e., the second heat exchanger may be a flat-type brazed heat exchanger with 2 ft2of heat exchanger area, such as a heat exchanger commercially available from McMaster Carr, having product number 35115K61).

After flowing through the second heat exchanger54, the liquid fuel F flows into the reformer12. The reformer12may include powder catalysts comprising copper and nickel where the reforming of alcohol (e.g., ethanol) in the fuel F is driven by exhaust heat. The reformer12is typically maintained at a temperature of about 300-350° C. using the exhaust heat. The catalyst in the reformer12catalyzes the transformation of the alcohol component of the fuel into a mixture of permanent gases according to equations 1 and 2 for ethanol and equation 3 for methanol.
CH3CH2OH→CH3CHO+H2(1)
CH3CHO→CH4+CO  (2)
CH3OH→CO+2H2(3)
Gasoline vaporizes but does not react within the reformer12(i.e., gasoline does not react at the operating temperature of the reformer). Although the embodiment shown inFIG. 1has only one reformer12, if the vehicle has dual exhaust pipes, two reformers12can be employed, one on each pipe, preferably with separate fuel control valves50. The reformer12may be of another type without departing from the scope of the present invention.

The reformate mixture RM exits the reformer12and enters the reformer outlet line34. At least a portion of the gasoline in the reformate mixture is vapor as it exits the reformer12. The reformate mixture RM flows through the second heat exchanger54where the mixture is cooled by the incoming liquid fuel F (i.e., heat is transferred from the reformate mixture RM to the fuel F). The reformate mixture RM then flows through the first heat exchanger32, where the reformate mixture is further cooled by the incoming fuel F. Cooling of the reformate mixture RM at the second and first heat exchangers54,32promotes condensation of the liquid F (e.g., the gasoline) in the reformate mixture RM.

After flowing through the first heat exchanger32, the reformate mixture RM flows to the buffer tank16. Referring toFIG. 2, in one embodiment, the buffer tank16includes a body60defining an interior volume62. A liquid or condensate outlet64in communication with the interior volume62is located at a bottom or lower portion of the body60, and a reformate outlet66in communication with the interior volume is located at a top or upper portion of the body. A demister70comprising a pad of demisting material, for example, is located in at an upper portion of the body60between the interior volume62and the reformate outlet66. The demister70inhibits condensate droplets (or mist) from entering the reformate outlet66. Suitable demisting materials, such as metal mesh, can be obtained from Amistco Separation Products of Alvin, Tex. A demister support72may retain the demister70in the upper portion of the body60while allowing reformate R to pass through the demister support and the demister70and enter the reformate outlet66. As an example, the demister support72may include a wire or perforated metal screen and the demister70may be compressed between the support and the upper portion of the body60in order to prevent bypass.

In the illustrated embodiment, the reformate mixture RM enters the interior volume62of the buffer tank via a reformate mixture inlet76. In the illustrated embodiment, the inlet76comprises a horizontal inlet conduit (e.g., pipe or tubing) received in the interior volume62. The inlet conduit76includes downwardly directed spray holes78for directing the reformate mixture RM toward a bottom of the buffer tank body60. In another example, reformate downflow in the buffer tank16can be achieved using deflector plates or an angled inlet tube. The bottom of the body60may funnel (e.g., have a conical or inverted dome shape) in order drain liquid condensate to the re-introduction system20located below the buffer tank16. As such, the reformate mixture RM that enters the buffer tank16separates into gas (e.g., hydrogen (H2), carbon monoxide (CO), and methane gas CH4) and liquid condensate (e.g., gasoline, unreformed alcohol, and acetaldehyde). The condensate (i.e., fuel F) flows to the bottom of the interior volume62and enters the re-introduction system20via the condensate outlet64. The reformate R flows through the demister support72and the demister70and into the reformate outlet66.

In one embodiment, the buffer tank16defines an interior volume62sufficient to supply enough reformate R for cold start of the engine E. Clean cold start can be achieved by fueling the engine with 50% reformate, and 50% E85 or similar ethanol or methanol-rich gasoline blend fuel until the catalytic converter reaches lightoff temperature. Larger buffer tank sizes provide a larger reserve, but this may be balanced against the space constraints on the vehicle. The body60cross section may be large enough to reduce the reformate R superficial velocity below that required to suspend liquid droplets, although for a buffer tank body60having a cross sectional diameter of 10 cm or greater this may not be a concern.

