Engine system, and a method to control recirculation ofammonia within an engine system

Abstract

An engine system includes an engine, a hydrogen generation system, an emission control system, and a heater. The engine receives a fluid mixture of fuel and air and provides an exhaust based on combustion of the fluid mixture. The hydrogen generation system receives ammonia from at least an ammonia source, generates hydrogen from the ammonia, and provides the hydrogen to the engine. The emission control system includes an ammonia recirculation unit that receives the exhaust from the engine and dissolves remaining ammonia in the exhaust into aqueous ammonia, and a hydrogen control unit that receives the exhaust from the ammonia recirculation unit, converts remaining hydrogen in the exhaust into water, and outputs remaining nitrogen in the exhaust. The heater receives the aqueous ammonia from the ammonia recirculation unit, heats the aqueous ammonia to generate dry ammonia, and provides the dry ammonia to the hydrogen generation system.

Description

ENGINE SYSTEM, AND A METHOD TO CONTROL RECIRCULATION OFAMMONIA WITHIN AN ENGINE SYSTEMCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 567,525, filed March 20, 2024, which is incorporated herein by reference in its entirety and for all purposes.TECHNICAL FIELD

[0002] The present application relates generally to engine systems.BACKGROUND

[0003] Engine systems can include internal combustion engines that receive fuel and air, combust the fuel and air, and release exhaust generated based on combustion of the fuel and air.SUMMARY

[0004] In one embodiment, an engine system includes an engine that receives a fluid mixture of fuel and air, combusts the fluid mixture, and provides an exhaust based on combustion of the fluid mixture. The engine system further includes a hydrogen generation system that receives ammonia from at least an ammonia source, generates hydrogen from the ammonia, and provides the hydrogen to the engine. The fuel includes the hydrogen. The engine system further includes an emission control system that includes an ammonia recirculation unit that receives the exhaust from the engine and dissolves remaining ammonia in the exhaust into aqueous ammonia, and a hydrogen control unit disposed downstream of the ammonia recirculation unit. The hydrogen control unit receives the exhaust from the ammonia recirculation unit, converts remaining hydrogen in the exhaust into water, and outputs remaining nitrogen in the exhaust. The engine system further includes a heater disposed downstream of the ammonia recirculation unit. The heater receives the aqueous ammonia from the ammonia recirculation unit, heats the aqueousammonia to generate dry ammonia, and provides the dry ammonia to the hydrogen generation system.

[0005] In another embodiment, an engine system includes an engine that receives a fluid mixture of fuel and air, combusts the fluid mixture, and provides an exhaust based on combustion of the fluid mixture. The engine system further includes a hydrogen generation system that receives ammonia from at least an ammonia source, generates hydrogen from the ammonia, and provides the hydrogen to the engine. The fuel includes the hydrogen. The engine system further includes an emission control system. The emission control system further includes an exhaust aftertreatment system disposed downstream of the engine. The exhaust aftertreatment system receives the exhaust from the engine and treats the exhaust using at least a portion of the hydrogen generated by the hydrogen generation system to reduce or remove nitrogen oxides from the exhaust. The emission control system further includes an ammonia recirculation unit disposed downstream of the exhaust aftertreatment system. The ammonia recirculation unit receives the exhaust from the exhaust aftertreatment system, dissolves remaining ammonia in the exhaust, and provides the ammonia to the hydrogen generation system.|0006| In yet another embodiment, a method to control recirculation of ammonia within an engine system includes receiving, by a controller from an ammonia concentration sensor, an ammonia concentration signal associated with a level of ammonia in an aqueous solution within the ammonia recirculation unit. The method further includes determining, by the controller based on the ammonia concentration signal, a concentration of the ammonia within the ammonia recirculation unit. The method further includes receiving, by the controller from an ammonia amount sensor, an ammonia amount signal associated with a volume of the aqueous solution within the ammonia recirculation unit. The method further includes determining, by the controller based on the ammonia amount signal, an amount of the ammonia within the ammonia recirculation unit. The method further includes, in response to determining that the concentration of the ammonia within the ammonia recirculation unit is equal to or above a concentration threshold and that the amount of the ammonia within the ammonia recirculation unit is equal to or above an amount threshold, operating, by the controller, a pump to receive at least a portion ofan aqueous ammonia from the ammonia recirculation unit and provide the at least the portion of the aqueous ammonia to a heater disposed downstream of the ammonia recirculation unit. The method further includes operating, by the controller, the heater to receive the at least the portion of the aqueous ammonia from the pump, heat the at least the portion of the aqueous ammonia to remove moisture and produce dry ammonia, and provide the dry ammonia to a hydrogen generation system.BRIEF DESCRIPTION OF THE DRAWINGS[0007| The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the disclosure will become apparent from the description, the drawings, and the claims, in which:(0008] FIG. l is a block schematic diagram of an engine system according to an example embodiment;

[0009] FIG. 2 is a flow diagram of a method to control recirculation of ammonia according to an example embodiment;(0010] FIG. 3 is an example graph of an ammonia conversion percentage relative to an oxygen-to-ammonia ratio; and[00111 FIG. 4 is an example graph of nitrogen oxide and nitrous oxide concentrations relative to the oxygen-to-ammonia ratio.

[0012] It will be recognized that the Figures are schematic representations for purposes of illustration. The Figures are provided for the purpose of illustrating one or more implementations with the explicit understanding that the Figures will not be used to limit the scope or the meaning of the claims.DETAILED DESCRIPTION

[0013] Following below are more detailed descriptions of various concepts related to, and implementations of, methods, apparatuses, and systems for an engine system. The various concepts introduced above and discussed in greater detail below can be implemented in any of a number of ways, as the described concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

