CA1088826A - Diesel engine combustion chambers - Google Patents

Abstract

DIESEL ENGINE COMBUSTION CHAMBERS
Abstract of the Disclosure Combustion chamber arrangements for divided cham-ber (prechamber) type diesel engines characterized by relatively low emissions of HC, CO and NOx, relatively low noise and physical stress and good fuel economy and power output and having:
1. canted valves in the heads and forming therewith lateral wedge-shaped valve recesses, 2. cooperating wedge recesses in the pistons forming disc or pancake-like valve pockets in conjunction with the cylinder head recesses, and 3. in-head prechambers closed by flame cups having wide connecting passages in their floors and side outlets for connection through channels with the edges of the valve pockets.

Description

Speci ication This application is a division of application Serial No. 283,109, filed July 19, 1977.
This invention relates to internal combustion engines and, more paxticularly, to divided or precombustion type combustion chamber arrangements for use in diesel engines, particularly of the automotive type.
The present in~ention provides an improve~ precham-ber type combustion chamber arran~ement including in preferred form overlapping pancake or disc-like valve pockets preferably formed partially in the cylinder heads by ~ed~e-shaped recesses under the heads of canted valves and partially in the pi.stons by wedye-shaped valve clearance recesses connectiny with ~he , cy].incl~r head rec~ise5 . rrhe valve pockets are connect~d with , in-head E~rechambers c]os~d by ~lam~ cups having wide connect~
in-y or dis~ arge passages in their floors and transversely , directecl side ou~lets. Th~se connect through lat~ral channels in the heads with eleva~ed sides or edges o~ the -turbulence pockets to clischarge hot combustion yases laterally, and at ~ ~
comparatively moderate flow rates, over the associated piston, ;'~ ~ ' .... . . ..
val~e and cylinder head surfaces, thereby spreading -the heat tr~ns~er eEfects over the surfaces and dividing the thermal ~' load more or less equally between the cylinder head including ;~
the valves and the associated pistons, thus lirniting localized hea-t transEer -to the piston heads as compared to other arrange-ments. ,~
The present invention further provides an improvedarrangement wherein a portion of the prechamber floor is heated on one side by the alternate passage of compression and ' combustion gases into and out of the prechamber and the heated `'~' portion is contacted on its other side by rich burning gases -~
and fuel droplets,' the hot surface aiding in vaporization of ;;
the fuel charge. Also the invention provides a fuel,injection spray tip having at least one pair of an~ularly disposed ori~
fices arranged on axes lying in a plane generally para]lel to '~' .
the associated,cylinder axis and oriented to direct fuel in a broad path outwardly and downwardly toward the heated~floor portion of the prechamber.
Other features are also included in the,inventi,on which vary in some arrangements and provide in varying degrees ' '~
advantageous combinations of operating characteris~ics including, relatively low emissions of HC, CO and NOX, smooth combustion ' ~; '' Witll result~ln~ low no.i:;e level ancl co~ onent 3~rel3C3~ good control o~ smoke or vi.sible em;ssions and good Eue]. economy.
Sucll di~erse ~eatures of ~he invention include variations in -the entrance angle and position of the connecting passages in their respective prechambers to control the rate o~ swîrl therein at the t.ime of ignition. Also, variations in the locations and orientation of ~he fuel nozzles, spray ori- . -fices and glow plu~s can var~ the balance of exhaust emissions, . .
combusti.on smoothness, visible smoke and fuel economy with resultant effects on noise levels and cornponent stress. The preferred en~odiment is thought to provide the most favorable combination of such features.
In preferred form the engine includes a piston .;~ - .
movable on an axis cooperating with a cylinder head having .
at least one poppet valve disposed on an axis canted in .. ~ :
relation to the piston axis and defining at the piston top ,~
dead center position a shallow pancake-like pocket under the valve head and normal to ~he valve axis and a precombustion ~-chamber having a discharge passage with a generally straight 1;`
20 clischarge portion in substantial alignment with the elevated li side of the pocket and connected therewith to direct gaseous discharge into the pocket ~rom the prechamber, the discharge ~:
passa~e at its end distal from the pocket having a portion extendin~ sharply upward from the straight portion and open- 1 ~
illCJ in~o khe precombus~ion chamber which in turn extends l.. ..
back Erom the opening toward the canted axis so as to form ¦ :
a wall bounded by the discharge passage and precombustion chamber, and means to inject fuel into the~.precombustion 1 chamber in a:plane generally parallel to the piston axis .
and ~owards the wall so that the air dis~harge into the 'htj prech~mbcr clu:ci.ng eacll colnpre~sion stroke generates a swirl ~:
init:ially curving inwarclly -to~ards -the piston axis and then .raveling do~:n~ardly yenerally parallel to khe piston axis - :
~0~7ards the wall and the injected fuel travels with the swirliny alr i.nto a temporarily locally rich mixture space above khe wall wherein combustion occurs under conditions relatively unfavorable to NO pro~uction, the size of the prechamber being roughly e~uivalen~ to the volume of the .~ .
rnain chamber with the proportions being such that gase~ -clischarging from the precombustion chamber an out against khe valve head and cylinder head and the piston so that the piStOII thermal load is comparable to the thermal load ~ .
o~ the valve and cylinder head in the main chamber. Other ~-spec.ific ~eatures and alternative embodiments are also dis-closed.
These and other advantages and features of the ;~, -invent.ion will be more fully understood from thb following ::
description of certain preferred and alternative embodiments chosen Eor purposes of illustration, taken together with the 20 accompanying drawings. ~.
In the drawings: :
Figure 1 is a ~ragmentary transverse cross-sectional view along the axls of a cylinder of an internal combustio en~ine :Eormed in accordance with a pre~erred form of the inven-tion with the valve i.njector and ylow plug in side elevation and the valve port sectianed along the valve a~is;
Fiyure 2 is a cross-sectional view t~rough the com-bustion chamber of the pre~erred embodimenk taken generally in the plane indicated by the line 2-2 o e Figure l; ~'~

