US2248456A - Muffling and cooling device for internal combustion engines - Google Patents

Description

E. H. HARRIS July 8, 1941.

MUFFLING AND COOLING DEVICE FOR INTERNAL COMBUSTION ENGINES Filed Aug. 1 9, 1958 IN VENTOR. m

Patented July 8, 1941 UNITED STATES PATENT OFFICE MUFFLING AND COOLING DEVICE FOR INTERNAL COMBUSTION ENGINES 4 Claims.

My invention relates to a method for cooling the exhaust from an internal combustion engine in combination with the muffiing of noise therefrom.

The cooling and muffling of the exhaust from a combustion engine requires a device of small size and light weight with a minimum of resistance offered to the free passage of hot gases. The art has broadly developed the requirements as to the muffiing of sound. My invention has to do particularly with the cooling of these gases in conjunction with the fulfillment of the other functional demands of a mufiler as disclosed herein.

The drawing shows one embodiment of my invention wherein the objects of cooling and mufiling the exhaust gases from a combustion engine may be obtained.

Fig. I represents the preferred design of a device for the cooling and muflling of the gases exhausted from an internal combustion engine wherein external air is introduced through an arrangement of nozzles.

In Fig. I the shape of the enclosing shell of the muflier l is designed to offer least resistance to the air when the body is in movement, as on an automobile or aeroplane. There is an inlet conduit 2 through which the exhaust gases pass to the muliler .I. At the discharge end of the inlet 2 there is a vena contracta or flow line contraction of the conduit 3 so designed as to increase the velocity of the gases entering the muffler. External to the vena contracta 3 is an annular or segmental annular opening 4 through which air will be injected to the muflier by the entraining or injector action of the exhaust gases as they leave the vena contracta 3. The combined air and exhaust gas enter the expansion chamber 5 having its downstream walls curved as indicated in the drawing, with a resultant decrease in velocity. This expansion may be expedited by the use of deflecting vanes 5 which, as shown in the drawing, would also impart a rotary motion to the air and gases, thus causing more rapid mixture of the gases with consequent decline in temperature of the exhaust gas. A velocity nozzle 1 is formed in the conduit leading downstream from. the expansion chamber 5, wherein the combined air and exhaust gas will increase its velocity and decrease its static pressure as it passes from the expansion chamber 5 through the vena contracta of nozzle 1 and up to the throat and from the throat the gases will lose velocity and gain in static pressure as they pass downstream from the throat through the expanding portion of the nozzle. For the sake of brevity the term velocity nozzle will be used to describe such a contracting expanding conduit as is described immediately above. A series of apertures 8 in the downstream wall of expansion chamber 5 at locations near the inlet of nozzle 1, allow some gas to pass into the impedance chamber l0. These orifices should be at a point where positive static pressure exists, prior to the change of the static energy to the kinetic energy of motion. Passing through the nozzle I the gases again reach an expansion chamber. There will be a suction created at the annular opening 9 by the low static pressure of the gas leaving the nozzle 1 which will draw gases from the impedance chamber l0 and through the orifices 8. A second expansion chamber H is formed. Additional nozzles and expansion chambers with corresponding orifices and impedance chambers may be employed, depending upon the degree of silence desired. The outlet from the mufiler is in the form of a large parabolic nozzle l2 so as to reduce pressure loss as the gases leave the muflier. I

The computations to determine the dififerent areas are simple but the range of conditions is varied. The size of the inlet pipe 2 must depend upon the volume of exhaust gas, having chosen the allowable velocity from the assigned pressure loss through the given length of the exhaust pipe. The frequency of the impulsive movement of the incoming exhaust is sufficiently high to allow consideration as a constant stream, as far as this affects gas flow. In computing the size of air injector nozzle it may be assumed, for instance. that the nozzle coeiiicient lies between .96 and .99. The required weight of free air will be computed from the total mass of the gas entering the mufller, multiplied by its specific heat for constant pressure at the temperature obtained and the change in temperature required to reduce the gas to a heat below the flash point of the fuel used. This, then, represents the heat to be absorbed and determines the temperature rise of theincoming air (t t The required weight of air is obtained by dividing the total heat by the specific heat for constant pressure of air at average temperature obtained, and the total change in air temperature.

W :weight of exhaust gases W:weight of free air S :specific heat for constant pressure of gas S :specific heat for constant pressure of free air t :temperature of incoming exhaust t :temperature of cooled exhaust 1& :temperature of free air The computations should be for the average operating conditions. When maximum conditions occur the increased temperatures are compensated for by increased pressure of free air against the injector inlet and this actually more than balances. At miles per hour air speed, pressure of 27.4 lbs. per sq. ft. will develop against the free air opening, while at 100 miles per hour, the pressure will be 49.8 lbs. per sq. ft. For exactly this reason it isseen that the injector design will vary widely according to the average speeds to be considered.

The injector may be figured from any of the available formulae. For reduction of air at throat of nozzle to about l2 /2% St. Venants theoretical formula may be used.

where P=abs. pressure per. sq. in. at throat of nozzle V=mass of air in lbs. T=absolute temperature in degrees centigrade With the pressure at point of intake of air the fiow may be determined from the pressure drop thus fixing the area.

