WO1999032781A1

WO1999032781A1 - Direct secondary air injection system for internal combustion engine

Info

Publication number: WO1999032781A1
Application number: PCT/IB1998/002098
Authority: WO
Inventors: Richard Walter Anderson; William Allen Rimkus
Original assignee: Ford Global Technologies, Inc.
Priority date: 1997-12-19
Filing date: 1998-12-18
Publication date: 1999-07-01
Also published as: AU1501499A

Abstract

An internal combustion engine includes a fuel system having the capability of injecting a fuel and air mixture, or air alone, for providing a secondary air charge directly into the combustion chamber (22) after combustion of a primary air and fuel charge has begun. The secondary air charge functions to increase turbulence in the combustion chamber (22) so as to make more oxygen available to further oxidise unburned hydrocarbon remaining from the fuel charge.

Description

DIRECT SECONDARY AIR INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINE

The present invention relates to a method and system for providing a secondary air mass directly into the combustion chamber of an internal combustion engine so as to reduce the level of unburned hydrocarbons within the combustion chamber.

Although it is well known in the art of automotive engine design to provide secondary air injection downstream of the combustion chamber, for example, in the exhaust ports or exhaust pipe, so as to provide additional oxygen for the control of unburned hydrocarbons, such secondary injection has not proven to be particularly effective for a variety of reasons. The simple fact is that it is highly desirable to complete the combustion process within the combustion chamber, as opposed to completing combustion within an exhaust after-treatment device.

In contrast with previous schemes for providing secondary air to an engine, a system according to the present invention provides secondary air directly to the engine' s combustion chamber so that hydrocarbon-rich gases remaining after combustion are caused to mix with otherwise unavailable air contained within the combustion chamber. In this manner, the unburned hydrocarbons within the post- combustion gases will be oxidised so as to reduce the level of unburned hydrocarbons in the exhaust.

The present invention provides an internal combustion engine including a cylinder bore, a piston slidingly housed within the cylinder bore, and a cylinder head which cooperates with the cylinder bore and piston to form a combustion chamber. At least one intake valve is mounted within the cylinder head. The intake valve allows a primary air charge to enter the combustion chamber through an intake port. A fuel injector provides fuel directly to the combustion chamber. An air injector provides a secondary air charge directly to the combustion chamber after combustion of the primary air charge and fuel has begun.

Although it is known to provide multiple injections of fuel into an engine cylinder, the present invention contemplates the injection of neat air following initiation of the combustion process.

The secondary air charge is injected with a velocity sufficient to cause turbulent flow in the gases contained within the combustion chamber. In turn, this causes further oxidation of substantially all of the unburned hydrocarbons remaining within the combustion chamber at the time of the secondary air injection.

The secondary air charge is preferably injected during the power stroke at approximately bottom dead centre (BDC) of the power stroke. Alternatively, the secondary air charge may be injected approximately at the midpoint of the power stroke.

Fuel and air injectors embodying the present invention may comprise a variety of configurations. For example, they may comprise a combination fuel and air injector having a common antechamber upstream from a common injection nozzle with the fuel being injected into the combustion chamber along with a small quantity of air. Alternatively, it may comprise separate fuel and air injectors using a common injection nozzle, or completely separate fuel and air injectors using separate nozzles.

Regardless of the type of injector used, the fuel spray emanating from the injectors may be directed into the combustion chamber in such a manner that stratification of the fuel charge results. In this case, the secondary air charge may be directed into a combustion chamber such that the hydrocarbon-rich zone caused by the stratification is expanded in size. The mass of secondary air charge is preferably about 2-4% of the mass of the primary air charge, but could be as much as 10%, depending upon the needs of any particular engine. According to another aspect of the present invention, a method for operating a reciprocating internal combustion engine having a combustion chamber defined by a cylinder, a piston reciprocally housed therein, and a cylinder head, includes the steps of admitting a primary air charge into the combustion chamber, directly injecting a quantity of fuel into the combustion chamber with the quantity of fuel being selected so as to allow a nearly stoichiometric fuel and air mixture to form in the combustion chamber, and igniting the fuel and air mixture by means of a spark plug. Finally, a quantity of secondary air comprising a secondary air charge is injected directly into the combustion chamber, after combustion has begun, to further oxidise unburned hydrocarbons within the combustion chamber. According to this method, the quantity of secondary air injected into the combustion chamber is sufficient to cause the overall air/fuel ratio within the combustion chamber to be lean of stoichiometric, for the purpose of assisting exhaust catalyst light-off. The quantity of secondary air injected into the combustion chamber may comprise about 10-15 mass percent of the primary air charge.

