EP4722505A1

EP4722505A1 - Exhaust systems and methods for hydrogen internal combustion engines

Info

Publication number: EP4722505A1
Application number: EP24205081.3A
Authority: EP
Inventors: Stuart Clarke; John PIGNON; Andrew YORK
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 2024-10-07
Filing date: 2024-10-07
Publication date: 2026-04-08
Also published as: WO2026078359A1

Abstract

Exhaust systems (2) and methods for hydrogen internal combustion engines (ICE) (1). A valve arrangement (11) is used to direct exhaust gas through either a primary (8) or secondary channel (9) of the exhaust system (2) based on one or more switching variables. The secondary channel (9) comprises a water separator (10) configured to reduce a water content of the exhaust gas prior to the exhaust gas reaching and contacting a downstream substrate (6) comprising a catalyst. The switching variables relate to a water content and/or temperature of the exhaust gas, a time period elapsed from a start-up event, and/or a temperature of one or more components of the hydrogen ICE (1); and/or a temperature of one or more substrate.

Description

Field of the disclosure

The present invention relates to exhaust systems and methods applied to hydrogen internal combustion engines (ICEs).

Background

Hydrogen has been receiving significant attention as a potential future alternative fuel for powering internal combustion engines (ICEs). It is envisioned that low-carbon hydrogen could be produced via hydrolysis of water using renewable electricity supplied by wind and solar powerplants. This produces so-called 'green hydrogen' with essentially zero greenhouse gas (GHG) emissions. Different "types" of hydrogen are commonly referred to using a colour scheme that reflects the degree of upstream GHG emissions. For example, black/grey hydrogen is produced from fossil fuels, black hydrogen being produced from coal and grey hydrogen being produced from natural gas using steam reformation of methane; blue hydrogen is essentially the same as grey hydrogen, but with its CO₂ sequestered or repurposed; turquoise hydrogen is produced from natural gas via pyrolysis (with solid carbon as a by-product); pink/red/purple hydrogen is produced using nuclear power though electrolysis, thermolysis or a combination thereof; white hydrogen is produced as a by-product of industrial processes such as fracking; and yellow hydrogen produced by electrolysis of water using grid electricity, typically derived from a mixture of renewable energies and fossil fuels.
It is known to fuel a compression ignition engine with a fuel mixture comprising diesel fuel and a minority fuel mass of hydrogen (see e.g. K.S. Varde et al, International Journal of Hydrogen Energy, 7, 549-555 (1983)). It is also known to fuel a spark-ignition engine with a fuel mixture comprising gasoline (petrol) and a minority fuel mass of hydrogen (see M. Al-Baghdadi et al, Energy Conversion and Management, 41, 77-91 (2000)). Hydrogen may be derived on the vehicle by use of an on-board fuel reformer (see e.g. WO2014/118574A1 and WO2012/063082A1 ). For further information, Applicant refers to DieselNet Technology Guide >> Alternative Fuels >> "Hydrogen" particularly section "5. Hydrogen Fuelled Engines", Author: H. Jääskeläinen, Revision 2023.07 available at https://dieselnet.com/tech/fuel_hydrogen.php.
In contrast to prior art disclosures of a minority fuel mass of hydrogen, the present invention is directed to exhaust systems and methods applied to internal combustion engines configured to run on a mixture of air and fuel, wherein the fuel of the mixture of air and fuel is a gaseous fuel comprising a majority fuel mass of hydrogen. A 'majority fuel mass' can be at least 70 vol% hydrogen gas (H₂), e.g. of one of the colour sources discussed above or a mixture of two or more thereof.
An exhaust system for H₂-fuelled ICEs typically comprises an oxidation catalyst for converting H₂ and optionally also NO in the exhaust to H₂O and NO₂. The catalyst may be provided on or in (e.g. extruded) a substrate. Exhaust gas of ICE engines powered wholly or in part by H₂ include H₂ itself and oxides of nitrogen (NO and NO₂, collectively NO_x). Combustion of lubricating oil can generate CO, hydrocarbons, and particulate matter, as well as urea-generated particles where selective catalytic reduction is used to reduce NO_x. Particulates derived from these sources may require filtration. Ammonia emissions could also be possible under conditions that generate rich combustion. To compare to the redox composition of prior art diesel and gasoline exhaust gas, the lambda value of exhaust gases emitted by internal combustion engines configured to run on a mixture of air and fuel, wherein the fuel of the mixture of air and fuel is a gaseous fuel comprising a majority fuel mass of H₂, can vary widely, e.g. from 1 to 30, which can make catalytic aftertreatment difficult. Lambda can be calculated using the Brettschneider Equation.
H₂ ICEs typically produce relatively high water levels in their exhaust gases compared to ICEs fuelled by gasoline or diesel. For example, average water levels during World Harmonized Transient Cycle (WHTC) tests may be 15-20%. At idle, water levels may be around 12%. Maximum water levels of up to 30% may be encountered, for example during a cold start of the H₂ ICE. The relatively high water content of the exhaust gases, especially during cold starts, is an additional factor that can make catalytic aftertreatment difficult. For example, high water content in the exhaust gas may lead to leaching of catalytic components from the catalytic composition and/or accelerated ageing of the substrate catalyst/impact on catalyst durability.
Applicant has now developed an exhaust system engineering design for H₂ ICE engines to assist with managing the relatively high water exhaust gas exposure of catalysts disposed in the exhaust system, with the goal of extending the durability and working life of the catalyst.

Summary of the disclosure

In a first aspect of the present invention, there is provided an exhaust system of a hydrogen internal combustion engine (ICE), comprising:

an inlet fluidly coupled to the hydrogen ICE and configured to receive exhaust gas from the hydrogen ICE;
a substrate comprising a catalyst for treating the exhaust gas;
an outlet for discharging the exhaust gas;
a primary channel that provides fluid communication for the exhaust gas to flow from the inlet, through the substrate, and then to the outlet;
a secondary channel that provides fluid communication for the exhaust gas to flow from the inlet, through a water separator, then through the substrate, and then to the outlet;
a valve arrangement operable to control flow of the exhaust gas between the primary channel and the secondary channel, the valve arrangement comprising at least one valve element located in or upstream of the primary channel or at a junction of the primary and secondary channels; and
a controller configured to operate the valve arrangement;

the valve arrangement being configurable between a primary flow configuration and a secondary flow configuration, wherein in the primary flow configuration the valve arrangement directs the exhaust gas through the primary channel and in the secondary flow configuration the valve arrangement directs the exhaust gas through the secondary channel;
the controller being configured to switch the valve arrangement between the primary flow configuration and the secondary flow configuration based on one or more switching variables comprising or consisting of:
- - a water content of the exhaust gas; and/or
- - a time period elapsed from a start-up event; and/or
- - a temperature of the exhaust gas; and/or
- - a temperature of one or more components of the hydrogen ICE; and/or
- - a temperature of one or more substrate.

