EP0120847A1 - Diesel engine combination fuel vaporizer and air/fuel mixer - Google Patents

Abstract

A diesel-type prechamber (20) has a centrally disposed heated tubular member (36) the interior of which is supplied with hot air through a secondary neck or transfer passage (40), the air vaporizing the fuel atomized against it. the outer surface (46) of the hot organ and also mixing with the vaporized fuel as air passes through transpiration holes (42) in the organ.

Description

DIESEL ENGINE COMBINATION FUEL VAPORIZER AND AIR/FUEL MIXER

This invention relates in general to compression-ignition type engine. More particularly, i relates to one having a combustion chamber constructio that minimizes the emission of particulates. The conventional diesel engine is of the divide combustion chamber type. A precombustion chamber formed i the cylinder head is connected by a small diameter throa or transfer passage to a smaller facing chamber located i a recess in the piston, such, for example, as is shown i U.S. 2,594,681, Ricardo et al . The fuel is injected o sprayed directly into the center of the prechamber into swirling flow of air pushed into the chamber during, th engine compression cycle.

While the above construction may be satisfactor for some installations, it does not always provide adequat fuel vaporization or mixing of the fuel with the air resulting in the formation of particulates. Attempts hav been made to minimize particulates by including, fo example, a hot bar inserted crosswise in the prechamber an heated by the hot air flow. However, mixing of the fue vapor with the air is limited by this construction so tha particulate emissions are only slightly reduced as compare to the conventional swirl chamber type engine.

Another commercially available diesel engin includes a secondary throat or transfer passage that pushe additional air into the prechamber in an opposing directio to set up opposing swirl motions and, therefore, provid better mixing. However, again, this results in onl slightly lower particulate emissions as compared to conventional swirl chamber system.

This invention relates to a prechamber that has heated tubular member located in the center of the chamber spaced from the chamber walls so that air flows in the clearance between the two; a portion of the outer surface of the tubular member being wet by the fuel ^"sprayed into the chamber to vaporize the fuel; the tubular member being heated by hot air forced into the member through a secondary transfer passage during the compression cycle of the engine; the member having transpiration holes in its wall that permit the flow of the hot air outwardly into the clearance space to provide rapid.mixing of the air and fuel vaporized by contact with the hot tubular member .

Constructions are known in the prior art that include hot bodies adjacent the prechamber to better vaporize the fuel injected. For example, U.S. 1,887,072, Suder et al , shows a domed-like member G inserted between the transfer passage and the opening to the prechamber and provided with directional holes for controlling the flow of air into the prechamber. to better mix the air and fuel.

U.S. 1,981,874, Mock, shows in Figures 1 and 2 a prechamber with a conical insert against which fuel is sprayed for fogging the air/fuel mixture. Figure 3 shows the use of a ball attached to the engine side of the valve member .

U.S. 2,223,090, Boxan, and U.S. 2,242,274, Thysse, both show the use of secondary transfer passages and an insert to provide better air/fuel mixing and vaporization.

U.S. 2,766,738, Hoffmann, U.S. 2,761,431, Nallinger, U.S. 2,778,347, Mallinckrodt, U.S. 3,102,521, Slem ons, U.S. 4,071,001, Goto, and U.S. 4,076,000, Goto et al, are further illustrations of heated bodies and angled passages to provide vaporization and mixing of the air and fuel . It will be noted in each of the above instances that there is no separate tubular member inserted centrally within the prechamber having a hollow interior connected by a secondary transfer passage with the hot air in the main combustion chamber during the compression stroke of this engine that passes through the tubular member into the clearance space between it and the prechamber wall to mi with the vaporized fuel therein to reduce particulates, th fuel injected being sprayed against a portion of the oute surface of the tubular member to wet the same and be heate and vaporized at that point to be thereafter mixed with th air swirling around the member. The prior art reference show either the use of secondary transfer passages alone or the use of heated projecting members that are no supplied internally with secondary air in the manne described.

