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'Nov. 13, 1962
Filed March 21, 1961
2 Sheets-Sheet 1
Nov. 13, 1962
Filed March 21, 1961
2 Sheets-Sheet 2
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Patented Nov. 13, 1%52
of the attenuator cavity results in maximum heat shielding
of the attenuative material from the combustion ?ame, and
minimization of hot spots within the attenuative material.
A unique accomplishment'of the invention is that place
ment 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 e?fect. In
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 com
bustion abnormalities, such as violent pressure shocks
and gas vibration, in internal combustion engines, by
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
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 teach
ing of the invention for piston engines necessarily covers
all of the important concepts for other combustion cham
bers. Moreover, the piston engine con?gurations encom 20
pass all of the various operating cycles, including spark
ignition, diesel, four cycle, two cycle, etc.
should be designed so that this natural resonant frequency
corresponds to a frequency at which offensive large ampli
tude gas vibration has been found to occur. The use,
in connection with this “tuned” cavity, of attenuative ma
terial 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 re
sponse-qualities which are ordinarily largely inconsistent
with one another. The present invention, comprising loca
tion of the attenuative material to attenuate the wave pre
Reference is made to my prior patents in this ?eld,
dominantly, or substantially exclusively, in the high im
notably Patent No. 2,573,536 for basic teaching, and
pedance region of the cavity, reconciles these qualities and
Patent No. 2,752,907 which is of interest by way of 25 permits broader band tuning without material loss of reso
contrast with the present invention.
nant attenuation response.
A general object of the invention is to provide a fre
The invention will be better understood from the follow
quency responsive cavity, having broadened band fre
ing detailed description of certain present illustrative em
quency response as regards acoustic attenuation, and
bodiments thereof, reference for this purpose being had
which is acoustically coupled to the chamber to be con 30 to the accompanying drawings, in which:
FIG. 1 is a section through the combustion chamber of
An attenuator with a somewhat broadened frequency
an engine showing an attenuator in accordance with the
response has many advantages, in correspondence with
invention in longitudinal section;
the objects of this invention, as follows: (1) More liberal
FIG. 2 shows an alternative attenuator;
production tolerance, (2) less critical maintenance, (3)
FIG. 3 is a view similar to FIG. 1, but showing a modi?
less temperature sensitivity as regards speed of sound in
the gas, (4) less critical location in relation to the com
In FIG. 1, there is fragmentarily shown a valve-in-head
bustion chamber, and (5) more complete coverage of
engine having water-cooled block 10 and water-cooled
detonation frequency spectrum.
In my prior Patent No. 2,752,907 the suppression cav
ities have their freqeuncy response broadened by a damp
ing means (?brous 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 ?brous
head 11, the block having cylinder bore 12 containing
piston 13. The combustion chamber 14, de?ned by head
11 over cylinder bore 12, is of a ?at 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
or porous materials are located in these regions of low 45 for a spark plug 22, and a similar threaded port 23 to
acoustic impedance. Note the porous ‘body 40 interposed
receive the threaded slightly reduced neck 24 of a quar
inside the neck and ahead of the cavity 46 of the at
ter wave type elongated attenuator cavity 25 or wave
tenuator 22, and the ?brous material extending along the
guide' This cavity comprises an interior generally cy
cavity wall 51 in the attenuator 23. In the latter, the
lindrical wave guide of quarter wave length for a sound
?brous material begins at a low impedance point ad
wave of the gas vibration wave frequency to be combatted,
jacent the neck of the cavity, where the attenuative e?ect
the calculation of wave length taking into account the
exerted by the ?brous material is maximized, and is
elevated temperature of the combustion gases wherein
thickened in the direction away from the low impedance
the gas vibration occurs. The cavity is thus resonant to
region to avoid discontinuities in impedance which might
cause wave re?ections. These prior attenuators are char
acterized by and effective because of location of attenua
tive material in regions of high gas vibration velocity.
In accordance with the present invention, the attenuative
55 this vibration frequency.
In this illustrative embodi
ment, 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,
material is located so as to be primarily, preponderantly,
and a body 30 of high heat resistant sound ‘wave attenua
or even exclusively, in the high impedance, closed inner 60 tive material packed inside cap 27. This body of mate
end region of an attenuator cavity, where gas vibration
rial 30 may be comprised of ?brous material, such as
velocity is minimized, and the attenuative material is
glass ?ber, or a porous ceramic or metal, and is here
located as far as possible from the combustion ?ame.
illustrated in the latter form.
Thereby, there results (1) minimum attenuation for in
The neck 24 communicates one end of the interior of
nocuous, or even useful, gas vibration of small amplitude, 65 the attenuator cavity with the combustion chamber, and
(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
by proper choice of dimensions, an acoustic coupling is
thereby accomplished with a component of the gas vibra
tion 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 di?erent combustion chambers. The type
bustion. Finally, the attenuator has the advantage that
the porous element is located fairly remotely from the
?ame, and is therefore not prone to develop hot spots
which might become sources of combustion irregularities.
