Systems and methods for controlling on-board generation and use of hydrogen fuel mixtures

Abstract

This is a system for generating hydrogen on-board the vehicle from compressed natural gas (CNG) in select ratios to create hydrogen-enriched CNG (HCNG) fuel for use in internal combustion engines. The on-board generation of hydrogen is comprised of a reforming system of CNG fuel with direct contact with exhaust gases. The reforming system controls for production of HCNG fuel mixtures is based on specific engine operating conditions. The vehicle's engine controls and operating parameters are modified for combustion of selective ratios of HCNG fuel mixtures throughout engine operating cycle. The reforming system controls and engine controls modifications are also used to minimize combustion emissions and optimize engine performance.

Claims

1. An engine system, comprising: an on-board vehicle system configured to operate on-board a vehicle, the on-board vehicle system including: a combustion system configured to combust natural gas to generate energy and exhaust gas; a pre-reforming system configured to receive unreformed natural gas and coupled to the combustion system to receive at least a portion of the exhaust gas, the pre-reforming system configured to generate a partial oxidation reaction between the unreformed natural gas and the exhaust gas to generate partial oxidation reaction products; a reforming system including a steam reformer, a carbon dioxide reformer, and a first water-gas-shift reformer, the reforming system coupled to the pre-reforming system and configured to reform the partial oxidation reaction products to produce reformed natural gas; a mixing system coupled to the reforming system and configured to mix reformed natural gas and unreformed natural gas that is provided as the natural gas to the combustion system; and a reforming control system coupled to the pre-reforming system and configured to control the supply of the exhaust gas to the pre-forming system so the supplied exhaust gas has a first ratio with the unreformed natural gas based on a first operating condition and is configured to control the supply of the exhaust gas so the supplied exhaust gas has a second ratio with the unreformed natural gas based on a second operating condition.

2. The engine system of claim 1, wherein the reforming control system is further configured to control an amount of the unreformed natural gas delivered to the pre-reforming system as a ratio with the generated exhaust gas.

3. The engine system of claim 1 further comprising an engine control unit, and wherein the reforming system is integrated with the engine control unit.

4. The engine system of claim 3, wherein the reforming control system is configured to extract the exhaust gasses from the combustion system based on inputs from the engine control unit for required amounts of steam and carbon dioxide for generation of hydrogen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments are illustrated in the referenced figures of the drawings. It is intended that the embodiments and the figures disclosed herein are to be considered illustrative rather than limiting.

(2) FIG. 1 is the equilibrium concentration graph for a steam methane reformer, illustrating the concentrations of CH.sub.4, CO.sub.2, CO, H.sub.2O and H.sub.2 in moles versus temperature in degrees Celsius (C) and at initial conditions CH.sub.4 is 1 mole for this illustration.

(3) FIG. 2 is a block diagram of a process flow for steam-methane reforming in a prior art

(4) FIG. 3 is a schematic view of a system on-board a vehicle for producing HCNG

(5) FIG. 4 is a block diagram illustrating a process flow in an on-board vehicle system for producing a hydrogen-enriched natural gas fuel

(6) FIG. 5 is a block diagram illustrating the interaction and connectivity between the Reforming System Controls and Engine Controls Unit and the Reformers and Reactors of the System

(7) FIG. 6 is a block diagram illustrating steps in producing HCNG on-board a vehicle

DETAILED DESCRIPTION

(8) The following definitions are used in the present disclosure. CNG means compressed natural gas; HCNG means Hydrogen-enriched compressed natural gas; CH.sub.4 is the chemical composition of methane, the main component of natural gas; POX means Partial Oxidation process in methane reforming as described by reaction III; Hydrogen Ratio in HCNG refers to weight and not volume.