Selectively flowing the exhaust gas through the water separator enables the water content of the exhaust gas to be reduced by the extraction of water within the water separator.
By provision of the primary and secondary channels together with the ability to switch the flow of exhaust gas between them, the exhaust system of the present invention enables the water content of the exhaust gas to be reduced before it reaches the substrate at times when a water content of the exhaust gas is expected to be undesirably high or otherwise unsuitable for passing through the substrate. Such times especially include upon start-up of the ICE in cold conditions. By so doing the risk of liquid water contacting the substrate - for example condensing and pooling of liquid water within the substrate or substrate housing - is reduced. This is beneficial in reducing the likelihood of premature ageing of the catalyst of the substrate, leaching of catalytic components, and/or delamination of catalyst washcoat from the substrate (i.e. separation of the washcoat layer from the underlying scaffold of the substrate).
The valve arrangement may be configurable between the primary flow configuration, the secondary flow configuration and a mixed flow configuration, wherein in the mixed flow configuration the valve arrangement directs the exhaust gas through both the primary channel and the secondary channel; and the controller is configured to switch the valve arrangement between the primary flow configuration, the secondary flow configuration and the mixed flow configuration based on the one or more switching variables. In this way a portion of the exhaust gas may be directed into each of the primary and secondary channels. This may be beneficial during certain periods of operation. For example, once the exhaust gas temperature has exceeded an exhaust gas temperature threshold a portion of the exhaust gas may for a time still be directed through the secondary channel, and hence the water separator, to evaporate and drive off liquid water previously collected in the water separator.
The switching variables may be monitored against one or more threshold values. For example, the water content of the exhaust gas may have an associated water content threshold value, the time period elapsed from a start-up event may have an associated time period threshold, the temperature of the exhaust gas may have an associated exhaust gas temperature threshold, and the temperature of one or more components of the hydrogen ICE may have an associated ICE temperature threshold.
The values of the various threshold values may be chosen based on the specific layout and geometry of the exhaust system. In some examples the values of the various threshold values may be established by experimental means.
The switching variables may be monitored against the one or more threshold values to enable the controller to switch the valve arrangement to the primary flow configuration when the risk of condensation of water in proximity to the substrate is, or is expected to be, at an acceptably low level and/or when the water content of the exhaust gas is, or is expected to be, at an acceptably low level.
For example, the controller may switch the valve arrangement to the primary flow configuration (or retain the valve arrangement in such a configuration) when the water content of the exhaust gas is below the water content threshold value, and/or the time period elapsed from the start-up event exceeds the time period threshold, and/or the temperature of the exhaust gas exceeds the exhaust gas temperature threshold, and/or the temperature of one or more components of the hydrogen ICE exceeds the associated ICE temperature threshold. The controller may switch the valve arrangement to the primary flow configuration (or retain the valve arrangement in such a configuration) when one, two, three or all of the threshold conditions are met. For example, the controller may switch the valve arrangement to the primary flow configuration when e.g. the time period threshold or the exhaust gas temperature threshold alone is exceeded. This may allow for easier monitoring to be achieved. In another example, the controller may switch the valve arrangement to the primary flow configuration when the time period threshold and the exhaust gas temperature threshold are both exceeded. This may allow for redundancy and enhanced confirmation to be achieved that condensation of liquid water in proximity to the substrate is unlikely.
As noted above the mixed flow configuration may optionally be used when the water content of the exhaust gas is below the water content threshold value, and/or the time period elapsed from the start-up event exceeds the time period threshold, and/or the temperature of the exhaust gas exceeds the exhaust gas temperature threshold, and/or the temperature of one or more components of the hydrogen ICE exceeds the associated ICE temperature threshold in order to allow some flow of hot exhaust gas through the water separator allowing for evaporation of collected water.
The water content of the exhaust gas may, for example, be monitored by a measure of the water content of the exhaust gas, e.g. using a humidity sensor. The time period elapsed from the start-up event may, for example, be monitored by a clock module of the controller. The temperature of the exhaust gas may, for example, be monitored by a direct measurement of the exhaust gas using e.g. a thermocouple arranged in contact with the flow of exhaust gas within the exhaust system or by receipt of a signal from a controller of the ICE that is indicative of the exhaust gas temperature entering the exhaust system. The temperature of one or more components of the hydrogen ICE may, for example, be monitored by a direct measurement of said component(s) using e.g. a thermocouple arranged in thermal contact with the component(s) or by receipt of a signal from a controller of the ICE that is indicative of temperature of said component(s). As just one example, the controller (e.g. an ECU) of the ICE may provide a signal indicating the engine coolant fluid temperature of the ICE and this may be used as a switching variable.
The controller may be configured to configure the valve arrangement in the secondary flow configuration on detection of a start-up event of the hydrogen ICE. The start-up event may be, for example, a key-on event used to start up the engine. Use of the secondary flow configuration on start-up, especially in cold conditions, can be of particular benefit since the chance of water condensation in or near the substrate may be particularly high at this stage of operation of the H₂ ICE prior to the ICE reaching its normal operating temperature.
The controller may be configured to always configure the valve arrangement in the secondary flow configuration on detection of a start-up event of the hydrogen ICE. Consequently, in some examples the exhaust system may default to initially operating with the valve arrangement in the secondary flow configuration.
The controller may be configured to switch the valve arrangement from the primary flow configuration to the secondary flow configuration based on changes in the one or more switching variables. Thus, in some examples the exhaust system has the ability to switch between primary and secondary flow configurations during running of the H₂ ICE as required. For example, this may be desirable during periods of idling of the engine. However, in other examples, it will be sufficient for the exhaust system to remain running in the primary mode (e.g. once the H₂ ICE has warmed up to its normal operating temperature) until the H₂ ICE is keyed off.
In the primary flow configuration the valve arrangement may be configured to direct all or substantially all of the exhaust gas through the primary channel. In the secondary flow configuration the valve arrangement may be configured to direct all or substantially all of the exhaust gas through the secondary channel.. This enables to maximise the amount of water extracted from the exhaust gas and also to minimise or eliminate any exhaust gas that has a high water content reaching the substrate in a condition where condensation within the substate is likely without the exhaust gas first passing through the water separator.
In some examples the water separator comprises a cyclone. This has been found to be a particularly beneficial form of water separator for the present invention.
The cyclone may comprise a housing having a peripheral inlet configured to receive exhaust gas and a central outlet configured to discharge exhaust gas such that a flow of the exhaust gas through the cyclone is spirally inwards from the peripheral inlet to the central outlet. The spiral flow from outer periphery to inner centre advantageously increases the path length of the exhaust gas within the water separator increasing the time for water extraction. In addition, the exhaust gas initially entering at the peripheral inlet initially flows along an inner face of the housing making good thermal contact with the (typically) relatively cold housing. For example, the housing may be made of metal. This thermal contact aids cooling of the exhaust gas and condensation of water from the exhaust gas.
The central outlet may be longitudinally offset from the peripheral inlet such that the flow of exhaust gas through the cyclone spirals along a longitudinal axis of the housing. The longitudinal flow advantageously increases the path length of the exhaust gas within the water separator increasing the time for water extraction.
The peripheral inlet may be located at or towards an upper end of the housing and the central outlet may be located below the peripheral inlet. Such an arrangement may be used to impart a reversal of flow direction to the exhaust gas, e.g. from moving longitudinally in one direction within the water separator to moving longitudinally in the other direction.
The central outlet may communicate with a discharge conduit that is orientated such that water condensing from the exhaust gas within the discharge conduit drains back under gravity into the housing. For example, the central outlet may be a conduit that extends upwards, for example vertically upwards, from an interior of the water separator. In this way the amount of condensed water that may flow into, or be aerosolised and carried by the exhaust gas into, downstream portions of the secondary channel when the valve arrangement is in the secondary flow configuration can be reduced. This helps to reduce the amount of water, and especially liquid water, making contact with the substrate.
A lower portion of the housing may form a collector for holding condensed water. For example, the collector may be a sump of the water separator. The collector assists by providing a residence volume for liquid water enabling the water separator to hold a volume of liquid water and at the same time permit exhaust gas to flow through the water separator.
In some examples the collector may be an empty void space of the water separator. In alternative examples the collector may contain an adsorbent, for example a woven or non-woven fabric, optionally a gauze. The adsorbent may function to help retain the liquid water within the water separator and minimise or prevent passage of liquid water into the downstream portions of the secondary channel.
In some examples the water separator may comprise a drain for discharging condensed water from the collector. This allows the collector, e.g. sump, to be periodically emptied preventing the water separator becoming saturated with liquid water and ineffective. In some examples the drain may comprise a valve for controlling water discharge. The valve may be a timed valve under control of the controller, e.g. configured to discharge water at set time intervals. Alternatively, a water level sensor may be provided in the water separator and the controller may be configured to actuate the valve based on a sensed water level within the collector.
In some examples the water separator, optionally a lower portion thereof, comprises, or is coupled with, a heat exchanger for supplying heat energy to evaporate water held in the water separator. The heat exchanger may be configured to receive a flow of an engine fluid of the hydrogen ICE, optionally a flow of engine coolant fluid. In some examples the evaporated water may be carried with the exhaust gas along the secondary channel towards the outlet, for example when the valve arrangement is in the secondary or mixed flow configurations.
In some examples the secondary channel and primary channel are co-axial. In some examples the secondary channel surrounds the primary channel.
The secondary channel may contain an adsorbent. The adsorbent may be a molecular sieve or alternatively a woven or non-woven fabric, optionally a gauze. The adsorbent may be located in the secondary channel upstream and/or downstream of the water separator.
The valve arrangement may, for example, consist of one, two or more valve elements. Where multiple valve elements are provided these may be actuated separately or may be actuated in a co-ordinated manner, for example with a mechanical or electro-mechanical connection operating between the valve elements.
In some examples, the valve arrangement may comprise or consist of a first valve element located in or upstream of the primary channel and a second valve element located in the secondary channel. The first and second valve elements may be configured to operate in a co-ordinated manner, e.g. with one valve element opening as the other valve element shuts. The or each valve element may comprise a flap valve or a poppet valve. The valve arrangement may comprise a mixture of valve elements of different types.
In some other examples, the valve arrangement may consist of a single valve element located at a junction between the primary and secondary channels, i.e. at a splitting point of the primary and secondary channels. In the secondary flow configuration, the single valve element may force all of the exhaust gas into the secondary channel by completing occluding the primary channel or a path to the primary channel. In the primary flow configuration, the single valve element may force all of the exhaust gas into the primary channel by completing occluding the secondary channel or a path to the secondary channel. In the mixed flow configuration, the single valve element may force some of the exhaust gas into each of the primary and secondary channels. In some examples the single valve element comprises a flap valve. In other examples the single valve element comprises a poppet valve.
In a second aspect of the present invention, there is provided an exhaust system of a hydrogen internal combustion engine (ICE), comprising:

the valve arrangement being configurable between a primary flow configuration and a secondary flow configuration, wherein in the primary flow configuration the valve arrangement directs the exhaust gas through the primary channel and in the secondary flow configuration the valve arrangement directs the exhaust gas through the secondary channel;
the controller being configured to switch the valve arrangement between the primary flow configuration and the secondary flow configuration based on one or more switching variables;
wherein the water separator comprises a cyclone.

The features and advantages of the first aspect apply equally to the second aspect.
The one or more switching variables may comprise or consist of:

a water content of the exhaust gas; and/or
a time period elapsed from a start-up event; and/or
a temperature of the exhaust gas; and/or
a temperature of one or more components of the hydrogen ICE; and/or
a temperature of one or more substrate.

In some examples the valve arrangement may be configurable between the primary flow configuration, the secondary flow configuration and a mixed flow configuration, wherein in the mixed flow configuration the valve arrangement directs the exhaust gas through both the primary channel and the secondary channel; and the controller is configured to switch the valve arrangement between the primary flow configuration, the secondary flow configuration and the mixed flow configuration based on the one or more switching variables.
The exhaust system of the first and/or second aspects described above is preferably coupled to a hydrogen internal combustion engine. The hydrogen internal combustion engine may be configured to run on a mixture of air and fuel, wherein the fuel of the mixture of air and fuel is a gaseous fuel comprising a majority fuel mass of hydrogen. A 'majority fuel mass' can be at least 70 vol% hydrogen gas (H₂). The hydrogen internal combustion engine may be coupled to a fuel reservoir containing a source of H₂.
In some examples the exhaust system of the first or second aspect additionally comprises a heater for heating the exhaust gas that exits the water separator. The heater may be an electrical heater. The heater may be located between the water separator and the substrate in the secondary channel. In some examples the heater is located immediately upstream of the substrate. The heater functions to increase the temperature of the exhaust gas to compensate for a temperature reduction of the exhaust gas caused by water condensation within the water separator. In some examples, the heater may be configured to operate when the exhaust system is operating with the valve arrangement in the secondary flow configuration and/or the mixed flow configuration and be switched off when the exhaust system is operating with the valve arrangement in the primary flow configuration. In some examples the heater may also function as a mixer, e.g. a static mixer. The heater may in this way generate turbulence in the exhaust gas as it enters the substrate thereby improving heat transfer between the exhaust gas and the substrate.
Additionally, or alternatively the substrate may comprise or consist of an electrically heated catalyst, for example a substrate comprising a resistive material that can be heated when electrically energised. The resistive material may comprise a sintered metallic material of the substrate monolith that bears the catalytic coating. Alternatively the resistive material may comprise a metal foil element that is mounted to the substrate and upon which the catalytic material is layered.
In a third aspect of the present invention, there is provided a method of treating emissions from a hydrogen internal combustion engine (ICE) by coupling an exhaust outlet of the hydrogen ICE to an inlet of an exhaust system such that the exhaust system receives exhaust gas from the hydrogen ICE, the exhaust system being of the type comprising:

a substrate comprising a catalyst for treating the exhaust gas;
an outlet for discharging the exhaust gas;
a primary channel that provides fluid communication for the exhaust gas to flow from the inlet, through the substrate, and then to the outlet;
a secondary channel that provides fluid communication for the exhaust gas to flow from the inlet, through a water separator, then through the substrate, and then to the outlet;
a valve arrangement operable to control flow of the exhaust gas between the primary channel and the secondary channel, the valve arrangement comprising at least one valve element located in or upstream of the primary channel or at a junction of the primary and secondary channels; and
a controller configured to operate the valve arrangement;

the method comprising the steps of:
- - using the controller to selectively configure the valve arrangement into a primary flow configuration and a secondary flow configuration based on one or more switching variables, wherein in primary flow configuration the valve arrangement directs the exhaust gas through the primary channel and in the secondary flow configuration the valve arrangement directs the exhaust gas through the secondary channel;
wherein the one or more switching variables comprises or consists of:
- - a water content of the exhaust gas; and/or
- - a time period elapsed from a start-up event; and/or
- - a temperature of the exhaust gas; and/or
- - a temperature of one or more components of the hydrogen ICE; and/or
- - a temperature of one or more substrate.

