Abstract: The present invention relates to a method for charging the cell by electrodeposition of metal fuel on the anode thereof.

Abstract: The present invention relates to a reversible solid oxide electrochemical cell that may operate in two modes: a discharge mode (power generation) and a charge mode (electrolytic fuel production). A thermal system that utilizes a SOFB and is inclusive of selection of operating conditions that may enable roundtrip efficiencies exceeding about 80% to be realized is disclosed. Based on leverage of existing solid oxide fuel cell technology, the system concept is applicable to energy storage applications on the kW to MW scale.

Abstract: In a fuel cell system, a controller is programmed to control a first gas supply mechanism to deliver a first gas containing a fuel gas to a cathode in a pre-stop process performed at a system stop of the fuel cell system. The controller is programmed to control the first gas supply mechanism to stop the delivery of the first gas in a first state where a partial pressure difference between an anode and the cathode with respect to at least the fuel gas of remaining gases in the anode and in the cathode is reduced to or below a preset reference value.

Abstract: Apparatus, methods and systems reside in the decomposition of ammonia into a hydrogen-containing product mixture. An ammonia-rich gaseous mixture containing ammonia and oxygen enters a conduit, within which combustion and decomposition of the mixture is initiated, thereby liberating hydrogen. A mixture of products, resulting from the reactions, is expelled from the outlet of the conduit, the mixture including non-combusted hydrogen gas, which may then be used for other purposes. The incoming reactants, including ammonia and oxygen, are heat exchanged with the outgoing product mixture containing non-combusted hydrogen gas.

Abstract: The present invention relates to a method of operating a fuel cell system comprising one or more fuel cells with a proton exchange membrane, wherein the membrane is composed of a polymeric material comprising acid-doped polybenzimidazole (PBI). The method comprises adjusting the operating temperature of the fuel cell to between 120 and 250° C., supplying an oxidant stream to the cathode, and supplying a humidified fuel stream to the anode, said fuel stream comprising dimethyl ether, wherein dimethyl ether is directly oxidised at the anode.

Abstract: A PEM-fuel-cell-stack backup electric generator comprising: a fuel-cell stack, formed by a plurality of stacked PEM fuel cells electrically connected in series for supplying electrical energy to an electrical load; a cell-voltage monitor for measuring the voltage supplied by each fuel cell; an electrical-energy management and conditioning unit, connected between the fuel-cell stack and the electrical load; a blower for supplying the amount of air necessary for the chemical reactions that occur in the fuel cells; a hydrogen recirculator for recirculating hydrogen between the outlet and the inlet of the fuel-cell stack; a hydrogen-purging device for carrying out a primary purging of hydrogen at a lower flow rate, and a secondary purging of hydrogen at a higher flow rate; and a controller, programmed for managing operation of the electric generator differently at start-up, at shut-down, and during normal operation thereof.

Abstract: A fuel cell module includes in a casing: a fuel cell stack that is formed by stacking a plurality of unit cell; an oxidant gas distributing member that is disposed at a side surface, that extends in a stack direction of the unit cells, of the fuel cell stack that extends in a direction from one end to another end of each of the unit cells, and that supplies the oxidant gas to the another end of each unit cell after supplying the oxidant gas through the oxidant gas distributing member from the one end to the another end; a reformer disposed at the one end; and a combustion portion that is disposed between the one end and the reformer. The oxidant gas distributing member has a higher thermal conductivity at the one end side of the unit cells than at the another end side of the unit cells.

Abstract: The invention is a hydrogen passivation shut down system for a fuel cell power plant (10, 200). During shut down of the plant (10, 200), hydrogen fuel is permitted to transfer between an anode flow path (24, 24?) and a cathode flow path (38, 38?). A passive hydrogen bleed line (202) permits passage of a smallest amount of hydrogen into the fuel cell (12?) necessary to maintain the fuel cell (12?) in a passive state. A diffusion media (204) may be secured in fluid communication with the bleed line (202) to maintain a constant, slow rate of diffusion of the hydrogen into the fuel cell (12?) despite varying pressure differentials between the shutdown fuel cell (12?) and ambient atmosphere adjacent the cell (12?).

