WO2008052359A1

WO2008052359A1 - Liquid fuel introduction device for fuel processor

Info

Publication number: WO2008052359A1
Application number: PCT/CA2007/001985
Authority: WO
Inventors: Richard Allan Sederquist; Jacobus Neels
Original assignee: Nxtgen Emission Controls Inc.
Priority date: 2006-11-03
Filing date: 2007-11-02
Publication date: 2008-05-08

Abstract

A fuel introduction tube is employed to introduce a liquid fuel stream into a hot oxygen-containing gas stream for downstream chemical conversion in a fuel processor. The introduction tube introduces the fuel stream into the oxygen-containing gas stream in a narrow and focused pattern, or jet, thereby inhibiting migration of the fuel to the downstream vessel wall, inhibiting wall wetting, and inhibiting formation of carbon. The fuel processor can be utilized in an engine system, in which the hot oxygen-containing gas stream comprises engine exhaust. The introduction tube can be passively or actively thermally shielded to reduce undesirable boiling of the liquid fuel stream within the tube.

Description

LIQUID FUEL INTRODUCTION DEVICE FOR FUEL PROCESSOR

Field of the Invention

The present invention relates to the introduction of a liquid fuel into a hot oxygen-containing gas stream, such as an engine exhaust stream, for downstream chemical conversion in a fuel processor to produce a hydrogen-containing gas stream, such as a syngas stream. The fuel introduction tube that is used can be passively or actively thermally shielded to reduce undesirable boiling of the liquid fuel stream within the tube.

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 typically require periodic in-situ regeneration, desulfation 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 onboard 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 (H₂) and carbon monoxide (CO), known as syngas. The H₂ and CO can be beneficial in the processes used to regenerate exhaust after-treatment devices. A portion of the engine exhaust stream can be used as an oxidant for the fuel conversion process. The exhaust stream typically contains oxygen (O₂), water (H₂O), carbon dioxide (CO₂), nitrogen (N₂) and sensible heat, which can be useful for the production of syngas. Additional air can optionally be added. The fuel supplied to the SGG can conveniently be chosen to be the same fuel that is used in the 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 generally 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 engine exhaust stream and fuel 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. The liquid fuel is typically atomized, vaporized and 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-exhaust gas mixture to produce H₂ 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 stream 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 - A -

primary processes happening in each of the zones are as described above.

Conversion of liquid fuels, especially heavy hydrocarbons, into syngas can be difficult due to the various components that make up the fuel. These various components react at different temperatures and rates. 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. Chemical decomposition of the fuel can also lead to formation of carbon and residues, starting at temperatures even as low as about 200⁰C. 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.

In known engine systems, such as those in which a fuel (from which hydrogen can be derived) is introduced upstream of an after-treatment device with or without first passing through a fuel processor, liquid fuel is typically sprayed into the hot engine exhaust gas or oxidant stream through a nozzle. This method typically yields reduced fuel conversion efficiency. As the liquid fuel is sprayed, the fuel stream is broken into droplets, or atomized and forced into the exhaust gas stream over a wide spray pattern.

Heat, from the engine exhaust stream, vaporizes the atomized fuel. The fuel is then mixed by the turbulent flow of the exhaust gas stream. The temperature of the engine exhaust stream can reach over 600⁰C. At elevated temperatures, there is a limited time in which to effectively vaporize and mix the two streams before undesirable carbon forming reactions will start to occur.

The engine exhaust gas stream speed can aid in fuel vaporization and in mixing of the fuel with the exhaust gas stream. However, a lower gas speed can occur along the wall of the fuel processor or reaction chamber 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.

Some of the shortcomings of using prior techniques and devices, such as hydraulic nozzles, air-assist nozzles or injectors, to introduce liquid fuel into hot oxygen-containing gas streams such as engine exhaust gas streams for downstream fuel conversion are outlined below.

(a) Nozzles often create a wide spray pattern that can cause the fuel to be sprayed onto the interior wall surfaces of the mixing tube or reactor, creating a wall wetting effect. Nozzles can also create a combustible mixture with potential for auto-ignition or flashback. (b) Large droplet sizes and/or a wide range of droplet sizes can sometimes result in a heterogeneous, localized fuel-rich, diffusion-limited reaction condition that is likely to cause coke or soot formation.

