Abstract: Technologies are generally described for recovery of energy from engines. The described technology may be applied to systems, methods, and/or apparatuses. An example exhaust energy recovery apparatus (50) may include at least one thermal to electrical energy conversion element (60) having at least one side for thermal coupling along a substantial length (34, 35, 36) of an exhaust duct (30) for a combustion engine. The example apparatus (50) may also include a cover (52) located over at least a portion of the exhaust duct (30) adjacent to the at least one energy conversion element (60). A channel (53) may be formed between the cover (52) and an exterior portion of the exhaust duct (30), the channel having at least one inlet (54, 56) for admission of cooling fluid.

Abstract: A method is provided for controlling varnish build-up in a variable geometry turbine (VGT) of a diesel engine turbocharger. According to the method, it is determined whether an operation parameter is at a level established for initiating a varnish build-up control sequence. Upon determining that the operation parameter is at the established level, the varnish build-up control sequence is initiated. The sequence comprises increasing exhaust temperature upstream of the VGT to a first exhaust temperature, and changing an opening size of a VGT nozzle between a smaller and a larger opening size in association with increasing the exhaust temperature to the first exhaust temperature. A diesel engine arrangement is also provided.

Abstract: An exhaust gas heat exchanger includes a tube through which exhaust gas flows, a fin disposed in the tube, and protruded tabs protruded from the tube or the fin. Each of the protruded tabs is inclined to an upstream side, and has a polygonal shape more than a quadrilateral shape having at least a bottom side, one lateral side and another lateral side. An angle of the one lateral side to the bottom side is set smaller than 90 degrees and than an angle of the other lateral side to the bottom side. The bottom side is placed to intersect with a perpendicular direction to the exhaust gas flow direction, and the other lateral side is located upstream from the one lateral side. According to the exhaust gas heat exchanger, it is possible to improve heat exchange efficiency by generating a swirl flow for facilitating heat transfer effectively.

Abstract: Various methods and systems are provided for cooling exhaust system components. In one example, a method comprises directing compressed air onto an exterior of an engine exhaust passage valve.

Abstract: An exhaust system for an engine is disclosed herein. The exhaust system includes a catalytic converter, an exhaust manifold upstream from the catalytic converter, and a heat pipe in thermal contact with the exhaust manifold and atmosphere. The system further includes a phase changing material that passively absorbs heat after catalytic light-off.

Abstract: A tractor-trailer truck engine coolant manifold comprises a first supply port for receiving coolant from an engine or radiator, and a first return port for returning coolant to the engine or radiator. The manifold also has a second supply port in fluid communication with the first supply port, and a second return port in fluid communication with the first return port. Further, the manifold can have a third supply port in fluid communication with the first supply port, and a third return port in fluid communication with the first return port. The coolant manifold can further have one or more internal flow paths that are configured so that coolant flow rate or pressure exiting one supply port is different from the coolant flow rate or pressure exiting from another supply port, pre-selected based upon the thermal requirements of the heat source or heat sink components.

Abstract: A transport refrigeration system includes a transport refrigeration unit having a refrigerant circuit through which a refrigerant is circulated in heat exchange relationship with air drawn from a cargo box, a fuel-fired engine for powering the refrigeration unit and having an exhaust system through which exhaust gases generated by the engine are discharged and an engine coolant circuit, an engine exhaust gases to engine coolant heat exchanger, and an engine coolant circuit to refrigeration unit heat exchanger.

Abstract: An object of the invention is to prevent a situation in which failure diagnosis for an exhaust system component in an internal combustion engine cannot be completed from continuing for an unduly long period of time. A warm-up system for an exhaust system of an internal combustion engine according to the invention includes a warm-up control performing unit that performs warm-up control for warming up an exhaust system component upon start-up of the internal combustion engine and a failure diagnosis performing unit that performs failure diagnosis for the exhaust system component after the completion of warm-up of the exhaust system component.

Abstract: A heat exchanger plate for an evaporator includes a flow transverse distribution device. Disks of the flow transverse distribution device conduct the medium to be evaporated to the flow channel extending in the direction of the longitudinal axis. The disks include openings allowing a flow of the medium in the direction of the longitudinal axis with comparatively higher flow resistance than in the direction of the transverse axis. The number of disks arranged one behind the other in the direction of the longitudinal axis varies over the width of the heat exchanger plate in the direction of the transverse axis. On each width section, in which the entry of the medium into the disks arranged one behind the other is intended, the comparatively largest number of disks is provided one behind the other. As the distance from the entrance increases, the number decreases in the direction of the transverse axis.