(9) FIG. 3 is a schematic view of an on-board vehicle system for producing HCNG. Engine exhaust gases are used for the reforming process as most reactions in these systems are highly endothermic and require high temperatures for the conversion of CH.sub.4 to hydrogen. CNG and HCNG combustion exhaust gases contain the water vapor or steam necessary for the reforming of methane which eliminates the need for dedicated water supply tanks and heat exchangers for steam production. Not only does this decrease vehicle weight and deliver energy cost savings, but the recirculation of exhaust gases through the reforming system further reduces engine emissions.

(10) The first step in the on-board vehicle methane reforming process is POX reforming of CNG due to the excess air present in exhaust gases. HCNG requires excess air fuel ratios in the combustion process. POX reactions are exothermic and provide additional heat to the reforming system. The reforming controls system responds to engine operating conditions and inputs from the engine controls unit to determine the both the amount of exhaust gases to be extracted and the input quantity of methane for the POX reactions. The resulting POX reaction products are injected into the CNG reforming system. The CNG is reformed in both a steam reformer and a carbon dioxide reformer at high temperatures in presence of catalysts to generate a hydrogen-rich gas stream. Both reforming reactions are highly endothermic, requiring heat and high temperatures, which is supplied by both POX exothermic reactions and exhaust gases. The hydrogen-rich gas stream is then treated in a Water Gas Shift reactor (WGS) with a catalyst to reduce carbon monoxide (CO) concentrations and generate additional hydrogen. A second WGS reactor may be implemented at lower temperatures to produce a more pure hydrogen gas stream. The next step is mixing the hydrogen-rich gas stream with CNG to generate HCNG fuel for engine combustion. The ratios of hydrogen in HCNG fuel are calibrated by the reforming system controls based on engine operating conditions. Also, engine controls unit modifications and adjustments are configured for HCNG fuel mixtures.

(11) FIG. 4 illustrates a System (10) for the On-Board Vehicle production of HCNG as an alternative fuel according to one embodiment of the present invention. The following are the named processes or systems that are components of a System (10) as represented in FIG. 4:

(12) 12 Motor Vehicle

(13) 14 Reforming System Controls

(14) 16 Reforming System

(15) 18 Engine Controls Unit (ECU)

(16) 20 Vehicle Engine

(17) 22 POX Reforming Reactor

(18) 24 Steam Reformer

(19) 26 Carbon Dioxide Reformer

(20) 28 Water Gas Shift Reactor 1 (WGS1)

(21) 30 Water Gas Shift Reactor 2 (WGS2)

(22) 32 HCNG Mixing Apparatus

(23) 34 Vehicle Main CNG Fuel Tank

(24) 35 Process

(25) 36 Control Systems

(26) FIG. 4 depicts a System (10) that includes a Reforming System (16), Reforming Controls (14), and an ECU (18) on-board a Motor Vehicle (12). The Reforming System (16) may include the following components: POX Reactor (22), Steam Reformer (24), Carbon Dioxide Reformer (26), WGS1 (28), WGS2 (30). The Reforming System (16) produces a hydrogen-rich gas stream that is blended with CNG in a Mixing Apparatus (32) to produce an HCNG fuel supply for a Vehicle Engine (20). A Process (35) is the synchronized configuration of the Reforming System Controls (14) and ECU (18) for the operation of the Reforming System (12) and Vehicle Engine (20). Reforming System Controls (14) manage production of selective ratios of hydrogen in HCNG fuel based on engine operating conditions. The weight ratio of hydrogen in HCNG fuel can range from 20% to 30% depending on engine cycle requirements.

