GB2079365A

GB2079365A - Diesel engine with precombustion chamber

Info

Publication number: GB2079365A
Application number: GB8114748A
Authority: GB
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1980-05-23
Filing date: 1981-05-14
Publication date: 1982-01-20
Also published as: GB2079365B

Abstract

A precombustion chamber 20 communicates with the cylinder space above a piston 4 through an opening 12 under the control of a valve 16. The valve is closed near the beginning of the exhaust stroke and fuel is then injected through an injector 24 to be heated by heat transfer from the walls of the chamber 20, transfer being promoted by fins 28. The temperature of the walls is kept up (within the range 200 DEG C to 650 DEG C) by insulating material 26 and/or embedded heater wires 30. The valve 16 is opened near the end of the compression stroke and compressed air rushes into the chamber 20 which is shaped to promote efficient mixing and the formation of a shock wave which promotes combustion in conjunction with a glow plug igniter 22. <IMAGE>

Description

SPECIFICATION Diesel engine with precombustion chamber This invention relates to diesel engines and is particularly directed to means for enhancing fuel combustion in diesel engines.

In recent years, increasing concern over the limits of the world's petroleum reserves has caused increased interest in diesel engines because of their greater fuel efficiency over conventional internal combustion engines and their ability to burn alternative fuels. Unfortunately, diesel engines still fall far short of complete efficiency, and tend to outdo conventional engines in producing particulate emissions which contribute significantly to air pollution.

Many attempts have been made to improve the efficiency of diesel engines and to decrease their production of pollutant emissions. However, none of the prior art techniques has been entirely satisfactory, and the search for improvement continues.

Accordingly, it is an object of the present invention to provide an improved diesel engine having improved combustion characteristics, improved fuel efficiency and reduced particulate exhaust emissions.

The engine according to the invention is defined in claim 1 below.

By preheating and pre-vaporizing the fuel within the precombustion chamber, while isolating the precombustion chamber from the engine cylinder during a substantial portion of the engine cycle in order to maintain conditions of pressure and temperature most suitable for vaporization and admitting compressed air from the engine cylinder into the precombustion chamber near the end of the compression stroke of the piston, the improved combustion is achieved. Preferably the precombustion chamber is shaped so as to enhance mixing of the compressed air with the preheated and vaporized fuel.

The invention will be described in more detail by way of example, with reference to the accompanying drawings, in which: Figure lisa diagrammatic representation of a diesel engine embodying the present invention; Figure2 is a transverse section through the diesel engine of Figure 1, taken on the line 2-2 of Figure 1; Figure 3 is a view, similar to that of Figure 2, showing an alternative form of the present invention; and Figure 4 is a vertical section through the precombustion chamber of Figure 3.

In Figure 1, a diesel engine 2 has a piston 4 within a cylinder 6. The head 8 of the cylinder 6 is formed with openings 10 and 12. Valve 14 represents an intake and/or exhaust valve which serves to close opening 10 and is operable, in a conventional manner, to permit intake of air and discharge of exhaust products. An isolation valve 16 is seated in the opening 12 and is operable to close the opening 12 from the beginning of the exhaust stroke of the piston 4 to near the end of the compression stroke.

The opening 12 communicates, via a throat 18, with a precombustion chamber 20 and a fuel injector 22 serves to deliver fuel into the precombustion chamber 20, in a predetermined manner, for subsequent ignition by means such as glow plug 24.

As seen in Figures 1 and 2, the precombustion chamber 20 may be surrounded by a layer 26 of ceramic or other thermal insulating material to retard heat loss from the precombustion chamber 20 and to maintain the temperature of the precombustion chamber in the range of about 200"C to 650"C thereby enhancing vaporization of the fuel delivered by the injector 22. If desired, vanes 28 or other protuberances may be provided on the walls of the precombustion chamber 20 to further enhance thermal transfer to the fuel and, hence, to promote vaporization. As an additional alternative, heating means such as electrical resistance wires 30 may be embedded in the walls of the precombustion chamber 20 and be energized to maintain the temperature of the precombustion chamber 20 within the desired range.

As shown, the precombustion chamber 20 is formed with two generally circular portions 32 and 34, separated by a generally rectangular portion, as indicated by dashed lines at 36 in Figure 2. The portions 32 and 34 are configured to promote mixing of the air entering the precombustion chamber 20 to further enhance mixing of the air with the prevaporized fuel. Although the portions 32 and 34 are shown as being generally circular, it will be understood that other configurations which promote mixing would be equally desirable. The rectangular portion 36 provides an abrupt wall 38 directly in the path of the air entering the precombustion chamber 20 through the opening 12 and throat 18, and serves to establish a standing shock wave in the region of the rectangular portion 36 in front of wall 38.This shock wave contributes to rapid ignition of the vaporized fuel and aids in mixing the incoming air with the vaporized fuel. The throat 18 forms the incoming air into a jet, which entrains the fuel vapours, enhances formation of the shock wave, and promotes the mixing action induced by the portions 32 and 34. If desired, the shock wave formation may be enhanced by elongating the rectangular portion 36 of the precombustion chamber, as seen at 40 in Figure 3.