A system and method according to the present invention offers an advantage inasmuch as an engine may be operated in a lean quench combustion mode in which a fuel contained within a rich region located in the vicinity of the spark plug burns outwardly until the flame extinguishes, leaving hydrocarbon rich exhaust gas. As noted above, these unburned hydrocarbons will be further oxidised by the present secondary air system. Another advantage of the present system is that with direct cylinder injection of fuel, the unburned hydrocarbons remaining in the cylinder after the initial combustion may be further oxidised by secondary air injection to the point that the unburned hydrocarbon leaving the cylinder will be equivalent to the level of unburned hydrocarbon leaving the cylinder of a highly developed port fuel injection engine. The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of an engine according to the present invention during the compression stroke;

Figure 2 is a schematic representation of the engine of Figure 1 at the time combustion is initiated;

Figure 3 is a representation of the engine of Figures 1 and 2 during the engine's power stroke; Figure 4 is a schematic representation of a first type of fuel injection system according to the present invention;

Figure 5 is a schematic representation of a second type of fuel injection system having two separate air and fuel injectors according to the present invention; and

Figure 6 is a third type of fuel injection system having an integrated, single nozzle type of injector according to the present invention.

As shown in Figures 1-3, engine 12 is equipped with exhaust valve 16 and intake valve 14 which allows air to pass through intake port 24. Intake valve 14 and exhaust valve 16 are mounted within cylinder head 20, as is spark plug 18. Piston 30, which is mounted upon connecting rod 32, is slidingly housed within cylinder bore 28. Cylinder head 20, cylinder bore 28, and piston 30 cooperate to form combustion chamber 22.

Fuel and air injector 34, which is shown schematically in Figures 1-3, may have any of the configurations shown in Figures 4-6.

Operation of an engine embodying the present invention is shown beginning with Figure 1. Zone 36, which is located in the centre of the cylinder and labelled "Φ>1" is a fuel- rich zone. It is noticed that outside of fuel-rich zone "36", equivalence ratio Φ is shown as being less than one. In other words, the fuel is stratified within combustion chamber 22. Fuel can be injected either neat, i.e., without any injected air, or by means of an accompanying air charge, so that the fuel is premixed with air. An injector for accomplishing this mixed injection is shown in Figure 4. There, injector 40, which is a combination fuel and air mixing injector assembly, includes fuel valve 42, air valve 44, mixing chamber 46, and air and fuel solenoid 48. Injection is completed by means of injection nozzle 50. With the type of injector shown in Figure 4, the air and fuel are admitted to mixing chamber 46, and when air and fuel solenoid 48 opens, a jet of air and fuel penetrates into combustion chamber 22.

Figure 2 illustrates engine 12 in which piston 30 has moved close to its top dead centre position. Notice that zone 36 having equivalence ratio Φ>1 is moved to within closer proximity of spark plug 18. Thus, spark plug 18 will be able to initiate combustion of the air/fuel mixture within combustion chamber 22.

Figure 3 illustrates the result of introducing a secondary air charge directly into combustion chamber 22 after combustion of the fuel and air has begun. Injection of air would most likely occur after combustion during the engine's power stroke, when the cylinder pressure is low enough to allow a jet to emanate from the air injector. In this manner, enhanced mixing of the air within the cylinder and the unburned component of the fuel is promoted. Notice, from Figure 3, that air introduced by means of fuel and air injector 34 has caused the rich zone of Φ>1 to expand in volume and surface area. This increase in volume and surface area is accompanied by enhanced localised turbulence within combustion chamber 22. This localised turbulence greatly increases the mixing of the hydrocarbon-rich gases contained within zone 36 with the higher oxygen content gases lying outside zone 36. Figure 5 illustrates separate air-only injector 54 and separate high pressure fuel injector 56. The orientation shown in Figure 5 allows the air from air injector 54 to be directed precisely toward spark plug 18, with the result that the zone 36 will be expanded as shown in Figure 3. Fuel injector 56 is also directed toward spark plug 18. Figure 6 illustrates a low sac volume injector 58 having fuel solenoid 60, air solenoid 62, and common injection nozzle 64. Fuel injector 58 may be positioned so as to allow a fuel rich zone of Φ>1 to be clustered about spark plug 18 while allowing secondary air to be introduced in the manner illustrated in Figure 3. Turbulent mixing of hydrocarbon-rich zone 36 will be promoted during the expansion stroke, thus oxidising much of the unburned hydrocarbon before it leaves the cylinder.