(27) The Reforming System (16) is located on-board the Motor Vehicle (12) in FIG. 4. The Reforming System (16) produces a hydrogen-enriched gas stream by methane reforming in the following sequence of processes: POX Reforming Reactor (22), Steam Reformer (24), Carbon Dioxide Reformer (26), WGS1 (28), and WGS2 (30). The gas flow inputs to the Reforming System (16) are methane in the form of CNG from the Vehicle Main CNG Fuel Tank (34) and exhaust gases from the engine combustion process. The Reforming System (16) controls CNG flows and the amount of exhaust gas extracted for use in powering the vehicle 12. The calibrated extraction of exhaust gas supplies the required amounts of steam and carbon dioxide in methane Reformers (24) and (26). Prior to Reformers (24) and (26) the exhaust gases react with methane in the POX Reforming Reactor (22) based on the amount of excess air fuel ratio in the combustor process. The combustor operation with HCNG, in preferred embodiments, is best optimized for emissions and performance with excess air fuel ratios in the 1.3 to 1.8 range. To use exhaust gases in direct contact with methane in Reformers (24), (26), (28), and (30) the concentration of oxygen is minimized by POX Reforming Reactor (22) Reaction III:
CH.sub.4+O.sub.2.fwdarw.CO+2H.sub.2(III)

(28) Reaction III generates 2 moles of hydrogen for every 1 mole of CH.sub.4 supplied to the POX Reforming Reactor (22). The data interchange between the ECU (18) and the Reforming System Controls (14) determines exhaust gas and CNG flows required for the POX Reforming Reactor (22) operation. The POX Reforming Reactor (22) operates in sub-stoichiometric conditions and supplies additional heat or energy input for endothermic reactions in Reformers (24), (26), (28), and (30). The hydrogen generation from the POX Reforming Reactor (22) contributes a smaller H.sub.2 ratio to HCNG fuel; most of the hydrogen generated by the System (10) occurs in the other Reforming Reactions of components (24), (26), (28), and (30).

(29) The Reforming System (16) depicted in FIG. 4 includes the Steam Reformer (24) configured to generate hydrogen through reaction of methane with water vapor as shown in Reaction I:
CH.sub.4+H.sub.2O.fwdarw.CO+3 H.sub.2(I)

(30) Reactions in Steam Reformer (24) occur in the presence of catalysts, such as nickel-based catalysts, operating in a temperature range between 650 C. and 900 C. Water vapor in exhaust gases supply the steam required for the Steam Reformer (24). Direct contact of exhaust gases with methane in Steam Reformer (24) provides needed temperature, heat and energy for the reactions with the added benefit of not damaging the catalysts. The direct contact method construct also eliminates the need for installing a heat exchanger in the on-board System (10). The Steam Reformer (24) contains catalysts in reaction tubes to maximize contact of reactive gases with catalyst surfaces. The flow of both exhaust gases and CNG to the Steam Reformer (24) is monitored and controlled by the Reforming System Controls (14). Note that the catalysts are not limited to the aforementioned example and one skilled in the art will recognize this fact.

(31) The Reforming System (16) depicted in FIG. 4 includes the Carbon Dioxide Reformer (26) configured to generate hydrogen through reaction of methane with carbon dioxide as shown in Reaction IV:
CO.sub.2+CH.sub.4.fwdarw.2H.sub.2+2CO(IV)

(32) Reactions in Carbon Dioxide Reformer (26) occur in the presence of catalysts, such as rhodium and iron-based catalysts, operating in a temperature range between 700 C. to 800 C. (Note that the catalysts are not limited to the aforementioned example and one skilled in the art will recognize this fact.) Exhaust gases supply the CO.sub.2 required for the Carbon Dioxide Reformer (26). Direct contact of exhaust gases with CH.sub.4 in Carbon Dioxide Reformer (26) provides needed temperature, heat and energy for the reactions with the added benefit of not damaging the catalysts. This direct contact method also eliminates the need for installing a heat exchanger in the System (10). The Carbon Dioxide Reformer (26) contains catalysts in reaction tubes to maximize contact of reactive gases with catalyst surfaces. The flow of both exhaust gases and CNG to the Carbon Dioxide Reformer (26) is monitored and controlled by the Reforming System Controls (14).