The computation of the subsequent nozzles is relatively simple. It is based on the assumption that the velocity of the air and exhaust gas shall be a factor of the resonance frequency of the exhaust at the speed for which the muffler is designed. In order to mufile other frequencies, the downstream nozzles should be designed for resonance not in harmonic relation to the first frequency considered. The distance from the mouth of the nozzle to the opposite wall of the expansion chamber shall be such that the sound waves reflected from said opposite wall will arrive at the said point in the nozzle in a time equal to onehalf the time for one wave cycle of the frequency to be attenuated. Certain other assumptions were found permissible. These are: (l) downstream of the mixing chamber 5 adiabatic conditions exist; (2) for short lengths of tail pipe used, not over 12", the resonance effect of this pipe may be disregarded; (8) the shape of the impedance chamber may be disregarded; (4) the combined area of the orifices shall be less than seven eighths of the area at the throat of the nozzle; (5) the nozzles shall be conoidal parabolas.

Fig. II represents any type of mufiier I with an inlet 2 and an outlet l2. There is a nozzle 3' to reduce the static pressure of the incoming gases to the mullier. There is an annular opening 4' through which external air will be .rawn by lower pressurecreated by the action of the injector nozzle 3.

Fig. III consists of a muffler I" with inlet 2 and outlet l2. Inside the muffler shell l" at the end of the inlet pipe 2 there is a disk, or propeller type fan l4" consisting of a single set of blades occupying the full diameter of the muffler shell I or two sets of blades, the first of a diameter equal to that of the inlet pipe 2 and a second set in the annular space between the external diameter of the inlet pipe-2" and the shell I, all mounted on a single shaft. The incoming gases will cause the fan to rotate. The action of the rotating fan in the annular space will cause external air to be drawn through the annular space 4" which will become mixed with the exhaust gases and cool them. The combined gases then pass through the muilier and the outlet pipe l4". If the muffler is to be used on an aeroplane it will be seen that the velocity of the exhaust gas will be less than the velocity of the aeroplane. Therefore it is obvious that without the use of fan M" or nozzle 3" the pressure at 4" can be greater than inside the pipe 2". Thus for an aeroplane the nozzle 3 and fan I4" may be omitted and the inlet to the annular space 4" flared out as indicated in the drawing, with the resultant inflow of free air as may be required.

I claim as my invention:

1. A muifier of the class described including an imperforate exterior shell equipped with an inlet pipe having a vena contracta at its downstream terminus, a discharge pipe for egress of exhaust gases, a concentric conduit circinnferentially disposed about said inlet pipe, the upstream terminus of said concentric conduit being exterior to said imperforate shell, the downstream terminus of said concentric conduit connected integrally to a velocity nozzle, the throat of said velocity nozzle being disposed in circumferential relationship to said vena contracta, a wall within said imperforate shell joined to the downstream terminus of said velocity nozzle and following such an expanding curve as to meet with the wall of the imperforate shell at a point upstream of its maximum diameter, a further wall of semispherical shape having curvature opposite to that of the first wall and having an outlet centrally located, a conduit joined to said semispherical wall about said outlet, said conduit having a vena contracta within its length, deflectors, each twisted and spirally bent with minimum diameter of spiral located close to the nozzle of said concentric conduit, orifices in the spherical wall upstream of its outlet, orifices in said conduit near the section of its minimum diameter, additional walls and conduits having similar shapes to previous walls and their conduits with orifices in similar locations and deflectors in similarly disposed relationship to said walls.

2. In combination a mufiler of the class described, an outer casing having an inlet and outlet for exhaust gases, a third opening for the inlet of air to the interior of said casing, said exhaust inlet having a vena contracta at its downstream terminus within said casing, a conduit for said inlet of air with its downstream openings circumferentially disposed with respect to said inlet pipe, a chamber formed by approximately spherical walls within said casing having the diameter of the spherically formed chamber coincide approximately with the maximum interior diameter of said casing, a velocity nozzle centrally located in the downstream spherical wall of said chamber, orifices in said downstream spherical wall in locations around the said velocity nozzle, other orifices in the wall of said velocity nozzle near its vena contracta, additional chambers similarly formed but each successive chamber having a diiferent axial length from that of the next adjacent chamber.

3. A muffler for use with internal combustion engines comprising an exterior shell fitted with inlet and outlet openings at opposite extremities, aninletpipe having a vena contracta at its downstream terminus within said shell, means for supplying external air at the terminus of said inlet pipe at its vena contracta, a wall having curvature concaved from the inlet extending across said mufiler to form a chamber within said mufiier, an outlet centrally located in said curved wall, a conduit connected to said curved wall at said outlet with a vena contracta at some point in its length, a second wall of opposite curvature to that of the preceding wall with an opening at its center joined to the downstream edge of said conduit, said second wall joined at its periphery to the exterior shell, another wall curved convexly to the inlet again dividing the mufiler into an additional chamber, another similar chamber of curvature of said spherical wall being coincident with the terminus of said inlet pipe, an opeir ing in the center of said spherical wall, a conduit joined to said spherical wall about said opening, a velocity nozzle within the length of said coilduit, orifices in said spherical wall upstream of the opening, other orifices in said conduit near smallest cross-sectional area, additional walls of similar design with similar orifices, openings and conduits and having the radius of each semispherical wall different from all other such radii.

E. HUNTINGTON HARRIS.

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