(c) The higher mass flow rates typical of prior injectors are not necessarily suitable for applications requiring relatively low volume syngas production.

(d) Many injectors and nozzles are designed for intermittent or pulsed (non-continuous) flow, rather than continuous flow.

(e) There is typically a high pressure drop across conventional nozzles and injectors, thus significant energy is required to introduce the liquid fuel. (f) High injection stream speeds typical of prior devices can work against maintaining a differential between the engine exhaust gas stream speed and the speed of the fuel that is being introduced, (g) Typical commercially available nozzles have a turndown ratio of approximately 3: 1. If the flow rates through the nozzle fall out of the designed range or turndown ratio, the spray characteristics such as droplet size and cone spray angle can change, detrimentally affecting vaporization and leading to carbon formation.

(h) High cost of the hydraulic nozzles or injectors. (i) High temperature of nozzles or injectors causing internal fuel boiling and expansion, interrupting the flow of fuel.

(j) Local high temperatures on the nozzle, which causes fuel cracking, gum formation and coke deposition, resulting in fouling and clogging of the fuel flow channels.

Summary of the Invention A fuel introduction tube can be used to introduce a liquid fuel stream (herein meaning a fuel that is a liquid when under IUPAC defined conditions of standard temperature and pressure) into an oxygen-containing gas stream which is at a temperature above the boiling point of the liquid fuel, for downstream chemical conversion in a fuel processor. In preferred embodiments, the fuel introduction tube is thermally shielded from the hot oxygen- containing gas stream to reduce boiling of the fuel which would otherwise occur within the fuel introduction tube, and preferably to maintain the liquid fuel stream below its boiling point within the introduction tube.

A fuel processor assembly for producing a hydrogen- containing fluid stream comprises an oxidant stream inlet and at least one fuel introduction tube for directing a liquid fuel stream from a fuel source into the fuel processor. In preferred embodiments, the fuel introduction tube comprises thermal shielding for maintaining the liquid fuel stream below its boiling point while it is passing through the fuel introduction tube during operation of the fuel processor.

A method of operating a fuel processor comprises introducing a liquid fuel stream into an oxygen-containing gas stream via a fuel introduction tube, wherein the temperature of the oxygen-containing gas stream is above the boiling point of the liquid fuel stream. The fuel stream is maintained below its boiling point while it is in the fuel introduction tube, for example, by passively or actively thermally shielding the fuel introduction tube from the hot oxygen-containing gas stream. An embodiment of the method with active thermal shielding of the tube comprises flowing a thermal shielding fluid in contact with the fuel introduction tube. The thermal shielding fluid is at a temperature below the boiling point of the liquid fuel stream.

The above-described apparatus and method relating to use of a fuel introduction tube to introduce a liquid fuel stream into an oxygen-containing gas stream can 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. For example, such an engine system can comprise a combustion engine connected to receive a fuel stream from a liquid fuel source. The combustion engine has an exhaust stream outlet. The fuel processor comprises an inlet fluidly connected to the engine exhaust stream outlet, such that at least a portion of the engine exhaust stream is directed to the fuel processor during operation of the combustion engine. The fuel processor further comprises at least one fuel introduction tube for directing a liquid fuel stream from a fuel source into the engine exhaust stream. The fuel source is preferably the same for the engine and the fuel processor, but can be different. In preferred embodiments the at least one fuel introduction tube is thermally shielded from the engine exhaust stream.

Methods of operating such engine systems comprising a combustion engine and a fuel processor can comprise directing an engine fuel stream and an oxidant stream to the combustion engine and operating the combustion engine to produce an engine exhaust stream. At least a portion of the engine exhaust stream, and optionally a supplemental air stream, is directed to the fuel processor as an oxidant stream. A liquid fuel stream is introduced into the oxidant stream (comprising engine exhaust gas) via a fuel introduction tube, to form a combined reactant stream, and the fuel processor is operating to generate a hydrogen-containing gas stream from the combined reactant stream.

