US3063438A - Means for suppressing combustion abnormalities in internal combustion engines - Google Patents

Description

Nov. 13, 1962 A. e. BODINE. JR 3,063,438

MEANS FOR SUPPRESSING COMBUSTION ABNORMALITIES IN INTERNAL COMBUSTION ENGINES 2 Sheets-Sheet 1 Filed March 21, 1961 Nov. 13, 1962 A. e. BODINE. JR 3,063,433

MEANS FOR SUPPRESSING COMBUSTION ABNORMALITIES IN INTERNAL COMBUSTION ENGINES 2 Sheets-Sheet 2 Filed March 21, 1961 INVENTOR. 4.451577 6 flaw/V412.

v a i fi'g fa -3- fig 3,%3,438 new... is.) Patented Nov. 13, 1%52 of the attenuator cavity results in maximum heat shielding 3,063,438 of the attenuative material from the combustion flame, and

MEANS FOR SUIPRESSING COMBUSTION AB- NGRWIALITES IN INTERNAL COMBUSTIGN ENGWES Aihert G. Bodine, In, 13120 Moor-park, Sherman Oaks, Calif. Filed Mar, 21, 1961, Ser. No. 97,236 4 Claims. (Cl. 123-191) This invention is concerned with suppression of combustion abnormalities, such as violent pressure shocks and gas vibration, in internal combustion engines, by suppressing acoustic waves at the frequency at which such phenomena occurs. Although this invention is useful in any engine combustion chamber, including gas turbines and rockets, it will be explained primarily in connection with piston engine combustion chambers since the teaching of the invention for piston engines necessarily covers all of the important concepts for other combustion chambers. Moreover, the piston engine configurations encompass all of the various operating cycles, including spark ignition, diesel, four cycle, two cycle, etc.

Reference is made to my prior patents in this field, notably Patent No. 2,573,536 for basic teaching, and Patent No. 2,752,907 which is of interest by way of contrast with the present invention.

A general object of the invention is to provide a frequency responsive cavity, having broadened band frequency response as regards acoustic attenuation, and which is acoustically coupled to the chamber to be controlled.

An attenuator with a somewhat broadened frequency response has many advantages, in correspondence with the objects of this invention, as follows: (1) More liberal production tolerance, (2) less critical maintenance, (3) less temperature sensitivity as regards speed of sound in the gas, (4) less critical location in relation to the combustion chamber, and (5) more complete coverage of detonation frequency spectrum.

In my prior Patent No. 2,752,907 the suppression cavities have their freqeuncy response broadened by a damping means (fibrous or porous bodies) located essentially near the low impedance or velocity antinode type of region. The cavities have neck regions, of low acoustic impedance (regions of large gas oscillation velocity), and the fibrous or porous materials are located in these regions of low acoustic impedance. Note the porous body 40 interposed inside the neck and ahead of the cavity 46 of the attenuator 22, and the fibrous material extending along the cavity wall 51 in the attenuator 23. In the latter, the fibrous material begins at a low impedance point adjacent the neck of the cavity, where the attenuative efiect exerted by the fibrous material is maximized, and is thickened in the direction away from the low impedance region to avoid discontinuities in impedance which might cause wave reflections. These prior attenuators are characterized by and effective because of location of attenuative material in regions of high gas vibration velocity.

In accordance with the present invention, the attenuative material is located so as to be primarily, preponderantly, or even exclusively, in the high impedance, closed inner end region of an attenuator cavity, where gas vibration velocity is minimized, and the attenuative material is located as far as possible from the combustion flame. Thereby, there results (1) minimum attenuation for innocuous, or even useful, gas vibration of small amplitude, (2) effective attenuation of harmful gas vibration of large amplitude and (3) minimization of hot spots within the attenuator such as might hinder or interfere with the basic chemistry of regular combustion. It will be seen that, in the latter connection, the location of the attenuative ma terial substantially exclusively at the far inner extremity minimization of hot spots within the attenuative material.

A unique accomplishment'of the invention is that placement of the attenuative material substantially exclusively in the high impedance region of the attenuator makes it possible to broaden the tuning of cavity, without reduction in resonant strengthening of the attenuative efifect. In this connection, it is to be understood that a cavity such as here used, for example, a Helmholtz cavity, or a quarter wave pipe, has a natural resonant frequency. The cavity should be designed so that this natural resonant frequency corresponds to a frequency at which offensive large amplitude gas vibration has been found to occur. The use, in connection with this tuned cavity, of attenuative material located at the high impedance region thereof, then attenuates the gas vibration to be combatted. It will be evident that it is desirable that the attenuative cavity be both broad tuning, and still have high peak resonance response-qualities which are ordinarily largely inconsistent with one another. The present invention, comprising location of the attenuative material to attenuate the wave predominantly, or substantially exclusively, in the high impedance region of the cavity, reconciles these qualities and permits broader band tuning without material loss of resonant attenuation response.

