GB2596846A

GB2596846A - Secondary air injection system and control method

Info

Publication number: GB2596846A
Application number: GB2010561.5A
Authority: GB
Inventors: Jones Steve
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2020-07-09
Filing date: 2020-07-09
Publication date: 2022-01-12
Anticipated expiration: 2040-07-09
Also published as: GB202010561D0; DE102021207243A1; GB2596846B

Abstract

A secondary injection system 3 for an internal combustion engine 10 comprising a mixing arrangement 36 configured to mix reductant with unburned air and an injection port 23 configured to deliver the mixture into the exhaust port 10c to mix with the exhaust stream. The reductant may be gaseous such as LPG, compressed natural gas, or hydrogen. There may be a mixing body 36b, a storage tank 40, throttle 36a or a check valve 46, and/or an actuator to control delivery. There may be a pump 34b to obtain the secondary air. There may be a pump to pressurise the fresh secondary air before mixing. A control system for the secondary air injection system may provide a stoichiometric fuel-air ratio to the engine, and may maintain fuel injection pressure into the combustion chamber 10a at the same fuel pressure regardless of whether the secondary air injection system is operational. Also claimed are a control method, and computer software to execute said method.

Description

SECONDARY AIR INJECTION SYSTEM AND CONTROL METHOD

TECHNICAL FIELD

The present disclosure relates to a secondary air injection system and control method. In particular, but not exclusively it relates to a secondary air injection system and control method for an internal combustion engine of a vehicle.

BACKGROUND

Internal combustion engines comprise various fluid injectors such as fuel injectors, secondary air injectors, water injectors, and exhaust gas recirculation systems.

A secondary air injector is typically placed in an exhaust manifold outside a cylinder head, to inject unburned ambient air into the exhaust gas stream. Atmospheric oxygen in the unburned air promotes oxidization of unburned and partially burned fuel already in the exhaust, and helps to raise the exhaust temperatures for catalyst and particulate filter requirements.

SUMMARY OF THE INVENTION

It is an aim of the present invention to improve fluid injector technology.

Aspects and embodiments of the invention provide a secondary air injection system, an engine, a control system, a vehicle, a method, and computer software as claimed in the appended claims.

According to an aspect of the invention there is provided a secondary air injection system for an internal combustion engine, wherein the secondary air injection system comprises: a mixing arrangement configured to mix a reductant with unburned air to form a mixture; and an injection port configured to inject the mixture into an exhaust port of the internal combustion engine, to mix with an exhaust stream.

Pre-mixing ensures that the air and reductant have adequate time to mix, for homogeneous combustion. A further advantage is that the engine does not need to run rich in order to supply unburned fuel.

The reductant may be a gaseous reductant, for easier self-ignition. The reductant may comprise at least one of liquefied petroleum gas; compressed natural gas; and hydrogen.

The mixing arrangement may comprise a mixing body configured to receive the unburned air and the reductant to form the mixture.

The mixing arrangement may comprise a throttle configured to reduce pressure at a location where the reductant is mixed with the unburned air.

The secondary air injection system may comprise a reductant storage tank.

The secondary air injection system may comprise a reductant actuator configured to control flow of the reductant separately from flow of the unburned air.

The secondary air injection system may comprise a check valve between the mixing arrangement and the injection port.

The secondary air injection system may comprise a secondary air obtaining means, including a secondary air pump configured to pressurize the unburned air upstream of the mixing arrangement.

The secondary air injection system may comprise an unburned air accumulator upstream of the mixing arrangement.

According to an aspect of the invention there is provided an engine comprising the secondary air injection system.

The internal combustion engine may be a petroleum-fuelled engine or a diesel-fuelled engine.

According to an aspect of the invention there is provided a control system for controlling a secondary air injection system for an internal combustion engine, the control system comprising one or more controllers, wherein the control system is configured to: control a secondary air pump to pressurize a source of unburned air; and control a mixing arrangement to mix a reductant with the unburned air to form a mixture, so that the pressurized mixture is injected into an exhaust port of the internal combustion engine by an injection port, to mix with an exhaust stream.

The control system may be configured to control fuel injection pressure to a combustion chamber of the internal combustion engine to provide a substantially stoichiometric air-fuel mixture, while the secondary air injection system is operational.

The control system may be configured to control fuel injection pressure to a combustion chamber of the internal combustion engine, to supply substantially the same fuel pressure for a given operating point of the internal combustion engine, regardless of whether the secondary air injection system is operational or not operational.

