FUEL PROCESSOR WITH CRITICAL FLOW VENTURI

Field of the Invention

The present invention relates to fuel processors in which a critical flow venturi is used to introduce a reactant stream into the fuel processor for downstream chemical conversion to produce a hydrogen-containing gas stream.

Background of the Invention

Governments have legislated emissions regulations to reduce the exhaust emissions from internal combustion engines. To meet upcoming regulations, new exhaust after-treatment solutions are being developed, especially in the diesel industry. Some of the exhaust after-treatment devices include Lean NOx Traps (LNT), Diesel Particulate Filters (DPF) and Diesel Oxidation Catalysts (DOC). These devices can require periodic in-situ regeneration, dcsulfation and-Or heating to maintain their desired performance.

A hydrogen-containing gas can be used to regenerate, desulfate and/or heat such engine exhaust after-treatment devices. In vehicular or other mobile applications, the supply of hydrogen is preferably generated on-board due to challenges related to on-board storage of a secondary fuel (for example, hydrogen) and the current absence of a hydrogen refueling infrastructure. The required hydrogen-containing gas can be generated by various methods such as introducing a hydrocarbon fuel directly into the engine exhaust stream upstream of the after-treatment devices (so that hydrogen is formed in-situ within the after-treatment device), or with the use of a fuel processor, such as a syngas generator (SGG), in which hydrogen is generated and then directed to the after-treatment device.

An SGG can convert a fuel into a gas stream containing hydrogen (H ₂ ) and carbon monoxide (CO), known as syngas. The H ₂ and CO can be beneficial in the processes used to regenerate exhaust after-treatment devices. A portion of the internal combustion engine exhaust stream can be used as an oxidant for the fuel conversion process. The exhaust stream typically contains oxygen (O ₂ ). water (1 1 ₂ O). carbon dioxide (CO ₂ ), nitrogen (NT) and sensible heat, which can be useful for the production of syngas. Additional air can optionally be added. The fuel used by the SGG can conveniently be chosen to be the same fuel that is supplied to the internal combustion engine. Alternatively a different fuel can be used, although this would generally require a separate secondary fuel source and supply system specifically for the SGG. In vehicular or other mobile applications, the on-board SGG should generall) be low cost, compact, light-weight and efficiently packaged with other components of the engine system.

Syngas production can be segregated into three main processes: mixing, oxidizing and reforming, as illustrated in Figure 1. The first process is the mixing process and it generally takes place at or near the inlet, where the oxidant and fuel streams are introduced into the SGG, in the so-called "mixing zone". The primary function of the mixing process is to supply an evenly mixed and distributed fuel-exhaust gas mixture for subsequent combustion and reformation. If the fuel is a liquid it is typically atomized and vaporized as well as being mixed with engine exhaust gas stream in this zone. The next process, the oxidizing process, takes place downstream of the mixing zone, in the so called '"combustion zone". The primary function of the oxidizing process is to ignite the fuel-oxidant mixture to produce H ₂ and CO as primary products as well as the sensible heat required for the downstream endothermic reformation reactions. This can be achieved by catalytically reacting and/or combusting the fuel with the oxygen in the engine exhaust stream. The final process, the reforming process, is where the oxidation products and remaining fuel constituents are further converted to hydrogen and carbon monoxide via reactions typical of reformation processes. The syngas then exits the SGG and

is directed to the appropriate exhaust after-treatment device for regeneration or heat production. There is not strict separation between the zones; rather the zones transition or merge into one another, but the primary processes happening in each of the zones are as described above.

For proper functioning of the fuel processor in engine system applications and in other fuel processor applications, the supply of both the fuel and the oxidant streams should be suitably metered or controlled. Also there should be adequate mixing of the two reactant streams, as well as adequate atomization and vaporization of the fuel if it is a liquid. Furthermore, since there is combustible mixture within the fuel processor, preferably there is some means of mitigating the risk of flashback. Flashback is uncontrolled combustion that can occur and propagate back from the combustion zone into to the mixing zone in the fuel processor. A flashback arrestor or flame arrestor is a safety device that inhibits or prevents a flame from propagating back toward the fuel source. Some of the conventional techniques that have been used for reactant metering, mixing and flashback arrest in various fuel processor applications and other applications are described below.