Figure 3 is a ~raymentary cross-sectional view through ' , . ~ - . , . -. . .

the injection no~le spray tip a~ viewed Erom the plane indi-cated by the line 3--3 of Figure 1 with p~rts in elevation Figure 4 is a fragmentary cross-sectional view through the precombustion chamber o the preferred e~bodiment as viewed from the plane indicated by the line 4-4 of Figure l;
Figure 5 is a fragmentary cross-sectional view throu~h the main and precombustion chambers as viewed from the transverse plane through their axes indicated by the line 5-5 of Figure 2; :~ :
Figure 6 is a pictorial vi~w from underneath a ~ :
portion of a cylinder head o ~he preferred embodiment and showing portions of the c~mbustion chamber forming surfaces;
Figure 7 is a pictorial view from above of a piston for use in the preferred embodiment and showing the piston head configuration; ~-Figuxe 8 is a pictorial view of a prechamber cup for use in the preferred embodiment;
Figures 9, 10 and 11 are cross-sectional views with parts in elevation similar to Figure 1, but illustrating various al~ernative embodiments of combustion chamber arrange-~ .-.
ments formed according to the invention; and Figure 12 is a cross-sectional view through the chamber o the last mentioned embodiment as viewed from the plane indicated by the line 10-10 o~ F1gure 11.
Referring first to the embodiment of Figures 1-8 of the drawings, numeral 10 generally indicates an internal com~
bustion engine o~ the ~our-stroke automotive diesel t~pe.
Engine 10 is conventlonally provided with a cylinder blocX 12 defining a plurality of cylinders 14 having axes 15, only one of the cylindexs being shownO Each of the cylinders opens through an end wall of the cylinder block 12 which is formed as a flat machined surface 16. Each cylinder has reciprocably ..