Typically, at least some of the time during operation of the engine system, the temperature of the oxidant stream is higher than the boiling point of the liquid fuel stream. The temperature of the liquid fuel is preferably maintained below its boiling point within the fuel introduction tube by passively or actively thermally shielding the fuel introduction tube. An embodiment of the method with active thermal shielding of the tube comprises flowing a thermal shielding fluid in contact with the fuel introduction tube.

The thermal shielding fluid is at a temperature below the temperature of the oxygen-containing gas stream, and preferably below the boiling point of the liquid fuel stream.

It is convenient if the engine fuel stream is drawn from the same source as the liquid fuel stream that is directed to the fuel processor, although it need not be. The liquid fuel stream can be directed to the fuel introduction tube at low pressure, utilizing the fuel supply system of the engine

In embodiments of the above described methods of operating engine systems comprising a combustion engine and a fuel processor, the degree of fuel stream atomization occurring as the liquid fuel stream is introduced into the oxidant stream comprising engine exhaust, via the introduction tube, is substantially independent of the pressure of the liquid fuel stream supplied to the fuel introduction tube and/or is substantially unaffected by the liquid fuel stream mass flow rate through the fuel introduction tube.

In the above-described fuel processor assembly and engine system embodiments, the fuel introduction tube can have a passive or active thermal shielding mechanism associated therewith. In some embodiment the thermal shielding of the fuel introduction tube can comprise a thermal insulating sleeve disposed around the fuel introduction tube. There can be an air gap between the sleeve and the tube. In actively shielded embodiments, an apparatus or mechanism for flowing a thermal shielding fluid in contact with the fuel introduction tube can be provided. For example, the thermal shielding fluid can be directed to flow between the fuel introduction tube and a sleeve disposed around the fuel introduction tube.

In preferred embodiments of the above-described methods for operating a fuel processor and operating an engine system using a fuel introduction tube, the divergent angle of the fuel stream as it exits the fuel introduction tube is less than about 10^° from the longitudinal axis of the fuel introduction tube; the liquid fuel stream speed within the fuel introduction tube is between about 0.1 and about 10.0 m/sec; and/or the pressure drop across the fuel introduction tube is less that about 690 kPag (100 psig), and preferably less than about 69 kPag (10 psig).

Brief Description of the Drawings

Figure 1 is a process flow chart illustrating a typical fuel conversion process in a syngas generator.

Figure 2 is a schematic process flow diagram of an embodiment of an internal combustion engine system with an exhaust after-treatment sub-system and a syngas generator.

Figure 3 is a schematic cross-sectional view of an embodiment of a passively thermally shielded introduction tube assembly and a typical mixing tube, located in an oxidant stream upstream of the mixing zone in a fuel processor

Figure 4 is a schematic cross-sectional view of an embodiment of an air-shielded introduction tube assembly. Figure 5 shows cross-sectional views of other embodiments of introduction tube and mixing tube configurations. Figure 5a shows an angled introduction tube. Figure 5b shows an angled tube and fuel stream. Figure 5c shows an off-center introduction tube.

Figure 6 is a cross-sectional view of an embodiment with multiple introduction tubes.

Detailed Description of Preferred Embodiment(s)

The present apparatus comprising a fuel introduction tube is particularly suited for introducing liquid fuels into hot oxygen- containing gas streams for downstream chemical conversion in a fuel processor. In situations where the temperature of the hot gas stream exceeds the boiling point of the liquid fuel at least some of the time during operation of the fuel processor, preferably the fuel introduction tube comprises thermal shielding. Similarly, methods of introducing a liquid fuel into a hot oxygen-containing gas stream comprise utilizing a fuel introduction tube as described herein. The fuel introduction tube can be passively or actively thermally shielded to reduce boiling of the fuel within the introduction tube, and preferably to maintain the liquid fuel stream below its boiling point within the fuel introduction tube.

The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid. Fuels such as diesel and gasoline typically boil over a temperature range as they are made up of a variety of components. As used herein the term "boiling point" refers the temperature at which the fuel stream would begin to boil (also known as the "initial boiling point^*") under the particular conditions in the fuel introduction tube.