Other examples of engine combustion chamber containing vaporizing members are shown, for example, i German patents 251981, 714661, and Netherlands patent N.R. 36124. In each of these instances, a perforated membe extends into or is adjacent the combustion chamber fo receiving fuel and/or air to be directed through holes t mix the fuel and air. In these cases, however, the fuel i not sprayed directly against the outer surface of a tubula hollow member containing hot air from the engine fo passage through holes into the remaining portion of th prechamber of the engine.

Finally, U.S. 1,129,316, Svalin, shows a combus tion chamber in which fuel is injected through an air mixing tube containing laterally directed holes tha receive air during the compression cycle of the engine an eject the air/fuel mixture at other times, for mixing purposes. Again, the construction is unlike that of the invention having a heated tubular member in the prechamber against which the fuel is sprayed and vaporized and mixed thoroughly with the usual supply of hot air swirling in the prechamber and additional air ejected from the inside of the tubular member.

It is a primary object of the invention, there¬ fore, to provide a compression ignition type engine with a prechamber that includes a heated tubular member that helps to vaporize the fuel injected or sprayed into the pre¬ chamber and mixes with the fuel air that has been trans¬ ferred into the tubular member through a secondary or supplemental transfer passage. Other objects, features and advantages of the invention will become more apparent upon reference to the succeeding detailed description thereof, and to the drawings illustrating the preferred embodiments thereof; wherein, Figure 1 is a cross-sectional view of a compression-ignition type engine embodying the invention;

Figure 2 is an enlarged cross-sectional view of a portion of the Figure -1 showing; and,

Figures 3, 4 and 5 are cross-sectional views illustrating modifications of the construction shown in Figures 1 and 2.

Except for the construction of the prechamber, Figure 1 illustrates a portion of an essentially conven¬ tional compression-ignition or diesel type engine. More specifically, it contains the usual engine block 10 having a cylinder bore 12 within which is slidably movable a piston 14. The upper end of piston 14 is formed with a shallow depression 16, which together with the piston face and the usual cylinder head 18 defines the main chamber of a divided combustion chambe . The other chamber 20 is defined by an insert 22 located in a recess 24 in cylinder head 18, and connected to chamber 16 by a primary throat or transfer passage 26. A conventional fuel injector 28 is adapted to spray fuel through the narrow angle indicated into the prechamber for mixing with the air that is swirled around therein in the usual manner. The cylinder head 18 contains the usual intake and exhaust passages 30 and 32, each controlled by a valve (only exhaust valve 34 shown). Further details of construction and operation of the engine pe se are not given since they are known and believed to be unnecessary for an understanding of the invention.

As best seen in Figure 2, located centrally withi prechamber 20 is a tubular ball shaped member 36 that i spaced equally from the walls of prechamber 20 as shown t permit the circulation of swirling air between the two. I is located so that its outer surface will be wet by th direct spray of fuel thereagainst as shown. Hot air i connected to the interior of the ball by means of a ste like tube 38 connected to a secondary or supplementa transfer passage 40 that is branched from the main o primary throat passage 26. A number of air transpiratio holes 42 bored through the wall of ball member 36 connec the hot air to the clearance space 44 during the compres sion cycle of the engine for mixing with the fuel vaporize in the prechamber.

It should be noted that the spacing of holes 4 where the fuel spray wets the outer surface 46 of ball 3 is circumferentially wider than the width of the fuel spra to avoid fuel rich combustion near the fuel spray. Accord ingly, it will be seen that as the fuel is . sprayed agains the outer surface of ball 36, hot air from the interior o the ball will be forced outwardly through holes 42 during the compression stroke of the engine to mix with th vaporized fuel as it is swirling around the prechamber prior to exhaust through primary transfer passage 26 into main combustion chamber 16.

Figure 3 shows an alternative construction in which the outer surface 46 of ball 36 adjacent the trailing edge of holes 42 are provided with stepped portions 48. The latter define ramps that set up vortices to the air and fuel motion passing into contact with these portions to provide better mixing of the air and fuel.