of coupling here illustrated between the attenuation cavity
and the combustion chamber, or the wave pattern therein,
however, is generally effective as regards patterns com
monly encountered. In any speci?c case, of course, the
frequently of the gas vibration component’ to be com
batted can be ?rst ascertained by any suitable measure~
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
merit technique, and the length of the'cavity then cal
'etry, and resulting acoustic properties. Thus, its length
culated. In this connection it should be mentioned that
is less than a quarter wave length for the resonant wave
‘the quarter wave length dimension should be measured
from the neck region of the cavity to, and within, the 10 frequency component, or frequency band component, that
is to be attenuated, and its diameter is enlarged as com
pared with the attenuator of FIG. 1, so that it has more
of a bottle-like shape. It consists, in the nature of a
antinode' (region of maximum gas oscillation velocity)
Helmholtz resonator cavity of a threaded neck 41 adapted
at the neck, and a pressure antinode (region of maximum
15 to be screwed inside wall 20, and an enlarged chamber
pressure oscillation) within the porous body.
porous body. A quarter wave length standing wave then
tends to be established in the attenuator, with a velocity
4'2 joined to neck 41. The chamber 42 comprises cy
lindrical 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 porous body contains a large number of inter
communicating 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 re?ec
tive properties. Gas particles under the driving influence
of the wave thus enter and scrub against the wall sur
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 _
faces de?ning the interior openings of the porous body,
or responsive wave frequency. Its’ neck region is a region
and their energy is thus dissipated. The entering gas
vibration wave is thus only poorly re?ected, and very 25 of high gas oscillation velocity, and one therefore of low
impedance. The closed rear end of the attenuator, ad
largely attenuated.
jacrent the face of the porous plug, is a region of minimized
The closed inner end region of the quarter wave length
gas oscillation velocity, but of maximized gas pressure
attenuator pipe or cavity is known as one of high imped
oscillation amplitude, and is therefore a region of high
ance, the impedance being the ratio of the ampitude of
gas pressure oscillation to the amplitude of gas particle 30 impedance. Energy of the gas wave is dissipated by gas
pressure excursions into the intercommunicating pores of
oscillation velocity. It is recalled in this connection that
in an energized quarter wave pipe, gas pressure oscilla
tion is at a, maximum in the region of the closed inner
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 inven
end of the pipe, and gas particle oscillation velocity is at
35 tion behaves as, and has the advantages of, the embodi
a minimum at the same place, giving high impedance.
ment ?rst described.
As stated before, the porous body at the closed inner
Reference is next directed to the embodiment of FIG. 3,
end of the quaterwavelength attenuator interferes wtih
showing an engine much as in FIG. 1. Parts in FIG. 3
gas pressure wave re?ection, thus “spoiling” the wave,
corresponding to parts in FIG. 1 will be identi?ed by the
with the energy of the wave absorbed by the attenuative
material at the inner end of the attenuator, in this case, 40 same reference numerals, but with the suffix a added in
FIG. 3, and will not be further described. In the engine
the porous body.
of FIG. 3, the bottom of the head is somewhat ?attened
Since the wave in the attenuator cavity is driven and
to provide space, between the head and the block, for
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 at
The attenuator in the form now described has the ad
vantages 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 ?brous, at
tenuative body does not establish a highly de?nite effec
tive 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 broad
ened frequency band response.
That is to say, it at
tenuates 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 notwith
standing a fairly liberal departure from peak resonance
frequency. The attenuator, with its absence of attenuative
material at the high gas velocity, low impedance region,
an insert wall 50 which is bored so as to circumscri‘oe the
cylinder bore.
The inner periphery 51 of this bored
insert wall 50 thus de?nes 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 ring
shaped porous body 53. A narrow annular channel 54
atfords gas communication and acoustic wave coupling be
tween the combustion chamber (and the gas vibration pat
tern therein), and the porous ring 53‘.
The space formed by the channels 52 and 54 is equiva
lent 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 di
mensions 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:
1. The combination comprising: an engine combustion
does not have an effective attenuative effect on gas oscil
chamber having walls con?ning combustion gas vibration
therein, sm‘d gas vibration having a characteristic fre
lations of low amplitude, which are not harmful, and
may even have a bene?cial effect on controlled com 75 quency pattern, an acoustic attenuator cavity acoustically
coupled to said gas vibration in said combustion chamber,
said attenuator cavity having an open portion in com
munication with said combustion chamber and having
a closed region most distant from said open portion, and
a body of acoustic \attenuative material located pre
dominantly in said closed region of said cavity and ar
ranged to present an acoustic attenu-ative response pre
dominantly in said closed region, said attenuator cavity
containing said body of acoustic attenuative material
and the bottle-shaped volume thereof providing said closed
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 op
posite side of said cavity providing said closed region, and
with said one side having its opening of Helmholtz
being resonant in the range of said characteristic fre 10 resonator dimensions in relation to the volume of said
quency pattern of said gas vibration in said combustion
cavity, the resonant frequency of said cavity being that
of said characteristic frequency pattern.
2. The apparatus of claim 1 wherein said attenuator
References Cited in the ?le of this patent
cavity is an elongated wave guide substantially one quarter
of a Wave length in major dimension for a component or" 15
said characteristic frequency pattern, with said open por
Bodine ______________ .. Oct. 30, 1951
tion 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 20
the neck portion thereof providing said open portion,
Bodine _______ _._-_____ __ July 12, 1955
Bodine _____________ __ Mar. 20, 1956
Bodine ______________ __ July 3, 1956
Bodine ____________ __ Aug. 28, 1956
Bodine _____________ __ Mar. 18, 1958
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