Fuel introduction tubes are inexpensive, industry standard products. The fuel introduction tube, unlike hydraulic nozzles or injectors, introduces the fuel in a narrow and focused pattern, or jet, preferably substantially axially in or towards the center of the oxygen-containing gas stream. This reduces the migration of fuel to the pipe wall, reducing the wall wetting effect and the formation of carbon.

Embodiments of the present apparatus and method are particularly suitable for fuel processors that are used in engine system applications where a liquid fuel stream is to be introduced into an oxidant stream comprising hot engine exhaust gas, for downstream conversion into a hydrogen-containing gas stream.

Here the temperature of the oxidant stream often exceeds the boiling point of the liquid fuel (typically diesel or gasoline). Boiling of the fuel in the tube is more of an issue in this particular application than in other applications (such as fuel burners), because the quantity of liquid fuel being introduced into the hot gas stream is typically much lower. In the absence of adequate thermal shielding, heat from the hot oxidant stream and fuel processor can transfer to the fuel introduction tube causing the liquid fuel to boil, which can create gas bubble blockages and prevent the steady flow of liquid fuel through the tube. The fuel introduction tube generally allows for a continuous fuel flow, with desirable (relatively low) mass flow rates that suit engine system applications, reduced fuel supply pressure requirements, and reduced introduction speeds so that the fuel can be introduced at a slower speed than the speed of the oxidant stream. The atomization, vaporization and mixing of the fuel with the oxidant stream can be aided by additional devices within the fuel processor, downstream of the introduction tube but upstream of the reaction zone. The introduction of the fuel into the oxidant stream, as described herein, facilitates downstream atomization, vaporization and mixing of the fuel with the oxidant stream.

In engine system applications, the hydrogen-containing gas stream can optionally be directed to an exhaust after-treatment device, such as a lean NOx trap. The engine can be part of a vehicular or non-vehicular system. There are other potential uses for the hydrogen-containing gas stream within such systems.

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

Figure 2 illustrates schematically an embodiment of a diesel engine system with a fuel processor and an exhaust after-treatment sub-system. In this illustrated embodiment the fuel processor is a syngas generator (SGG). In Figure 2, vehicular diesel fuel tank 1, supplies diesel fuel through fuel supply line 2, to diesel engine 3. Fuel tank 1, or fuel supply line 2, typically includes a fuel filter, fuel pump and fuel return line (all not shown). Diesel engine 3 produces mechanical power and emits an engine exhaust stream through engine exhaust line 4. The engine exhaust stream in line 4, can drive an optional turbo compressor exhaust gas impeller 5, which can in turn drive a coupled turbo compressor air intake impeller (not shown) to compress the engine air intake stream (not shown). Engine exhaust line 4, continues from the turbo compressor 5, to a diesel particulate filter (DPF) 6, where particulate matter in the exhaust stream is trapped. The engine exhaust stream then proceeds into a lean NOx trap (LNT) 7, where NOx from the engine exhaust stream is adsorbed. The engine exhaust stream then proceeds into an optional diesel oxidation catalyst (DOC) device 8, where most of the residual hydrocarbons and CO are converted into water and CO₂. The remaining treated exhaust gas stream Hows through exhaust pipe 9, and exits into the surrounding atmosphere. An optional noise muffler (not shown) can be installed in-line with exhaust pipe 9. DPF 6, LNT 7, and DOC device 8, can be integrated with one another to form one or more devices and can be arranged in a different sequence.