Mechanical or electrical valves, controls, sensors or combinations thereof have been commonly used to meter or regulate the mass flow of fluids in various industries and applications, including in fuel processors. For example, sensors can be used to detect various parameters at the inlet or outlet of a fuel processor, and provide a signal to a controller. The controller, based on the sensor signal and pre-programmed controller logic, can transmit a signal to a valve actuator, opening, closing or adjusting a valve. The position of the valve could thereby meter the flow of a reactant into the fuel processor. However, such "active' ^" reactant metering systems, with multiple moving and interconnected components, typically:

(a) add to the overall complexity and cost of the system; (b) reduce the system reliability and durability;

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(c) increase the likelihood of fluid leakage; and

(d) slow the dynamic response time.

In known reactant mixing systems, such as those in a fuel processor or in which a fuel is introduced upstream of an engine exhaust after-treatment device without first passing through a fuel processor (for in situ hydrogen generation), liquid fuel is typically sprayed into the hot engine exhaust gas stream through a nozzle. T he nozzle atomizes or converts the liquid fuel into a spray, mist or collection of droplets. The size of the droplets and spray distribution influence the effectiveness of the vaporization and mixing process. Heat from the engine exhaust stream heats the fuel and converts it into a gaseous state. The turbulent flow of the exhaust gas stream then mixes the vaporized fuel with the engine exhaust stream. There is typically a high pressure drop across conventional nozzles, thus significant fuel supply pressure and energy is required. They can be fouled and/or plugged up by various solids and deposits, resulting in increasing pressure drop over time.

Also they typically have limited turndown, plus they can be expensive, heavy and/or bulky.

Known flashback arrest methodologies include:

(a) creating a gas speed higher than the flame speed of the combustible mixture;

(b) using a pressure sensitive check valve; or

(c) using a heat absorbing device to absorb the heat from the combustible mixture.

The use of valves or heat absorbing devices can add to the pressure drop across the fuel processor, as well as to the system cost, weight and complexity.

There are some particular challenges associated with the design of fuel processors used in engine systems to convert a fuel and engine exhaust gas stream into a hydrogen-containing stream. These challenges mean that, at

least for this application, some of the conventional techniques described above for reactant metering, reactant mixing and for flashback arrest have shortcomings. The challenges include the following:

(a) The engine exhaust stream output parameters, such as mass flow, pressure, temperature, composition and emission levels, vary significantly over the operating range of the engine. Metering the engine exhaust stream supplied to the fuel processor is therefore a challenge due to the significantly variable exhaust gas supply, as well as the desire to control the oxygen-to-carbon (O/C) or oxygen-to-fuel ratio, and also due to the variable syngas requirements in the system (see below).

(b) The engine exhaust stream pressure is limited, especially at idle conditions. The pressure available to aid in the mixing and distribution of fuel in the engine exhaust stream is therefore limited under some operating conditions.

(c) High engine exhaust back-pressure can decreases the engine's efficiency and performance, increasing the operating cost. The pressure drop across the fuel processor and its associated components (for example, mixing and metering devices, and flashback arrestors) preferably should therefore be kept low.