Referring again toFIG. 1, a pressure sensor80(e.g., a pressure transducer) monitors the pressure of the reformate R in buffer tank16. The pressure sensor80may be used to correct reformate fuel injector pulsewidths for variations in reformate pressure. In the illustrated embodiment, the pressure sensor80is immediately downstream of the buffer tank16and measures the pressure of the reformate R in a reformate line82(e.g., pipe, conduit, tubing). The reformate line82may lead downstream to reformate port injectors (not shown) for delivering the reformate R to the engine E. Although the detailed mode of operation of the engine using alcohol reformate R is outside the scope of the present disclosure, which is directed to supplying a stream of reformate R, substantially free of condensate droplets to an engine utilizing either port fuel injection or fumigation in order to introduce the reformate into the engine, such modes of operation are known to those skilled in the art. Furthermore, the present disclosure is intended to supply from about 10% to about 75%, more typically, from about 20% to about 75% of the fuel F to the engine E as reformate R at low-to-mid engine load and more preferably from about 25% to about 60% during cold start and after reformer warmup. At high load (2000 rpm, 8.5 bar NMEP) the dilution tolerance provided by reformate gas R may not improve efficiency in part because the amount of diluent (EGR or excess air) that can be used is limited and also because of the value of the charge cooling of liquid ethanol at high load. The present disclosure does, however, encompass certain general operating principles for reformate utilization as set forth below.

In one embodiment, in order for the reformate injectors to accurately meter reformate R into engine E, the pressure and temperature of reformate R in the reformate rail (not shown) must be known accurately so that the volumetric concentration of reformate can be calculated from the ideal gas law by the engine control unit (e.g., control unit or controller52or another control unit). The pressure sensor80communicates the pressure of the reformate R in the reformate line82and/or the pressure of the reformate R in the buffer tank16to the controller (e.g., controller52). A temperature sensor86(e.g., a thermocouple) may be located in the fuel rail (or rails). The fuel rails can act as radiators, thereby cooling the reformate R below the temperature of the reformate in the buffer tank16. Therefore, it may be preferred to have the temperature sensor86located at the fuel rails rather than the buffer tank16, although the temperature sensor may be located at the buffer tank.

Moreover, the reformate pressure should be above a threshold value in order to accurately meter the reformate R. The threshold pressure depends on the type of injector used, but is typically at least about 4 bar. For this reason, preferably, the engine E will not utilize reformate R when the pressure in the buffer tank16is below the threshold value. In addition, the engine E preferably does not utilize reformate at high power points where it does not contribute to efficiency. If the buffer tank16is at adequate pressure at the beginning of the drivecycle, these conditions ensure that engine E will utilize reformate R for cold start (or warm start) and for a further time until the buffer tank16reaches its lower pressure limit, then wait for reformer12warmup and start of reformer operation which results in a rise in buffer tank pressure.

Referring toFIG. 1, the fuel re-introduction system20includes a re-introduction line90(pipe, conduit, tubing) which fluidly connects the components of the fuel re-introduction system with the condensate outlet64of the buffer tank16. A flow control device92is downstream of the buffer tank16, and a valve94(e.g., a shutoff valve) is downstream of the flow control device to inhibit backflow of condensate fuel into the buffer tank. The valve94may be a solenoid valve and may be controlled by a controller, such as controller52. The pressure in the re-introduction line90is measured by a pressure sensor96(e.g., a pressure transducer), for reasons explained below. The re-introduction line90fluidly connects to the fuel line26at the re-introduction location FL, as explained above.

As can be understood, re-introduction of condensate fuel F in the fuel system14affects the composition of the fuel F which is routed to the liquid fuel injectors46. This is because the condensate fuel F consists primarily of gasoline, so when the condensate fuel is combined (e.g., mixed) with fresh incoming fuel F from the fuel tank22(e.g., E20 to E85 in the case of ethanol) the alcohol content of the fuel in the fuel line26is reduced by dilution. Two operational complications arise from the dilution. First, the reduced ethanol concentration renders the liquid fuel F more susceptible to knock if the engine E is operating at high torque. Fluctuations in the rate at which condensate is blended back into the fresh fuel cause variations in ethanol content or “octane noise.” Under adverse circumstances—low ethanol content at a high torque point in the drivecycle—the risk of engine knock increases. Further, variations in the alcohol concentration of the liquid fuel system14affect the stoichiometric air:fuel ratio. In modern automobiles, the air:fuel ratio is controlled at its stoichiometric value using an oxygen sensor in the exhaust. Fluctuations in the fuel composition on a timescale of seconds can destabilize the oxygen sensor control loop, potentially compromising the efficacy of exhaust after-treatment and reducing fuel economy.