According to an aspect of the invention there is provided a vehicle comprising the secondary air injection system, or the engine, or the control system.

According to an aspect of the invention there is provided a method of controlling a secondary air injection system for an internal combustion engine, the method comprising: controlling a secondary air pump to pressurize a source of unburned air; and controlling a mixing arrangement to mix a reductant with the unburned air to form a mixture, so that the pressurized mixture is injected into an exhaust port of the internal combustion engine by an injection port, to mix with an exhaust stream.

According to an aspect of the invention there is provided computer software that, when executed, is arranged to perform any one or more of the methods described herein.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination that falls within the scope of the appended claims. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination that falls within the scope of the appended claims, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig 1 illustrates an example of a vehicle; Fig 2 illustrates an example of a secondary air injection system; Figs 3A, 3B illustrate an example of a control system and of a computer-readable storage medium; and Fig 4 illustrates an example of a method.

DETAILED DESCRIPTION

Fig 1 illustrates an example of a vehicle 1 in which embodiments of the invention can be implemented. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications.

The vehicle 1 comprises an internal combustion engine 10 such as a gasoline or diesel engine, and may optionally comprise other torque sources (not shown). The vehicle 1 also comprises an exhaust gas aftertreatment apparatus 11. The exhaust gas aftertreatment apparatus 11 may comprise a catalytic converter and/or a particulate filter.

As shown in Fig 2, the internal combustion engine 10 comprises a secondary air injection system 3 for injecting unburned air into the exhaust port 10c.

In accordance with aspects of the present disclosure, the unburned air is mixed with a reductant. The reductant is a suitable agent that can burn in the presence of the oxygen to raise temperature, such as gasoline vapour, diesel vapour, liquid petroleum gas (LPG), compressed natural gas (CNG) or Hydrogen. In an implementation, gaseous small molecules such as LPG, CNG or Hydrogen are used, for easier self-ignition without the need for a spark.

The reductant is pre-mixed with the unburned air prior to injection. Pre-mixing ensures that the air and reductant have adequate time to mix, for homogeneous combustion. A further advantage is that the engine 10 does not need to run rich in order to supply unburned fuel. This arrangement wastes less fuel, and lowers emissions (unburned hydrocarbons and carbon monoxide).

The mixture is injected as far upstream the exhaust path as practicable, within the exhaust port 10c inside the cylinder head. At this location, the exhaust gas temperature is high enough to support self-ignition of the mixture, whereas outside the cylinder head the gas temperature falls rapidly, resulting in less complete ignition. This location also maximises the mixing length upstream of the exhaust gas aftertreatment apparatus 11, which is useful because the high pressure (>3bar) and velocity (>700m/s) of exhaust gases makes homogeneous mixing difficult to achieve in the limited space available. However, the reductant should not be injected directly into the combustion chamber during an exhaust stroke, as this would result in high temperatures and generate high levels of nitrogen oxides.

Fig 2 illustrates various elements of the secondary air injection system 3 according to an example implementation.

Firstly, the secondary air injection system 3 comprises a secondary air obtaining means (secondary air source). The secondary air obtaining means comprises the hardware for obtaining and supplying the unburned air, for example from an air intake of an aspiration system of the engine 10, or from outside the vehicle 1. The secondary air obtaining means 34 comprises various channels or conduits for distributing the secondary air to different parts of the secondary air injection system 3.

The illustrated secondary air obtaining means 34 also comprises a secondary air pump 34b configured to pressurise the secondary air. The pressure should be higher than that in the exhaust port 10c, to push air into the exhaust port 10c and optimise the mixing. The specific pressure depends on implementation.

In some, but not necessarily all examples, the secondary air obtaining means 34 further comprises an unburned air accumulator 34c, configured to store air that has been pressurized by the secondary air pump 34b. The secondary air injection system 3 may either comprise a high-pressure secondary air pump 34b without an unburned air accumulator 34c, or a low-pressure secondary air pump 34b with an unburned air accumulator 34c.

The secondary air injection system 3 of Fig 2 further comprises an unburned air actuator such as an air switching valve (ASV) 36c. The ASV 36c is any suitable valve that can be opened and closed via an actuator such as a solenoid, to control the flow of unburned air towards the secondary air injector(s). The ASV 36c may have binary open/closed positions or may comprise intermediate open positions, to regulate flow. The illustrated ASV 36c is in fluid communication with the outlet side of the secondary air pump, but could be elsewhere.