[0014] FIG. 1 illustrates an engine system 100. The engine system 100 comprises an engine 102 configured to receive a fluid mixture of fuel and air, combust the fluid mixture, and provide an exhaust based on combustion of the fluid mixture. The engine system 100 further comprises a hydrogen generation system 110 configured to receive ammonia from at least an ammonia source 104, generate hydrogen from the ammonia, and provide the hydrogen to the engine 102. The fuel comprises the hydrogen. The engine system 100 further comprises an emission control system 150 comprising an ammonia recirculation unit 152 configured to receive the exhaust from the engine 102 and dissolve remaining ammonia in the exhaust into aqueous ammonia. The emission control system 150 further comprises a hydrogen control unit 154 disposed downstream of the ammonia recirculation unit 152. The hydrogen control unit 154 is configured to receive the exhaust from the ammonia recirculation unit 152, convert remaining hydrogen in the exhaust into water, and output remaining nitrogen in the exhaust. The engine system 100 further comprises a heater 170 disposed downstream of the ammonia recirculation unit 152. The heater 170 is configured to receive the aqueous ammonia from the ammonia recirculation unit 152, heat the aqueous ammonia to generate dry ammonia, and provide the dry ammonia to the hydrogen generation system 110.(0015] In some embodiments, the engine system 100 includes the engine 102 configured to receive the fluid mixture of fuel and air, combust the fluid mixture, and provide the exhaust based on combustion of the fluid mixture. The engine system 100 further includes the hydrogen generation system 110 configured to receive ammonia from at least the ammonia source 104,generate hydrogen from the ammonia, and provide the hydrogen to the engine. The fuel includes the hydrogen. The engine system 100 further includes the emission control system 150. The emission control system 150 includes an exhaust aftertreatment system 156 disposed downstream of the engine. The exhaust aftertreatment system 156 is configured to receive the exhaust from the engine 102 and treat the exhaust using at least a portion of the hydrogen generated by the hydrogen generation system 110 to reduce or remove nitrogen oxides from the exhaust. The emission control system 150 further includes the ammonia recirculation unit 152 disposed downstream of the exhaust aftertreatment system 156. The ammonia recirculation unit 152 is configured to receive the exhaust from the exhaust aftertreatment system 156, dissolve remaining ammonia in the exhaust, and provide the ammonia to the hydrogen generation system 110.[0016J The engine 102 can be an internal combustion engine, such as a spark-ignition engine or a compression-ignition engine. Examples of the engine 102 include a hydrogen engine, a diesel engine, a gasoline engine, a propane engine, a dual-fuel engine, a natural gas engine, etc. The engine 102 is configured to receive the fluid mixture of the fuel (e.g., hydrogen, diesel, gasoline, propane, natural gas, etc., or a combination of fuels), from the hydrogen generation system 110, and the air, from an air source 106 (e.g., air intake, etc.), and combust the fluid mixture to produce energy that can be utilized by various outputs. For example, the engine 102 can produce energy that is utilized to drive a movement member (e.g., wheel, tread, propeller, impeller, turbine, rotor, etc.) or power a generator. The engine 102 can be implemented in a vehicle (e.g., truck, car, construction vehicle, freight vehicle, commercial vehicle, emergency vehicle, military vehicle, maritime vehicle, etc.). In some embodiments, the engine system 100 can include a fuel cell instead of, or in combination with, the engine 102.

[0017] The ammonia provided by the ammonia source 104 and / or other components during recirculation (e.g., ammonia recirculation unit 152, etc.) can be utilized as a hydrogen carrier for energy storage and transportation. The utilization of ammonia as the hydrogen carrier can offer various advantages. For example, ammonia possesses a relatively high energy density, such that ammonia is capable of storing a relatively high energy per unit volume. Additionally, ammoniaexhibits facile liquefaction under relatively low pressures, allowing for storage and transportation under ambient conditions. Furthermore, ammonia is relatively accessible and can be synthesized from renewable sources, such that ammonia can be a sustainable and environmentally conscious energy carrier.

[0018] The hydrogen generation system 110 can include an ammonia cracking unit 112 configured to receive the ammonia from at least the ammonia source 104 and convert the ammonia (i.e., crack the ammonia, etc.) into hydrogen and nitrogen. In some embodiments, the ammonia cracking unit 112 does not convert an entirety of the ammonia into the hydrogen and the nitrogen. For example, the ammonia cracking unit 112 can be configured to receive the ammonia from at least the ammonia source 104, convert a first portion of the ammonia into the hydrogen and nitrogen, and provide an inlet mixture through an inlet mixture stream 114 that includes the hydrogen, the nitrogen, and a second portion of the ammonia. The second portion of the ammonia includes unreacted (e.g., unconverted, uncracked, etc.) ammonia that did not convert into the hydrogen and the nitrogen by the ammonia cracking unit 112.[00.1.9] The hydrogen generation system 110 includes a hydrogen separation unit 116 disposed downstream of the ammonia cracking unit 112. The hydrogen separation unit 116 can include an ammonia hydrolysis unit 118 that is configured to receive the inlet mixture from the ammonia cracking unit 112 through the inlet mixture stream 114, remove the second portion of the ammonia from the inlet mixture through an ammonia outlet stream 120, and provide the hydrogen and the nitrogen from the inlet mixture to a downstream component of the hydrogen separation unit 116, the hydrogen generation system 110, and / or the engine system 100. The ammonia hydrolysis unit 118 can receive and / or utilize water to perform a hydrolysis reaction on the ammonia, in which the ammonia and the water are the reactants and ammonium and hydroxide are the products. The hydrolysis reaction can be exothermic and can occur substantially spontaneously at room temperature.

[0020] The hydrogen generation system 110 can include a first pump 122 disposed downstream of the ammonia hydrolysis unit 118 and a first heat exchanger 124 disposeddownstream of the first pump 122. The first pump 122 is configured to receive the second portion of the ammonia from the ammonia hydrolysis unit 118 through the ammonia outlet stream 120 and provide the second portion of the ammonia to the first heat exchanger 124. The first heat exchanger 124 is configured to receive the second portion of the ammonia from the first pump 122, receive a heated coolant from the engine 102 via a heated coolant stream 126, extract heat from the heated coolant, provide the heat to the second portion of the ammonia to remove moisture from the second portion of the ammonia, provide dry ammonia (e.g., non-aqueous ammonia, ammonia that lacks, or substantially lacks, moisture, etc.) through a first dry ammonia stream 128, and provide water (i.e., water extracted from the second portion of the ammonia) through a first water stream 130. By utilizing heat from the heated coolant, the first heat exchanger 124 promotes improved fuel efficiency by maximizing heat recycling within the engine system 100.

[0021] The first heat exchanger 124 provides the dry ammonia upstream of the ammonia cracking unit 112 through the first dry ammonia stream 128, such that the ammonia cracking unit 112 is configured to receive ammonia (e.g., dry ammonia) from at least the ammonia source 104 and the first heat exchanger 124 via the first dry ammonia stream 128.

[0022] In some embodiments, the first heat exchanger 124 releases the water through the first water stream 130 to an ambient environment. In other embodiments, the first heat exchanger 124 releases the water through the first water stream 130 to components of the engine system 100, the hydrogen generation system 110 (e.g., the ammonia hydrolysis unit 118, etc.), and / or the emission control system 150.[00231 In some embodiments, in which a temperature of the heated coolant from the engine 102 is higher than a temperature of the second portion of the ammonia from the first pump 122 and / or the ammonia hydrolysis unit 118 within the first heat exchanger 124, the first heat exchanger 124 is utilized to extract moisture from the second portion of the ammonia and provide the dry ammonia.[0024| In other embodiments, in which the temperature of the heated coolant from the engine 102 is equal to or lower than the temperature of the second portion of the ammonia from the first pump 122 and / or the ammonia hydrolysis unit 118 within the first heat exchanger 124, or in which heat provided by the first heat exchanger 124 via the heated coolant is insufficient to extract, or substantially extract, moisture from the second portion of the ammonia, the hydrogen generation system 110 includes an additional heater (e.g., grid gas heater, surface heater, resistance heater, electrical heater, etc.) to provide heat, or additional heat (i.e., when utilized in combination with the first heat exchanger 124), to the second portion of the ammonia to remove moisture from the second portion of the ammonia and provide the dry ammonia.