Abstract: An anode reactant recycling system for a fuel cell is disclosed, the system including a hollow main body, a bleed conduit, an injector, a water separator, and a hydrophilic porous media. The anode reactant recycling system for a fuel cell is adapted to minimize a required number of components, eliminate the need for the anode heat exchanger, use a single valve for removal of condensate and reactant byproducts from the anode reactant recycling system, and provide an upstream volume for startup pressurization.

Abstract: A fuel purification system includes a fuel cell stack and a fuel purification unit, such as a distillation unit. The fuel cell stack is adapted to provide heat to the fuel purification unit, and the fuel purification unit is adapted to provide a purified fuel to the fuel cell stack.

Abstract: A fuel cell system (1), especially for motor vehicles, is provided with at least one fuel cell (2), which has at least two electrodes (3) for connecting at least one electric user (4). Simplified operation is achieved if a voltage-measuring device (5), for measuring an electric voltage at the electrodes (3), is provided and if a control (15) actuates an anode gas feed device (6) as a function of the measured voltage.

Abstract: A thermally integrated fuel cell system includes a stack zone, a burner zone and a low temperature zone. The fuel is combined with steam and passed sequentially through a primary reformer and a secondary reformer or a radiative fuel heat exchanger. Air may be passed sequentially through an afterburner heat exchanger and a radiative air heat exchanger such that the radiative heat exchanger may be used to heat the stack zone. The stack exhaust is combusted in an afterburner. Afterburner exhaust heats the primary reformer, the high temperature air heat exchanger, the low temperature air heat exchanger and steam generator. The stack zone includes the stacks, the secondary reformer and the radiative heat exchanger. The burner zone includes the afterburner which includes a start burner, the primary reformer and the high temperature air heat exchanger. The low temperature zone includes the low temperature air heat exchanger and a steam generator.

Abstract: The present invention involves methods and apparatus for supplying hydrogen to a fuel cell to produce electricity. Water may be supplied in the form of steam for input to a catalytic converter. The converter may have a substrate element disposed therein coated with an oxide that may be oxidizable with steam and reducible back to an original state without use of a chemical agent. The steam may be converted to hydrogen and oxygen with the hydrogen channeled to an input and the oxygen channeled to an output of the fuel cell. The hydrogen output of the fuel cell and the oxygen may be combined to produce steam. The steam from the output may be recycled to the converter.

Abstract: A fuel cell system comprises a fuel gas supply conduit which supplies fuel gas to a fuel cell, a circulation conduit which returns discharged fuel gas discharged from the fuel cell to the fuel gas supply conduit, and a control device. When the control device determines that freezing may occur, the control device releases the discharged fuel gas from a water discharge valve of a gas-liquid separator provided in the circulation conduit to the outside, and reduces the flow volume of the discharged fuel gas returned to the fuel gas supply conduit in order to reduce moisture contained in the gas. Consequently, freezing can be prevented using a simple structure.

Abstract: A dual stack fuel cell system comprising a first fuel cell stack comprising a first anode side, adapted to receive fuel and to output a first anode exhaust, and a first cathode side, a second fuel cell stack comprising a second anode side, adapted to receive processed anode exhaust derived from the first anode exhaust and to output a second anode exhaust, and a second cathode side, adapted to receive oxidant gas and to output a first cathode exhaust, wherein the first cathode side receives at least the first cathode exhaust outputted from the second cathode side; and wherein the first fuel cell stack includes indirect internal reforming and the second fuel cell stack may not include any indirect internal reforming.

Abstract: A fuel cell system in which excess water vapor or nitrogen gas is prevented from remaining inside the fuel cell in intermittent operation. The fuel cell system is provided with a fuel cell having a cell stack formed by stacking a plurality of unit cells each having an anode electrode, a cathode electrode, an electrode membrane located between the anode electrode and the cathode electrode, and a reaction gas flow channel.

Abstract: An ejector apparatus for a fuel cell includes an ejector main body including an inlet port, an outlet port, a suction port, and an oxidizer-gas supply port, a first to third chambers provided in the body, a nozzle having a nozzle hole discharging the fuel gas, a diffuser mixing the fuel gas discharged from the nozzle hole and the fuel offgas exhausted from the fuel cell and returned to the suction port, a needle fixed on a side of the body and extending along an axial direction of the nozzle in a hollow portion thereof, and first and second diaphragms arranged to oppose each other, and changing an opening area in a gap between the nozzle hole and an outer peripheral face of a top end of the needle, wherein a pressure receiving area of the first diaphragm is set to be larger than that of the second diaphragm.