(d) The output required from the fuel processor is typically variable. The regeneration and/or heating requirements of the exhaust after-treatment devices can be intermittent and/or sporadic. For example, the requirement for syngas depends on the engine exhaust emission output, the capacity of the after- treatment devices, the regeneration cycle of the after-treatment devices, the temperature of the exhaust gas stream and the heat loss of the exhaust system, as well as on the requirements for syngas elsewhere in the engine system. (e) Thorough mixing of vaporized liquid fuel with the engine exhaust stream is important. With liquid fuels, inadequate

vaporization and mixing of the fuel with the engine exhaust stream can lead to localized fuel-rich conditions, resulting in the formation of coke or soot (carbon) and hot spots. At typical SGG operating temperatures, the time to vaporize the fuel and effectively mix the fuel with the engine exhaust stream is limited. Pre-heating of the fuel can aid in the vaporization process, however excess heating can cause residues and carbon to form. Hydrocarbon fuels have a relatively high viscosity and surface tension. This prevents the fuel from dispersing easily, making it difficult to form small droplets with a large surface area. Also heavy hydrocarbon fuels, such as diesel, comprise various components that react at different temperatures and rates. Chemical decomposition of the fuel can also lead to formation of carbon and residues, starting at temperatures even as low as about 200°C. 1 he engine exhaust gas stream temperature can reach over 600°C, while the internal temperature of the SGG can reach over 1200°C. Carbon deposits can impede the flow of gases in the SGG and after- treatment devices, increasing the back pressure in the engine exhaust system. Large accumulations of carbon also have the potential to create excessive amounts of heat if the carbon is oxidized in a short period of time. Insufficient mixing can also affect the fuel conversion efficiency, causing an increase in fuel consumption and operating cost. Furthermore, a boundary layer effect along the interior wall surfaces of the SGG can create a lower gas speed along the walls than at the center of the stream. If fuel droplets are allowed to migrate to the wall, the low gas speed can allow fuel droplets to fall out of suspension and accumulate on the walls. The reduced surface area of the accumulated fuel, with the lower temperatures along the walls can reduce the vaporization of the fuel. This is

known as "wall wetting", and it can create localized fuel-rich conditions, lead to carbon formation and reduced fuel conversion efficiency.

(1) High system reliability and durability are required. (g) The internal combustion engine exhaust after-treatment market has cost, volume, and weight constraints, particularly for vehicular applications.

Summary of the Invention The present invention relates to fuel processors comprising a critical flow venturi (CFV). methods of operating such fuel processors, and systems incorporating such fuel processors.

A method of operating a fuel processor comprises directing a reactant stream through a venturi for downstream chemical conversion to generate a hydrogen-containing gas stream. The venturi is capable of operating as a critical flow venturi. In particular, it is capable of operating as a critical flow venturi during the designed or anticipated normal operating range of the fuel processor. At least a portion of the time during operation of the fuel processor, the reactant stream is choked as it passes through the venturi. Preferably the venturi is operated under a choked condition during a predominant portion of the time during operation of the fuel processor to produce the hydrogen- containing gas stream. For example, in some embodiments of the method it may be choked at least 85% of the time. In some embodiments of the method, the speed of the reactant stream through the venturi is in the range from about 300 to about 700 m/s.

The reactant stream directed through the venturi can be a single reactant stream to which one or more other reactants are added downstream or can be a mixture comprising, for example, a fuel stream and an oxidant stream. In some embodiments, the fuel stream is a liquid when at standard

temperature and pressure, for example, it could be diesel or gasoline. The oxidant stream can be an oxygen-containing gas stream such as air, and in some embodiments comprises, or consists essentially of, engine exhaust gas from a combustion engine. In some embodiments, the reactant stream that is directed through the venturi comprises substantially all of the oxidant stream that is supplied to the fuel processor during operation thereof, so that no additional oxidant stream is added downstream of the venturi.

The supply of a reactant stream to the fuel processor can be passively metered by directing it through the venturi. Thus, the need for active flow control devices associated with the fuel processor can be reduced or eliminated at least for one of the reactants.

In certain embodiments of the method, a predominant portion of the time during operation of the fuel processor, the speed of the reactant stream as it passes through the venturi is greater than the flame speed of the reactant mixture that is in the fuel processor downstream of the venturi.

In one aspect, a fuel processor for producing a hydrogen-containing gas stream, comprises a unitary device, in particular a critical flow venturi, capable of metering a reactant stream supplied to the fuel processor, mixing a fuel stream with an oxidant stream, and arresting flashback from downstream combustion of the mixed fuel and oxidant streams within the fuel processor.