[0025] The first heat exchanger 124 can include sensors, such as temperature sensors, that can provide signals to a controller (discussed in further detail below) that are indicative of the temperatures of the heated coolant and the second portion of the ammonia. The controller can determine the temperatures of the heated coolant and the second portion of the ammonia based on the signals from the sensors and control the first heat exchanger 124 and / or the additional heater based on the determined temperatures.

[0026] The hydrogen separation unit 116 includes a hydrogen selective membrane 132 disposed downstream of the ammonia hydrolysis unit 118. The hydrogen selective membrane 132 is configured to receive the hydrogen and the nitrogen from the ammonia hydrolysis unit 118 and separate the hydrogen and the nitrogen. In some embodiments, the hydrogen selective membrane 132 is configured to provide the hydrogen through a hydrogen outlet stream 134 and the nitrogen through a first nitrogen stream 136. In some embodiments, the hydrogen selective membrane 132 releases the nitrogen through the first nitrogen stream 136 to the ambient environment and / or components of the engine system 100, the hydrogen generation system 110, and / or the emission control system 150.

[0027] The hydrogen generation system 110 can include a hydrogen tank 138 disposed downstream of the hydrogen selective membrane 132 and upstream of the engine 102. The hydrogen tank 138 is configured to receive the hydrogen from the hydrogen selective membrane132 through the hydrogen outlet stream 134, retain the hydrogen, and provide at least a portion of the hydrogen to the engine 102 as the fuel or a portion of the fuel. The hydrogen tank 138 can act as a fuel buffer for the engine 102 such that the engine 102 receives a steady (i.e., uniform) stream of hydrogen from the hydrogen generation system 110.

[0028] In some embodiments, the hydrogen generation system 110 includes multiple hydrogen tanks 138 (i.e., a primary tank, a secondary tank, an auxiliary tank, or any one or combination thereof, multiple primary tanks, multiple secondary tanks, multiple auxiliary tanks, or any one or combination thereof, etc.).

[0029] The hydrogen generation system 110 can include a second heat exchanger 140 configured to receive the exhaust, extract heat from the exhaust, provide the heat to the ammonia cracking unit 112, and output the exhaust downstream to a component of the emission control system 150. The ammonia cracking unit 112 utilizes the heat provided by the second heat exchanger 140 to convert the ammonia, or the first portion of the ammonia, to hydrogen and nitrogen. By utilizing heat from the exhaust, the second heat exchanger 140 promotes improved fuel efficiency by maximizing heat recycling within the engine system 100.

[0030] In some embodiments, the hydrogen generation system 110 can include multiple second heat exchangers 140. For example, the hydrogen generation system 110 can include two second heat exchangers 140 that include an upstream heat exchanger and a downstream heat exchanger downstream of the upstream heat exchanger. The upstream heat exchanger can be configured receive the exhaust, extract heat from the exhaust, provide the heat to the ammonia cracking unit 112, and output the exhaust downstream to the component of the emission control system 150 and / or to the downstream heat exchanger. The downstream heat exchanger can be configured to receive at least a portion of the exhaust from the upstream heat exchanger, extract additional heat from the at least the portion of the exhaust, provide the additional heat to the ammonia cracking unit 112 or another ammonia cracking unit that is similar but separate from the ammonia cracking unit 112, and output the at least the portion of the exhaust downstream to the component of the emission control system 150.[00311 In some embodiments, an ammonia conversion percentage of the ammonia cracking unit 112 can be based on an operating temperature of the ammonia cracking unit 112. In some examples, the higher the operating temperature of the ammonia cracking unit 112 is, the higher the ammonia conversion percentage is of the ammonia cracking unit 112. For example, at relatively high operating temperatures, the ammonia conversion percentage of the ammonia cracking unit 112 can approach 100%. In some embodiments, the ammonia cracking unit 112 converts the ammonia, or the first portion of the ammonia, to hydrogen and nitrogen when operating under an operating temperature between about 250 degrees C (e g., + / - 15%, + / - 10%, + / - 5%, + / -!%, etc. of 250 degrees C) and about 550 degrees C, inclusive.|0032| The hydrogen generation system 110 can include a first heater 142 (e.g., grid gas heater, surface heater, resistance heater, electrical heater, etc.) that is configured to provide heat, or additional heat (i.e., when utilized in combination with the second heat exchanger 140), to the ammonia cracking unit 112.

[0033] In some embodiments, in which a temperature of the exhaust is higher than a temperature of the ammonia, or the first portion of the ammonia, in the ammonia cracking unit 112, the second heat exchanger 140 is utilized to provide heat to the ammonia cracking unit 112. In other embodiments, in which the temperature of the exhaust is equal to or lower than the temperature of the ammonia, or the first portion of the ammonia, in the ammonia cracking unit 112, or in which heat provided by the second heat exchanger 140 via the exhaust is insufficient for the ammonia cracking unit 112 to convert, or substantially convert, the ammonia, or the first portion of the ammonia, into hydrogen and nitrogen, the first heater 142 is configured to provide heat, or additional heat (i.e., when utilized in combination with the second heat exchanger 140), to the ammonia cracking unit 112.[0034J The second heat exchanger 140 can include sensors, such as temperature sensors, that can provide signals to the controller (discussed in further detail below) that are indicative of the temperatures of the exhaust and the ammonia, or the first portion of the ammonia. The controller can determine the temperatures of the exhaust and the ammonia, or the first portion of theammonia, based on the signals from the sensors and control the second heat exchanger 140 and / or the first heater 142 based on the determined temperatures.

[0035] The emission control system 150 includes an exhaust aftertreatment system 156 disposed downstream of the engine 102 and upstream of the ammonia recirculation unit 152. The exhaust aftertreatment system 156 is configured to receive the exhaust from the engine 102 and treat the exhaust using a treatment fluid received from a treatment fluid source 158 (e.g., a treatment fluid tank, a treatment fluid line, etc.) to reduce or remove nitrogen oxide (NOx) compounds and / or nitrous oxide (N2O) by-products from the exhaust.

[0036] The treatment fluid can be, for example, a reductant (e.g., hydrogen, urea, diesel exhaust fluid (DEF), Adblue®, a urea water solution (UWS), an aqueous urea solution (e.g., AUS32, etc.), and / or other similar fluids) or a hydrocarbon fluid (e.g., fuel, oil, additive, etc.). When the treatment fluid is introduced into the exhaust, reduction of emission of undesirable components (e.g., NOx compounds, N2O by-products, etc.) in the exhaust can be facilitated. When the hydrocarbon fluid is introduced into the exhaust, the temperature of the exhaust can be increased (e.g., to facilitate regeneration of components of the exhaust aftertreatment system 156, etc.). For example, the exhaust aftertreatment system 156 can include a spark plug (e.g., igniter, etc.) configured to increase the temperature of the exhaust by combusting the hydrocarbon fluid within the exhaust.

[0037] The engine system 100 can include a first bypass valve 160 disposed downstream of the hydrogen tank 138 and upstream of the engine 102. The engine system 100 can further include a first bypass line 162 fluidly coupled to the first bypass valve 160 and the treatment fluid source 158. The first bypass valve 160 is configured to selectively adjust a flowrate of the hydrogen received by the treatment fluid source 158 from the hydrogen tank 138 via the first bypass line 162.