In Figure 2, a portion of the engine exhaust stream from line 4 is directed to SGG 13 via SGG exhaust gas inlet line 10. The engine exhaust stream directed to SGG 13 is employed as an oxidant stream for SGG 13. Optionally, air from an air supply subsystem (not shown in Figure 2) can also be introduced into SGG 13 to form part of the oxidant stream, via exhaust gas inlet line 10 and/or via one or more other inlets, at some points or continuously during operation of SGG 13. Optionally, the oxidant stream can be preheated with an optional preheater (not shown in Figure 2) located upstream of the mixing zone within SGG 13. The oxidant stream is metered internally in SGG 13. Liquid diesel fuel from vehicular fuel tank 1 is supplied from fuel supply line 2, to SGG 13 via SGG fuel inlet line 1 1. A fuel metering assembly 12 in line 11 controls the mass flow and pressure of the diesel fuel, prior to introduction into SGG 13. SGG 13 coverts the diesel fuel and the oxidant stream comprising engine exhaust into the product syngas. The syngas stream exits SGG 13 via syngas outlet line 14 and flows to a passive or controlled How splitter 15. Flow splitter 15, diverts the syngas stream to any or all of the DPF 6 via line 16, the LNT 7 via line 17, and the DOC device 8 via line 18, as required for regeneration and/or heating purposes. Flow splitter 15, which could for example be a valve assembly, can be electronically controlled by control module 19, through control line 21. Control module 19, can also control fuel metering assembly 12.

In Figure 3, an embodiment of a passively thermally shielded (or insulated) introduction tube assembly 31 , comprises an introduction body 32, which attaches and locates introduction tube 38 and outer sleeve 39, forming an annular gap between introduction tube 38, and outer sleeve 39. In the illustrated embodiment, the annular gap at the distal end of introduction tube 38 and outer sleeve 39 from introduction body 32 is open. Introduction body 32 is attached to an external wall of fuel processor 33. Introduction tube assembly 31 is used to introduce a liquid fuel, such as diesel or gasoline, substantially axially into oxidant stream 36. Mixing tube 34, located at the inlet of or inside the fuel processor 33, directs the fuel jet 37 and oxidant stream 36, to further downstream processes, not shown in Figure 3. Fuel processor fuel inlet stream 35, is supplied via a fuel supply sub- system that can be similar to that described in Figure 2. Oxidant stream 36 is supplied by an oxidant reactant supply sub-system that can be similar to that described in Figure 2.

In Figure 3, fuel processor fuel inlet stream 35, flows through introduction tube 38, via introduction body 32, and is introduced into the center portion of mixing tube 34. The end of the introduction tube 38, is substantially planar in the radial direction (that is, squared-off) and terminates at or near the inlet of mixing tube 34. In other embodiments, the end of the introduction tube can be angled, cylindrical and/or another convenient shape instead of being squared off. Mixing tube 34 can have features that promote fuel atomization, fuel vaporization and mixing of the oxidant stream with fuel. These features are not shown in Figure 3. The fuel jet 37, exits the introduction tube 38, in a narrow and focused pattern or jet. Fuel jet 37 is introduced into oxidant stream 36 at or near the entrance to mixing tube 34. In engine system applications and some other applications, oxidant stream 36 can reach temperatures exceeding 600⁰C. The narrow spray pattern of the jet reduces the amount of fuel that comes in contact with the interior walls of mixing tube 34, reducing wall wetting and the undesirable formation of carbon (coke or soot). It is desirable to maintain the temperature of the liquid fuel stream traveling through introduction tube 38, below its boiling point. Without adequate thermal shielding, heat from the SGG and oxidant stream can otherwise cause the liquid fuel stream to boil, which can create a disruption to the flow of fuel and the formation of carbon and residues. The contact area between introduction body 32 and introduction tube 38 is preferably kept small in order to reduce the conductive thermal path from SGG 33, via introduction body 32 and introduction tube 38, to the fuel stream flowing in tube 38. In the embodiment illustrated in Figure 3, thermal shielding of the introduction tube is achieved by locating introduction tube 38 co-axially inside a larger outer sleeve 39. The annular gap between outer sleeve 39 and introduction tube 38 reduces the convective heat transfer from oxidant stream 36, via outer tube 39 and introduction tube 38, to the liquid fuel stream flowing in introduction tube 38. In this embodiment, introduction tube assembly 31 , is passively thermally shielded which offers the advantage of eliminating the requirement for a shielding fluid supply sub-system

In engine systems incorporating a fuel processor for the generation of hydrogen or syngas, it is believed to be advantageous if the liquid fuel is introduced into the oxidant stream at a lower speed than the oxidant stream speed. The speed differential and the resulting acceleration of the fuel stream can assist the atomization process downstream of the fuel introduction tube.