Abstract: A stop method for a fuel cell system including a fuel cell unit in which hydrogen is supplied to an anode, and air is supplied to a cathode so as to generate electrical power via an electrochemical reaction. The stop method includes the steps of stopping supply of hydrogen to the anode, electrically connecting the anode and the cathode via an electrical load, and supplying air to the anode.

Abstract: The invention relates to a high-temperature fuel cell system which can be operated with at least one hydrocarbon compound, preferably with methane or a gas containing methane such as natural gas or biogas. It is the object of the invention to increase the efficiency of high-temperature fuel cell systems and to allow a more flexible operation. In the system in accordance with the invention, individual fuel cells are present which are connected electrically in series and form the stacks.

Abstract: The invention relates to devices for operating fuel cells. According to the invention, the two functions “cooling” and “humidification” are combined in a functional unit (10) to adjust the temperature of the air (1) supplied as the reaction medium and to humidify it. Membranes (5) are used that consist of a temperature-resistant material.

Abstract: A fuel cell system (10) of the present invention comprises determination means (50) for consuming a fuel gas present at a gas leak detection portion of a fuel gas supply system (31, 32) through the power generation of a fuel cell (20), and performing a gas leak determination on the basis of a pressure decrease margin of the fuel gas present at the gas leak detection portion, and comprises discharge means (H51) for reducing the pressure at the gas leak detection portion by purging the fuel gas present at the gas leak detection portion to the outside of the fuel gas supply system (31, 32). By not only consuming the fuel gas present at the gas leak detection portion through power generation, but also purging the fuel gas to the outside of the fuel gas supply system, the pressure at the gas leak detection portion can be brought close to a target pressure within a short time period, and the gas leak determination can be performed in a short period of time and with a high level of precision.

Abstract: A thermal management system for high-temperature fuel cell mainly comprises a first mixer to introduce external fuel to a reformer, a reformer to adjust the gaseous fuel to a proper composition ratio and output the fuel to the anode input of the fuel cell, a second mixer to introduce external ambient air to the cathode input of the fuel cell, a cathode thermal cycle pipeline to deliver the high-temperature air from the cathode output of the fuel cell to pass through the second mixer and the reformer and also heat the second mixer and the reformer to recover the heat, an anode thermal cycle pipeline to introduce the water steam from the anode output of fuel cell, remaining fuel and thermal energy to the first mixer to mix with incoming fuel, and provide sufficient water-to-carbon ratio and the inlet temperature required for the reformer.

Abstract: A fuel cell system having a cooling water pump provided in cooling water piping that sends cooling water to a fuel cell and sending the cooling water under pressure, fuel gas supply piping connected to the fuel cell and supplying fuel gas to the fuel cell, fuel gas circulation piping connected to both the fuel cell and the fuel gas supply piping and circulating fuel gas, discharged from the fuel cell, in the fuel gas supply piping, and a fuel gas pump provided in the fuel gas circulation piping and sending under pressure the fuel gas, discharged from the fuel cell, to the fuel gas supply piping. After operation of the fuel cell is stopped, the fuel gas, discharged from the fuel cell, is sent under pressure by the fuel gas pump, and cooling water is send under pressure by the cooling water pump to cool the fuel cell to thereby reduce the temperature of the fuel cell to a level lower than the temperature of the fuel gas pump.

Abstract: A power generator comprising a hydrogen generator and a fuel cell stack having an anode exposed to hydrogen from the hydrogen generator and a cathode exposed to an ambient environment. Hydrophobic and hydrophilic layers are used to promote flow of water away from the cathode. A diffusion path thus separates the fuel cell cathode from the hydrogen generator. In one embodiment, water vapor generated from the fuel cell substantially matches water used by the hydrogen generator to generate hydrogen.

Abstract: A thermally integrated fuel cell system includes a stack zone, a burner zone and a low temperature zone. The fuel is combined with steam and passed sequentially through a primary reformer and a secondary reformer or a radiative fuel heat exchanger. Air may be passed sequentially through an afterburner heat exchanger and a radiative air heat exchanger such that the radiative heat exchanger may be used to heat the stack zone. The stack exhaust is combusted in an afterburner. Afterburner exhaust heats the primary reformer, the high temperature air heat exchanger, the low temperature air heat exchanger and steam generator. The stack zone includes the stacks, the secondary reformer and the radiative heat exchanger. The burner zone includes the afterburner which includes a start burner, the primary reformer and the high temperature air heat exchanger. The low temperature zone includes the low temperature air heat exchanger and a steam generator.