The invention will be better understood from the following detailed description of certain present illustrative embodiments thereof, reference for this purpose being had to the accompanying drawings, in which:

FIG. 1 is a section through the combustion chamber of an engine showing an attenuator in accordance with the invention in longitudinal section;

FIG. 2 shows an alternative attenuator;

FIG. 3 is a view similar to FIG. 1, but showing a modification.

In FIG. 1, there is fragmentarily shown a valve-in-head engine having water-cooled block 10 and water-cooled head 11, the block having cylinder bore 12 containing piston 13. The combustion chamber 14, defined by head 11 over cylinder bore 12, is of a flat pancake type. The top chamber wall 15 accommodates seats for intake and exhaust valves 16, and the head structure affords intake and exhaust port tubes as shown.

The side combustion wall 29 has a threaded port 21 for a spark plug 22, and a similar threaded port 23 to receive the threaded slightly reduced neck 24 of a quarter wave type elongated attenuator cavity 25 or wave guide' This cavity comprises an interior generally cylindrical wave guide of quarter wave length for a sound wave of the gas vibration wave frequency to be combatted, the calculation of wave length taking into account the elevated temperature of the combustion gases wherein the gas vibration occurs. The cavity is thus resonant to this vibration frequency. In this illustrative embodiment, the cavity or wave guide 25 comprises a cylindric wall 26 extending from neck 24, a cylindric cap 27 threadedly connected to wall 26, as at 23, and extending therebeyond, an end closure wall 29 for cylindric cap 27, and a body 30 of high heat resistant sound wave attenuative material packed inside cap 27. This body of material 30 may be comprised of fibrous material, such as glass fiber, or a porous ceramic or metal, and is here illustrated in the latter form.

The neck 24 communicates one end of the interior of the attenuator cavity with the combustion chamber, and by proper choice of dimensions, an acoustic coupling is thereby accomplished with a component of the gas vibration patterns occurring within the combustion chamber. It will of course be understood that gas vibration patterns vary as to frequency band, orientation, and mode of vibration, with difierent combustion chambers. The type of coupling here illustrated between the attenuation cavity and the combustion chamber, or the wave pattern therein, however, is generally effective as regards patterns commonly encountered. In any specific case, of course, the frequently of the gas vibration component to be combatted can be first ascertained by any suitable measuremerit technique, and the length of the'cavity then calculated. In this connection it should be mentioned that the quarter wave length dimension should be measured from the neck region of the cavity to, and within, the porous body. A quarter wave length standing wave then tends to be established in the attenuator, with a velocity antinode (region of maximum gas oscillation velocity) at the neck, and a pressure antinode (region of maximum pressure oscillation) within the porous body.

The porous body contains a large number of intercommunicating pores, crevices and interstices, and the gas vibration wave entering the neck of the attenuator, and then traversing the cavity to this porous body, encounters this porous structure, instead of a wall of good reflective properties. Gas particles under the driving influence of the wave thus enter and scrub against the wall surfaces defining the interior openings of the porous body, and their energy is thus dissipated. The entering gas vibration wave is thus only poorly reflected, and very largely attenuated.

The closed inner end region of the quarter wave length attenuator pipe or cavity is known as one of high impedance, the impedance being the ratio of the ampitude of gas pressure oscillation to the amplitude of gas particle oscillation velocity. It is recalled in this connection that in an energized quarter wave pipe, gas pressure oscillation is at a maximum in the region of the closed inner end of the pipe, and gas particle oscillation velocity is at a minimum at the same place, giving high impedance.

As stated before, the porous body at the closed inner end of the quaterwavelength attenuator interferes wtih gas pressure wave reflection, thus spoiling the wave, with the energy of the wave absorbed by the attenuative material at the inner end of the attenuator, in this case, the porous body.

Since the wave in the attenuator cavity is driven and energized by the coupled gas vibrations occurring in the combustion chamber, the energy dissipation within the attenuator is actually dissipation of the energy of the gas vibration occurring in the combustion chamber, and the combustion chamber gas vibration is therefore attenuated.

The attenuator in the form now described has the advantages and advantageous results preliminarily stated. Because of its broad band tuning, its dimensions are not critical, and liberal production tolerances may be allowed. Its maintenance is non-critical, and its porous element may be very readily replaced when it becomes clogged with carbon. The porous, or alternatively fibrous, attenuative body does not establish a highly definite effective acoustic length for the quarter wave length pipe or cavity, and thus there is reduced sensitivity to variances in the speed of sound in the heated combustion gases as regards the effect of gas temperature on the design dimensions of the cavity.

The attenuator in the form now described has a broadened frequency band response. That is to say, it attenuates received acoustic gas vibration waves within a broader band Width than an attenuator having a rigid termination. And it attains this broad band attenuative response or coverage without material loss of desired resonant augmentation of the attenuative effect notwithstanding a fairly liberal departure from peak resonance frequency. The attenuator, with its absence of attenuative material at the high gas velocity, low impedance region, does not have an effective attenuative effect on gas oscillations of low amplitude, which are not harmful, and may even have a beneficial effect on controlled com- 'etry, and resulting acoustic properties.

bustion. Finally, the attenuator has the advantage that the porous element is located fairly remotely from the flame, and is therefore not prone to develop hot spots which might become sources of combustion irregularities.