The features and advantages of the first and second aspects apply equally to the third aspect.
The method may comprise selectively configuring the valve arrangement into the primary flow configuration, the secondary flow configuration and a mixed flow configuration based on the one or more switching variables.
The method may comprise the controller configuring the valve arrangement into the secondary flow configuration on detection of a start-up event of the hydrogen ICE.
The valve arrangement when in the primary flow configuration may not pass the exhaust gas through a water separator or condenser. The valve arrangement when in the secondary flow configuration may pass exhaust gas through a cyclone water separator.
The controller may configure the valve arrangement into the secondary flow configuration on detection of a start-up event of the hydrogen ICE.
In some examples the method may further comprise supplying heat energy to evaporate water held in the water separator. The heat energy may be supplied from a flow of an engine fluid of the hydrogen ICE, optionally a flow of engine coolant fluid, and/or a flow of the exhaust gas e.g. when the valve arrangement is in the mixed flow configuration. In some examples the evaporated water may be carried with the exhaust gas along the secondary channel towards the outlet.
The method of the third aspect may be used with a hydrogen internal combustion engine. The hydrogen internal combustion engine may be configured to run on a mixture of air and fuel, wherein the fuel of the mixture of air and fuel is a gaseous fuel comprising a majority fuel mass of hydrogen. A 'majority fuel mass' can be at least 70 vol% hydrogen gas (H₂). The hydrogen internal combustion engine may be coupled to a fuel reservoir containing a source of H₂.
In a fourth aspect of the present invention, there is provided a controller configured to operate a valve arrangement and/or an exhaust system and/or a hydrogen internal combustion engine coupled to an exhaust system using the method of the third aspect of the present invention.
The features and advantages of the first to third aspects apply equally to the fourth aspect.
The controller may comprise or consist of a pre-programmed computer processor unit.
H₂-ICE engines can be spark-ignition (SI) engines or High Pressure Direct Injection (HPDI) engines, such as pilot injection HDPI engines, a variation on commercially available heavy-duty natural gas engine technology. For the avoidance of any doubt, the claimed invention is intended to cover exhaust systems and methods applied to both SI and HPDI engines.
In any of the aspects of the present invention the substrate can be a ceramic substrate or a metallic substrate. The ceramic substrate may be made of any suitable refractory material, e.g., alumina, silica, titania, ceria, zirconia, magnesia, zeolites, silicon nitride, silicon carbide, zirconium silicates, magnesium silicates, aluminosilicates, metalloaluminosilicates (such as cordierite and spudomene), or a mixture or mixed oxide of any two or more thereof.
The metallic substrates may be made of any suitable metal, and in particular heat-resistant metals and metal alloys such as titanium and stainless steel as well as ferritic alloys containing iron, nickel, chromium, and/or aluminium in addition to other trace metals.
The substrate may be a flow-through substrate, e.g., a flow-through monolith having a honeycomb structure with many small, parallel thin-walled channels running axially through the substrate and extending throughout from an inlet or an outlet of the substrate. The channel cross-section of the substrate may be any shape, but is preferably square, sinusoidal, triangular, rectangular, hexagonal, trapezoidal, circular, or oval. The flow-through substrate may have porous channel walls which allows catalyst coatings to penetrate into the substrate walls. For certain applications, the flow-through monolith substrate has a cell density of about 600 to 800 cells per square inch, and/or an average internal wall thickness of about 0.18-0.35 mm, or about 0.20-0.25 mm. For certain other applications, the flow-through monolith substrate has a low cell density of about 150-600 cells per square inch, or about 200-400 cells per square inch.
The substrate may be a filter substrate. For example, the filter substrate may be a wall-flow monolith filter substrate. The channels of a wall-flow filter are alternately blocked, which allow the exhaust gas stream to enter a channel from the inlet, then flow through the channel walls, and exit the filter from a different channel leading to the outlet.
The catalyst of the substrate may comprise a washcoat. The washcoat can be a composition that coats on and/or within the channel walls. The washcoat generally comprises a catalyst composition. The catalyst composition can be a diesel oxidation catalyst (DOC), a three-way catalyst (TWC), a NO_x absorber, a selective reduction catalyst (SCR), or a hydrocarbon trap, for example.
When the catalyst composition is DOC catalyst, the washcoat generally comprises one or more platinum group metals (PGM). Preferably the PGMs are present in a total amount such that the final coating contains at least 1 g/ft³. In addition to the PGM, the washcoat may comprises a support material. Suitable support materials include silica, alumina, ceria, ceria-zirconia and the like. Preferably the support material comprises alumina. One or more support materials may be present. The support material such as alumina can be doped with a dopant. The dopant can be selected from the group consisting of La, Sr, Si, Ba, Y, Pr, Nd, Ce, and mixtures thereof. Preferably, the dopant is La, Ba, or Ce. Most preferably, the dopant is La. The dopant content in the inorganic oxide support can be from 1 to 30 wt%.
When the catalyst composition is TWC catalyst, the catalyst comprises one or more platinum group metals (PGM), a support material, and an oxygen storage capacity (OSC) material. Suitable OSC material may comprises a mixed oxide of cerium, zirconium; a mixed oxide of cerium, zirconium, and aluminium; a mixed oxide of cerium, zirconium, and neodymium; or a mixed oxide of cerium, zirconium and praseodymium. The term "mixed oxide" as used herein generally refers to a mixture of oxides in a single phase, as is conventionally known in the art.
The present invention finds particular application where the catalyst composition is for selective catalytic reduction (SCR). In particular, it has been found that the catalytic components of SCR compositions, in particular copper- or vanadium-containing SCR compositions can be prone to leaching when exposed to high water levels. When the catalyst composition is SCR catalyst, the catalyst generally comprises an oxide of a base metal, a molecular sieve, a metal-exchanged molecular sieve, or a mixture thereof. The base metal can be selected from the group consisting of cerium (Ce), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), tungsten (W), vanadium (V), and mixtures thereof. SCR catalysts consisting of vanadium supported on a refractory metal oxide such as alumina, silica, zirconia, titania, ceria and combinations thereof are well known and widely used commercially in mobile applications. The SCR catalyst may comprise vanadium and cerium.
The SCR catalyst can comprise a molecular sieve or a metal-exchanged molecular sieve. As is used herein "molecular sieve" is understood to mean a metastable material containing tiny pores of a precise and uniform size that may be used as an adsorbent for gases or liquids. The molecular sieve can be a zeolitic molecular sieve, a non-zeolitic molecular sieve, or a mixture thereof.
A zeolitic molecular sieve is a microporous aluminosilicate having any one of the framework structures listed in the Database of Zeolite Structures published by the International Zeolite Association (IZA). The framework structures include, but are not limited to those of the CHA, BEA, FAU, LTA, MFI, and MOR types. Non-limiting examples of zeolites having these structures include chabazite, faujasite, zeolite Y, ultrastable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X, and ZSM-5. Aluminosilicate zeolites can have a silica-to-alumina molar ratio (SAR, defined as SiO₂/Al₂O₃) from 5 to 200, from 10 to 180, or from about 20 to 150.
As used herein, the term "non-zeolitic molecular sieve" refers to corner sharing tetrahedral frameworks where at least a portion of the tetrahedral sites are occupied by an element other than silicon or aluminium. Specific non-limiting examples of non-zeolitic molecular sieves include silicoaluminophosphates such as SAPO-34, SAPO-37 and SAPO-44. The silicoaluminophosphates can have framework structures that contain framework elements that are found in zeolites, such as BEA, CHA, FAU, LTA, MFI, MOR and other types.
In any of the aspects of the present invention the term "controller" may refer to a function that may comprise hardware and/or software. The controller may comprise a control unit or may be a computer program running on a dedicated or shared computing resource. The controller may comprise a single unit or may be composed of a plurality of sub-units that are operatively connected. The controller may be located on one processing resource or may be distributed across spatially separate processing resources. The controller may comprise a microcontroller, one or more processors (such as one or more microprocessors), memory, configurable logic, firmware, etc. In some preferred examples the controller comprises or consists of a pre-programmed computer processor unit.