The secondary air injection system 3 further comprises a source of reductant. If the reductant is a different chemical from the fuel burned by the engine 10, the reductant may be stored separately in a reductant storage tank 40, as shown in Fig 2. If the reductant is the same chemical that is burned by the engine 10 (e.g. gasoline vapour or diesel vapour), the source of reductant may be an existing component of the vehicle 1 such as a fuel vapour purge system.

The secondary air injection system 3 further comprises a reductant pump 42 configured to pump the reductant from the reductant storage tank 40.

The secondary air injection system 3 of Fig 2 further comprises a reductant actuator such as a reductant switching valve (RSV) 36d. The RSV 36d is any suitable valve that can be opened and closed via an actuator such as a solenoid, to control the flow of reductant towards the secondary air injector(s). The RSV 36d may have binary positions or may comprise intermediate open positions, to regulate flow. The RSV 36d is in fluid communication with the outlet side of the reductant pump 42, but could be elsewhere.

The secondary air injection system 3 of Fig 2 comprises a mixing arrangement 36 configured to form a mixture of the reductant and unburned air. The mixing arrangement 36 comprises a mixing body 36b within which the air and reductant are joined. The mixing body 36b may comprise a two-to-one valve or a reductant injector, for example. The mixing arrangement 36 includes suitable actuators such as the ASV 36c and/or the RSV 36d, for controlling the ratio of the mixture.

The mixing arrangement 36 of Fig 2 further comprises a throttle 36a, configured to reduce pressure at the mixing body 36b. The throttle 36a may be any suitable device for introducing a local pressure loss just upstream of the mixing body 36b. The reduced pressure helps to pull in the reductant. The throttle 36a may comprise a passive constriction such as a Venturi, forming a vacuum pump just downstream of the constriction. In some implementations, the throttle 36a may be an active throttle such as an actuatable valve.

The secondary air injection system 3 of Fig 2 further comprises a check valve 46 downstream of the mixing arrangement 36. This prevents exhaust gases from entering the secondary air injection system 3 when secondary air injection is not active. In some examples, further check valves may be provided, for example to keep air out of the reductant tank 40.

The specific number and arrangement of the valves may differ from that shown in Fig 2. The functionality could be achieved with more or fewer valves. In addition, the order in which the components are shown may be changed. For example, the ASV 36c could be relocated downstream of the mixing arrangement 36.

The secondary air injection system 3 of Fig 2 then comprises one or more injection ports 23 configured to inject the mixture into an exhaust port 10c of the internal combustion engine 10, to mix with an exhaust stream.

As illustrated in Fig 2, the injection ports 23 may be provided by a probe injector 35 or a wall injector 2, or both as illustrated. Wall injectors comprise apertures on the wall of the exhaust port 10c, whereas a probe injector 35 is inserted into the exhaust gas stream, away from the walls.

The probe injector 35 in Fig 2 has been inserted into the gas stream of the exhaust port 10c, to inject in a generally retrograde direction. A probe injector 35 is relatively easy to package, compared with a wall injector 2. However, the probe injector 35 does not mix as effectively as a wall injector 2, because the probe injector 35 only injects at one location, whereas wall injectors 2 can comprise distributed injection ports 23 to inject at multiple locations. Probe injectors 35 can increase emissions as the injected gas may enter the combustion chamber, causing hotter combustion temperatures. Probe injectors 35 also tend to be further downstream where the exhaust gas is less hot.

As shown in Fig 2, the wall injector 2 may be an annular insert comprising the injection ports 23, obviating the need to drill multiple holes into the cylinder head 10b. The annular shape may comprise a circular central aperture through which exhaust gases can flow, thus making the insert part of the wall of the exhaust port 10c. The injection ports 23 may be circular holes as illustrated, or may be grooves in a surface of the insert that abuts another surface such as the cylinder head 10b. Fig 2 shows a plurality of injection ports 23 spaced around the periphery of the exhaust port 10c, facing into the central aperture. This arrangement of ports 23 enables more complete mixing The annular insert may be integrated with a valve seat 20, for example attached to a valve seat 20. The valve seat 20 is a component that forms a seal with the back of a valve head 30a of an exhaust poppet valve 30. This ensures that injection is as far upstream as possible in the exhaust system. This location is also readily accessible during manufacture: a small shelf can be added to the cylinder head 10b to accommodate press fitting of the annular insert and the valve seat 20 in one step.