In another aspect, a fuel processor for producing a hydrogen- containing gas stream comprises a venturi having a convergent inlet section and a throat, and further comprises a divergent section located immediately downstream of the venturi throat. There is a step that forms a discontinuity (a sudden increase in flow cross-sectional area) between the throat and the divergent outlet section. The divergent section and the step can be part of the venturi or the step can be at the interface between the venturi and another component, such as a mixing tube that incorporates the divergent section.

The above-described method and apparatus can be advantageously used in engine systems that incorporate a fuel processor, such as a syngas generator, for producing a hydrogen-containing gas stream, such as a syngas stream. Such engine systems comprise a fuel source and a combustion engine connected to receive a fuel stream from the fuel source. The combustion engine has an exhaust stream outlet. The fuel processor comprises a venturi that is fluidly connected to the engine exhaust stream outlet, such that at least a portion of the engine exhaust stream can be directed to the fuel processor via the venturi during operation of the combustion engine. The venturi is preferably capable of operating as a critical flow venturi. In particular, it is capable of operating as a critical flow venturi during the designed or anticipated normal operating range of the fuel processor. In preferred embodiments of the system, the fuel processor comprises a single oxidant stream inlet located upstream of the venturi, via which the engine exhaust stream is introduced without downstream addition of supplemental oxidant streams.

The venturi is preferably also fluidly connected to receive a fuel stream from the same fuel source (or less preferably from a secondary fuel source). The venturi is preferably capable of mixing the engine exhaust stream and the fuel stream. Preferably the venturi is also capable of arresting flashback from downstream combustion of the engine exhaust stream and the fuel stream within the fuel processor.

In preferred embodiments of the engine system there is no flow metering device between the exhaust stream outlet and the venturi for controlling the How rate of engine exhaust stream directed to the fuel processor. Instead the venturi is capable of passively metering the supply of engine exhaust stream to the fuel processor.

Embodiments of an engine system can further comprise an exhaust after-treatment subsystem, with the fuel processor connected to at least

intermittently supply the hydrogen-containing gas stream to the exhaust after- treatment subsystem.

Brief Description of the Drawings Figure 1 is a process flow chart illustrating a typical fuel conversion process in a syngas generator (SGG).

Figure 2 is a graph of the operating regime of a conventional venturi and a critical flow venturi (CFV), illustrating the relationship between the mass flow of a fluid stream through the venturi and inlet pressure.

Figure 3 is a cross-sectional view of an embodiment of a CFV incorporated in the inlet region of a fuel processor.

Figure 4 is a cross-sectional view of an embodiment of a critical flow venturi. illustrating its various /ones and profiles.

Figure 5 is a schematic process flow diagram of an embodiment of an internal combustion engine system with an exhaust after-treatment system and syngas generator (SGG).

Detailed Description of Preferred Embodiment(s)

Figure 1 illustrates a typical SGG fuel conversion process, and is described above.

CFVs (also known as sonic nozzles, critical flow nozzles, sonic chokes, and converging-diverging nozzles) have a convergent section (inlet) upstream of the throat (the point of minimum flow area) and typically a conical divergent section on the other side of the throat. Thus, as the fluid stream mov es through the CFV (in the principal flow direction) it sequentially traverses a convergent zone, a throat and a divergent zone. A CFV can accelerate the fluid flow to sonic speed at the throat, when the pressure at the

throat relative to the inlet pressure is reduced to or below a critical value. For example, the critical throat-to-inlet pressure is 0.528 for air. When the fluid reaches sonic speed or the critical velocity, the mass flow rate of fluid flowing through the CFV is at the maximum possible value for the upstream conditions, and the CFV is said to be operating at a choked, critical, or sonic condition. Under choked conditions, mass flow through the CFV is not affected by changes in the flow downstream, and remains substantially constant even if the downstream pressure changes.