Brief description of the drawings

Aspects and embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a block diagram of a hydrogen internal combustion engine and an exhaust system according to the present invention;
Figure 2 is a schematic diagram of a first embodiment of an exhaust system of a hydrogen internal combustion engine according to the present invention operating with its valve arrangement in a secondary flow configuration;
Figure 3 is a schematic sectional view of a portion of the first embodiment of Figure 2;
Figure 4 is a schematic diagram of the first embodiment operating with its valve arrangement in a primary flow configuration;
Figure 5 is a schematic diagram of a second embodiment of an exhaust system of a hydrogen internal combustion engine according to the present invention; and
Figure 6 is a flow chart of a method of treating emissions from a hydrogen internal combustion engine according to the present invention.

Detailed description

The skilled reader will recognise that one or more features of one aspect or embodiment of the present disclosure may be combined with one or more features of any other aspect or embodiment of the present disclosure unless the immediate context teaches otherwise.
Figure 1 shows a hydrogen internal combustion engine 1 (ICE) and an exhaust system 2 according to the present invention.
The exhaust system 2 comprises an inlet 4 fluidly coupled to the hydrogen ICE 1 that is configured to receive exhaust gas from the hydrogen ICE 1, for example along an inlet conduit 5.
The exhaust system 2 further comprises a substrate 6 for treating the exhaust gas and an outlet 7 for discharging the exhaust gas.
A primary channel 8 is provided to enable fluid communication for the exhaust gas to flow from the inlet 4, through the substrate 6 comprising a catalyst, and then to the outlet 7. In addition, a secondary channel 9 is provided to enable fluid communication for the exhaust gas to flow from the inlet 4, through a water separator 10, then through the substrate 6, and then to the outlet 7.
A valve arrangement 11 is located in or upstream of the primary channel 8 and is operable to control flow of the exhaust gas between the primary channel 8 and the secondary channel 9.
The valve arrangement 11 may comprise or consist of one or more valve elements 11a, 11b.
A controller 12 is provided that is configured to operate the exhaust system 2 by configuring the valve arrangement 11 into a primary flow configuration and a secondary flow configuration as required. The controller 12 may be linked in a wired or wireless manner to the required components of the exhaust system 2, e.g. the valve arrangement 11, etc. In some preferred examples the controller 12 comprises or consists of a pre-programmed computer processor unit.
In the secondary flow configuration the valve arrangement 11 is configured to direct the exhaust gas through the secondary channel 9 such that the exhaust gas flows through the water separator 10 to thereby reduce a water content of the exhaust gas prior to the exhaust gas reaching and contacting the substrate 6. Preferably all or substantially all of the exhaust gas flows into the secondary channel 9 when the valve arrangement 11 is in the secondary flow configuration.
In the primary flow configuration the valve arrangement 11 is configured to direct the exhaust gas through the primary channel 8. Preferably all or substantially all of the exhaust gas flows into the primary channel 8 when the valve arrangement 11 is in the primary flow configuration.
The valve arrangement 11 may also be configured into a mixed flow configuration in which some of the exhaust gas is directed into each of the primary channel 8 and the secondary channel 9.
The controller 12 is configured to switch the valve arrangement 11 between the primary flow configuration and the secondary flow configuration (and optionally the mixed flow configuration) based on one or more switching variables comprising or consisting of:

The water content of the exhaust gas may be measured directly or indirectly. For example a humidity sensor may be provided in the exhaust system 2 or the upstream hydrogen ICE 1. The time period may be measured by the controller 12, for example by a clock module of the controller 12. The temperature of the exhaust gas may be measured directly, for example by means of a temperature sensor, e.g. a thermocouple, within the primary channel 8 or secondary channel 9 or in the inlet conduit 5 or in the upstream hydrogen ICE 1. Alternatively, the temperature of the exhaust gas may be inferred from a temperature of another component of the hydrogen ICE 1, for example the engine coolant fluid temperature.
Figures 2 to 4 show a first embodiment of an exhaust system 2 according to the present invention. In this embodiment the water separator 10 comprises a cyclone. The substrate 6 comprising the catalyst may be of the types described above, for example a flow-through SCR catalyst substrate.
The primary channel 8 and the secondary channel 9 run (functionally) in parallel to each other from a first junction 13 where the channels split to a second junction 14 where the channels merge together. The second junction 14 is located upstream of the substrate 6.
In the illustrated example of Figures 2 to 4, the valve arrangement 11 consists of two valve elements 11a, 11b, each comprising a flap valve. The first valve element 11a is located in the primary channel 8. The valve elements 11a, 11b are interlinked to move in a co-ordinated manner. In alternative examples a single valve element, e.g. a flap valve, poppet valve or other valve type may be provided at the first junction 13 where the primary channel 8 and the secondary channel 9 split.
The cyclone comprises a housing 15 having a peripheral inlet 16 configured to receive the exhaust gas and a central outlet 17 configured to discharge exhaust gas, as shown in Figure 3. Consequently, the flow of the exhaust gas through the cyclone is spirally inwards from the peripheral inlet 16 to the central outlet 17.
The central outlet 17 is longitudinally offset from the peripheral inlet 16 such that the flow of exhaust gas through the cyclone spirals is also along a longitudinal axis 18 of the housing 15.
The peripheral inlet 16 is located at or towards an upper end of the housing 15 and the central outlet 17 is located below the peripheral inlet 16.
The central outlet 17 communicates with a discharge conduit 19 that is orientated upwards such that water condensing from the exhaust gas within the discharge conduit 19 drains back under gravity into the housing 15.
In the illustrated example of Figures 2 to 4, a lower portion of the housing forms a collector 20 for holding condensed water. In the example shown the collector 20 contains an adsorbent 21 for capturing water condensing in the water separator 10. The adsorbent 21 may be, for example, a woven or non-woven fabric, a gauze, or a molecular sieve.
The water separator 10 may comprise a drain 22 for discharging condensed water from the collector 20, in particular from a sump 23 of the collector 20.
In the illustrated example of Figures 2 to 4, the water separator 10, optionally a lower portion thereof, may comprise or be coupled with a heat exchanger 24 for supplying heat energy to evaporate water held in the water separator 10. In the illustrated example the heat exchanger 24 receives a flow of engine coolant fluid 25 from the hydrogen ICE 1. The heat exchanger 24 may be operated intermittently to heat up the housing 15 of the water separator 10 to encourage evaporation of condensed water from within the sump 22.
One or other or both of the drain 22 and the heat exchanger 24 may be provided.
In the illustrated example of Figures 2 to 4, an electrical heater 26 is provided for heating the exhaust gas that exits the water separator 10. The electrical heater 26 is located in the primary channel 8 immediately upstream of the substrate 6 comprising the catalyst. Additionally or alternatively the substrate may be an electrically heated catalyst comprising resistive material that is enabled to be heated when energised.
In use, the controller 12 may be configured to configure the valve arrangement 11 into the secondary flow configuration (Figure 2) on detection of a start-up event of the hydrogen ICE 1. The start-up event may be, for example, a key-on operation of the hydrogen ICE 1. At start up the hydrogen ICE 1 will typically initially be cold such that the exhaust gas entering the exhaust system 2 will initially be at a relatively low temperature but with a high water content resulting in a likelihood of water condensation within the substrate 6.
Thus, during operation in the secondary flow configuration the exhaust gas is diverted into the secondary channel 9 due to the fully closed valve element 11a in the primary channel 8 with the exhaust gas flowing through the water separator 10 where it is cooled, in particular by contact with the thermal mass of the housing 15. Water condenses within the housing 15 and is fed downwards into the sump 23 of the collector 20. Exhaust gas with a reduced water content is then fed out of the water separator 10 through the discharge conduit 19 where it is passed to the electrical heater 26 to have its temperature raised before entering the substrate 6. The reduced water content of the exhaust gas compared to the exhaust gas output from the hydrogen ICE 1 reduces the chances of water condensation within the substrate 6.
Collected water in the sump 23 may be emptied as required by operation of the drain 22, for example by operation of a drain valve.
Continued operation of the hydrogen ICE 1 will result in the exhaust gas temperature and the engine coolant fluid temperature increasing. The controller 12 monitors the switching variables in order to reconfigure the valve arrangement 11 into the primary flow configuration (Figure 4) at an appropriate point. In the primary flow configuration the exhaust gas flows directly to the substrate 6 without passing through the water separator 10 due to the closed valve element 11b that occludes the secondary channel 9.
The controller 12 may switch the valve arrangement 11 to the primary flow configuration when a water content of the exhaust gas is below a water content threshold value, and/or a time period elapsed from the start-up event exceeds a time period threshold, and/or a temperature of the exhaust gas exceeds a exhaust gas temperature threshold, and/or a temperature of one or more components of the hydrogen ICE 1 exceeds an ICE temperature threshold; and/or a temperature of one or more substrate.
As shown in Figure 2 all of the exhaust gas will flow into the secondary channel 9 since valve element 11a is fully closed and valve element 11b is fully open. However, the valve arrangement 11 may adopt its mixed flow configuration by having both valve elements 11a, 11b partially open. The proportion of the exhaust gas directed to each of the primary channel 8 and secondary channel 9 can be controlled by the degree that each valve element 11a, 11b is opened/closed. Flap valve elements may be particularly suitable for such an arrangement.
In some examples the controller 12 is configured to always initially configure the valve arrangement 11 in the secondary flow configuration on detection of a start-up event of the hydrogen ICE 1. For example, after a key-on operation of the hydrogen ICE 1 the secondary flow configuration may be the default configuration of the valve arrangement 11.
In an example of operation the controller 12 may initially configure the valve arrangement 11 into the secondary flow configuration while the exhaust gas temperature is below the exhaust gas temperature threshold. During this period the exhaust gas passes through the water separator 10 and water is extracted and collected in the sump 23. Once the exhaust gas temperature exceeds the exhaust gas temperature threshold the controller 12 reconfigures the valve arrangement 11 into the primary flow configuration. Optionally at this point (or later) the controller 12 may configure the valve arrangement 11 into the mixed flow configuration such that a quantity of now hot exhaust gas is passed through the water separator 10 to evaporate water from the sump 23 and pass the water vapour through the substate 6 and out of the exhaust system 2. Since the water vapour is only passed through the substrate 6 once the exhaust gas is hot enough the chances of liquid water condensing in the substrate or in its proximity are reduced. Additionally or alternatively, water in the sump 23 may be drained. After a suitable time period to allow evaporation of the water in the sump 23 the controller 12 may reconfigure the valve arrangement 11 into the primary flow configuration to reduce back pressure within the continued operation of the exhaust system 2. If required e.g. during periods of engine idling, cylinder cut out, etc. the valve arrangement 11 may be configured back into the secondary flow configuration to once again separate water from the exhaust gas. On engine key-off the controller 12 may default to configuring the valve arrangement into the secondary flow configuration in preparation for the next key-on operation.
Figure 5 shows a second embodiment of an exhaust system 2 according to the present invention. In this embodiment, the secondary channel 9 and primary channel 8 are co-axial, with the secondary channel 9 surrounding the primary channel 8. In particular, the secondary channel 9 and the primary channel 8 run co-axially.
The secondary channel 9 contains an adsorbent 21, optionally a molecular sieve or other adsorbent as discussed above with respect to the first embodiment.
The valve arrangement 11 controlling exhaust gas flow between the primary channel 8 and the secondary channel 9 is shown as a single flap valve. In alternative examples the valve arrangement 11 may be a poppet valve. The valve arrangement 11 may be positioned in the primary channel 8 or at the first junction 13. The second junction 14 may be formed at the terminus of the primary channel 8 as shown in Figure 5.
The second embodiment may also comprise an electrical heater (not shown in Figure 5) in the same manner as in the first embodiment.
Operation of the second embodiment is as described above for the first embodiment with the flow of exhaust gas between the primary channel 8 and the secondary channel 9 being under the control of the controller 12 through operation of the valve arrangement 11.
Figure 6 illustrates in flow-chart form an example operation of the exhaust system 2 of the embodiments. This flow-chart operation may be controlled e.g. by a pre-programmed processor of an Engine Control Unit (ECU). At step 100 a key-on event of the hydrogen ICE 1 is detected. At step 101 a determination is made whether water reduction of the exhaust gas is required based on the switching variables. If the determination is `Yes', the method moves to step 103 wherein the valve arrangement 11 is configured into the secondary flow configuration so that the exhaust gas is passed through the water separator 10. Alternatively, if at step 101 the determination is 'No' the method moves to step 102 and the primary flow configuration of the valve arrangement 11 is used. At step 104 a determination is made whether a key-off operation of the hydrogen ICE 1 is detected. If yes, the method terminates at step 105 by switching off the hydrogen ICE 1. In no, the method returns to step 101 for a further determination of whether water reduction of the exhaust gas is (still) required.
The invention can also be defined according to one or more of the following statements of invention:

1. An exhaust system of a hydrogen internal combustion engine (ICE), comprising:
- an inlet fluidly coupled to the hydrogen ICE and configured to receive exhaust gas from the hydrogen ICE;
- a substrate comprising a catalyst for treating the exhaust gas;
- an outlet for discharging the exhaust gas;
- a primary channel that provides fluid communication for the exhaust gas to flow from the inlet, through the substrate, and then to the outlet;
- a secondary channel that provides fluid communication for the exhaust gas to flow from the inlet, through a water separator, then through the substrate, and then to the outlet;
- a valve arrangement operable to control flow of the exhaust gas between the primary channel and the secondary channel, the valve arrangement comprising at least one valve element located in or upstream of the primary channel or at a junction of the primary and secondary channels; and
- a controller configured to operate the valve arrangement;
- the valve arrangement being configurable between a primary flow configuration and a secondary flow configuration, wherein in the primary flow configuration the valve arrangement directs the exhaust gas through the primary channel and in the secondary flow configuration the valve arrangement directs the exhaust gas through the secondary channel;
- the controller being configured to switch the valve arrangement between the primary flow configuration and the secondary flow configuration based on one or more switching variables comprising or consisting of:
  - - a water content of the exhaust gas; and/or
  - - a time period elapsed from a start-up event; and/or
  - - a temperature of the exhaust gas; and/or
  - - a temperature of one or more components of the hydrogen ICE; and/or
  - - a temperature of one or more substrate.
2. The exhaust system of 1, the valve arrangement being configurable between the primary flow configuration, the secondary flow configuration and a mixed flow configuration, wherein in the mixed flow configuration the valve arrangement directs the exhaust gas through both the primary channel and the secondary channel; and the controller is configured to switch the valve arrangement between the primary flow configuration, the secondary flow configuration and the mixed flow configuration based on the one or more switching variables.
3. The exhaust system of 1 or 2, wherein the controller is configured to configure the valve arrangement in the secondary flow configuration on detection of a start-up event of the hydrogen ICE.
4. The exhaust system of any of 1 to 3, wherein the controller is configured to switch the valve arrangement from the primary flow configuration to the secondary flow configuration based on changes in the one or more switching variables.
5. The exhaust system of any of 1 to 4, wherein in the secondary flow configuration the valve arrangement is configured to direct all or substantially all of the exhaust gas through the secondary channel.
6. The exhaust system of any of 1 to 5, wherein the water separator comprises a cyclone.
7. The exhaust system of 6, wherein the cyclone comprises a housing having a peripheral inlet configured to receive exhaust gas and a central outlet configured to discharge exhaust gas such that a flow of the exhaust gas through the cyclone is spirally inwards from the peripheral inlet to the central outlet.
8. The exhaust system of 7, wherein the central outlet is longitudinally offset from the peripheral inlet such that the flow of exhaust gas through the cyclone spirals along a longitudinal axis of the housing.
9. The exhaust system of 7 or 8, wherein the peripheral inlet is located at or towards an upper end of the housing and the central outlet is located below the peripheral inlet.
10. The exhaust system of any one of 7 to 9, wherein the central outlet communicates with a discharge conduit that is orientated such that water condensing from the exhaust gas within the discharge conduit drains back under gravity into the housing.
11. The exhaust system of any one of 7 to 10, wherein a lower portion of the housing forms a collector for holding condensed water.
12. The exhaust system of 11, wherein the collector contains an adsorbent; and optionally wherein the adsorbent is a woven or non-woven fabric, optionally a gauze.
13. The exhaust system of 11 or 12, wherein the water separator comprises a drain for discharging condensed water from the collector.
14. The exhaust system of any one of 1 to 13, wherein the water separator, optionally a lower portion thereof, comprises, or is coupled with, a heat exchanger for supplying heat energy to evaporate water held in the water separator; and optionally wherein the heat exchanger is configured to receive a flow of an engine fluid of the hydrogen ICE, optionally a flow of engine coolant fluid.
15. The exhaust system of any one of 1 to 5, wherein the secondary channel and primary channel are co-axial, and optionally the secondary channel surrounds the primary channel.
16. The exhaust system of 15, wherein the secondary channel contains an adsorbent, optionally a molecular sieve.
17. The exhaust system of any one of 1 to 16, wherein the at least one valve element of the valve arrangement comprises a flap valve or a poppet valve.
18. An exhaust system of a hydrogen internal combustion engine (ICE), comprising:
- an inlet fluidly coupled to the hydrogen ICE and configured to receive exhaust gas from the hydrogen ICE;
- a substrate comprising a catalyst for treating the exhaust gas;
- an outlet for discharging the exhaust gas;
- a primary channel that provides fluid communication for the exhaust gas to flow from the inlet, through the substrate, and then to the outlet;
- a secondary channel that provides fluid communication for the exhaust gas to flow from the inlet, through a water separator, then through the substrate, and then to the outlet;
- a valve arrangement operable to control flow of the exhaust gas between the primary channel and the secondary channel, the valve arrangement comprising at least one valve element located in or upstream of the primary channel or at a junction of the primary and secondary channels; and
- a controller configured to operate the valve arrangement;
- the valve arrangement being configurable between a primary flow configuration and a secondary flow configuration, wherein in the primary flow configuration the valve arrangement directs the exhaust gas through the primary channel and in the secondary flow configuration the valve arrangement directs the exhaust gas through the secondary channel;
- the controller being configured to switch the valve arrangement between the primary flow configuration and the secondary flow configuration based on one or more switching variables;
- wherein the water separator comprises a cyclone.
19. The exhaust system of 18, wherein the one or more switching variables comprises or consists of :
- a water content of the exhaust gas; and/or
- a time period elapsed from a start-up event; and/or
- a temperature of the exhaust gas; and/or
- a temperature of one or more components of the hydrogen ICE; and/or
- a temperature of one or more substrate.
20. The exhaust system of 18 or 19, the valve arrangement being configurable between the primary flow configuration, the secondary flow configuration and a mixed flow configuration, wherein in the mixed flow configuration the valve arrangement directs the exhaust gas through both the primary channel and the secondary channel; and the controller is configured to switch the valve arrangement between the primary flow configuration, the secondary flow configuration and the mixed flow configuration based on the one or more switching variables.
21. A method of treating emissions from a hydrogen internal combustion engine (ICE) by coupling an exhaust outlet of the hydrogen ICE to an inlet of an exhaust system such that the exhaust system receives exhaust gas from the hydrogen ICE, the exhaust system being of the type comprising:
- a substrate comprising a catalyst for treating the exhaust gas;
- an outlet for discharging the exhaust gas;
- a primary channel that provides fluid communication for the exhaust gas to flow from the inlet, through the substrate, and then to the outlet;
- a secondary channel that provides fluid communication for the exhaust gas to flow from the inlet, through a water separator, then through the substrate, and then to the outlet;
- a valve arrangement operable to control flow of the exhaust gas between the primary channel and the secondary channel, the valve arrangement comprising at least one valve element located in or upstream of the primary channel or at a junction of the primary and secondary channels; and
- a controller configured to operate the valve arrangement;
the method comprising the steps of:
- - using the controller to selectively configure the valve arrangement into a primary flow configuration and a secondary flow configuration based on one or more switching variables, wherein in primary flow configuration the valve arrangement directs the exhaust gas through the primary channel and in the secondary flow configuration the valve arrangement directs the exhaust gas through the secondary channel;
  wherein the one or more switching variables comprises or consists of:
  - - a water content of the exhaust gas; and/or
  - - a time period elapsed from a start-up event; and/or
  - - a temperature of the exhaust gas; and/or
  - - a temperature of one or more components of the hydrogen ICE; and/or
  - - a temperature of one or more substrate.
22. The method of 21, comprising selectively configuring the valve arrangement into the primary flow configuration, the secondary flow configuration and a mixed flow configuration based on the one or more switching variables.
23. The method of 21 or 22, wherein the controller configures the valve arrangement into the secondary flow configuration on detection of a start-up event of the hydrogen ICE.
24. The method of any one of 21 to 23, wherein, when the valve arrangement is in the primary flow configuration the exhaust gas does not pass through a water separator or condenser; and/or
wherein, when the valve arrangement is in the secondary flow configuration the exhaust gas passes through a cyclone water separator.
25. A controller configured to operate a valve arrangement and/or an exhaust system using the method of any one of 21 to 24.