Abstract: The present invention provides a fuel control system and method, e.g., for a vehicle fuel cell system, which can efficiently supply hydrogen to a fuel cell stack and increase the efficiency of an ejector. For this purpose, the present invention provides a fuel control system having a series-connected multi-stage pressure control structure, in which an additional injector is provided in series between an injector for controlling the pressure of hydrogen supplied, a pressure control valve, or a pressure control actuator and a hydrogen recirculation ejector in a hydrogen supply passage, through which hydrogen is supplied from a hydrogen supply unit to a fuel cell stack, such that the pressure of hydrogen supplied is controlled in stages.

Abstract: An exhaust emission reduction system of a vehicle having an internal combustion engine with an at least one cylinder coupled to an exhaust system comprises a NOx reduction catalyst disposed in the exhaust system downstream of the engine exhaust system; and a fuel cell disposed in the exhaust system downstream of the NOx reduction catalyst.

Abstract: A reactor system is integrated internally within an anode-side cavity of a fuel cell. The reactor system is configured to convert higher hydrocarbons to smaller species while mitigating the lower production of solid carbon. The reactor system may incorporate one or more of a pre-reforming section, an anode exhaust gas recirculation device, and a reforming section.

Abstract: Process for the direct amination of hydrocarbons to aminohydrocarbons, which comprises the steps: a) reaction of a feed stream E comprising at least one hydrocarbon and at least one aminating reagent to form a reaction mixture R comprising aminohydrocarbons and hydrogen and b) electrochemical separation of at least part of the hydrogen formed in the reaction from the reaction mixture R by means of a gastight membrane-electrode assembly having at least one selectively proton-conducting membrane and at least one electrode catalyst on each side of the membrane, where at least part of the hydrogen is oxidized to protons over the anode catalyst on the retentate side of the membrane and the protons are, after passing through the membrane, b1) reduced to hydrogen and/or b2) reacted with oxygen from an oxygen-comprising stream O which is brought into contact with the permeate side of the membrane to form water over the cathode catalyst on the permeate side.

Abstract: Process for the direct amination of hydrocarbons to aminohydrocarbons by reaction of a feed stream E comprising at least one hydrocarbon and at least one aminating reagent to form a reaction mixture R comprising aminohydrocarbon and hydrogen in a reaction zone RZ and electrochemical separation of at least part of the hydrogen formed in the reaction from the reaction mixture R by means of a gastight membrane-electrode assembly having at least one selectively proton-conducting membrane and at least one electrode catalyst on each side of the membrane, where at least part of the hydrogen is oxidized to protons at the anode catalyst on the retentate side of the membrane and the protons pass through the membrane and on the permeate side are reacted with oxygen to form water, where the oxygen originates from an oxygen-comprising stream O which is brought into contact with the permeate side of the membrane, over the cathode catalyst.

Abstract: A fuel cell system includes a fuel cell stack and a fuel gas piping system which supplies a fuel gas to the fuel cell stack, and is capable of, at starting below a freezing point, selectively performing a rapid warm-up operation to generate electric power at an air stoichiometric ratio lower than that at starting at ordinary temperature, while revolving a circulating pump, and the fuel cell system further includes a clogging determination unit which determines whether or not clogging arises from freezing in a fuel gas passage of the fuel cell stack, or the fuel gas piping system, wherein when the clogging arises, the circulating pump is stopped in the rapid warm-up operation, and termination conditions of the rapid warm-up operation are changed in accordance with a clogging volume.

Abstract: A system for determining the concentration of hydrogen in an anode sub-system of a fuel cell system. The fuel cell system includes at least one fuel cell, an anode inlet, an anode outlet, an anode recirculation line, a source of hydrogen gas and an injector for injecting the hydrogen gas. First and second acoustic sensors are provided in the anode recirculation line and are spaced a known distance from each other. A controller that is responsive to the output signals from the first and second acoustic sensors determines the concentration of hydrogen gas in the anode recirculation line based on the time between when the controller receives the sensor signal from the first sensor and receives the sensor signal from the second sensor.