~

dispos~d therein ~ piston 18 haviny the usual piston seali.ng rings 20 and having a generally flat upper surface 22 which, in the upper position of motion of the piston, known as the top dead centeL position, approximates a location of near alignment with the upper surface 16 of the cylinaer block.
At least one cylinder head 24 is mounted on the cylinder block 12, having a generally flat lower surface 26 opposing and sealingly engaging through a gasket 28 the flat upper surface 16 of the cylinder block. ~he flat head surface 26 also closes the end of each cylinder 14 and, lying opposite the flat piston surfaces 22, defines together with the piston and cylinder main combustion chamber portions 30 located at the ends of the cylinders 14.
At each cylinder location the cylinder head 24 is provided with a pair of adjacent ports including an inlet port 32 and an exhaust port 34~ These ports respectively connect the main combustion chamber 30 with suitable air inlet and exhaust gas aischarge systems, not shown, the movement of .
gas between the ports and the combustion chamber being con-trolled respectively by inlet and exhaust poppet valves 36, 38 having heads seatable at the ends of their respective ports to close the ports.
The valves 36, 38 are carried in the head for reci-procating movément on parallel axes 40 which are canted or inclined upwardly away from a plane passing through the c~lin-der axis 15 and preferably extending longitudinally of the engine. The canting of the valve re~uires the valve seats 41 in the cylinder head to be recessed on one side, resulting in the formation of wedge-shaped valve recesses 42, 43 which are defined by the ~ottoms of the valves and the surrounding wall ~ 2~

portions ~ tapering into the adjoining flat surface 26 of the cylinder hea~. These valve recesses are complemented by similar wedge-shaped recesses 46, 48 ~ormed in the 1at upper surface 22 of the piston to provide clearance for the initial opening or final closing motion o the heads of the respective valves. The valve recesses in the head and their related recesses in the piston cooperate to form ad~oining and over-lapping pancake or disc-like air turbulence valve pockets between the ends of the valves and the top of the piston and having elevated sides ormed largely within the cylinder head.
Use is made of these valve poc~ets in the design of the com-bustion chamber as will be subse~uently more fu~ly explained.
At each c~linder location, the cylinder head is provided with a preco~bustion chamber (prechamber) S0 which is located in the head above one edge of the piston and on the side of the inlet and e~haust ports opposite the direction of upward inclination of their valva axes 40. Each precombustion chamber 50 is formed in the head by a recess 52 that extends ~-upwardly from the cylinder head bottom sur~ace 26 and is closed at the bottom by a flame cup insert 54 The flame cup insert comprises a unitary body having a floor (or bottom wall) portion 56 with upp~r and lower sur~
aces 58, 60 and a flanged outer edge 62 interference fitted in a complementary portion of the prechamber recess 52 to retain the inser~ in the head. A portion of the insert opposes the upper surface 16 of the cylinder block and engages the gasket ~-28 so as to positively retain the insert 54 in the cylinder head after the engine is assembled. The rem~inder o~ the insert floor lower surface 60 extends into the cylinder in opposition to the flat upper piston surface 22. I~ should be noted that the fu}l extent of the lower surface 60 is unbroken by any opening.

Supported on the floor, the unitary flame cup ~ur-ther includes an upstanding cylindrical wall 63, the outer surface of which is spaced from the corresponding cylindrical portion of the recess 52 to provide an insulating barrier that tends to retain heat in the wall portion 63. A part cylindrical protrusion 64 cast on the exterior of wall 63 mates with a vertical drilled recess or slot 65 in the wall , ' of head recess S2 to positively locate ~he ~lame cup in the desired position. The interior of the wall 63 is curved and smoothly connected with the upper surface 58 of the floor to define a cup-shaped interior cham~er portion 660 Near its upper edge at 67, the wall in~erior has a part spherical portion. This portion opens to and blends with the upper portion of the recess 52 which is of part spherical configu~
ration to form the total volume of the precombustion chamber 50.
The prechamber 50 is connected with the main chamber portion 30 by a wide and relatively shallow gas connecting and discharge passage in the floor portion 56. The passage includes a first wide mouth generally straigh~ passage portion 20 68 that is in substantial alignment with the associated valve 1`
pockets and registered wi~h the elevated sides thereo~.
Passage portion 68 extends laterally in the floor 56 on an axis that preferably lies in a plane approximately at right angles to the longitudinal plane defined by the valve axes. Thus~ the passage portion 68 extends at a slight upward angle between the upper and lower surfaces 58, 60 of the flame cup floor, from an opening 70 in ~he side of the floor that does not break through the lower surface to a junction point beyond the center of the `~
floor. Here the first passage portion joins with a second wide~
0 passage portion 72 that extends sharply upwardly toward the ~`

~ . . ~,.
.