[0038] The first bypass valve 160 is operable between multiple positions, e.g., a first position, a second position, and a third position. For example, at the first position (i.e., a closed position), the first bypass valve 160 allows a maximum amount of the hydrogen to flow from thehydrogen tank 138 to the engine 102 and prevents, or substantially prevents (e.g., allows a minimum amount of), the hydrogen from flowing from the hydrogen tank 138 to the treatment fluid source 158 via the first bypass line 162. At the second position (i.e., an open position), the first bypass valve 160 allows a maximum amount of the hydrogen to flow from the hydrogen tank 138 to the treatment fluid source 158 via the first bypass line 162 and prevents, or substantially prevents (e.g., allows a minimum amount of), the hydrogen from flowing from the hydrogen tank 138 to the engine 102, such that the hydrogen bypasses the engine 102. At the third position (i.e., a partially open position, a partially closed position, etc.), the first bypass valve 160 allows a first portion of the hydrogen to flow from the hydrogen tank 138 to the treatment fluid source 158 via the first bypass line 162 and allows a second portion of the hydrogen to flow from the hydrogen tank 138 to the engine 102, such that the first portion of the hydrogen bypasses the engine 102.

[0039] The exhaust aftertreatment system 156 can include a catalyst member (e.g., a Selective Catalytic Reduction (SCR) catalyst member, etc.). The treatment fluid can be injected upstream of the catalyst member such that the catalyst member receives a mixture of the treatment fluid and the exhaust. The treatment fluid droplets undergo the processes of evaporation, thermolysis, and hydrolysis to form non-NOx emissions (e.g., gaseous ammonia, etc.) downstream of the exhaust aftertreatment system 156.

[0040] In some embodiments, the exhaust aftertreatment system 156 excludes an ammonia slip catalyst (ASC), such that the ammonia in the exhaust is passed downstream of the exhaust aftertreatment system 156 for recirculation, rather than being removed (e.g., oxidized, etc ), partially or totally, by the ASC. Exclusion of the ASC within the exhaust aftertreatment system 156 can mitigate generation of NOx and / or N2O by-products in the exhaust that can result from oxidation of the ammonia by the ASC due to presence of hydrogen in the exhaust.

[0001] In some embodiments, the second heat exchanger 140 is disposed downstream of the exhaust aftertreatment system 156. In other embodiments, the second heat exchanger 140 is disposed upstream of the exhaust aftertreatment system 156.[0042| The emission control system 150 can include a valve 164 disposed downstream of the second heat exchanger 140 and / or the exhaust aftertreatment system 156 and upstream of the ammonia recirculation unit 152. The valve 164 can include a backflow preventer that prevents the exhaust from backflowing (i.e., flowing from the ammonia recirculation unit 152 upstream to the second heat exchanger 140, flowing from the ammonia recirculation unit 152 upstream to the exhaust aftertreatment system 156, etc.). The backflow preventer is configured to operate based on a pressure difference between the exhaust upstream of the backflow preventor and the exhaust downstream of the backflow preventor.

[0043] The backflow preventer can include one or more check valves that control and limit a flow direction of the exhaust to one direction. For example, the one or more check valves allow the exhaust to flow from the second heat exchanger 140 and / or the exhaust aftertreatment system 156 to the ammonia recirculation unit 152, and the one or more check valves prevent the exhaust from flowing from the ammonia recirculation unit 152 to the second heat exchanger 140 and / or the exhaust aftertreatment system 156. The one or more check valves of the backflow preventer are operable between an open position in which the one or more check valves allow the exhaust to flow therethrough and a closed position in which the one or more check valves prevent the exhaust from flowing therethrough.

[0044] The one or more check valves operate in the open position when a pressure of the exhaust upstream of the backflow preventor (e.g., the valve 164), such as at the second heat exchanger 140 and / or the exhaust aftertreatment system 156, is greater than a pressure of the exhaust downstream of the backflow preventor, such as at the ammonia recirculation unit 152. Under normal operating conditions, the pressure of the exhaust at the second heat exchanger 140 and / or the exhaust aftertreatment system 156 is higher than the pressure of the exhaust at the ammonia recirculation unit 152, such that the one or more check valves operate in the open position.

[0045] The one or more check valves operate in the closed position when the pressure of the exhaust upstream of the backflow preventor (e.g., the valve 164), such as at the second heatexchanger 140 and / or the exhaust aftertreatment system 156, is less than the pressure of the exhaust downstream of the backflow preventer, such as at the ammonia recirculation unit 152. In some embodiments in which the one or more check valves of the backflow preventor are in the closed position (i.e., when the pressure of the exhaust downstream of the backflow preventor is greater than the pressure of the exhaust upstream of the backflow preventor), the one or more check valves of the backflow preventer close to prevent aqueous ammonia from flowing from the ammonia recirculation unit 152 to the second heat exchanger 140 and / or the exhaust aftertreatment system 156.

[0046] In some embodiments, the emission control system 150 includes a second bypass valve 165 disposed downstream of the second heat exchanger 140 and / or the exhaust aftertreatment system 156 and upstream of the valve 164. The emission control system 150 can include a second bypass line 167 that is fluidly coupled to the second bypass valve 165 and the hydrogen control unit 154. The second bypass valve 165 is configured to, when the one or more check valves of the backflow preventer are in the closed position, communicate the exhaust from the second heat exchanger 140 and / or the exhaust aftertreatment system 156 to the hydrogen control unit 154 via the second bypass line 167, thereby bypassing the ammonia recirculation unit 152. In these embodiments, residual ammonia and hydrogen that remain in the exhaust can be converted to water and hydrogen via a hydrogen slip catalyst of the hydrogen control unit 154.

[0047] The ammonia recirculation unit 152 is configured to receive the exhaust from the second heat exchanger 140, the exhaust aftertreatment system 156, and / or the engine 102, dissolve remaining ammonia in the exhaust into aqueous ammonia, and provide the aqueous ammonia through an aqueous ammonia stream 166. The ammonia recirculation unit 152 can provide the benefit of recirculating ammonia in the exhaust as input into the hydrogen generation system 110 and / or the ammonia cracking unit 112, while also removing or reducing emission of ammonia into the ambient environment by the exhaust. In some embodiments, the ammonia recirculation unit 152 is pre-charged with the aqueous ammonia, which can prevent or minimize freezing of the ammonia within the ammonia recirculation unit 152.[0048| The engine system 100 can include a second pump 168 disposed downstream of the ammonia recirculation unit 152 and a second heater, e.g., the heater 170 (e.g., grid gas heater, surface heater, resistance heater, electrical heater, etc.) disposed downstream of the second pump 168. The second pump 168 is configured to receive the aqueous ammonia from the ammonia recirculation unit 152 through the aqueous ammonia stream 166 and provide the aqueous ammonia to the heater 170. The heater 170 is configured to receive the aqueous ammonia from the second pump 168, heat the aqueous ammonia to remove moisture from the aqueous ammonia, provide dry ammonia (e.g., non-aqueous ammonia, ammonia that lacks, or substantially lacks, moisture, etc.) through a second dry ammonia stream 172, and provide water extracted from the aqueous ammonia through a second water stream 174.[0049 In some embodiments, the heater 170 releases the water through the second water stream 174 to the ammonia hydrolysis unit 118, where the ammonia hydrolysis unit 118 utilizes the water from the heater 170 to perform the hydrolysis reaction. In other embodiments, the heater 170 releases the water through the second water stream 174 to the ambient environment and / or other components of the engine system 100, the hydrogen generation system 110, and / or the emission control system 150.