Abstract: A fuel cell includes a plurality of electrolyte electrode assemblies and a pair of separators sandwiching the electrolyte electrode assemblies. A fuel gas supply channel formed by a channel member fixed to the separator is connected to a fuel gas inlet formed in an inner end of a trapezoidal section. Unburned hydrogen in an exhaust fuel gas consumed in the reaction at the anode, and discharged from the fuel gas channel to an oxygen -containing gas supply unit, is mixed with an oxygen-containing gas before consumption, burned, and then supplied to an oxygen-containing gas channel.

Abstract: A fuel cell comprises an anode comprising an anode catalyst, a cathode comprising a gas diffusion electrode and a cathode catalyst on the gas diffusion electrode, a microfluidic channel contiguous with the anode, and a liquid comprising fuel in the channel. The concentration of the fuel in the liquid is 0.05-0.5 M.

Abstract: A system for delivering a supply fluid stream to a fuel cell stack that discharges an unused fluid stream is provided. A fuel supply is adapted to provide a pressurized supply fluid stream. An expander is in fluid communication with the fuel supply and is configured to receive the pressurized supply fluid stream to reduce the pressure of the pressurized supply fluid stream and to generate mechanical energy in response to reducing the pressure of the pressurized supply fluid stream. An electric machine is operably coupled to the expander and for selectively converting the mechanical energy generated by the expander into electrical energy. A compressor/blower is capable of being driven by at least one of the mechanical energy and the electrical energy to control the flow of the unused fluid stream to the fuel cell stack for recirculating the unused fluid stream back to the fuel cell stack.

Abstract: The amount of moisture discharged from within a fuel cell is increased by a simple construction. The fuel cell system includes a fuel cell for generating electrical power after causing an anode to receive a hydrogen-containing anode gas and causing a cathode to receive an oxygen-containing cathode gas; an exhaust gas valve provided downstream of the fuel cell in a gas circulation system that supplies an anode gas to the fuel cell; a regulator that is provided upstream of the fuel cell in the gas circulation system and raises gas pressure in the gas circulation system; and an ECU that opens the exhaust gas valve, with the gas pressure kept raised to a level higher than in normal times by use of the regulator. As a result of this, it is possible to increase the gas flow rate and flow velocity within the fuel cell, and it becomes possible to increase the discharge amount of moisture stagnating within the fuel cell.

Abstract: In at least one embodiment, a fuel cell anode exhaust system includes a fuel cell anode having an input and an output. The system also includes a first conduit loop communicating with the anode input and output. The system also includes a second conduit loop having an input and an output. The input and output communicate with the first conduit loop. A gas separator is disposed on the second conduit loop for purifying an exhaust stream fed into the gas separator.

Abstract: The present invention is directed to a fuel cell system having fuel cells, a supply flow path for supplying a fuel gas from a fuel supply source to the fuel cells; a variable gas supply device for regulating a gas condition of the supply flow path; a first control device for driving and controlling the variable gas supply device; an off-gas flow path configured to release a fuel off-gas from the fuel cells to the outside through a discharge valve; a second control device for driving and controlling the discharge valve; and a defect detection device for detecting a defect of the discharge valve. By using a gas supply command amount for the variable gas supply device, the defect detection device detects a valve opening defect that the discharge valve does not return from an open state to a closed state.

Abstract: A technique includes lowering a temperature of a cathode exhaust flow from an electrochemical cell to produce a second flow and routing the second flow to a contaminant trap.

Abstract: The present invention relates to a method for operating a fuel cell system, wherein the fuel cell system comprises at least one reformer for generating a reformate gas and at least one fuel cell for generating an electric current. An increased lifespan for the anode is achieved when with said anode an anode state value is continuously determined which correlates to a current degree of loading with carbon of the anode of the at least one fuel cell and when depending on the anode state value an oxygen-carbon ratio is varied in the reformate gas which is fed to the anode of the respective fuel cell.

Abstract: A fuel cell system (100) includes two supply passages (30, 32) for supplying the hydrogen to the anode (14). Valves (22, 23) which control flow amounts of the hydrogen passing through the two supply passages (30, 32) are provided. An exhaust passage (34) which outputs exhaust gas from the anode (14) is provided on the supply passage, and a valve (24) is also provided. When the valve (24) on the exhaust passage (34) is closed, the flow amount ratios of the hydrogen passing through the two supply passages (30, 32) are varied in time. Therefore, impurities such as nitrogen can be diffused. Thereby, a hydrogen purge amount can be reduced.