~L.O~

center of the precombustion chamber 50, forming an acute angle with th~ first p~ssag~ portion and opening to the cup-shaped portion 66 of the prechamber through an opening 74 in the floor upper surface 58 at a point beyond the center of the floor 56 from the openiny 70. From opening 74, the extension of the prechamber primarily back toward the cylinder and valve axes, causes the portion of the floor 56 between its upper surface 58 and the s~raigh~ passage portion 68 to form a hot wall 75, heated in operation by combustion gases on both sides.
The sharp change in angle and orientation of the second pa~sage portion 72 toward the center of the precombus- : -tion chamber SO has the purpose of directing incoming gases into the prechamber with a very low degree of swirl and tur bulence as compared to most other known pxechamber arrange-ments, including the alternative embodiments o the present :~
invention to be subsequently described. Both portions of the Eloor passage 68, 72 are relatively wide in relation ~o their depth (or thickness) in order to provide a relatively large area flow path. T~e dimensions of the first passage poxtion, as disclosed, involve a passage width about foux times its depth, while the upwardly extending second passage portion has a width somewhat more than two and one~half times its thick~
ness in the narrower lateral direction.
The 1ame cup passage 68, 72 connects with the elevated deeper edges o the valve recesses 42, 44 through a channel 76 cut laterally in the surface of the cylinder head and of a width substantially equal to the first passage portion 68 of the flame cup, of which the channel constitutes an 30 extension. ~-The arrangement directs hot gases rom the precom bustion chambsr laterally into the edges of the valve pockets : :`

formed between the cylinder hc~d and pis ton so th;~t the g~s is directed in a wide path, fanning out across the width of the opposing cylinder head and pi~ton surfaces rathex than down upon the piston as is common practice in prechamber diesel engines. Our improved arrangement reduces l~calized heat trans~er to the piston surface and spreads heat flow to the piston over a greater surface area while also permitting the cylinder head and valves to provide an increased proportion of heat dissipation. As a result, the piston head can accept the heat load imposed thereon without an increase in thickness sufficient to require an increase in height of the cylinder block over the height of a comparable gasoline engine of the same cylinder dimensions, thereby permitting the use of common tooling for machining both diesel and gasoline engine cylinder block~.
In order to provide a combustible mixture o air and fuel in the precombustion chamber 50, the cylinder head mounts at each cylinder lvcation a pencil type fuel i~jection nozzle 78 which is located in a bore 80 having an axis preferably parallel to the cylindex axis and opening through the upper wall of the prechamber almost tangential to the inner wall ~ ;
~urface 82 of the prechamber at the point closest to the cylinder axis. The fuel injection nozzle is provided with a spray ~ip 84, best shown in Figure 3, having a needle valve 85 and at least two angularly disposed orifices 86, 88 which `.
lie in a plane parallel to the cylinder axis and direct injected fuel downwardly, generally parallel to the cylinder and piston axis 15, in a wide, fan like, relatively so~t spray pattern toward the sides and bottom hot wall 75 of ~he flame 0 cup insert. If desired, additio~al orifices may be disposed in the injection no~æJ.~ spray tip to d:irect the ~uel in an even softer pattern toward additional areas of the flame cup sides and bottom wall~
The fuel spray is preferably directed generally tangen~ially to and in the direc~ion of the ~wirling airflow in the prechamber. It is thought this forms a locally uel rich-zone in the prechamber which auring combus~ion helps limit or control formation of nitrogen oxides. Subsequent mixing of the burning rich gases and air in the main combus-tion chamber provides for completion of combustion reactionsand holds emissions of hydrocarbons and carbon monox;de to normally low diesel engine levels.
The cylinder head also mounts a glow plug 90 at each ~
cylinder location. Each plug 90 is secured in an opening 92 ~ ~;
having an axis that lies in a common plane with the axis of the fuel injection nozzle bore 80 and, preferably, the pre~
chamber connecting passage 68, 72, the plane lying parallel with and preferably encompassing the axis of the cylinder Each glow plug 90 has an elongated end 94 that ex~ends into 20 the prechamber in or near the path o~ fuel spray from the ~ ;
i : ~
injector nozzle orifices, thus providing a hot spot to aid the prompt ignition of fuel delivered to the prechambar by the ;
injector during engine starting and warm-up.
The various features of the above described embodi- .
ment of the invention when incvrporated in an automotive type four-stroke diesel engine have been shown to provide an advan~
tageous combination of high combustion e~ficiency, low smoXe and emission levels and relatively low combustion noise~
Through analy~is of the result of tests, it is considered that 30 the various features obtain the following specific advantages ~ :~
when combined in the manner illustrated. ~ :