Abstract: A heat exchanger (10) is provided and in a highly preferred form is an EGR cooler (52) having first and second passes (56A,56B) that are connected to an inlet/outlet manifold (70) by a pair of corresponding thermal expansion joints (87,93) to allow differential thermal expansion between the various structural components of the heat exchanger (10).

Abstract: A combined emission control device and exhaust gas heat exchanger for connection to the exhaust gas flow from an engine of a motor vehicle is disclosed having a number of exhaust gas transfer passages and a number of coolant passages so as to permit heat to be transferred from exhaust gas flowing through the exhaust gas heat exchanger to coolant used to supply heating for a cabin of the motor vehicle. The exhaust gas heat exchanger includes a tapping to permit cooled exhaust gas to be extracted for use in a Low Pressure Exhaust Gas Recirculation system. The exhaust gas heat exchanger thereby provides dual functionality being able to recuperate heat for use in a cabin heater and cool exhaust gas for use in the Low Pressure Exhaust Gas Recirculation system.

Abstract: An exhaust gas manifold having thermoelectric devices in the exhaust manifold of a stirling engine is disclosed.

Abstract: A heater tube for an exhaust system is disclosed. The heater tube may have an open end to receive heated exhaust from a pre-heater. The heater tube may have a closed end located opposite the open end. The heater tube may also have an outer surface extending from the open end to the closed end. The heater tube may further have a fin attached to the outer surface. In addition, the heater tube may have an opening disposed on the outer surface to discharge the heated exhaust.

Abstract: A heat exchanger (18) is provided for an internal combustion engine (1) for heat transfer between a gas stream (8) and a working medium stream (10). The heat exchanger (18) comprises a housing (28), which encloses a gas path (38), and with at least one spiral tube (29), which carries a working medium path (30) and which is arranged in the gas path (38) and which extends helically in relation to the central longitudinal axis (31) of the housing (28). Increased fatigue strength is achieved with an elastic outer mounting layer (32). The elastic outer mounting layer (32) is arranged between the housing (28) and the at least one spiral tube (29).

Abstract: Systems, methods, and computer readable storage media are described in which exhaust gas is routed to a hydrocarbon retaining device during starting, and purged to the engine intake manifold. Various alternative approaches are described for controlling operation and diagnosing degradation. Further, various interrelated configurations are described.

Abstract: A system for regenerating a particulate filter mounted on an exhaust pipe of a gasoline engine including a plurality of cylinders and an ignition device for igniting fuel and air in the cylinder, a three-way catalyst device mounted on the exhaust pipe connected to the gasoline engine, and to oxidize or reduce exhaust gas, the particulate filter mounted on the exhaust pipe downstream of the three-way catalyst device to trap particulate matter and regenerate the particulate matter using heat of the exhaust gas, a differential pressure sensor mounted upstream and downstream of the particulate filter and to measure a pressure difference of the particulate filter, and a control portion to receive the measured pressure difference and control parameters to determine an amount of non-ignited fuel which is not ignited and flows to the three-way catalyst device among the fuel flowing into the plurality of cylinders.

Abstract: An internal combustion engine is coupled to an electric power generator. An exhaust manifold for the engine includes an exhaust gas conduit. A housing includes a catalyst in fluid communication with the conduit to receive exhaust produced by the engine. The catalyst is operable to reduce one or more constituents of the exhaust.

Abstract: A motor vehicle exhaust system, including at least one pollutant-removing member, for example a catalytic converter or a particle filter, including a first outlet and connected to an exhaust line of an associated vehicle, and a second outlet for collecting exhaust gases with a view to recycling the same, the second outlet being connected to an inlet pipe of an exchanger for cooling exhaust gases, an outlet pipe of which is connected to a housing that receives a valve for controlling exhaust gases. The housing of the control valve includes a sole plate to be attached to an end sole plate of the outlet pipe of the exchanger, and the housing is attached directly onto a body of the exchanger.

Abstract: A heat transfer apparatus and system for transferring heat for use onboard a vehicle includes a conductor arranged to conduct fluid transferring heat from a vehicle engine to a heat exchanger to heat a second fluid to heat and/or dry utility compartments of the vehicle. The heat transfer system includes a tube arranged to conduct fluid so that heat is transferred from the exhaust gas to the fluid.