The attenuator 40 shown in FIG. 2 may be used in the engine of FIG. 1 by substitution for the attenuator 25. It dilfers from the attenuator of FIG. 1 only in its geom- Thus, its length is less than a quarter wave length for the resonant wave frequency component, or frequency band component, that is to be attenuated, and its diameter is enlarged as compared with the attenuator of FIG. 1, so that it has more of a bottle-like shape. It consists, in the nature of a Helmholtz resonator cavity of a threaded neck 41 adapted to be screwed inside wall 20, and an enlarged chamber 4'2 joined to neck 41. The chamber 42 comprises cylindrical side Wall 43 extending from neck 41, and a cylindric cap 44 screwthreaded to wall 43, and an end closure wall 45. In this cap is porous body 46.

The attenuator 40 operates acoustically as a Helmholtz resonator, rather than as a quarter wavelength pipe. The volume of its chamber space 47, inclusive of the gas space within the porous body 46, determines its resonant or responsive wave frequency. Its neck region is a region of high gas oscillation velocity, and one therefore of low impedance. The closed rear end of the attenuator, adjac ent the face of the porous plug, is a region of minimized gas oscillation velocity, but of maximized gas pressure oscillation amplitude, and is therefore a region of high impedance. Energy of the gas wave is dissipated by gas pressure excursions into the intercommunicating pores of the porous body, wherein the wave is scrubbed and attenuated. Otherwise than for the difference between a quarter wave pipe and a Helmholtz resonator, the invention behaves as, and has the advantages of, the embodiment first described.

Reference is next directed to the embodiment of FIG. 3, showing an engine much as in FIG. 1. Parts in FIG. 3 corresponding to parts in FIG. 1 will be identified by the same reference numerals, but with the suffix a added in FIG. 3, and will not be further described. In the engine of FIG. 3, the bottom of the head is somewhat flattened to provide space, between the head and the block, for an insert wall which is bored so as to circumscrioe the cylinder bore. The inner periphery 51 of this bored insert wall 50 thus defines or forms a portion of the side wall of the combustion chamber. Radially outward of inner periphery 51, there is sunk in the underside of wall 50 an annular channel 52 which accommodates a ringshaped porous body 53. A narrow annular channel 54 atfords gas communication and acoustic wave coupling between the combustion chamber (and the gas vibration pattern therein), and the porous ring 53.

The space formed by the channels 52 and 54 is equivalent to a Helmholtz resonator, the inner margin of the channel forming the neck thereof and the volume in back of the neo forming the cavity. The dimensions are made such that the resonant frequency of the cavity corresponds with the frequency of the wave to be combatted in the combustion chamber. The porous body 53 is at the closed end of the cavity, which is a high impedance, low gas-velocity region; and attenuation of the wave occurs at and within this body 53, entirely in the high impedance, low gas velocity region. Broad band attenuation is thus attained.

The invention has been illustrated and described in several typical forms. It will be understood, however, that various changes in design, structure and arrange ment may be made without departing from the spirit and scope of the invention or of the appended claims.

I claim: a

1. The combination comprising: an engine combustion chamber having walls confining combustion gas vibration therein, smd gas vibration having a characteristic frequency pattern, an acoustic attenuator cavity acoustically 3 coupled to said gas vibration in said combustion chamber, said attenuator cavity having an open portion in communication with said combustion chamber and having a closed region most distant from said open portion, and a body of acoustic attenuative material located predominantly in said closed region of said cavity and arranged to present an acoustic attenu-ative response predominantly in said closed region, said attenuator cavity containing said body of acoustic attenuative material being resonant in the range of said characteristic frequency pattern of said gas vibration in said combustion chamber.

2. The apparatus of claim 1 wherein said attenuator cavity is an elongated wave guide substantially one quarter of a Wave length in major dimension for a component or" said characteristic frequency pattern, with said open portion at one end and said closed portion at the other end.

3. The apparatus of claim 1 wherein said attenuator cavity is a Helmholtz type resonator, responsive to a component of said characteristic frequency pattern, with the neck portion thereof providing said open portion,

and the bottle-shaped volume thereof providing said closed region.

4. The apparatus of claim 1 wherein said attenuator is an annular cavity disposed circumferentially around at least a segment of said combustion chamber, one side of said cavity being open into said combustion chamber and thereby providing said open portion, with the opposite side of said cavity providing said closed region, and with said one side having its opening of Helmholtz resonator dimensions in relation to the volume of said cavity, the resonant frequency of said cavity being that of said characteristic frequency pattern.

References Cited in the file of this patent UNITED STATES PATENTS 2,573,536 Bodine Oct. 30, 1951 2,712,816 Bodine July 12, 1955 2,738,781 Bodine Mar. 20, 1956 2,752,907 Bodine July 3, 1956 2,760,472 Bodine Aug. 28, 1956 2,827,033 Bodine Mar. 18, 1958

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