-~t)~ 2t~

The provision of inclined or canted v~lves combined with the side prechamber outlet -throuc~h a thin wide passage av~ids excessive localized pi~ton head temper~tures ana also results in good utilization of air in ~he main chamber, making possible adequate power output with low smolce while utilizing a bore stroke ratio generally considered too high to be favor-able for diesel engines and permitting a relatively low ratio of engine weight to power output. Another result is good mixing in the main chamber, giving relatively complete com-bustion and low emissions of hydrocarbons and carbon monoxideO
The abrupt bend in the flame cup connecting p~ssageand the radial entry into the precombustion chamber cavity gives a low rate of air swirl in the prechamber compared to most swirl chamber engines~ This contributes to smooth com-bustion with resulting low noise and stress levels.
Placement of the fuel injector nozzle centerline close to the prechamber wall and the use of a nozzle configu-ration giving a wide and thin spray with low penetration and in the direction of air swirl in the prechamber forms a fuel-rich region near the prèchamber wall but without excessive collection of fuel on the wall~ Combustion, thus occurs under locally rich conditions and in a locally low temperature zone, which aids in giving smooth combustion and low formation of nitrogen oxides.
Division of the prechamber connecting passa~e into two distinct flow portions permits the flow area and orienta-tion of these portions to be optimized separately for the control of mixing in the main chamber and air motion in the prechamber.
The use of a wide thin floor in the precham~er pro-viaes a local high temperature wall area 75 which reduces ; . . , - : . . -- ..

ignition delay and pr~v~n~ ~uel ~rom ~ccumul~-tiny on ~h~ wall, This aids in providing smooth combustion and low hydrocar~on emissions.
In addition to the foregoing features, the associated fuel pump is preferably provided with relatively low injection pressure and slower than normal injection rates~ which, when combined with precise control of injection timing, provide for combustion to beyin at controlled optimum points over ~he speed ~:
and load range~ thus contributing to the smooth combustion and low emission performance of the en~ine.
Re~erence will now be made to Figures 9-12 of the drawings in which various alternative emboaiments of ~he invention are illustrated. In the main, the constructions ~f the various embodiments are identical. The features of dif~er~
ence reside in the placement and configuration of ~he pre~
combustion chamber, as well as with the location and orientation of the fuel injection nozæle and glow plug for each cylinder.
Thus, description of the alternative embodiments will be limited to these differing Eeatures, it being understood that 20 the remainder of the construction in each case is identical ~o ..
the first described embodimentO Simi~ar or identical com- .
ponents in the various embodiments are identified by re~erence numerals differing by multiples of one hundred.
Re~erring now to the embodiment of Figure 9 in which xe~erence numerals i~ the 100 series are utilized, the arrange- .
ment ~hown is identical to that of the first described embodi- ~:
ment, with the exception of the location and orientation o~ ~ :
the fuel injection nozzle 178 and the glow plug 190. In this ~.
embodiment, glow plug 190 is located near the prechamber inner wall surface 182, being mounted in an openiny 192 inwardly of, but having an axis coplanar with, the fuel injection noæzle . .