Abstract: A system and method of operating a waste heat recovery system for a vehicle is provided. The system includes an expander/compressor portion mechanically linked to wheels of the vehicle, the expander/compressor portion including an inlet valve and an exhaust valve. A combustion engine is provided having an exhaust portion. A working fluid path is thermally coupled between the combustion engine and a working fluid, the working fluid path being fluidly coupled to the expander/compressor portion. A boiler portion is fluidly coupled to the working fluid path, the boiler portion further being thermally coupled to the exhaust portion. An accumulator tank portion having a cavity is operative to receive and store the working fluid, the accumulator tank portion fluidly coupled to the inlet valve and the exhaust valve. A condenser is fluidly coupled to the working fluid path and the exhaust valve.

Abstract: A vehicle includes a coolant circuit that circulates a flow of an engine coolant therethrough. The coolant circuit includes an Exhaust Gas Heat Recover (EGHR) system for transferring heat from a flow of exhaust gas from an internal combustion engine to the flow of the engine coolant. A control valve is disposed downstream of the EGHR system, and directs the flow of the engine coolant along either a first fluid flow path back to the internal combustion engine to heat the internal combustion engine, or a second fluid flow path including a transmission fluid warming system to heat a supply of transmission fluid to reduce transmission spin loss.

Abstract: A method and to a device for the regeneration of a particle filter arranged in the exhaust gas tract of an internal combustion engine with at least one NO oxidation catalyst for the oxidation of NO, especially to NO2, which is arranged upstream of the particle filter and through which an exhaust gas stream flows. At least one heater, especially a heating catalyst, through which another gas stream, i.e., a second exhaust gas stream, flows and which heats the additional gas steam, is provided upstream of the particle filter. The heated additional gas stream is mixed upstream of the particle filter with the exhaust gas stream coming from the NO oxidation catalyst, i.e., the gas stream loaded in particular with NO2.

Abstract: The disclosure provides a waste heat recovery (WHR) system including a Rankine cycle (RC) subsystem for converting heat of exhaust gas from an internal combustion engine, and an internal combustion engine including the same. The WHR system includes an exhaust gas heat exchanger that is fluidly coupled downstream of an exhaust aftertreatment system and is adapted to transfer heat from the exhaust gas to a working fluid of the RC subsystem. An energy conversion device is fluidly coupled to the exhaust gas heat exchanger and is adapted to receive the vaporized working fluid and convert the energy of the transferred heat. The WHR system includes a control module adapted to control at least one parameter of the RC subsystem based on a detected aftertreatment event of a predetermined thermal management strategy of the aftertreatment system.

Abstract: The invention relates to a latent heat storage catalyst (3) for an exhaust system (1) in an internal combustion engine, in particular of a motor vehicle, comprising a member (5) that includes several parallel ducts (6). First ducts (6?) contain a phase change material (7), and second ducts (6?) have a catalytic coating (14). In order to be able to produce said latent heat storage catalyst at a low cost, the member (5) is formed by at least one layered structure (9) comprising two metal sheets (10, 11), at least one of which is corrugated and which rest against each other and are attached to one another such that the ridges of the at least one corrugated metal sheet (10) form the ducts (6).

Abstract: A device for cooling an exhaust gas stream, having an exhaust gas pipe receiving the exhaust gas stream, the exhaust gas pipe being surrounded at least in places by a heat shield arranged spaced therefrom, which together with the outside of the exhaust gas pipe forms a convection region for air supplied from the surrounding environment. A mouth region of the exhaust gas pipe extended relative to the heat shield projects in such a way into an open end of an adjoining outlet port that a reduced pressure relative to the surrounding environment may be produced in a suction region between the mouth region of the exhaust gas pipe and the outlet port as the air heated in the convection region due to the exhaust gas stream rises.

Abstract: A system for controlling regeneration in an after-treatment component comprises a feedback module, an error module, a gain module, and a regeneration control module. The feedback module is configured for determining a rate of change of the value of a controlled parameter. The error module is in communication with the feedback module and is configured for determining a value of an error term by subtracting a value of a target parameter from the value of the controlled parameter. The gain module is configured for determining a value of a proportional gain factor by raising a mathematical constant “e” to the negative power of the value of a tuned gain exponent and for determining a value of a derivative gain factor by multiplying the value of the proportional gain factor by a tuning factor. The regeneration control module is configured for determining a value of a rational control increment.