In order to prevent excessive variation in the alcohol (e.g., ethanol) content of the fuel F supplied to the liquid fuel injectors46, it is preferable to maintain a steady drain of condensate fuel F from the buffer tank16at a rate that is close the rate of accumulation in the buffer tank. This is equivalent to maintaining a constant condensate level in the buffer tank16. In general, the object is to maintain a steady trickle of condensate back into the fuel system14and avoid abrupt slugs of condensate flow. Introduction of condensate fuel F upstream of the second pump42, as shown inFIG. 1, is preferred because pressure downstream of the second pump will typically exceed pressure in the buffer tank16. This is particularly true if the engine E utilizes direct fuel injection (DI), but backpressure due to the reformer12can also be significant.

One way to achieve control of condensate level and flow is to provide continuous monitoring of condensate level in the buffer tank16while controlling level using the solenoid valve. Level can be monitored by a float or by conductance or capacitance probes (not shown), and the flow control device or flow restrictor92is installed between the buffer tank16and the solenoid shutoff valve94in order to minimize peak condensate drain flowrates. The solenoid valve94may be closed whenever the pressure in the fuel line26, monitored by the pressure sensor96, exceeds the pressure of the buffer tank16. The solenoid valve94may also be used to shut off condensate flow when the engine E is operating at high BMEP, as described below.

The flow restrictor92may be sized to limit condensate flow at the buffer tank pressure to from about 4 to about 10 times the average rate of condensate flow. The average condensate flow can be estimated if the design ratio of reformate to liquid fuel is known. For example, for an E50 vehicle using 30% reformate in the engine (with 70% liquid fuel) at 100% ethanol conversion in the reformer, condensate flow averages 30% of the average total fuel flow. It is prudent to assume some degree of alcohol “slip” in the reformer. Thus the flow restrictor is preferably sized to about 40% of total fuel flow for an E50 vehicle. In other embodiments, float valves may be effective. A float valve does not rely on a level sensor which is vulnerable to level noise due to liquid slosh in a moving vehicle, although use of a flow restrictor smoothes the flow noise.

Referring toFIGS. 4-6, in one example the flow restrictor92may comprise a float or “pintle” valve. In this example, the solenoid valve94is not necessary for condensate level control although it is retained for other purposes, and the level sensors can be omitted. Float valves are a well-known, inexpensive, and reliable means of maintaining level in a vessel, for example, a small engine carburetor bowl. As shown inFIG. 4, the valve92includes a valve body100having an inlet port100A fluidly connected to the outlet64or the line90and an outlet port100B fluidly connected to the line90. A stem, generally indicated at102, includes a float104and a conical-shaped disc106that fits within a seat108(FIGS. 5 and 6) of the body100. Referring toFIG. 5, when fuel condensate level is low, the disc106settles into a conical seat (FIGS. 5 and 6), and inhibits condensate from flowing out the outlet100B. Referring toFIG. 5, as fuel condensate F accumulates, the stem104floats off the seat108, enabling flow of condensate from the buffer tank16through the line90. For proper operation, the pressure downstream of the buffer tank16and float valve92is preferably maintained below the pressure in the buffer tank in order to drive condensate out of the tank when the float valve opens and prevent backflow of liquid into the buffer tank. In the illustrated embodiment, the float valve92includes a permanent magnet110attached to the stem102. A reed switch112or other device adjacent the float valve92monitors the position of the float stem102in the body100, and communicates the position to a controller (e.g., controller52) to provide onboard diagnostics, assuring correct operation of the float valve.

Now that the individual components of the alcohol reforming system10have been described, the present disclosure will now describe exemplary operations of the reforming system10.

Control of Liquid Fuel (F) Flowrate to the Reformer

As has been discussed, the second pump42, which may be a direct injection fuel pump, provides the pressure required to drive fuel F through the reformer12. Direct injection fuel pumps can be either electric or mounted on the camshaft. This pump42supplies fuel to both the fuel injectors46(via a fuel rail) and to the reformer12, via the control valve50.