The dimensions of the introduction tube (for example, inside and outside diameter) will depend upon the size and desired output of the fuel processor. In one embodiment, the introduction tube can be constructed from stainless steel alloy, with an inside diameter of 0.69 mm (0.027 inches) and an outside diameter of 1.07 mm (0.042 inches). The outer sleeve can be constructed from stainless steel alloy, with an inside diameter of 2.68 mm (0.106 inches) and an outside diameter of 3.18 mm (0.125 inches). The interior wall surfaces of the introduction tube(s) can be polished or coated to reduce the formation of fuel by-product gums, residues or carbon on the wall.

The pressure drop across the introduction tube is low, for example, less than 690 kPag (100 psig) and preferably less than about 69 kPag (l Opsig). The fuel inlet stream is preferably at pressures up to about 414 kPag (60 psig). The introduction tube creates a low speed liquid fuel jet, preferably up to about 10 m/s (394 inches/s), with a narrow jet diameter. The narrow jet of fuel reduces the probability of creating a locally flammable or combustible mixture, reducing the probability of a flashback from occurring. The introduction tube could be a needle and is a low cost alternative to state of the art nozzles. Other nozzles generally require high fuel pressure in order to adequately atomize the fuel. The turndown ratio with such nozzles is limited because if the fuel pressure is reduced then poor atomization occurs. In the present approach, which typically uses a low fuel pressure, the turndown ratio is extremely large (even infinite). The primary function of the introduction tube is merely to introduce a liquid fuel into the hot oxidant stream. In the present approach, the atomization process does not depend in any significant way on the pressure or quantity of the fuel introduced. The oxidant stream is accelerated in the mixing tube and shears the low speed fuel jet creating fine droplets. A low pressure fuel pump can be utilized, or the system can operate without a fuel pump and rely on the venturi effect created by the oxidant stream flowing around the introduction tube to draw the fuel into the oxidant stream. Thus, small fuel quantities can be introduced and efficient atomization achieved using a continuous or intermittent flow.

In other embodiments, the introduction tube is actively thermally shielded, for example, it can be shielded with a stream of air or other fluid. Shielding of the fuel introduction tube can be achieved, for example, by surrounding the tube co-axially with a larger outer sleeve and directing a shielding fluid (such as water or) to flow between the tube and the outer sleeve. The outer sleeve can also provide structural support to the inner tube, reducing the possibility of it deforming. A detailed view of an embodiment of an air-shielded introduction tube is shown in Figure 4. In Figure 4, introduction tube connector 40 is attached to introduction tube 41. Wire 43, is coiled around introduction tube 41, which creates a gap and air flow channel between introduction tube 41 , and outer sleeve 44. Outer sleeve 44 is attached and sealed to male connector 45. Male connector 45 is attached to body 42. Body 42, is attached to the fuel processor housing or outer shell (not shown in Figure 4). T-fitting 46, is attached and sealed to outer tube 44, and introduction tube connector 40. Liquid fuel is supplied to and flows through introduction tube connector 40, and through introduction tube 41, exiting into the fuel processor (not shown in Figure 4). While the SGG is operational, a flow of air is supplied to and flows through T-fitting 46, proceeding through the air flow channel between introduction tube 41 and outer sleeve 44, and exiting, for example, into the SGG (not shown in Figure 4). The temperature of the air is substantially below the boiling point of the liquid fuel so that the flow of air in the annular gap between the introduction tube 41 , and the outer sleeve 44, thermally shields introduction tube 41 from heat radiating from the SGG via body 42, and male connector 45.

The introduction tube can be thermally shielded using other fluids besides air or water, or it can be actively shielded or cooled by other methods involving convection or conduction. The introduction tube can be thermally shielded from the reactor body by incorporating a shielding fluid at the reactor itself or at the body of the introduction tube, or both.