Abstract: An integrated load bank and exhaust heater for a diesel genset exhaust aftertreatment system of the type having a diesel particulate filter (DPF) and a selective catalytic reduction (SCR) section. The load bank/heater can function as a load bank when testing the genset, as a heat source to optimize SCR efficiency, as to thermally regenerate the DPF filter.

Abstract: A thermoelectric generator unit, in particular for coupling to an exhaust gas pipe of an internal combustion engine, comprises at least one inner tube (16) having gas flowing therein and whose outer circumference comprises at least one flat portion (24). An oval outer housing (12) completely surrounds the inner tube (16) in circumferential direction. A plurality of thermoelectric modules (14) are arranged on the flat portions (24) of the inner tube (16). At least one cooling element (18) is provided which comprises a flat side on which the thermoelectric modules (14) are arranged. The assembly unit made up of inner tube (16), thermoelectric modules (14) and cooling element (18) is surrounded by an elastic compensation element (20) which rests on the inner side of the outer housing (12) and is retained in the outer housing (12) by means of clamping.

Abstract: A trough filter integrated with a thermoelectric generator includes annular filter modules having a support structure at its inner circumference, a filter element, and a support structure at its outer circumference. The filter elements may be configured to form troughs. An annular exhaust gas outlet channel or gas inlet channel may be formed between filter modules. The thermoelectric generator may be positioned in the exhaust gas outlet or inlet channel. A vehicle includes the trough filter integrated with a thermoelectric generator downstream from an internal combustion engine. A method of treating exhaust gas uses a trough filter with an integrated thermoelectric generator.

Abstract: In a cogeneration apparatus, a heat exchanger includes an exhaust gas passageway for passage therethrough of exhaust gas, a heat medium passageway for passage therethrough of a heat medium that gives heat energy to a water heater etc., and a water passageway for taking heat from the exhaust gas and giving the heat to the heat medium. Cooling water for a water-cooled engine is given to the water passageway. The cogeneration apparatus requires reduced numbers of the heat exchanger and pipes, and hence a reduced number of necessary component parts, so that the cogeneration apparatus can be reduced in cost.

Abstract: The invention relates to an air-cooled exhaust gas heat exchanger, in particular exhaust gas cooler (1) for motor vehicles comprising channels (exhaust gas channels) which can be cross-flown by the exhaust gas of an internal combustion engine, between which ribs (4) for air cooling are arranged. According to the invention, the exhaust gas channels are embodied as tubes, in particular as flat tubes (3), which form the ribs (4) of a rib tube block (2) and the tube (3) has tube ends (3a) which are received in the collecting vessels (5) for the exhaust gas.

Abstract: A tail trim assembly for an exhaust pipe in a vehicle which may be mounted at a rear portion of the exhaust pipe that may be formed at an end of a vehicle muffler and discharges exhaust gas and condensed water from the muffler to the outside, may include a main body fitted around the rear portion of the exhaust pipe, at least a welding part formed at an end of the main body and welded to the exhaust pipe, and a collecting part formed at a rear end of the main body, wherein the rear end of the main body and a rear end of the rear portion in the exhaust pipe may be spaced with a predetermined gap to collect the condensed water discharged from the exhaust pipe therethrough.

Abstract: An exhaust manifold of a turbocharged engine includes a collar coolant jacket to maintain component temperatures within acceptable limits. The collar coolant jacket is specifically located around the exhaust outlet of the manifold.

Abstract: An exhaust aftertreatment system for treating an exhaust gas feedstream of an internal combustion engine includes a catalytic converter, a fluidic circuit and a Stirling engine. The Stirling engine is configured to transform thermal energy from a working fluid heat exchanger to mechanical power that is transferable to an electric motor/generator to generate electric power. The Stirling engine is configured to transform mechanical power from the electric motor/generator to thermal energy transferable to the working fluid heat exchanger.