bore 180. In this embodiment, the spray patt~rn of the fuel injection nozzle is aimed in the direction oP aîr swirl ana to~ard the inner portion o the prechamber walls and floor very close to the area toward which the spray pattern of the injector of the first described embodiment is also aimed.
Referring now to the embodiment of Figure 10 in which reerence numerals in the 200 series are utilized, the arrangement of the fuel injector 278 and ~low plug 290 is physically similar to the arrangement of these components in the embodiment of Figure 9. However, the pattern of fuel spray from the fuel injector nozzle may be modified to be directed gener~
ally across the center of the precombustion chamber 250 towaxd locations near the end of the second portion 272 of the flame cup connecting passage. However, the orientation of this second passage portion 272 is also altered s4 that it is direc-ted sharply upwardly at nearly right angles to the first passage portion 268, aiming at a location between the center of the prechamber and its outer side wall. The result is that this embodiment provides a greater amount o swirl in the pre- ;
20 chamber than the first two embodiments described, resulting in ~, , somewhat faster combustion and various other differences in -operating characteristics.
Referring now to the embodiment of Figures 11 and 12 in which reference numerals of the 300 series are utilized, it should be noted that placement of the fuel injector nozzle 378 i5 essentially the same as in the embodiments of Figures 9 and 10. The location and orientation of the glow plug 39~ differs, however, since it is placed on an axis that does not lie on a ;
transverse plane thxough the fuel in]ection nozzle and ~lame cup connecting passage. Also, the shape of the flame cup interior 366 is al~ered some~h~t wi~h a much sharpex junction of the inner portion uf the wall surface 382 wi~h the upper surface 358 of the flame c~lp floor. The connecting passage is also alter~d in that the second passage portion 372 intersects the first portion 368 in a sharp but obtuse angle and the second portion is directed almost tangentially along the adja- :
cent outer portion of the inner wall surface 382. ThiS axrange-ment provides a relatively high degree of swirl~
One other difference is that the prechamber 350 is relocated with respect to the cylinder axis so that the cen-txal plane of the connecting passage 368, 372 does not extend through the cylinder axis. To accommodate this, an alteration is made in the shape of the connecting channel 376 which carries gas flow between the side outlet opening 370 o~ the 1ame cup first passage portion and the wedge-shaped valve pockets 342, 343 of the cylinder hea~.
While various alternative embodiments have been illustrated which include many o~ the major features of the invention as disclosed in the irst described emhodiment, it should be understood that numerou~ other variations could be .
made within the scope of the inventive concepts tau~ht herein.
Accordingly, it is intended that the invention not be limited by the speciic embodiments disclosed but that it have the full scope permitted by the language of the following claims.

~,:
' ~

..~ ', ' ' ` .

' ':' `'' ' ', ' .' ~'; ' ' .

Claims (3)

Claims - C-3,038 The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A flame cup adapted for installation in a diesel engine cylinder head to form part of a precom-bustion chamber in said head, said flame cup comprising a unitary body having a floor with upper and lower surfaces, the latter being unbroken, and a continuous upstanding wall on said floor and having a curved interior surface smoothly connected with the upper surface of said floor to define a cup shaped interior chamber portion, and a gas passage through said floor and connecting with said cup shaped chamber portion, said gas passage comprising a first wide passage portion opening to the exterior of said floor at one side thereof above the lower surface, and extending transversely between said upper and lower surfaces to a junction point beyond the center of said floor, and a second wide passage portion extending upwardly from said junction point toward the interior of said cup shaped chamber portion at an angle with said first passage portion so as to direct gas flow into said cup shaped chamber portion in a manner to determine the resulting swirl or turbulence.

2. The flame cup of claim 1 wherein said first and second passage portions form a sharp angle with one another so as to limit the resulting swirl or turbulence.

3. The flame cup of claim 2 wherein said sharp angle is an acute angle.