[0050] The heater 170 provides the dry ammonia upstream of the ammonia cracking unit 112 through the second dry ammonia stream 172, such that the hydrogen generation system 110 and / or the ammonia cracking unit 112 is configured to receive ammonia (e.g., dry ammonia) from at least the ammonia source 104 and the heater 170 via the second dry ammonia stream 172. In some embodiments, the hydrogen generation system 110 and / or the ammonia cracking unit 112 is configured to receive ammonia (e.g., dry ammonia) from the ammonia source 104, the first heat exchanger 124 via the first dry ammonia stream 128, and the heater 170 via the second dry ammonia stream 172.

[0051] The hydrogen control unit 154 can include a hydrogen slip catalyst. In some embodiments, the hydrogen slip catalyst can be formulated with platinum group metals (PGM) in a range of 0.1 grams per cubic foot and 4 grams per cubic foot. In some further embodiments, thehydrogen slip catalyst is formulated with PGM in a range of 0.1 grams per cubic foot and 2 grams per cubic foot.

[0052] The hydrogen control unit 154 is configured to receive the exhaust from the ammonia recirculation unit 152, convert remaining hydrogen in the exhaust into water, provide the water through a third water stream 176, and output remaining nitrogen in the exhaust through a second nitrogen stream 178. In some embodiments, because the ammonia recirculation unit 152 dissolves the ammonia slip into aqueous ammonia, the hydrogen control unit 154 receives the hydrogen slip in the exhaust.

[0053] In some embodiments, the hydrogen control unit 154 releases the water through the third water stream 176 to the ambient environment. In other embodiments, the hydrogen control unit 154 releases the water through the third water stream 176 to components of the engine system 100, the hydrogen generation system 110, and / or the emission control system 150. For example, the hydrogen control unit 154 can release the water through the third water stream 176 to the ammonia hydrolysis unit 1 18.

[0054] In some embodiments, the hydrogen control unit 154 releases the nitrogen through the second nitrogen stream 178 to the ambient environment and / or components of the engine system 100, the hydrogen generation system 110, and / or the emission control system 150.|0055| The engine system 100 further includes the controller 180. The controller 180 is electrically or communicatively coupled to other components of the engine system 100, components of the hydrogen generation system 110, and / or components of the emission control system 150 and is configured to control operations of the electrically coupled components. For example, controller 180 can be electrically or communicatively coupled to the engine 102, the first pump 122, the first heat exchanger 124, the second heat exchanger 140, the first heater 142, the ammonia recirculation unit 152, the exhaust aftertreatment system 156, the first bypass valve 160, the second bypass valve 165, the second pump 168, the heater 170, etc.[0056| The controller 180 includes a processing circuit 182. The processing circuit 182 includes a processor 184 and a memory 186. The processor 184 can include a microprocessor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), etc., or combinations thereof. The memory 186 can include, but is not limited to, electronic, optical, magnetic, or any other storage or transmission device capable of providing a processor, ASIC, FPGA, etc. with program instructions. This memory 186 can include a memory chip, Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), flash memory, or any other suitable memory from which the controller 180 can read instructions. The instructions can include code from any suitable programming language. The memory 186 can include various modules that include instructions which are configured to be implemented by the processor 184.

[0057] In some embodiments, the controller 180 is configured to communicate with a central controller (e.g., engine control unit (ECU), engine control module (ECM), etc.) of the engine system 100. In some embodiments, the central controller and the controller 180 are integrated into a single controller.|0058| In some embodiments, the central controller is communicable with a display device (e.g., screen, monitor, touch screen, heads up display (HUD), indicator light, etc.). The display device can be configured to change state in response to receiving information from the central controller and / or the controller 180. For example, the display device can be configured to change between a static state (e.g., displaying a green light, displaying a “SYSTEM OK” message, etc.) and an alarm state (e.g., displaying a blinking red light, displaying a “SERVICE NEEDED” message, etc.) based on a communication from the central controller and / or the controller 180. By changing state, the display device can provide an indication to a user (e.g., operator, etc.) of a status (e.g., operation, in need of service, etc.) of the engine system 100, the engine 102, the hydrogen generation system 110, and / or the emission control system 150.|0059] The ammonia recirculation unit 152 can include one or more sensors 188. The sensors 188 are electrically or communicatively coupled to the controller 180 and are configured toprovide signals associated with the ammonia disposed in the ammonia recirculation unit 152 to the controller 180. The sensors 188 can include temperature, pressure, concentration, amount, level, etc. sensors.

[0060] The controller 180 is configured to receive the signals from the sensors 188. In some embodiments, at least one of the sensors 188 is an ammonia concentration sensor that transmits an ammonia concentration signal to the controller 180, where the controller 180 is configured to determine a concentration of the ammonia within the ammonia recirculation unit 152 based on the ammonia concentration signal. In some examples, the ammonia concentration sensor includes at least one element that measures a concentration (e.g., pH, etc.) of the ammonia within the ammonia recirculation unit 152, where the controller 180 is configured to determine a concentration of the ammonia within the ammonia recirculation unit 152 based on the ammonia concentration signal that is indicative of the concentration of the ammonia within the ammonia recirculation unit 152.

[0061] In some embodiments, at least one of the sensors 188 is an ammonia amount sensor that transmits an ammonia amount signal to the controller 180, where the controller 180 is configured to determine an amount (e.g., volume, etc.) of the ammonia within the ammonia recirculation unit 152 based on the ammonia amount signal. In some examples, the ammonia amount sensor includes at least one element that measures a level of the ammonia within the ammonia recirculation unit 152, where the controller 180 is configured to determine an amount of the ammonia within the ammonia recirculation unit 152 based on the ammonia amount signal that is indicative of the level of the ammonia within the ammonia recirculation unit 152.

[0062] In some embodiments, the controller 180 determines the concentration of the ammonia within the ammonia recirculation unit 152 based on both the ammonia concentration signal from the ammonia concentration sensor (i.e., at least one of the sensors 188) that is indicative of the concentration of the ammonia within the ammonia recirculation unit 152 and the ammonia amount signal from the ammonia amount sensor (i.e., at least one of the sensors 188) that is indicative of the level of the ammonia within the ammonia recirculation unit 152.[0063| In some embodiments, the controller 180 determines the amount of the ammonia within the ammonia recirculation unit 152 based on both the ammonia concentration signal from the ammonia concentration sensor (i.e., at least one of the sensors 188) that is indicative of the concentration of the ammonia within the ammonia recirculation unit 152 and the ammonia amount signal from the ammonia amount sensor (i.e., at least one of the sensors 188) that is indicative of the level of the ammonia within the ammonia recirculation unit 152.