For the avoidance of any doubt, the entire content of any and all documents cited herein is incorporated by reference into the present application.

Claims

An exhaust system of a hydrogen internal combustion engine (ICE), comprising:
- an inlet fluidly coupled to the hydrogen ICE and configured to receive exhaust gas from the hydrogen ICE;

- a substrate comprising a catalyst for treating the exhaust gas;

- an outlet for discharging the exhaust gas;

- a primary channel that provides fluid communication for the exhaust gas to flow from the inlet, through the substrate, and then to the outlet;

- a secondary channel that provides fluid communication for the exhaust gas to flow from the inlet, through a water separator, then through the substrate, and then to the outlet;

- a valve arrangement operable to control flow of the exhaust gas between the primary channel and the secondary channel, the valve arrangement comprising at least one valve element located in or upstream of the primary channel or at a junction of the primary and secondary channels; and

- a controller configured to operate the valve arrangement;

the valve arrangement being configurable between a primary flow configuration and a secondary flow configuration, wherein in the primary flow configuration the valve arrangement directs the exhaust gas through the primary channel and in the secondary flow configuration the valve arrangement directs the exhaust gas through the secondary channel;

the controller being configured to switch the valve arrangement between the primary flow configuration and the secondary flow configuration based on one or more switching variables comprising or consisting of:
- a water content of the exhaust gas; and/or

- a time period elapsed from a start-up event; and/or

- a temperature of the exhaust gas; and/or

- a temperature of one or more components of the hydrogen ICE; and/or

- a temperature of one or more substrate.
The exhaust system of claim 1, the valve arrangement being configurable between the primary flow configuration, the secondary flow configuration and a mixed flow configuration, wherein in the mixed flow configuration the valve arrangement directs the exhaust gas through both the primary channel and the secondary channel; and the controller is configured to switch the valve arrangement between the primary flow configuration, the secondary flow configuration and the mixed flow configuration based on the one or more switching variables.
The exhaust system of claim 1 or claim 2, wherein the controller is configured to configure the valve arrangement in the secondary flow configuration on detection of a start-up event of the hydrogen ICE.
The exhaust system of any preceding claim, wherein the controller is configured to switch the valve arrangement from the primary flow configuration to the secondary flow configuration based on changes in the one or more switching variables.
The exhaust system of any preceding claim, wherein in the secondary flow configuration the valve arrangement is configured to direct all or substantially all of the exhaust gas through the secondary channel.
The exhaust system of any preceding claim, wherein the water separator comprises a cyclone.
The exhaust system of claim 6, wherein the cyclone comprises a housing having a peripheral inlet configured to receive exhaust gas and a central outlet configured to discharge exhaust gas such that a flow of the exhaust gas through the cyclone is spirally inwards from the peripheral inlet to the central outlet.
The exhaust system of claim 7, wherein the central outlet is longitudinally offset from the peripheral inlet such that the flow of exhaust gas through the cyclone spirals along a longitudinal axis of the housing.
The exhaust system of claim 7 or claim 8, wherein the peripheral inlet is located at or towards an upper end of the housing and the central outlet is located below the peripheral inlet.
The exhaust system of any one of claims 7 to 9, wherein the central outlet communicates with a discharge conduit that is orientated such that water condensing from the exhaust gas within the discharge conduit drains back under gravity into the housing.
The exhaust system of any one of claims 7 to 10, wherein a lower portion of the housing forms a collector for holding condensed water.
The exhaust system of any preceding claim, wherein the water separator, optionally a lower portion thereof, comprises, or is coupled with, a heat exchanger for supplying heat energy to evaporate water held in the water separator; and optionally wherein the heat exchanger is configured to receive a flow of an engine fluid of the hydrogen ICE, optionally a flow of engine coolant fluid.
The exhaust system of any one of claims 1 to 5, wherein the secondary channel and primary channel are co-axial, and optionally the secondary channel surrounds the primary channel.
An exhaust system of a hydrogen internal combustion engine (ICE), comprising:
- an inlet fluidly coupled to the hydrogen ICE and configured to receive exhaust gas from the hydrogen ICE;

- a substrate comprising a catalyst for treating the exhaust gas;

- an outlet for discharging the exhaust gas;

- a primary channel that provides fluid communication for the exhaust gas to flow from the inlet, through the substrate, and then to the outlet;

- a secondary channel that provides fluid communication for the exhaust gas to flow from the inlet, through a water separator, then through the substrate, and then to the outlet;

- a valve arrangement operable to control flow of the exhaust gas between the primary channel and the secondary channel, the valve arrangement comprising at least one valve element located in or upstream of the primary channel or at a junction of the primary and secondary channels; and

- a controller configured to operate the valve arrangement;

the valve arrangement being configurable between a primary flow configuration and a secondary flow configuration, wherein in the primary flow configuration the valve arrangement directs the exhaust gas through the primary channel and in the secondary flow configuration the valve arrangement directs the exhaust gas through the secondary channel;

the controller being configured to switch the valve arrangement between the primary flow configuration and the secondary flow configuration based on one or more switching variables;

wherein the water separator comprises a cyclone.
A method of treating emissions from a hydrogen internal combustion engine (ICE) by coupling an exhaust outlet of the hydrogen ICE to an inlet of an exhaust system such that the exhaust system receives exhaust gas from the hydrogen ICE, the exhaust system being of the type comprising:
- a substrate comprising a catalyst for treating the exhaust gas;

- an outlet for discharging the exhaust gas;

- a primary channel that provides fluid communication for the exhaust gas to flow from the inlet, through the substrate, and then to the outlet;

- a secondary channel that provides fluid communication for the exhaust gas to flow from the inlet, through a water separator, then through the substrate, and then to the outlet;

- a valve arrangement operable to control flow of the exhaust gas between the primary channel and the secondary channel, the valve arrangement comprising at least one valve element located in or upstream of the primary channel or at a junction of the primary and secondary channels; and

- a controller configured to operate the valve arrangement;

the method comprising the steps of:
- using the controller to selectively configure the valve arrangement into a primary flow configuration and a secondary flow configuration based on one or more switching variables, wherein in primary flow configuration the valve arrangement directs the exhaust gas through the primary channel and in the secondary flow configuration the valve arrangement directs the exhaust gas through the secondary channel;

wherein the one or more switching variables comprises or consists of:
- a water content of the exhaust gas; and/or

- a time period elapsed from a start-up event; and/or

- a temperature of the exhaust gas; and/or

- a temperature of one or more components of the hydrogen ICE; and/or

- a temperature of one or more substrate.