(33) Reactions I and IV demonstrate that 5 moles of hydrogen is generated for every 2 moles of CH.sub.4 input to Reformers (24) and (26). Water Gas Shift reactions in WGS1 (28) and WGS2 (30) provide one additional mole of H.sub.2 for hydrogen enrichment of CNG fuel as shown in Reaction II:
CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2(II)

(34) The WGS1 (28) operates between 350 C. and 420 C. and employs catalysts, such as iron oxide-based catalysts, to convert CO formed in Reactions I and IV to hydrogen. CO concentrations in the Reforming System (16) hydrogen-rich gas stream exiting WGS1 (28) are reduced to less than 4%. Note that the catalysts are not limited to the aforementioned example and one skilled in the art will recognize this fact.

(35) The Reforming System (16) may employ a second WGS2 to further reduce CO concentrations in the gas stream. Because it operates at temperatures below 200 C., characterized by costly catalysts and slow reaction kinetics, WGS (30) should be used in systems requiring purer forms of hydrogen.

(36) Fuel Cell applications require stringently pure hydrogen for operation. In the Prior Art, the removal of impurities from a hydrogen-rich gas stream requires a significant investment in capital assets, operating expense, high energy consumption. Unlike Fuel Cell systems, the impurities in HCNG fuel hydrogen do not have a negative effect on the operation or performance of the Vehicle Engine (20) in the System (10).

(37) A hydrogen-rich gas stream from the Reforming System (16) is blended with CNG fuel in the HCNG Mixing Apparatus (32) to produce HCNG fuel for Vehicle Engine (20) combustion as shown in FIG. 4. Hydrogen for enrichment of CNG to create HCNG is generated by the System (10) on-demand at no additional cost to the Motor Vehicle (12) operator. This Just-in-Time process eliminates the cost and inefficiencies associated purchasing and storing hydrogen for use as a motor vehicle fuel both on-board the vehicle and upstream throughout the hydrogen fuel supply chain. Because hydrogen is generated on-demand in the System (10), Motor Vehicles (12) do not require the weight, space consumption, operating inefficiencies, and additional costs associated with existing hydrogen fuel systems.

(38) The Control Systems (36) for the System 10) is depicted in FIG. 5. The Control Systems (36) consists of two control modules: the Reforming System Controls (14) and the Engine Controls Unit or ECU (18). The Reforming System Controls (14) monitor and manage the on-board vehicle generation of hydrogen by producing selective H.sub.2 ratios in HCNG fuel mixtures for the System (10).

(39) FIG. 5 illustrates how the Reforming System Controls (14) and ECU (18) are connected by Data Link (40) to ensure the synchronized operation of the Reforming System (16) and Vehicle Engine (20). The ECU (18) collects operational and parametric data from the Vehicle Engine (20) then transmits that data to the Reforming System Controls (14). This data exchange calibrates the amount of engine exhaust gases to be extracted for the Reforming System (16) operation. Reforming System Controls (14) manage the flow rates of CNG and exhaust gas to the Reforming System (16). The CNG flow rate to POX (22) is based on excess air in the exhaust gas composition. The ECU (18) communicates air-fuel ratio from the combustion process to the Reforming System Controls (14) to determine the CNG flow rate to POX (22) for reaction with oxygen.

(40) The Reforming System Controls (14) determine the flow of CNG to Reformers (22), (24), and (26) to produce hydrogen in selective quantities. This is synchronized with the flow of exhaust gas to the Reforming System (16) to supply the correct amount of steam and CO.sub.2 required for the generation of hydrogen. The ECU (18) transmits Vehicle Engine (20) operating data, including fuel flow rate and combustor efficiency, to the Reformer System Controls (14) which determines the specific amount of H.sub.2O and CO.sub.2 in the Vehicle Engine (20) exhaust gas.