[0064] The sensors 188 can be real (e.g., physical, etc.) or virtual (e.g., a non-physical sensor that is structured as program logic in the controller 180 that makes various estimations or determinations). For example, the ammonia concentration sensor (e.g., at least one of the sensors 188) can be a real or a virtual sensor arranged to measure or otherwise acquire data, values, or information indicative of the concentration of the ammonia within the ammonia recirculation unit 152. When structured as a real sensor, the ammonia concentration sensor is structured to send the ammonia concentration signal to the controller 180 that is indicative of the ammonia concentration within the ammonia recirculation unit 152. When the ammonia concentration sensor is structured as a virtual sensor, at least one input can be used by the controller 180 in an algorithm, model, lookup table, etc. to determine or estimate the ammonia concentration within the ammonia recirculation unit 152.

[0065] Similar to the ammonia concentration sensor, the ammonia amount sensor (e.g., at least one of the sensors 188) can be a real or a virtual sensor arranged to measure or otherwise acquire data, values, or information indicative of the amount of the ammonia within the ammonia recirculation unit 152. When structured as a real sensor, the ammonia amount sensor is structured to send the ammonia amount signal to the controller 180 that is indicative of the ammonia amount within the ammonia recirculation unit 152. When structured as a virtual sensor, at least one input can be used by the controller 180 in an algorithm, model, lookup table, etc. to determine or estimate the ammonia amount within the ammonia recirculation unit 152.

[0066] FIG. 2 illustrates a flow diagram of a method 200 to control recirculation of the ammonia within the ammonia recirculation unit 152 according to an example embodiment. The controller 180 is structured to perform the method 200.

[0067] The method 200 includes receiving, by a controller 180 from an ammonia concentration sensor 188, an ammonia concentration signal associated with a level of ammonia in an aqueous solution within the ammonia recirculation unit 152. The method 200 further includes, at 202, determining, by the controller 180 based on the ammonia concentration signal, a concentration of the ammonia within the ammonia recirculation unit 152. The method 200 further includes receiving, by the controller from an ammonia amount sensor 188, an ammonia amount signal associated with a volume of the aqueous solution within the ammonia recirculation unit 152. The method 200 further includes, at 202, determining, by the controller 180 based on the ammonia amount signal, an amount of the ammonia within the ammonia recirculation unit 152. The method 200 further includes, in response to determining that, at 204, the concentration of the ammonia within the ammonia recirculation unit 152 is equal to or above a concentration threshold and that, at 206, the amount of the ammonia within the ammonia recirculation unit 152 is equal to or above an amount threshold, at 208, operating, by the controller 180, a pump 168 to receive at least a portion of an aqueous ammonia from the ammonia recirculation unit 152 and provide the at least the portion of the aqueous ammonia to the heater 170 disposed downstream of the ammonia recirculation unit 152. The method 200 further includes operating, by the controller 180, the heater 170 to receive the at least the portion of the aqueous ammonia from the pump 168, heat the at least the portion of the aqueous ammonia to remove moisture and produce dry ammonia, and provide the dry ammonia to the hydrogen generation system 110.

[0068] As noted above, the method 200 includes, at 202, determining, by the controller 180, the concentration and the amount of ammonia within the ammonia recirculation unit 152. For example, the controller 180 can determine the concentration of the ammonia within the ammonia recirculation unit 152 by receiving the ammonia concentration signal from the ammonia concentration sensor (e.g., at least one of the sensors 188) that is indicative of the ammoniaconcentration within the ammonia recirculation unit 152 and determining the ammonia concentration within the ammonia recirculation unit 152 based on the ammonia concentration signal. The controller 180 can determine the amount of the ammonia within the ammonia recirculation unit 152 by receiving the ammonia amount signal from the ammonia amount sensor (e.g., at least one of the sensors 188) that is indicative of the ammonia amount within the ammonia recirculation unit 152 and determining the ammonia amount within the ammonia recirculation unit 152 based on the ammonia amount signal.

[0069] The method 200 includes, at 204, determining, by the controller 180, whether the ammonia concentration within the ammonia recirculation unit 152 (determined at 202) is equal to or above a concentration threshold. In response to determining that the ammonia concentration within the ammonia recirculation unit 152 is not equal to or above the concentration threshold (i.e., below the concentration threshold), the process returns to 202 of the method 200 (e.g., the controller 180 determines again the ammonia concentration within the ammonia recirculation unit 152).

[0070] The method 200 includes, at 206, in response to determining that the ammonia concentration is equal to or above the concentration threshold (at 204), determining, by the controller 180, whether the ammonia amount within the ammonia recirculation unit 152 (determined at 202) is equal to or above an amount threshold. In response to determining that the ammonia amount within the ammonia recirculation unit 152 is not equal to or above the amount threshold (i.e., below the amount threshold), the process returns to 202 of the method 200 (e.g., the controller 180 determines again the ammonia amount within the ammonia recirculation unit 152).

[0071] It is to be appreciated that 204 and 206 of the method 200 can be performed in reverse order or simultaneously. For example, in some embodiments, at 206, the controller 180 determines whether the ammonia amount within the ammonia recirculation unit 152 (determined at 202) is equal to or above the amount threshold, and, in response to determining that the ammonia amount is equal to or above the amount threshold (at 206), at 204, the controller 180determines whether the ammonia concentration within the ammonia recirculation unit 152 (determined at 202) is equal to or above the concentration threshold. In other embodiments, 204 and 206 of the method 200 are performed substantially simultaneously, such that the controller 180 determines substantially simultaneously whether the ammonia amount within the ammonia recirculation unit 152 (determined at 202) is equal to or above the amount threshold and whether the ammonia concentration within the ammonia recirculation unit 152 (determined at 202) is equal to or above the concentration threshold.

[0072] The method 200 includes, at 208, in response to determining that the ammonia concentration within the ammonia recirculation unit 152 is equal to or above the concentration threshold (at 204) and that the ammonia amount within the ammonia recirculation unit 152 is equal to or above the amount threshold (at 206), facilitating, by the controller 180, recirculation of at least a portion of the ammonia within the ammonia recirculation unit 152 to the ammonia cracking unit 112 and / or the hydrogen generation system 110. For example, at 208, the controller 180 can control the second pump 168 to receive the at least the portion of the ammonia from the ammonia recirculation unit 152 and provide the at least the portion of the ammonia to the heater 170, and control the heater 170 to receive the at least the portion of the ammonia from the second pump 168, heat the at least the portion of the ammonia to remove moisture and produce dry ammonia, and provide the dry ammonia to the ammonia cracking unit 112 via the second dry ammonia stream 172.|0073| Oxidation of ammonia can be represented by a chemical Equation (1), as shown below.

[0074] 4NH3+ 3O2= 6H2O + 2N2; Hr= -1260 kJ / mol (1)

[0075] In Equation (1), the reactants include ammonia (NH3) and oxygen (O2), the products include water (H2O) and nitrogen (N2), and the reaction enthalpy (AHr) is -1260 kJ / mol.