Abstract: An energy generation system includes a carbon reformer, an enthalpy wheel, and an electrochemical cell. The system allows production of electrical power using a variety of carbon-based fuels through a carbon monoxide intermediate and a means to isolate the carbon monoxide from waste products prior to injection into the fuel cell. The fuel cell oxidizes carbon monoxide and reduces oxygen spontaneously to develop electric current.

Abstract: A fuel cell system having an excellent orientation free performance by separating a fluid into a liquid and a gas without being affected by shaking and/or rotation of the fuel cell system includes a fuel cell main body, a first liquid/gas separation unit, and a buffer line. The fuel cell main body receives a fuel containing hydrogen and an oxidizing gas containing oxygen and generates electrical energy through an electrochemical reaction between the hydrogen and the oxygen. The first gas/liquid separation unit is installed on a first recycling line extending from an anode outlet of the fuel cell main body to separate a gas byproduct from unreacted fuel discharged through the anode outlet.

Abstract: A method for controlling a peripheral system (or a plurality of peripheral devices) and a fuel cell system using the same. The method includes: allocating an operation priority to the peripheral devices; storing information of the operation priority; and sequentially operating the peripheral devices by using electric energy stored in a small capacity electricity storage device according to the operation priority. The fuel cell system includes: the plurality of peripheral devices; an electricity storage device electrically connected with the peripheral devices; and a controller for sequentially operating the peripheral devices by using electric energy stored in the electricity storage device according to an operation priority.

Abstract: In a fuel cell unit that generates electric power using fuel gas supplied via an anode gas passage and air supplied via a cathode gas passage, an anode-off gas passage is connected to the downstream side of the anode gas passage. An orifice is provided at the anode-off gas passage and anode-off gas is discharged to the downstream side via the orifice.

Abstract: A flat fuel cell including: at least two unit cells, a casing provided with supports for each of said unit cells, said supports offering a bearing surface to a periphery of the unit cells, a sealing member interposed between the periphery of each unit cell and the surface of an associated support, and a cover forming a compression element coming into abutment on the periphery of each unit cell opposite the sealing member and cooperating directly with the associated support in order to provide compression of the sealing member.

Abstract: Disclosed is a gas-liquid separator capable of allowing carbon dioxide to be exhausted to the atmosphere so as to recover and recycle only unreacted fuel discharged from an electric generator, and a fuel cell system having the same. The fuel cell system includes an electric generator to generate electricity by electrochemical reaction between hydrogen and oxygen, a fuel feeder to supply hydrogen containing fuel to the electric generator, an oxidant feeder to supply oxygen to the electric generator, and a recovering unit to recover unreacted fuel generated during the electrochemical reaction in the electric generator and supply the unreacted fuel to the fuel feeder. The recovering unit comprises a frame structure, and a gas-liquid separation film partially surrounding the frame structure. The gas-liquid separator forms a flow space inside the frame structure.

Abstract: A fuel cell system includes a fuel cell for generating electric power by using a fuel, a valve module that controls a flow of a low concentration fuel circulating through the fuel cell, and a flow of a high concentration fuel supplied from a fuel storage unit to the fuel cell, a pump for pumping at least one of the low concentration fuel and the high concentration fuel according to a fuel flow control of the valve module; and a mixer for mixing and supplying the low concentration fuel and the high concentration fuel pumped from the pump to the fuel cell.

Abstract: A technique includes operating a fuel cell, which produces an effluent flow. The technique includes routing the effluent flow through an electrochemical pump to extract fuel from the effluent flow and providing the extracted fuel to the fuel cell.

Abstract: A system and method for controlling the speed of a recirculation pump in an anode recirculation loop of a fuel cell system based on a predetermined ratio of fresh hydrogen to recirculated anode gas. The system uses a model to determine the volume flow of the recirculated gas through a fuel cell stack to determine the recirculation rate based on a measured temperature of the recirculated gas, a measured pressure drop across a recirculation pump, a pressure drop across the anode inlet and outlet of the stack, a percentage of hydrogen in the recirculated gas, and the density of the recirculated gas.