Figure 4 shows a further embodiment in which tubular member 36 is constructed with a mushroom-like shape having a domed outer surface 50 that provides additional surface upon which the fuel can spread for better mixing Additionally, the nonsymmetrical lower face portion 52 o the member provides a sharp change in direction to the flo of the air and fuel, with accompanying vortices, fo additional mixing. In all other respects, this embodimen is similar in operation to that of the Figures 2 and embodiments. Hot air is forced into the interior of th tubular member during the compression cycle of the engin and out through the transpiration holes 42 to mix with fue heated as it contacts the hot outer surface 50 of the dome member prior to passage of the mixture out into the engin through the primary throat transfer passage 26.

Figure 5 shows a somewhat different constructio for mixing and vaporizing the fuel. In this case, fuel i injected into a small diameter premixing tube 54 supplie with hot air from a small diameter parallel passage 5 connected to a secondary inlet throat or transfer passag 40'. The air inlet 58 would apply the secondary ai tangentially to tube 54 to provide a mixing action with th fuel spray, the mixture then exiting at the lower end o tube 54 to mix with the swirling air and fuel in th prechamber prior to exit -through the primary throat o transfer passage 26. The mixing air flow in this cas would be small enough to assure that the mixture withi tube 54 is richer than the flammability limit so tha combustion would not occur in the tube.

The operation of each of the embodiments describe is believed to be clear from a consideration of the abov description and the drawings and, therefore, will not b repeated. From the foregoing, therefore, it will be see that the invention reduces or- minimizes the production o particulates by providing a heated member located centrall in the prechamber and supplied internally with hot air fo both vaporizing fuel sprayed against its outer surface an for mixing with the vaporized fuel the air that passe through holes in the member .

While the invention has been shown and describ in its preferred embodiments, it will be clear to tho skilled in the arts to which it pertains that many change and modifications may be made^' thereto without departi from the scope of the invention.

Claims

1. A combination fuel vaporizer and air/fuel mixer for a compression ignition type engine having a divided combustion chamber including a main chamber contiguous to the face of the engine piston and a second prechamber in the cylinder head facing the main chamber and connected to the main chamber by a throat type transfer passage for the transfer of air in a tangential manner into the prechamber from the main chamber during the compression stroke of the engine to create a swirling motion to the air in the prechamber, and means for spraying fuel into the prechamber, the improvement comprising, the prechamber having a tubular member located centrally therein in the path of fuel sprayed into the prechamber to wet a portion of the outer surface thereof, the member being spaced from the walls of the prechamber for the flow of swirl air between the prechamber and member, supplementary air transfer passage means connecting a portion of the incoming hot air from the main chamber to the interior of the tubular member for heating the same and vaporizing fuel sprayed against the outer surface thereof, and a plurality of air transpiration holes in the wall of the tubular member connecting the air from the interior of the tubular member to the prechamber space surrounding the tubular member for mixing with the fuel.

2. A fuel vaporizer and mixer as in claim 1, wherein the holes are located at locations on the outer surface other than that on which the fuel is sprayed.

3. A fuel vaporizer and mixer as in claim 2, the supplementary transfer passage means including a tube extending into the prechamber connecting air to the tubular member from a secondary throat branched from the first mentioned transfer passage.

4. A fuel vaporizer and mixer as in claim 2, th tubular member comprising a hollow ball having th transpiration holes circumferentially spaced from on another, the spacing of the holes adjacent the surface we by the fuel spray being greater than the circumferentia extent of the wetted surface.

5. A fuel vaporizer and mixer as in claim 3, th tubular member including stepped edge portions in the oute wall surface contiguous to the holes for varying the ai flow motion to enhance mixing of the air and fuel.

6. A fuel vaporizer and mixer as in claim 3, th tubular member having a mushroom-like domed shape providin a large outer surface area over which the fuel spraye thereon can be spread.

7. A fuel vaporizer and mixer as in claim 5, th edge portions comprising mixing ramps providing vortices a the air/fuel flow flows past to better mix the air an fuel.