[0076] Decomposition of ammonia can be represented by a chemical Equation (2), as shown below.

[0077] 2NH3= 3H2+ N2; Hr= +46 kJ / mol )

[0078] In Equation (2), the reactant includes ammonia (NH3), the products include hydrogen (H2) and nitrogen (N2), and the reaction enthalpy (AHr) is +46 kJ / mol.

[0079] Oxidation and decomposition of ammonia can be represented by a chemical Equation (3), as shown below.

[0080] NH3+ xO2= 2xH2O + (1.5 - 2x)H2+ 0.5W2; x < 0.75 (3)(0081 [ In Equation (3), the reactants includes ammonia (NH3) and oxygen (O2), the products include water (H2O), hydrogen (H2), and nitrogen (N2), and an oxygen-to-ammonia ratio (x) is less than 0.75.

[0082] FIG. 3 illustrates an example graph of the ammonia conversion percentage (y-axis) (i.e., percent of ammonia that converts to hydrogen and nitrogen) relative to the oxygen-to- ammonia ratio (x-axis) within the ammonia cracking unit 112. In some embodiments, the results illustrated in FIG. 3 are captured at a constant temperature. In some examples, the constant temperature is between about 250 degrees C and about 550 degrees C, inclusive. As shown in FIG. 3, the ammonia conversion percentage increases as the oxygen-to-ammonia ratio increases, up to the point that the ammonia conversion percentage reaches about 100%.| 0083] FIG. 4 illustrates an example graph of nitrogen oxide and nitrous oxide concentrations relative to the oxygen-to-ammonia ratio within the ammonia cracking unit 112. In some embodiments, the results illustrated in FIG. 4 are captured at a constant temperature. In some examples, the constant temperature is between about 250 degrees C and about 550 degrees C, inclusive. As shown in FIG. 4, the nitrogen oxide and nitrous oxide concentrations are about 0 parts-per-million (ppm) for an oxygen-to-ammonia ratio range between about 0 and less than about 0.75. At the oxygen-to-ammonia ratio range of about 0.75 and higher, the nitrogen oxide and nitrous oxide concentrations increase as the oxygen-to-ammonia ratio increases.[0084| In view of the results shown in FIG. 4, it is desirable to maintain the oxygen-to- ammonia ratio within the ammonia cracking unit 112 below 0.75 to prevent, or substantially limit, formation of nitrogen oxide compounds and nitrous oxide by-products within the ammonia cracking unit 112. Furthermore, although, as illustrated in FIG. 3, increasing the oxygen-to- ammonia ratio can increase the ammonia conversion percentage, it is desirable to maintain the oxygen-to-ammonia ratio within the ammonia cracking unit 112 at 0 to maximize generation of hydrogen and minimize generation of water in the ammonia cracking unit 112, as shown in Equation (3).

[0085] In some embodiments, the ammonia cracking unit 112 operates in non-air conditions (i.e., substantially absent of air (air including about 78% nitrogen, about 21% oxygen, and about 1% of other elements or compounds), etc.), such that the conversion of the ammonia into hydrogen and nitrogen substantially lacks formation of water resulting from oxygen. In some embodiments, the ammonia provided by the ammonia source 104 is substantially pure ammonia and / or ammonia that substantially lacks oxygen. In some further embodiments, the dry ammonia provided by the first heat exchanger 124 through the first dry ammonia stream 128 and / or the dry ammonia provided by the heater 170 through the second dry ammonia stream 172 is substantially pure ammonia and / or ammonia that substantially lacks oxygen.

[0086] It is to be appreciated that the values provided in FIGS. 3 and 4 are for example purposes only, such that the values of the ammonia conversion percentage, the nitrogen oxide and nitrous oxide concentrations, and the oxygen-to-ammonia ratio are not limited to the values presented, and such that values other than the values presented (i.e., within the range presented, outside of the range presented, etc.) can be included.[0087| While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what can be claimed but rather as descriptions of features specific to particular implementations. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementationcan also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features can be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination can be directed to a subcombination or variation of a subcombination.100881 As utilized herein, “generally” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the present disclosure.(0089] The term “coupled” and the like, as used herein, mean the joining of two components directly or indirectly to one another. Such joining can be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining can be achieved with the two components or the two components and any additional intermediate components being integrally formed as a single unitary body with one another, with the two components, or with the two components and any additional intermediate components being attached to one another.(0090] The terms “fluidly coupled to” and the like, as used herein, mean the two components or objects have a pathway formed between the two components or objects in which a fluid, such as air, treatment fluid, an air-treatment fluid mixture, exhaust, hydrocarbon fluid, an airhydrocarbon fluid mixture, can flow, either with or without intervening components or objects. Examples of fluid couplings or configurations for enabling fluid communication can include piping, channels, or any other suitable components for enabling the flow of a fluid from one component or object to another.[00911 It is important to note that the construction and arrangement of the system shown in the various example implementations is illustrative only and not restrictive in character. All changes and modifications that come within the spirit and / or scope of the described implementations are desired to be protected. It should be understood that some features may not be necessary, and implementations lacking the various features can be contemplated as within the scope of the application, the scope being defined by the claims that follow. When the language “a portion” is used, the item can include a portion and / or the entire item unless specifically stated to the contrary.

[0092] Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. can be either X, Y, Z, X and Y, X and Z, Y and Z, or X, Y, and Z (i.e., any combination of X, Y, and Z). Thus, such conjunctive language is not generally intended to imply that certain embodiments require at least one of X, at least one of Y, and at least one of Z to each be present, unless otherwise indicated.

[0093] Additionally, the use of ranges of values (e.g., W1 to W2, etc.) herein are inclusive of their maximum values and minimum values (e.g., W1 to W2 includes W1 and includes W2, etc.), unless otherwise indicated. Furthermore, a range of values (e.g., W1 to W2, etc.) does not necessarily require the inclusion of intermediate values within the range of values (e.g., W1 to W2 can include only W1 and W2, etc.), unless otherwise indicated.

Claims

WHAT IS CLAIMED IS:

1. An engine system comprising: an engine configured to receive a fluid mixture of fuel and air, combust the fluid mixture, and provide an exhaust based on combustion of the fluid mixture; a hydrogen generation system configured to receive ammonia from at least an ammonia source, generate hydrogen from the ammonia, and provide the hydrogen to the engine, the fuel comprising the hydrogen; an emission control system comprising: an ammonia recirculation unit configured to receive the exhaust from the engine and dissolve remaining ammonia in the exhaust into aqueous ammonia, and a hydrogen control unit disposed downstream of the ammonia recirculation unit, the hydrogen control unit configured to receive the exhaust from the ammonia recirculation unit, convert remaining hydrogen in the exhaust into water, and output remaining nitrogen in the exhaust; and a heater disposed downstream of the ammonia recirculation unit, the heater configured to receive the aqueous ammonia from the ammonia recirculation unit, heat the aqueous ammonia to generate dry ammonia, and provide the dry ammonia to the hydrogen generation system.