In order to enable the mixture to reach the wall injector 2, a feed channel may extend through the cylinder head 10b. The feed channel 32 is a passage/gallery, such as a drilling in the cylinder head 10b, that carries the mixture from outside the cylinder head 10b to the wall injector 2. The feed channel 32 extends laterally, avoiding the exhaust valve bridge.

If multiple wall injection ports 23 are provided in a given wall injector 2, the feed channel may fluidly couple with a manifold 33 for distributing the mixture to the plurality of injection ports 23. The manifold 33 may be a hollow volume within the insert as shown in Fig 2, or may be an enclosed volume between the insert and the cylinder head 10b.

If the injection can be pulsed to coincide with exhaust valve opening and closing, a high-speed injection actuator may be provided, before or after the check valve 46. The high-speed injection actuator may be a piezo-actuator, for example. For a probe injector 35, the highspeed injection actuator may be integrated into the probe. For wall injection, the high-speed injection actuator may be provided inside the cylinder head 10b to enable better control of flow and timing, or the high-speed injection actuator may be located more accessibly outside the cylinder head 10b, between the mixing arrangement 36 and the feed channel 32. At least one high-speed injection actuator is provided per injector 2, 35/per exhaust port 10c.

The actuatable components of the secondary air injection system 3 can be managed by any suitable control system. Fig 3A illustrates how the control system 208 may be implemented.

The control system 208 of Fig 3A illustrates a controller 300. In other examples, the control system 208 may comprise a plurality of controllers on-board and/or off-board the vehicle 1.

The controller 300 of Fig 3A includes at least one processor 302; and at least one memory device 304 electrically coupled to the electronic processor 302 and having instructions 306 (e.g. a computer program) stored therein, the at least one memory device 304 and the instructions 306 configured to, with the at least one processor 302, cause any one or more of the methods described herein to be performed. The processor 302 may have an electrical input/output I/O or electrical input for receiving information and interacting with external components.

Fig 3B illustrates a non-transitory computer-readable storage medium 308 comprising the instructions 306 (computer software).

The control system 208 is operable to perform the illustrated method 400 of Fig 4. Block 402 of the method 400 comprises determining a secondary air injection event trigger, wherein satisfaction of the event trigger depends on at least one monitored variable that is associated with a condition of an exhaust gas aftertreatment apparatus 11. The condition may indicate that the temperature is too cold so that the temperature is too low for a catalytic reaction, or that the pressure loss across the apparatus 11 is too high due to soot accumulation. These scenarios require secondary air injection, to raise the operating temperature quickly. Another scenario is a change of power mode of the vehicle 1, so that injection can be performed at the beginning of a journey when the exhaust gas aftertreatment apparatus 11 is cold, prior to the torque being requestable from the engine 10 by the driver.

Block 404 of the method 400 comprises controlling the secondary air pump to pressurize the unburned air. The pump may be energized via any suitable means. Block 404 may further comprise controlling the reductant pump 42 to pressurized the reductant.

Block 406 of the method 400 comprises controlling the mixing arrangement 36 to mix the reductant with the unburned air in the desired ratio. For example, the ASV 36c and RSV 36d may be opened to expose the outlets of the respective pumps, to enable the air and reductant to flow to the two-to-one valve. A specific air/reductant ratio can be achieved in an open loop or closed loop manner by moving the ASV 36c/RSV 36d to an intermediate position, if available, and/or by controlling a duty cycle of the pumps/valves.

Optionally, the control system 208 may be configured to inhibit reductant injection without inhibiting the unburned air injection. Reductant can raise exhaust gas temperatures. If the exhaust gas is already very hot and/or engine load is high, cooling may be preferred. Injection of cold air without the reductant can provide a relative cooling effect. This cooling effect reduces or obviates the need to inefficiently run the engine rich for cooling purposes.

For example, block 408 determines whether a temperature and/or load on the engine is greater than a threshold. The temperature could be measured using an exhaust gas temperature sensor, a coolant temperature sensor, or another sensor. If the threshold(s) is/are exceeded, block 410 injects secondary air, but without reductant.

The secondary air injection may terminate upon satisfaction of a completion trigger, based on measured time, temperature or pressure in some examples.

While secondary air injection is operational, the control system may control fuel injection pressure (and air mass flow) to the combustion chamber 10a to provide a substantially stoichiometric air-fuel mixture. This is because the reductant is being supplied separately, without the need to run the engine 10 rich to supply fuel for oxidation. Therefore, an air/fuel ratio map of the control system may define substantially the same air/fuel ratio for a given engine operating point, regardless of whether the secondary air injection system 3 is operational or not operational.