A divergent section is commonly used downstream of the throat so that after the fluid passes through the throat of the CFV its speed decreases and the pressure increases, thereby prov iding some pressure recovery across the device.

The mass flow rate through the CFV is affected by the inlet fluid composition, pressure and inlet temperature, and also depends on the convergent profile, throat diameter and surface finish of the CFV. A CFV typically requires a surface roughness of about < 1.6 micron (1.6 μm or 6.3 x 10 ^"3 inches), while conventional Venturis typically can tolerate a rougher surface finish for most applications. When choked, the mass flow through the CFV is proportional to the inlet pressure and inversely proportional to the square root of absolute temperature for a given fluid composition.

In Figure 2, line 20, is a plot illustrating the relationship between the mass flow and inlet pressure of a venturi. Typically, a conventional venturi operates in regime 21 , while a venturi operating as a CFV operates in regime

22.

The present technique relies on properties that are particular to a CFV rather than a conventional venturi. In the present approach, preferably during a predominant portion of the operating duration of the CFV in the fuel processor, the fluid flow through the CFV is choked and the mass flow is proportional to the inlet pressure. This is illustrated in Figure 2, as line 20, in

regimc 22. The \ enturi can operate in both regime 21 and regime 22, but preferably operates as a CFV as in regime 22 for some, or preferably most, of the time. Typically, conventional Venturis operate with smaller pressure drops between inlet and outlet of the venturi, while the mass flow is proportional to the square root of the pressure drop, as illustrated in Figure 2, as line 20 in regime 21. The throat velocity of the CFV can be as high as 700 m/s, while a conventional venturi usually operates at a throat velocity less than 250 m/s.

Figure 3 shows a CFV incorporated in the inlet region of a fuel processor. In Figure 3, CFV 31 is attached to fuel processor body 32 (although in some embodiments the CFV could be located external to the outer shell or main housing of the fuel processor). Fuel 33 is supplied via a fuel inlet line (not shown in Figure 3) and introduced into oxidant stream 34 upstream of CFV 31. Oxidant stream 34 is directed to CFV 31 via an oxidant inlet line (not shown in Figure 3). The mixture of fuel 33 and oxidant stream 34 flows through CFV 31 and reaches sonic or near sonic speed, so that the

CFV is choked. If fuel 33 is a liquid, the acceleration to sonic or near sonic speed will shear the liquid fuel, reducing the droplet size of the fuel while increasing its surface area. The increase in surface area increases the heat transfer rate and reduces the vaporization time. Thus, a liquid fuel can be atomized and vaporized as it passes through the throat 36 of CFV 31.

Turbulent flow through the throat 36 of CFV 31 aids in mixing the fuel 33 and oxidant stream 34 to create combined reactant stream 35. Combined reactant stream 35 exits C ¹ FV 31 and proceeds downstream within the fuel processor to the combustion zone where oxidation reactions occur, and then on to the reforming process where further conversion to a hydrogen-containing gas stream occurs.

In Figure 4 a cross-sectional profile of an embodiment of a CFV 41 is shown schematically. λt the inlet of CFV 41 , convergent inlet section 42 reduces to throat 43. This reduction in cross-sectional area along convergent inlet section 42 causes pressure of the fluid mixture to drop, while the speed

increases. The throat diameter 45 is sized to create a choked condition at the desired maximum mass flow rate. λs the fluid mixture reaches sonic speed, the maximum flow rate across CFV 41 is reached. As the fluid mixture passes the through throat 43 it flows into the divergent section 44 where the speed of the mixture decreases and the pressure increases. The divergent angle 47 affects the pressure recovery through CFV 41 . The divergent angle or total cone angle, is typically less than 16°. and for certain preferred embodiments the preferred divergent angle has been found to be about 10° (that is about 5° on either side of the central longitudinal axis). The profile of the divergent zone can be straight (conical, as shown), or curved (trumpet-like). The divergent section can be part of the CFV (as shown in Figure 4) or can be a separate component connected to the CFV. such as a mixing tube, in which case the CFV will comprise just a convergent inlet section and a throat.