At low-to-medium engine load, the flow of fuel F to the reformer12is preferably controlled based on pressure in the buffer tank16, with the object of maintaining steady buffer tank pressure. “Low-to-medium engine load” in this case means points in the drivecycle in which the engine E can operate knock-free despite the loss of octane due to consumption of ethanol by the reformer12. “Feed forward” control based on the amount of reformate R actually being consumed by the engine E can be used, although this approach may be complicated by variations in the composition of fuel F being fed to the reformer12. In a one example, a modified version of proportional-integral-derivative (PID) control is used in which only the proportional “P” and integral “I” terms are utilized. In this example, the controller52or another controller may be preprogrammed with instructions for operating the reforming system10in accordance with the description below.

A full PID control scheme may not be preferred because the highly transient engine load makes the time derivative (“D”) noisy and not useful for control. A “PI” scheme is therefore used, based only on the difference between setpoint pressure and the instantaneous pressure in the buffer tank “P” and the integral term “I.” The control equation is given below in terms of ethanol flowrate only (kg/hr). Gasoline riding along with the ethanol is not reformed and does not influence buffer tank pressure.

In this equation, Kpand Kiare the parameters which govern PI control along with tintwhich parameterizes how far back in time the integral of the error function extends.

In addition to the PI control scheme that controls buffer tank pressure, a maximum flowrate to the reformer12may be fixed, which represents the maximum flow which the reformer can accept without developing unsafe backpressure. The value of the maximum flow depends on the design of the reformer12and the catalyst used. In addition, a maximum pressure, based on the pressure rating of the buffer tank16with a suitable safety factor, should be incorporated into the control algorithm cutting off fuel flow to the reformer12when the buffer tank pressure hits the limit. This portion of the control algorithm may incorporate hysteresis.

Preferably, fuel F is not supplied to the reformer in significant quantity (e.g., greater than about 0.1 kg/hour) unless the reformer is at an adequate temperature to enable the catalyst to reform the fuel, typically at least about 275° C. Thus, the reformer may be equipped with one or more thermocouples120. A very low flowrate of fuel F, such as less than or equal to about 0.1 kg/hour, may be supplied to the reformer12during the warmup period as this enables a more accurate measurement of reformer temperature while generating negligible amount of condensate in the buffer tank16.

Fuel F is supplied to the reformer12for a brief period following engine E shutoff until the maximum pressure buffer tank pressure16is achieved or the reformer falls below the minimum operating temperature. This utilizes residual heat in the reformer12that would otherwise be lost to the environment in order to fully charge the buffer tank16with reformate R. The condensate fuel shutoff valve94is preferably closed during this period following engine shutoff and opened at cold start in the next drivecycle. As a result, the liquid fuel is enriched in gasoline during cold start, which reduces hydrocarbon emissions.

Fuel Management when the Engine is at High Power

There are intervals in the drivecycle in which the engine E is operating at relatively high torque (BMEP). Maintaining a high ethanol content in the liquid fuel F is preferred during these periods in order to avoid knock. It is may be preferred to use only liquid fuel F without reformate R at high power points in order to maximize volumetric efficiency and because the efficiency improvement due to reformate is reduced at high BMEP.

For this reason, during high torque intervals the solenoid valve94downstream of the buffer tank16may be closed, thereby cutting off recycle of fuel condensate F. The condensate is nearly pure gasoline. Thus condensate recycle reduces the ethanol content of the liquid fuel F. In addition, preferably, the reformer fuel feed rate is increased to approximately its maximum value for several seconds. This serves to flush the mixing volume with fresh fuel from the fuel tank22. The high flow interval to the reformer12may be chosen to pass approximately one volume defined by the reservoir40through the reformer.

Utilization of Mid-Level Ethanol Blends (20-40%)

It is preferred to utilize a compression ratio greater than about 10:1 in vehicles using ethanol blends of 20% or higher in order to improve efficiency. For relatively low mid-level blends, generally E20-E40 (by volume), the reforming system10may be managed in order to maintain sufficient ethanol in the liquid fuel to avoid knock. The amount of ethanol required depends on the compression ratio and the high power threshold, above which only liquid fuel (without reformate) is used. The same considerations apply to methanol/gasoline blends in the 20-40% (by volume) methanol range.