2. The engine system of claim 1, wherein the emission control system further comprises an exhaust aftertreatment system disposed downstream of the engine and upstream of the ammonia recirculation unit, the exhaust aftertreatment system configured to receive the exhaust from the engine and treat the exhaust using a treatment fluid to reduce or remove nitrogen oxides from the exhaust.

3. The engine system of claim 2, wherein the treatment fluid comprises at least a portion of the hydrogen generated by the hydrogen generation system.

4. The engine system of claim 1, wherein the ammonia recirculation unit is pre-charged with the aqueous ammonia to prevent freezing.

5. The engine system of claim 1, wherein the emission control system further comprises a backflow preventer upstream of the ammonia recirculation unit.

6. The engine system of claim 1, wherein the hydrogen generation system comprises an ammonia cracking unit configured to receive the ammonia, convert a first portion of the ammonia into the hydrogen and nitrogen, and provide an inlet mixture comprising the hydrogen, the nitrogen, and a second portion of the ammonia.

7. The engine system of claim 6, wherein the hydrogen generation system further comprises a heat exchanger configured to receive the exhaust, extract heat from the exhaust, provide the heat to the ammonia cracking unit, and output the exhaust.

8. The engine system of claim 6, wherein the hydrogen generation system further comprises a hydrogen separation unit disposed downstream of the ammonia cracking unit, the hydrogen separation unit comprising: an ammonia hydrolysis unit configured to receive the inlet mixture, remove the second portion of the ammonia from the inlet mixture, and provide the hydrogen and the nitrogen from the inlet mixture; and a hydrogen selective membrane disposed downstream of the ammonia hydrolysis unit, the hydrogen selective membrane configured to receive the hydrogen and the nitrogen from the ammonia hydrolysis unit and separate the hydrogen and the nitrogen.

9. The engine system of claim 8, further comprising a hydrogen tank disposed downstream of the hydrogen selective membrane and upstream of the engine, the hydrogen tank configured to receive the hydrogen from the hydrogen selective membrane, retain the hydrogen, and provide at least a portion of the hydrogen to the engine.

10. The engine system of claim 8, wherein the hydrogen generation system further comprises a heat exchanger disposed downstream of the ammonia hydrolysis unit, the heat exchanger configured to receive the second portion of the ammonia from the ammonia hydrolysis unit, receive a heated coolant from the engine, extract heat from the heated coolant, provide the heat to the second portion of the ammonia to remove moisture from the second portion of the ammonia, and provide dry ammonia to the ammonia cracking unit.

11. The engine system of claim 8, wherein: the heater is configured to provide water extracted from the aqueous ammonia to the ammonia hydrolysis unit; and the ammonia hydrolysis unit is configured to utilize the water from the heater to perform a hydrolysis reaction.

12. The engine system of claim 6, wherein the ammonia cracking unit operates in non-air conditions that are substantially absent of air.

13. The engine system of claim 6, wherein the hydrogen generation system comprises a second heater configured to provide heat to the ammonia cracking unit.

14. The engine system of claim 1, wherein the ammonia recirculation unit comprises: an ammonia concentration sensor configured to measure a concentration of the ammonia within the ammonia recirculation unit; and an ammonia amount sensor configured to measure a level of the ammonia within the ammonia recirculation unit.

15. The engine system of claim 14, further comprising a pump disposed downstream of the ammonia recirculation unit and upstream of the heater, the pump configured to receive theaqueous ammonia from the ammonia recirculation unit and provide the aqueous ammonia to the heater.

16. The engine system of claim 15, further comprising a controller communicatively coupled to the ammonia concentration sensor, the ammonia amount sensor, and the pump, the controller configured to: receive, from the ammonia concentration sensor, an ammonia concentration signal associated with the concentration of the ammonia within the ammonia recirculation unit; determine, based on the ammonia concentration signal, a concentration of the ammonia within the ammonia recirculation unit; receive, from the ammonia amount sensor, an ammonia amount signal associated with the level of the ammonia within the ammonia recirculation unit; determine, based on the ammonia amount signal, an amount of the ammonia within the ammonia recirculation unit; and in response to determining that the concentration of the ammonia within the ammonia recirculation unit is equal to or above a concentration threshold and that the amount of the ammonia within the ammonia recirculation unit is equal to or above an amount threshold, control the pump to receive at least a portion of the aqueous ammonia from the ammonia recirculation unit and provide the at least the portion of the aqueous ammonia to the heater.

17. An engine system comprising: an engine configured to receive a fluid mixture of fuel and air, combust the fluid mixture, and provide an exhaust based on combustion of the fluid mixture; a hydrogen generation system configured to receive ammonia from at least an ammonia source, generate hydrogen from the ammonia, and provide the hydrogen to the engine, the fuel comprising the hydrogen; and an emission control system comprising: an exhaust aftertreatment system disposed downstream of the engine, the exhaust aftertreatment system configured to receive the exhaust from the engine and treat the exhaustusing at least a portion of the hydrogen generated by the hydrogen generation system to reduce or remove nitrogen oxides from the exhaust, and an ammonia recirculation unit disposed downstream of the exhaust aftertreatment system, the ammonia recirculation unit configured to receive the exhaust from the exhaust aftertreatment system, dissolve remaining ammonia in the exhaust, and provide the ammonia to the hydrogen generation system.

18. The engine system of claim 17, wherein the exhaust aftertreatment system excludes an ammonia slip catalyst.

19. The engine system of claim 17, further comprising: a hydrogen control unit disposed downstream of the ammonia recirculation unit, the hydrogen control unit configured to receive the exhaust from the ammonia recirculation unit, convert remaining hydrogen in the exhaust into water, and output remaining nitrogen in the exhaust; and a bypass valve disposed downstream of the exhaust aftertreatment system and upstream of the ammonia recirculation unit, the bypass valve configured to selectively communicate the exhaust from the exhaust aftertreatment system to the hydrogen control unit and bypass the ammonia recirculation unit.

20. A method to control recirculation of ammonia within an engine system, the method comprising: receiving, by a controller from an ammonia concentration sensor, an ammonia concentration signal associated with a level of ammonia in an aqueous solution within the ammonia recirculation unit; determining, by the controller based on the ammonia concentration signal, a concentration of the ammonia within the ammonia recirculation unit; receiving, by the controller from an ammonia amount sensor, an ammonia amount signal associated with a volume of the aqueous solution within the ammonia recirculation unit;determining, by the controller based on the ammonia amount signal, an amount of the ammonia within the ammonia recirculation unit; in response to determining that the concentration of the ammonia within the ammonia recirculation unit is equal to or above a concentration threshold and that the amount of the ammonia within the ammonia recirculation unit is equal to or above an amount threshold, operating, by the controller, a pump to receive at least a portion of an aqueous ammonia from the ammonia recirculation unit and provide the at least the portion of the aqueous ammonia to a heater disposed downstream of the ammonia recirculation unit; and operating, by the controller, the heater to receive the at least the portion of the aqueous ammonia from the pump, heat the at least the portion of the aqueous ammonia to remove moisture and produce dry ammonia, and provide the dry ammonia to a hydrogen generation system.

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