CFV 41 illustrated in Figure 4 has a step 46 in its profile just downstream of throat 43. This step 46 assists in stabilizing the location of the shock wave created by the sonic fluid speeds, thereby stabilizing the flow characteristic of the CFV. The step can be incorporated into a converging- divergent CFV. or can be located at the interface between the CFV and another immediately downstream component such as a mixing tube. The latter approach can simplify the manufacturing process and cost, as the step can act as the interface between two separate less expensive components of the fuel processor. In other embodiments, the step in the venturi profile between the venturi throat and divergent section can be eliminated, or there can be one or more steps in the throat or divergent section.

Figure 5 illustrates schematically an embodiment of an engine system with a fuel processor and an exhaust after-treatment system. In this illustrated embodiment the fuel processor is a syngas generator (SGG). In Figure 5, fuel tank 51 supplies liquid fuel, through fuel supply line 52, to internal combustion engine 53. An optional fuel filter, fuel pump, fuel pressure regulating device and fuel flow control device (all not shown in Figure 5) can

be integrated into fuel tank 51 or into fuel supply line 52. An optional fuel return line can return fuel back to fuel tank 51. Internal combustion engine 53 could be a diesel, gasoline, natural gas, propane, liquefied petroleum gas (LPG), methanol, ethanol, or similarly fueled engine of, for example, compression ignition or spark ignition type. The engine can be part of a vehicular or non-vehicular system. The internal combustion engine will comprise an air supply subsystem (not shown in Figure 5).

Engine exhaust line 54 directs at least a portion of the engine exhaust stream to exhaust after-treatment device 55. Engine exhaust line 54 can incorporate other emissions reduction devices such as exhaust gas recirculation (EGR) systems (not shown in Figure 5). Engine exhaust line 54 can contain a turbo-compressor and/or intercooler (not shown in Figure 5). Exhaust after-treatment device 55 can comprise various exhaust after- treatment components such as Lean NOx Traps (LNTs), Diesel Particulate Filters (DPFs), Diesel Oxidation Catalysts (DOCs), and a noise muffler and associated valves, sensors and controllers. The treated engine exhaust gas stream flows through exhaust pipe 56, and exits into the surrounding atmosphere.

A portion of the engine exhaust stream from line 54 is directed to SGG 60 via SGG oxidant inlet line 57. Optionally, air from an air supply subsystem (not shown in Figure 5) may also be introduced into SGG 60, via oxidant stream 57 and/or via one or more other inlets, at some points or continuously during operation of SGG 60. Fuel from fuel tank 51 is supplied from fuel supply line 52 to SGG 60 via SGG fuel inlet line 58. An optional fuel filter, fuel pump, fuel pressure regulating device and/or fuel heat exchanger (all not shown in Figure 5) can be integrated into SGG fuel inlet line 58. A fuel metering assembly 59 in line 58 controls the mass flow and pressure of the fuel supplied to SGG 60. The oxidant stream is metered internally in SGG 60 using a CFV as described below.

SGG 60 converts the fuel and the oxidant stream, comprising engine exhaust, into a syngas stream. At least a portion of the syngas stream produced is supplied via syngas outlet line 61 to exhaust after-treatment device 55. Syngas outlet line 61 can contain optional valves, sensors, controllers or similar equipment. The s> ngas stream is used to regenerate or to heat exhaust after-treatment device 55, and can be directed to other hydrogen consuming devices within the system, such as fuel cells (not shown) and/or to the engine itself.