The introduction tube can optionally function as a spark electrode or spark plug, forming part of an integrated ignition source for the fuel and engine exhaust stream mixture. The introduction tube can be electrically insulated from the SGG, and connected to a high voltage source. As the high voltage is supplied, a spark can be created between the introduction tube and the wall of the mixing tube. This can ignite the fuel and oxidant stream inside the mixing tube to initiate the combustion processes. In normal operation of embodiments of the fuel processor, it is only the liquid fuel stream that passes through the fuel introduction tube. Gaseous reactants, such as the oxidant stream, are introduced into the fuel processor via other devices. However, in some situations it can be desirable to be able flush or purge liquid fuel from the introduction tube using a gas, for example, when the system is shut down. A gas stream (such as air) can be introduced into the tube to purge the fuel from the tube. This can prevent the formation of carbon or deposit blockages inside the introduction tube.

In some embodiments multiple introduction tubes can be used. For example, multiple tubes could give better flow distribution, or it can be advantageous to be able to adjust the number of tubes that are used (active) at different engine power levels or depending on the output requirements from the SGG.

In other embodiments, the introduction tube can be disposed at an angle to the mixing tube, as shown in Figure 5a; the introduction tube can introduce the fuel stream at an angle to the mixing tube, as shown in Figure 5b; the introduction tube can be located off-center to the mixing tube, as shown in Figure 5c.

Multiple introduction tubes can be configured as shown in Figure 6. In Figures 5a, 5b, 5c and 6, a simple cylindrical introduction tube 51, is supported and attached to introduction body 52. Introduction body 52 is attached to an external wall of fuel processor 53. Mixing tube 54, located within the fuel processor 53, directs the diescl fuel jet 57 and oxidant stream 56, to further downstream processes, not shown in Figures 5 and 6. Fuel processor fuel inlet stream 55 is supplied through a fuel supply sub-system that can be similar to that described in Figure 2. Oxidant stream 56 is supplied by an oxidant supply sub-system that can be similar to that described in Figure 2.

Fuel introduction tubes, as described herein, can be used to introduce a liquid fuel into an oxidant stream upstream of the fuel processor or within the fuel processor. They can be used with various types of fuel processors including syngas generators, 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 liquid fuel could be for example, diesel, gasoline, methanol, ethanol or other alcohol fuels, liquefied petroleum gas

(LPG), or other liquid fuels from which hydrogen can be derived.

This approach for the introduction of liquid fuel into a hot oxidant stream, such as an engine exhaust stream, for subsequent fuel processing can be used in vehicular and non-vehicular systems. It is however particularly applicable in vehicular systems in which the on-board fuel processor is compact. Because of the physical constraints in such systems it is more important to control and restrict the spray pattern of the liquid fuel as it enters the fuel processor. The present method and apparatus utilizing a fuel introduction tube is particularly suited to the engine system applications discussed herein, but could also be useful other applications, and could be useful for the introduction of liquid fuel into other hot gaseous reactant streams besides engine exhaust gas streams.

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.

Claims

What is claimed is:

1. A fuel introduction tube for directing a liquid fuel stream into a hot oxygen-containing reactant stream of a fuel processor, for producing a hydrogen-containing fluid stream, wherein said fuel introduction tube is thermally shielded from said hot oxygen-containing reactant stream.

2. A fuel processor assembly for producing a hydrogen- containing fluid stream, said fuel processor assembly comprising: (a) an oxidant stream inlet;

(b) at least one fuel introduction tube for directing a liquid fuel stream from a fuel source into said fuel processor; wherein said fuel introduction tube comprises thermal shielding, for maintaining said liquid fuel stream below about its boiling point while it is passing through said fuel introduction tube during operation of said fuel processor.

3. The fuel processor assembly of claim 2 wherein said thermal shielding comprises a thermal insulating sleeve disposed around said fuel introduction tube.

4. The fuel processor assembly of claim 3 further comprising a mechanism for flowing a thermal shielding fluid between said fuel introduction tube and said sleeve.

5. The fuel processor assembly of claim 2 wherein said introduction tube is capable of functioning as a spark electrode to actuate fuel combustion.