(41) The Reforming System Controls (14) monitor and manage the flow rate of the hydrogen-rich gas stream and CNG to the Mixing Apparatus (32) to produce selective hydrogen ratios in HCNG fuel. The hydrogen ratios range from 20% to 30% of the HCNG fuel mixtures. The H.sub.2 ratio is based on engine operating data for optimal performance and emission controls. The Reforming System Controls (14) communicates the H.sub.2 ratio to the ECU (18) for setting combustor operating parameters.

(42) The ECU (18) is configured for HCNG fuel to increase efficiency, power output and to reduce emissions in the Vehicle Engine (20). The ECU (18) monitors and manages Vehicle Engine (20) parameters for combustion process for HCNG fuel throughout the Vehicle Engine's (20) complete operating cycle. A principle advantage of HCNG fuel is combustion with excess air fuel ratios. The addition of hydrogen raises CNG's lean burn limit which reduces Vehicle Engine (20) emissions, especially NOx and CO , and decreases fuel consumption. The lean burn limit of HCNG is increased because of the faster burn speed, flame velocity, and laminar burn properties of hydrogen . The ECU (18) can vary the excess air fuel ratio from 1.3 to 1.8 based on the Vehicle Engine's (30) operating data and the HCNG fuel's H.sub.2 ratio.

(43) HCNG fuel combustion with excess air fuel ratios requires ECU (18) to adjust ignition timing parameters based on operating conditions and H.sub.2 ratio. The ignition timing adjustments are optimized along with H.sub.2 ratios and excess air fuel ratios to increase engine efficiency, power output and to reduce exhaust emissions. Ignition timing configuration in ECU (18) is significant to engine (20) operation with HCNG fuel in order to avoid engine knock and increased NOx emissions.

(44) FIG. 6 is a block diagram illustrating the steps of the System (10) for producing HCNG on-board a Motor Vehicle (12). These steps may vary depending on the application. For example, some applications may not require the WGS2 step which delivers a higher level of hydrogen purity.

(45) The steps of the method in FIG. 6 include: Supply Compressed Natural Gas (CNG) to the Reforming System (16) in FIG. 4; Supply Vehicle Engine (20) exhaust gas to the Reforming System (16) in FIG. 4; Reacting CNG with exhaust gas in the POX Reforming Reactor (22); Reacting Steam from POX reaction products with CNG in a Steam Reformer (24) to produce a hydrogen-rich gas stream; Reacting CO.sub.2 from POX reaction products with CNG in a Carbon Dioxide Reformer (26) to produce a hydrogen-rich gas stream; Reacting Steam from POX reaction products with hydrogen-rich gas streams in Water Gas Shift Reactor 1 (28) to remove carbon monoxide (CO) and produce additional hydrogen; Reacting Steam from POX reaction products with hydrogen-rich gas streams in Water Gas Shift Reactor 2 (30) to further purify hydrogen; Mixing and blending the hydrogen-rich gas stream with CNG in the HCNG Mixing Apparatus (32) to produce HCNG alternative fuel.

(46) While the invention has been described with reference to certain preferred embodiments, as will be apparent to those skilled in the art, certain changes and modifications can be made without departing from the scope of the invention. Moreover, the foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. Similarly, the embodiments of the present invention and aspects thereof are described and illustrated in conjunction with a system and synchronized process, which are meant to be exemplary and illustrative, not limiting in scope.

(47) In the present disclosure, certain details are set forth in conjunction with the described embodiments of the present invention to provide a sufficient understanding of the invention. One skilled in the art will appreciate, however, that the invention may be practiced without these particular details. Furthermore, one skilled in the art will appreciate that the example embodiments described do not limit the scope of the present invention, and will also understand that various modifications, equivalents, and combinations of the disclosed embodiments and components of such embodiments are within the scope of the present invention. Embodiments including fewer than all the components of any of the respective described embodiments may also be within the scope of the present invention although not expressly described in detail. Finally, the operation of well-known components and/or processes has not been shown or described in detail below to avoid unnecessarily obscuring the present invention.