In one example, for fuels in the E20-E40 range, the ratio of fuel flow to the reformer12to the total fuel flow from the second pump42(flow to reformer and fuel injectors46combined) is held below a fixed value. This prevents the reformer12from stripping too much ethanol from the fuel. An optimized split ratio can be calculated based on the ethanol content of the fresh fuel F and the ethanol conversion expected from the reformer12. For example, for an E30 fuel (30% ethanol) with 80% reformer conversion, the ethanol concentration in the liquid fuel F to the fuel injectors46(“EPFI”) can be calculated from the split ratio (“SR”) by solving the following equation numerically or via the quadratic formula.
0=−80%·(SR)·EPFI2+[1+80%·(SR)]·EPFI−30%

The same equation can be used for other reformer conversions or ethanol content by changing the 80% and 30% in the equation to the appropriate values.

FIG. 7shows liquid ethanol content, EPFIas a function of the split ratio SR for the case of E30% with 80% reformer conversion. In order to maintain 20% ethanol in the liquid fuel, the split ratio, SR, should not be allowed to exceed 0.8. This is adequate for a compression ratio of 12:1.

Reforming with Lower Alcohol Blends (E5-E15)

The present reforming system10may also be used with fuels containing 5-15% methanol or ethanol (by volume), with a main value consisting of reductions of startup emissions. The configuration described above and shown schematically inFIG. 1is preferably modified slightly in a vehicle intended to operate only on fuels with alcohol levels of 15% by volume or below. These two changes reduce the cost and complexity of the reforming system while ensuring that adequate reformate supply and fuel-air mixing capability is achieved for clean cold start.

First, all of the condensate in the buffer tank16can be returned to the fuel tank22. The re-introduction system20is intended only to provide enough reformate over the drivecycle to pressurize the buffer tank16and enable low emissions at cold start. This requires a minimal amount of fuel F. Returning alcohol-depleted reformate to the fuel tank22will not appreciably change the octane rating or other characteristics of the fuel. Second, a separate fuel rail for reformate R is not required. Reformate R can be fumigated into the air supply. U.S. Publication No. US 2012/0097117 A1, the entirety of which is herein incorporated by reference, describes fumigation of reformate using a supercharger. A gas carburetor could also be employed.

As can be seen from the above disclosure, in general the reformer12is sized to provide reformate sufficient for mid-load operation of the engine E and provide no reformate at high engine load. The buffer tank enables reformate to be used during intervals of high-mid load operation, typically 2400 rpm, 6 bar BMEP.

In one example, the alcohol reforming system is configured to perform the following operations, each of which has been described above:

1. maintain adequate buffer tank pressure to enable reliable operation of the fuel injectors which supply reformate (e.g., H2, CO, and CH4) to the engine throughout as much of the drivecycle as possible;

2. disengage (i.e., separate) condensable liquids, primarily gasoline, from reformate; if droplets of condensate (e.g., gasoline) are present in the reformate stream, some fuel injection events may provide excessive fuel leading to cycle-to-cycle and cylinder-to-cylinder variations in the air:fuel ratio and increased tailpipe hydrocarbon and CO emissions; and

3. re-introduce the liquid condensate from the buffer tank12into the fuel system.

The latter two operations are significantly more challenging at lower blend levels than for from 20-50% alcohol by volume in the fuel (“E20” to “E50” for ethanol). First, with respect to disengaging condensable liquids, the higher levels of condensate due to the gasoline content increase the liquid disengagement load although, as described above, this can be managed by proper system design and operation according to one example.

One embodiment of the reforming system10of the present disclosure enables a steady return of the condensate to the fuel system with minimal octane noise while providing a reliable supply of reformate essentially free of condensate droplets at an adequate pressure to enable operation of the gaseous fuel injectors. These goals can be achieved in a reliable, cost-effective manner by a strategy comprising one or more of the following operations, each of which has been explained in more detail above:

1. use of substantially all of the fresh, alcohol-containing fuel F to cool the reformate mixture RM prior to introduction into the buffer tank16;

2. introduction of reformate mixture RM into the buffer tank16with flow directed downward;

3. inclusion of the demister70in the top of the buffer tank16to complete demisting;

4. monitoring of buffer tank pressure at least once per second in order to achieve tight control of the amount of reformate R injected by the gaseous fuel injectors (not shown);

5. the flow control device92adjacent the bottom of the buffer tank16, such as a flow restrictor or a float valve, which suppresses abrupt discharge of slugs of fluid condensate from the buffer tank16;

6. the shutoff valve94, such as a solenoid valve, positioned between the flow control device92and the re-introduction location FL where the condensate is re-introduced into the fuel system14; and

7. for operation with fuels F between 20% and 40% alcohol by volume, limitation of fuel flow to the reformer12.