6. A method of operating a fuel processor, said method comprising:

(a) introducing a liquid fuel stream into an oxygen- containing gas stream via a fuel introduction tube, wherein the temperature of said oxygen-containing gas stream is above the boiling point of said liquid fuel stream; and

(b) maintaining the fuel stream below its boiling point while it is in said fuel introduction tube.

7. The method of claim 6 wherein said fuel introduction tube is passively thermally shielded from said oxygen-containing gas stream.

8. The method of claim 6 wherein said fuel introduction tube is actively thermally shielded from said oxygen-containing gas stream.

9. The method of claim 8 wherein fuel introduction tube is actively thermally shielded by flowing a shielding fluid in contact with said fuel introduction tube.

10. The method of claim 6 wherein the divergent angle of the fuel stream as it exits said fuel introduction tube is less than about 10^° from the longitudinal axis of said fuel introduction tube.

1 1. The method of claim 6 wherein the liquid fuel stream speed within said fuel introduction tube is between about 0.1 and about 10.0 m/sec.

12. The method of claim 6 wherein the pressure drop across said fuel introduction tube is less that about 690 kPag (100 psig)-

13. An engine system comprising: (a) a liquid fuel source; (b) a combustion engine connected to receive a fuel stream from said liquid fuel source, said combustion engine comprising an exhaust stream outlet; and (c) a fuel processor for producing a hydrogen-containing fluid stream, said fuel processor comprising: (i) an oxidant stream inlet fluidly connected to said engine exhaust stream outlet, such that at least a portion of said engine exhaust stream is directed to said fuel processor oxidant stream inlet during operation of said combustion engine; (ii) at least one fuel introduction tube for directing a liquid fuel stream from said fuel source into said engine exhaust stream.

14. The engine system of claim 13 wherein said at least one fuel introduction tube is thermally shielded from said engine exhaust stream.

15. The engine system of claim 13 wherein said at least one fuel introduction tube has an active thermal shielding mechanism associated therewith.

16. The engine system of claim 13 wherein said active thermal shielding mechanism further comprises apparatus for flowing a thermal shielding fluid in contact with said fuel introduction tube.

17. A method of operating an engine system, said engine system comprising a combustion engine and a fuel processor, said method comprising:

(a) directing an engine fuel stream and an oxidant stream to said combustion engine and operating said combustion engine to produce an engine exhaust stream;

(b) directing at least a portion of said engine exhaust stream to said fuel processor; (c) introducing a liquid fuel stream into said engine exhaust stream via a fuel introduction tube, to form a combined reactant stream;

(d) operating said fuel processor to generate a hydrogen- containing gas stream from said combined reactant stream.

18. The method of claim 17 wherein at least some of the time during operation of said engine system, the temperature of said engine exhaust stream is higher than the boiling point of said liquid fuel stream.

19. The method of claim 17 wherein the temperature of said liquid fuel is maintained below its boiling point within said fuel introduction tube by thermally shielding said fuel introduction tube.

20. The method of claim 19 wherein thermally shielding said fuel introduction tube comprises flowing a thermal shielding fluid in contact with said fuel introduction tube.

21. The method of claim 17 wherein the degree of fuel stream atomization occurring as said liquid fuel stream is introduced into said engine exhaust stream via said introduction tube is substantially independent of the pressure of the liquid fuel stream supplied to said fuel introduction tube.

22. A method of claim 17 wherein the degree of fuel stream atomization occurring as said liquid fuel stream is introduced into said engine exhaust stream via said at least one introduction tube is substantially unaffected by the liquid fuel stream mass flow rate through said fuel introduction tube.

23. The method of claim 17 further comprising at least periodically directing a supplemental air stream to said fuel processor wherein said fuel processor is operated to generate said hydrogen-containing gas stream from said combined stream and said supplemental air stream.

24. The method of claim 17 wherein said engine fuel stream is drawn from the same source as said liquid fuel stream that is directed to said fuel processor.

25. The method of claim 17 further comprising, prior to ceasing operating said fuel processor, directing a gas stream through said fluid introduction tube to purge said liquid fuel stream from said tube.