In use, the isolation valve 16 serves to close the opening 12 from about the beginning of the exhaust stroke of the piston 4 until near the end of the precombustion stroke. Shortly after the valve 16 closes, the fuel injector 22 sprays a predetermined amount of fuel into the precombustion chamber 20.

This fuel will be vaporized in the precombustion chamber 20 under controlled conditions of pressure and temperature and while isolated from the charge of air contained in the cylinder 6. The vaporization takes place to a limited extent by heat transfer from the residual gases trapped in the precombustion chamber 20, and to a much greater extent from heat transferred to the fuel from the hot walls and vanes 28 of the precombustion chamber 20. For this reason, it is desirable to shape the precombustion chamber 20 and to direct the injector 22 so as to deposit the fuel on the walls of the precombustion chamber 20 and vanes 28 so as to form an evenly distributed thin film of fuel on these heated surfaces.

Afterthe isolation valve 16 has been opened, the highly compressed air from the cylinder 6 rushes through the opening 12 and throat 18 to form a jet which rapidly entrains the prevaporized fuel to form a combustible mixture. After ignition and combustion have been initiated, the contents of the precombustion chamber 20 will expand back through the opening 12 into the cylinder 6 to drive the piston 4 forthe power stroke.Obviously, the ignition and initial combustion of the fuel tends to heat the walls of the precombustion chamber 20 and insulation 26 and this, together with the heating wires 30 and the like, serves to maintain the temperature of the precombustion chamber 20 in the range of about 200"C to 650"C. Thus, when the valve 16 recloses and the next charge of fuel is delivered into the precombustion chamber 20, the elevated temperature will promote vaporization of the fuel.

Near the end of the compression stroke of the piston 4, the valve 16 opens and compressed air from the cylinder 6 rushes through the opening 12, is accelerated and formed into a jet by the throat 18 and is directed against the wall 38 to establish a standing shock wave in the rectangular region 36 adjacent the wall 38. The standing shock wave and the glow plug 24 promote ignition of the vaporized fuel which initially fills the precombustion chamber 20. The configuration creates a shear layer between the fuel vapour and the air jet, and induces swirling which enhances the mixing of the compressed air with the vaporized fuel which promotes more complete combustion of the fuel. This improved combustion provides increased fuel efficiency and yields significantly reduced particulate emissions.

Claims

1. A diesel enging comprising a precombustion chamber communicating with a cylinder through an opening with a valve, means arranged to close the valve near the beginning of the exhaust stroke of the piston in the cylinder, then to inject fuel into the chamber through an injector and to open the valve near the end of the compression stroke of the piston to allow compressed airto rush into the chamber from the cylinder.

2. A diesel engine according to claim 1,further comprising thermal stabilization means for maintaining the temperature in the precombustion chamber in the range of 200"C to 650"C.

3. A diesel engine according to claim 2, wherein the thermal stabilization means comprises a layer of insulating material surrounding the precombustion chamber

4. A diesel engine according to claim 2 or 3, wherein the thermal stabilization means comprises electrical heating wires embedded in the walls of the precombustion chamber.

5. A diesel engine according to any of claims 1 to 4, further comprising a plurality of protuberances projecting into the precombustion chamberto enhance heat transfer to fuel in the precombustion chamber.

6. A diesel engine according to claim 5, wherein the protuberances are vanes.

7. A diesel engine according to any of claims 1 to 6, wherein the precombustion chamber is formed to promote swirling of air entering the chamber to enhance vaporization of fuel within the chamber and mixing of the air with the fuel.

8. A diesel engine according to any of claims 1 to 7, comprising a throat connecting the precombustion chamber with the said opening and serving to accelerate the flow of air entering the opening and to form the flow into a jet.

9. A diesel engine according to any of claims 1 to 8, comprising an abrupt wall in the precombustion chamber in the path of air entering from the ,i opening.

10. A diesel engine according to any of claims 1 to 9, wherein the precombustion chamber comprises a generally rectangular portion located in the path of air entering from the opening and a pair of generally circular portions flanking the rectangular portion.

11. A method of operating a diesel engine having a cylinder, a piston slidable in the cylinder, and a precombustion chamber, comprising the steps of isolating the precombustion chamber from communication with the cylinder near the beginning of the exhaust stroke of the piston; then injecting fuel into the precombustion chamber; and opening the precombustion chamber to communicate with the cylinder near the end of the compression stroke of the piston.

12. A diesel engine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.