Abstract: System to reduce the amount of NOx in exhaust gases of a vehicle. The system includes a storage space 1 containing an agent, a SCR catalytic converter 5, an injection module 6c to inject the agent upstream of the converter, a heat exchanger 2 containing a porous matrix, a shutter or injector 11 to control the flow rate of the agent to the exchanger, a valve 12 between the storage space and exchanger, to transfer thermal energy to gases during the starting period. The shutter or injector controls the flow of agent into the exchanger during the starting period to raise its temperature, and is closed when gases have reached a certain temperature. The valve regulates exchanger pressure during a period at operating temperature and conveys the agent to storage space when the exchanger pressure is higher than storage space pressure.

Abstract: A method of regenerating a particulate filter that includes an electric heater is provided. The method includes determining a location of particulate matter that remains within at least one region of the particulate filter based on a regeneration event being extinguished; and selectively controlling current to a zone of a plurality of zones of the electric heater to initiate a restrike of the regeneration event based on the location of particulate matter.

Abstract: A method and system for raising the operating temperature of an emissions control device of an automotive vehicle. A generator converts the vehicle's mechanical braking energy to electrical energy. The electrical energy is delivered, without electrical storage, to an electric heater that heats either the emissions control device or the exhaust gas at the input to the device.

Abstract: An exhaust gas treatment system for an internal combustion engine is provided. The internal combustion engine has an engine off condition. The exhaust gas treatment system includes particulate filter (“PF”) device in fluid communication with an exhaust gas conduit, an electric heater, a primary energy storage device, a plurality of secondary energy storage devices, and a control module. The PF device has a filter structure for removal of particulates in the exhaust gas, and is selectively regenerated based on an amount of particulates trapped within the filter structure of the PF device. The electric heater is disposed upstream of the filter structure and is selectively energized to provide heat for regeneration of the PF device. The plurality of secondary energy storage devices are selectively connected to the primary energy storage device. The secondary energy storage devices selectively energize the electric heater.

Abstract: An exhaust assembly includes an exhaust pipe, a first venturi member at the inlet end of the pipe and a second venturi member at the outlet end of the pipe. A diffuser/mixer is mounted at the outlet end of the exhaust pipe. A shield pipe surrounds a portion of the exhaust pipe. A shield member is mounted to the shield pipe and covers a portion of the first venturi member. The first and second venturi members operate to combine ambient air with exhaust gases.

Abstract: The present disclosure is directed to a system for reducing the cold start time for a vehicle with a twin fuel engine. The system has an exhaust system, from which exhaust is discharged and collected on an exhaust manifold. A heat exchanger is positioned within the exhaust system, with coolant flow passages in thermal communication with the engine, and the heat exchanger. A control valve is coupled to a first flow path operable to direct the exhaust through the heat exchanger across the first flow path and a second flow path in selective amounts.

Abstract: A catalyst overheat prevention apparatus has a temperature obtaining portion that estimates a convergence temperature of a catalyst provided in the exhaust system of an internal combustion engine and the present temperature of the catalyst. The catalyst overheat prevention apparatus also has a fuel increment calculation portion, a comparison portion, a correction portion, and a fuel increment setting portion, which are used to execute OT fuel increase control when the convergence temperature and present catalyst temperature obtained by the temperature obtaining portion are equal to or higher than an OT determination temperature. The catalyst overheat prevention apparatus also has a present temperature correction portion that corrects the present catalyst temperature to be equal to the OT determination temperature when the present catalyst temperature is equal to or higher than the OT determination temperature and the convergence temperature is equal to the OT determination temperature.

Abstract: A device and a method for producing electrical energy from an exhaust gas of an internal combustion engine include a generator with an exhaust gas inlet, an exhaust gas outlet and a heat exchange portion therebetween. The heat exchange portion includes a plurality of flow paths for the exhaust gas. The flow paths are at least partially surrounded by thermoelectric elements which are in thermally conductive communication with a cooling device on a side facing away from the flow path. A motor vehicle having the device or carrying out the method, is also provided.

Abstract: A thermoelectric generator for a vehicle is mounted at an exhaust pipe and produces electricity using a temperature difference between the exhaust gas and coolant. The generator includes: a housing; thermoelectric modules mounted at an outer circumferential surface of the housing; a plurality of coolant tubes mounted so as to closely attach the thermoelectric module to the housing; first coolant containers mounted at both ends of the coolant tubes, respectively; and second coolant containers mounted at both ends of the coolant tubes, respectively. The coolant tubes are assembled to the first and second coolant containers as a modularized type, and thus assemblability may be improved and partial replacement of components in case of breakdown may be easily performed. In the coolant tube of the present invention, heat exchange is concentratedly performed at a portion in contact with the thermoelectric module, and thus generation efficiency may be more improved.