Direct cylinder injection of a secondary air charge may be used for controlling engine hydrocarbon emissions during cold starting. According to this method, after admitting a primary air charge into the combustion chamber past intake valve 14, a quantity of fuel will be directly injected into the combustion chamber with the quantity of fuel being selected so as to allow a nearly stoichiometric fuel and air mixture to form in combustion chamber 22. Then, following ignition of the fuel and air mixture by means of a spark plug, secondary air charge will be directly injected into combustion chamber 22 so as to further oxidise unburned hydrocarbons within combustion chamber 22. In this case, the quantity of secondary air injected into combustion chamber 22 is sufficient to cause the overall air/fuel ratio in combustion chamber 22 to be lean of stoichiometric, thus assisting light-off of a three-way catalyst. This mass of secondary air could comprise about 10-15 mass percent of the primary air charge.

The actual mass of secondary air used with the present system would be adjusted to result in the lowest practicable tailpipe emission levels, given the combination of in- cylinder burn-up of hydrocarbons, coupled with fast catalyst light-off and warmed-up catalyst operation. Those skilled in the art will appreciate in view of this disclosure that adaptation of the present system and method to any particular engine will require that the optimal injected mass of air be experimentally determined, considering the combustion system, exhaust after-treatment, and control system design.

Claims

1. An internal combustion engine, comprising: at least one cylinder bore (28); a piston (30) slidingly housed within the cylinder bore (28); a cylinder head (20) which co-operates with the cylinder bore (28) and piston (30) to form a combustion chamber (22) ; at least one intake valve (14), mounted within the cylinder head (20), for allowing a primary air charge to enter the combustion chamber (22) through an intake port (24); a fuel injector (40) for providing fuel directly to the combustion chamber (22); and an air injector (40) for providing a secondary air charge directly to the combustion chamber (22) after combustion of the primary air charge and said fuel has begun.

2. An engine according to Claim 1, wherein said air injector injects the secondary air charge with a velocity sufficient to cause turbulent mixing in the gases contained within the combustion chamber.

3. An engine according to Claim 1, wherein said fuel injector and said air injector use a common injection nozzle.

4. An engine according to Claim 1, wherein said fuel injector and air injector comprise a common antechamber upstream from a common injection nozzle, with said fuel being injected into the cylinder along with a small quantity of air.

5. A method for operating a reciprocating internal combustion engine with stratified charge, rich burn, lean quench combustion, with said engine having a combustion chamber defined by a cylinder, a piston reciprocally housed therein, and a cylinder head, with said method comprising the steps of: admitting a primary air charge into the combustion chamber; directly injecting a quantity of fuel into the combustion chamber; igniting the fuel and air mixture by means of a spark plug; and injecting a secondary air charge directly into the combustion chamber after combustion has begun, to further oxidise unburned hydrocarbons within the combustion chamber.

6. A method according to Claim 5, wherein the quantity of fuel injected into the combustion chamber is selected so as to allow a nearly stoichiometric fuel and air mixture to form in the combustion chamber.

7. A method according to Claim 6, wherein the quantity of secondary air injected into the combustion chamber is sufficient to cause the overall air/fuel ratio within the combustion chamber to be lean of stoichiometric.

8. A method according to any one of Claims 5 to 7, wherein the quantity of secondary air injected into the combustion chamber comprises about 10-15 mass percent of the primary air charge.

9. A method according to any one of Claims 5 to 8, wherein the secondary air charge is injected at approximately BDC of the power stroke or the midpoint of the power stroke.

10. A method according to any of Claims 5 to 9, wherein the secondary air charge is directed into the combustion chamber such that a hydrocarbon-rich zone is expanded in size.