Having described embodiments of the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

EXAMPLES

The following non-limiting example is provided to further illustrate the present invention.

A reforming system generally having the schematic layout shown inFIG. 1was assembled using a 21-tube, 3-stage vertical tube array reformer loaded with 119 g of copper-palladium on carbon pellets and 105 g of copper-plated nickel sponge catalyst. An overall view of the reforming system is shown inFIG. 8, with like components shown inFIG. 1being indicated by corresponding reference numerals. The system was designed to couple to a V6 engine. An exhaust line150(e.g., a pipe) exiting the reformer12and an exhaust bypass line152were balanced by a proportional diverter valve154. The diverter valve154utilized two independently actuated disc-valves operated pneumatically. The exhaust diverter valve154was controlled, such as by controller52, so as to maintain the temperature of reformate mixture exiting the reformer12at a temperature of 325-350° C. The exhaust lines were fabricated from 20-gauge steel in order to reduce thermal mass and improve heatup time.

Flat-plate type brazed heat exchangers with 2 ft2heat exchange area were used as the first and second heat exchangers32,54(McMaster Carr part number 35115K61). The buffer tank16was a 6-inch diameter, 12-inch tall cylindrical vessel with a volume of 5.5 liters. The reformate inlet (not shown) was located 6 inches above the bottom, but did not use the “shower type” configuration shown inFIG. 2. The level of fuel condensate F was controlled using a “known-volume pipe”158coupled to the outlet64of the buffer tank16by a manual shutoff valve160. The buffer tank16is shown inFIG. 9. Liquid level in the pipe158was sensed by two optical fluid sensors162,164inserted through ½-inch NPT openings. When condensate level reached the upper sensor162, it was drained by opening an electrically-powered solenoid valve94(FIG. 8), with Teflon seals and an explosion-proof design.

The reforming system of Example 1 was coupled to a 3.5 liter V6 engine with twin-independent variable cam timing (TiVCT). The engine utilized direct injection of liquid fuel. A second set of fuel rails enabled port fuel injection of reformate. This second set of fuel rails was fed from the buffer tank16via a control valve which maintained stable reformate pressure in the fuel rail. The high pressure pump on the engine used for the direct injection fuels rails also supplied high pressure fuel to the reformer in accordance with the scheme inFIG. 1. The compression ratio was 12:1 when using E85 fuel, but baseline data on gasoline was obtained at 10:1 compression ratio.

The engine-reformer system of Examples 1 and 2 was operated at steady state at the “worldwide mapping point”: 2.62 bar BMEP, 1500 rpm. This operating point is representative of a typical drivecycle. The engine was operating with a stoichiometric air:fuel ratio (λ=1) and high levels of internal EGR, achieved by late closing of the exhaust valves. In addition, late closing of the intake valve was utilized to further reduce throttling losses and improve dilution.

The system was supplied with E85 fuel. The engine was fueled with 20% reformate (by mass) produced by the vertical tube reformer supplied through port fuel injectors and 80% E85 supplied through the direct injectors. The condensate was not re-combined with the liquid fuel being fed to the engine in this study in order to make more accurate measurements of efficiency.

Valve and spark timing were optimized at this operating point. The optimal valve timing (and EGR level) in cylinders 1, 2, 4, and 5 led to excessive levels of EGR in cylinders 3 and 6 due to pressure pulses propagating in the exhaust manifolds and into the last cylinders.

Under these optimized conditions, brake thermal efficiency at the worldwide mapping point, 2.62 bar BMEP, 1500 rpm, improved to 28.8% using 80% liquid E84 and 20% reformate by mass compared to 26.4% for 100% liquid E85. Both values were obtained using a 12:1 compression ratio. The efficiency using reformate refers to the efficiency of the entire engine/reformer system.

The buffer-tank/known-volume pipe system removed all liquid condensate during these trials. No evidence of breakthrough of liquid droplets to the reformate fuel rail (which would cause instability of combustion) was observed.

The engine-reformer system of Examples 1 and 2 was operated at steady state at the “worldwide mapping point” using E30 fuel. The reformer operated efficiently on this fuel and the buffer-tank/known-volume pipe system successfully disengaged liquid condensate.