Abstract: An energy harvesting system comprises a first region and a second region having a temperature difference therebetween. A plurality of heat engines are located proximate to the conduit and configured for converting thermal energy to mechanical energy. The heat engines each include a shape memory alloy forming at least one generally continuous loop. The shape memory alloy driven to rotate by heat exchange contact with each of the first region and the second region. At least one pulley for each of the plurality of heat engines is driven by the rotation of the respective shape memory alloy, and each of the at least one pulleys is operatively connected to a component to thereby drive the component.

Abstract: In a commercial vehicle with an internal combustion engine, a muffler in the exhaust gas system, and a heat recovery system, including a medium-containing circuit having at least one pump, an evaporator, an expander, and a condenser, the evaporator present in the medium-containing circuit of the heat recovery system is placed so that the evaporator is integrated into the muffler, where it either is installed in the tailpipe or partially replaces it, or is attached externally to the muffler, and an end section of the tailpipe, or is integrated into the tailpipe, which extends from the muffler and proceeds vertically upward behind the driver's cab, the evaporator being either installed in the tailpipe or partially replacing it, or is integrated into a muffler, which is installed in an exhaust pipe proceeding vertically upward behind the driver's cab.

Abstract: An internal combustion engine in which an SOx trap catalyst (13) for trapping SOx contained in the exhaust gas contains an oxygen adsorbing and releasing material (54) which can adsorb SO2 contained in the exhaust gas and an SOx storage material (55) which can store SOx in the form of sulfates. The SO2 which is contained in the exhaust gas is chemically adsorbed at the oxygen adsorbing and releasing material (54) without being oxidized. If the temperature of the SOx trap catalyst (13) becomes higher than the start temperature of adsorbed SO2 movement, the SO2 which is chemically adsorbed at the oxygen adsorbing and releasing material (54) is oxidized and stored in the form of sulfates in the SOx storage material (55).

Abstract: An exhaust gas cooler assembly with an internally located bypass tube, spaced apart from and disposed within a core passage, with an exhaust gas inlet manifold directing exhaust gas to a plurality of cooling passages, or to the bypass tube by means of control valves. Further provided is a detachable valve cartridge with an actuator, with all moving components being included within the valve cartridge and actuator.

Abstract: A vehicle burner (6) for heating a gas flow (14) in a motor vehicle is provided with a fuel pump (10) for delivering a fuel to an injection nozzle (11) that can be actuated for injecting the fuel into a combustion chamber (7), with an air delivery device (16) for delivering air to the combustion chamber (7), with a control (17) for operating the. A vehicle burner (6), which is coupled with the fuel pump (10), with the air delivery and/or air regulating device (16) and with the injection nozzle (11). Burner waste gas, which is generated during the operation of the. A vehicle burner (6) by the reaction of fuel with air in the combustion chamber (7), is used to heat the gas flow (14). To increase efficiency, a control (17) determines a quantity of fuel, a quantity of air and a fuel pressure as a function of a presettable heat output.

Abstract: A heat transporting arrangement (10) for a motor vehicle, having at least one heat circuit (14, 16, 50) in which a heat transporting medium is accommodated and which is thermally coupled to one of the components of a drivetrain in order to exchange heat between the component and the heat transporting medium, a temperature control device (25) which is configured to heat a passenger compartment of a motor vehicle, and a heat store arrangement (30) which is coupled to the heat circuit (14, 16, 50) and to the temperature control device (25) and which is configured to store heat discharged from the heat transporting medium and to release said heat for of heating one of the components of the drivetrain and the passenger compartment.

Abstract: An annular heat exchanger for cooling hot gases comprises an inner shell, an intermediate shell and an outer shell. Where the heat exchanger is integrated with a catalytic converter for treatment of hot exhaust gases in a motor vehicle, the inner shell contains a catalyst for treatment of the exhaust gases. Inner and outer gas flow passages are provided between the shells, and a coolant flow passage is provided, either on the outer surface of the outer shell, or between the intermediate and outer shells. The exhaust gases change direction twice as they pass through the heat exchanger, and the annular structure of the heat exchanger provides a large surface area, and a large flow section, relative to volume, and thereby provides effective heat exchange without significantly increasing space requirements.