For purposes of this disclosure, it is to be understood that the controller(s) described herein can each comprise a control unit or computational device having one or more electronic processors. A vehicle 1 and/or a system thereof may comprise a single control unit or electronic controller or alternatively different functions of the controller(s) may be embodied in, or hosted in, different control units or controllers. A set of instructions could be provided which, when executed, cause said controller(s) or control unit(s) to implement the control techniques described herein (including the described method(s)). The set of instructions may be embedded in one or more electronic processors, or alternatively, the set of instructions could be provided as software to be executed by one or more electronic processor(s). For example, a first controller may be implemented in software run on one or more electronic processors, and one or more other controllers may also be implemented in software run on one or more electronic processors, optionally the same one or more processors as the first controller. It will be appreciated, however, that other arrangements are also useful, and therefore, the present disclosure is not intended to be limited to any particular arrangement. In any event, the set of instructions described above may be embedded in a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational device, including, without limitation: a magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

The blocks illustrated in Fig 4 may represent steps in a method and/or sections of code in the computer program 306. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted.

The present disclosure refers to the stem of the poppet valve being behind the head of the poppet valve. This would be understood as the stem being downstream of the head, wherein the stem extends through the exhaust port towards a poppet valve actuator. It would further be understood that as the stem is behind the head, the combustion chamber can be referred to as being in front of the head.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant reserves the right to claim protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. A secondary air injection system for an internal combustion engine, wherein the secondary air injection system comprises: a mixing arrangement configured to mix a reductant with unburned air to form a mixture; and an injection port configured to inject the mixture into an exhaust port of the internal combustion engine, to mix with an exhaust stream.
2. The secondary air injection system of claim 1, wherein the reductant is a gaseous reductant.
3. The secondary air injection system of claim 2, wherein the reductant comprises at least one of liquefied petroleum gas; compressed natural gas; and hydrogen.
4. The secondary air injection system of claim 1, 2 or 3, wherein the mixing arrangement comprises a mixing body configured to receive the unburned air and the reductant to form the mixture.
5. The secondary air injection system of any preceding claim, wherein the mixing arrangement comprises a throttle configured to reduce pressure at a location where the reductant is mixed with the unburned air.
6. The secondary air injection system of any preceding claim, comprising a reductant storage tank.
7. The secondary air injection system of any preceding claim, comprising a reductant actuator configured to control flow of the reductant separately from flow of the unburned air.
8. The secondary air injection system of any preceding claim, comprising a check valve between the mixing arrangement and the injection port.
9. The secondary air injection system of any preceding claim, comprising a secondary air obtaining means, including a secondary air pump configured to pressurize the unburned air upstream of the mixing arrangement.
10. The secondary air injection system of any preceding claim, comprising an unburned air accumulator upstream of the mixing arrangement.
11. An engine comprising the secondary air injection system of any one of the preceding claims.
12. The engine of claim 11, wherein the internal combustion engine is a petroleum-fuelled engine or a diesel-fuelled engine. 10
13. A control system for controlling a secondary air injection system for an internal combustion engine, the control system comprising one or more controllers, wherein the control system is configured to: control a secondary air pump to pressurize a source of unburned air; and control a mixing arrangement to mix a reductant with the unburned air to form a mixture, so that the pressurized mixture is injected into an exhaust port of the internal combustion engine by an injection port, to mix with an exhaust stream.
14. The control system of claim 13, configured to control fuel injection pressure to a combustion chamber of the internal combustion engine to provide a substantially stoichiometric air-fuel mixture, while the secondary air injection system is operational.
15. The control system of claim 13 or 14, configured to control fuel injection pressure to a combustion chamber of the internal combustion engine, to supply substantially the same fuel pressure for a given operating point of the internal combustion engine, regardless of whether the secondary air injection system is operational or not operational.
16. A vehicle comprising the secondary air injection system of any one of claims 1 to 10, or the engine of claim 11 or 12, or the control system of claim 13, 14 or 15.
17. A method of controlling a secondary air injection system for an internal combustion engine, the method comprising: controlling a secondary air pump to pressurize a source of unburned air; and controlling a mixing arrangement to mix a reductant with the unburned air to form a mixture, so that the pressurized mixture is injected into an exhaust port of the internal combustion engine by an injection port, to mix with an exhaust stream.
18. Computer software that, when executed, is arranged to perform a method according to claim 17.