SGG 60 incorporates a CFV (not shown in Figure 5) as described above. The CFV can be sized to meet the SGG output requirements. A CFV offers particular advantages as a device for passive control of reactant flow in situations where there are significant v ariations in the upstream pressure and temperature such as in engine exhaust applications. It provides high predictability and repeatability of the flow despite the upstream variations, and there are no moving parts in the device. The engine exhaust stream temperature, pressure, mass flow, composition and emission levels will vary significantly over the operating range of the engine. The CFV will be affected by the pressure and temperature of the engine exhaust stream upstream, but the CFV passively meters the How and reduces the effect of these fluctuations. Optionally, an exhaust gas and/or fuel heat exchanger can be integrated upstream of the CFV, internal or external to the fuel processor. The heat exchanger can be used modulate the temperature range of the stream entering the CFV. Because of its regulating effect, the CFV provides low turndown - in other words, even as the engine moves from idle to full power, the CFV passively meters the mass flow of engine exhaust stream to the SGG, reducing the turndown of the SGG (so that the output from the SGG does not change signilϊcantK with changes in the engine operation). The CFV can therefore replace the requirement for a complex and costly mass flow metering system and its associated devices. The O/C ratio within the SGG can be altered by adjusting the mass flow rate of the fuel stream into the SGG. Even if the fuel is introduced upstream of the CFV throat, adjustments to the mass flow rate of

the fuel do not significantly affect the metering of the engine exhaust or oxidant stream by the CFV.

The exhaust pressure created by the engine is limited, and increases to the engine exhaust backpressure can affect the performance, efficiency and fuel consumption of the engine. Another advantage of the CFV is the ability to recover some of the pressure that is lost as the reactant stream passes through the throat of the CFV. The pressure recovery can reduce the overall pressure drop across the CFV and SGG.

During certain SGG operating conditions, the combined reactant stream is combustible and within the auto-ignition temperature range. Under choked conditions the CFV creates a sonic or near sonic speed at the throat, which acts as a flashback arresting feature. The high speed created by the CFV is greater than the flame speed of the combined reactant stream, which can prevent a flashback from propagating back through the CFV, thereby reducing or eliminating the need for an additional flashback arresting device.

As described above, single or unitary device, in particular a CFV, can be used to meter the mass How of a reactant stream, aid in mixing of the fuel and oxidant streams, and act as a flashback arrestor in a fuel processor.

A CFV can be incorporated into various types of fuel processors including syngas generators (SGGs). reformers or reactors used to generate hydrogen-containing gas streams. These can be of various types , for example, catalytic partial oxidizers, non-catalytic partial oxidizers, and/or autothermal reformers.

The fuel supplied to the fuel processor can be a liquid fuel (herein meaning a fuel that is a liquid when under IUPAC defined conditions of standard temperature and pressure) or a gaseous fuel. A CFV assists in the efficient atomization and vaporization of liquid fuels as described above, therefore its use is particularly beneficial with a liquid fuel, but a CFV will

also provide efficient mixing of gaseous reactant streams. Instead of being introduced close to, but upstream of the CFV, the fuel could be introduced at or just downstream of the throat of the CFV. The speed and turbulent flow in the divergent zone will still generally provide satisfactory mixing of the reactant streams.

An optional combination of water, steam, oxygen, air, carbon monoxide and/or heat could be added upstream of the CFV. The CFV can be provided with small openings in the throat of the CFV, which allows introduction of other gases or liquids for modification of the gas composition. The fluid being introduced can be pressurized or drawn, based on the CFV acting like an ejector.

More than one CFV could be used to meter, mix or arrest flashback in a fuel processor. For example, each of several CFVs could have associated valves to adjust the number that are operational for different output levels, or CFVs with different flow characteristics could be used to give the desired mass flow behavior with varying inlet conditions, or in large fuel processors multiple CFVs could be used in parallel to give better coverage.

The CFV could be designed and sized to meter and/or mix below sonic speeds. In many cases the CFV will not operate at a critical condition over the entire operating range of the system. For example, the CFV could operate below critical (sonic) speed at engine idle.

Although the use of a CFV in a fuel processor offers particular advantages (as described herein) when used in an engine system, it could be advantageous to incorporate a CFV into fuel processors for other applications.

While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, that the invention is not limited thereto since modifications can be made by those

skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.