US 3646923 A
Automobile exhaust gases are recycled by means of a bypass duct which receives these gases at a restricted upstream end located within the environment of the hot gases of the exhaust system, passes in heat exchange relationship through the conventional intake manifold hotspot to facilitate heating of the latter, and discharges the hot exhaust gases in an upstream direction with respect to the inlet flow of the fuel-air mixture at a location directly below the throttle valve. The restriction of the upstream end is spaced from the hotspot to minimize heat loss to the latter, such that lead contaminants for example flow in a gaseous phase through the restriction without fouling the same. A bypass control plunger movable in response to the position of the throttle valve is insertable into the restriction to close and simultaneously clean the latter when the throttle valve moves either to its idle or wide open position.
Claims available in
Description (OCR text may contain errors)
United States Patent Sarto 5] Mar. 7, 1972  CONTROLLED FLOOR JET ENGINE EXHAUST RECIRCULATION  U.S.Cl. ..l23/1l9 A, 123/127  Int. Cl ..F02m 25/06  FieldofSearch ..123/119 A, 127
 References Cited UNITED STATES PATENTS 1,873,174 8/1932 Arthur ..l23/1l7A 2,154,417 8/1939 Anderson .....l23/l24 2,643,647 6/1953 Meyer et a1.. .....l23/l27 3,465,736 9/1969 Daigh et al... .,..123/119 A 3,542,003 10/1970 Sarto ..123/119 A FOREIGN PATENTS OR APPLICATIONS 196,333 4/1923 Great Britain ..123/119A 531,637 1/1941 GreatBritain ..123/1l9A Primary Examiner-Wendell E. Burns AttorneyTalburtt & Baldwin  ABSTRACT Automobile exhaust gases are recycled by means of a bypass duct which receives these gases at a restricted upstream end located within the environment of the hot gases of the exhaust system, passes in heat exchange relationship through the conventional intake manifold hotspot to facilitate heating of the latter, and discharges the hot exhaust gases in an upstream direction with respect to the inlet flow of the fuel-air mixture at a location directly below the throttle valve. The restriction of the upstream end is spaced from the hotspot to minimize heat loss to the latter, such that lead contaminants for example flow in a gaseous phase through the restriction without fouling the same. A bypass control plunger movable in response to the position of the throttle valve is insertable into the restriction to close and simultaneously clean the latter when the throttle valve moves either to its idle or wide open position.
13 Claims, 5 Drawing Figures CONTROLLED FLOOR JET ENGINE EXHAUST RECIRCULATION RELATED APPLICATION This application is a continuation in part of my copending application Ser. No. 807,705 filed March 17, 1969, now U.S. Pat. No. 3,542,003.
BACKGROUND AND SUMMARY OF THE INVENTION In the prior art, numerous systems have been devised to recycle exhaust gas into the fuel-air induction system of an automobile engine for the purposes of preheating and vaporizing the incoming air-fuel mixture to facilitate its complete combustion in the combustion zone, for reusing the unignited or partially burned portions of the fuel which would otherwise pass out the exhaust pipe and into the atmosphere, and for reducing the oxides of nitrogen emitted from the exhaust system into the atmosphere. It has been found that approximately l5 percent exhaust gas recycling is required at moderate loads to substantially reduce the nitrogen oxide content of the exhaust gases discharged in the atmosphere, that is, to below about 1,000 parts per million.
Although the prior art structures have had the desired effect of reducing the content of nitrogen oxides in the exhaust by reducing the maximum combustion temperature in consequence of diluting the fuel-air mixture with recycled exhaust gases during certain operating conditions of the engine, these structures have not been commercially acceptable from the standpoints of both cost and operating efficiency and have been complicated by the desirability of reducing the recycling during conditions of both engine idling when nitrogen oxide emission is a minor problem and wide open throttle when maximum power is required, while progressively increasing the recycling of exhaust gases with increasing engine speed during cruising condition or with increasing engine load at part open throttle. The nitrogen oxide emission is a direct function of combustion temperature and for that reason is less critical during engine idling when the rate of fuel combustion and the consequent combustion temperature are minimal, and during wide open throttle conditions which are ordinarily of short duration.
in the usual gasoline or hydrocarbon fuel-type engine, fuel combustion can take place at about l,200 F. The formation of nitrogen oxides does not become particularly objectionable until the combustion temperature exceeds about 2,200 F., but the usual engine combustion temperature which increases with engine load or the rate of acceleration at any given speed frequently rises to about 2,500 F. It is known that the recycling of at least l/th and not more than M; of the total exhaust gases through the engine, depending on the load or power demand, will reduce the combustion temperature to less than 2,200 F. The desired result is usually obtained with the ordinary engine upon the recycling of about 15 percent of the total exhaust gases during partially open throttle as aforesaid.
An important object of this invention is to provide improved means uncomplicated by moving parts comprising a restricted recycling or bypass duct for recirculating a portion of the combustion products from the exhaust system to the inlet system of an automobile engine to overcome or avoid the problems and deficiencies of the prior art, as well as to achieve a number of important results including preheating and improved mixing and carburetion of the fuel-air mixture in the inlet header, the reduction of ice formation on the customary throttle blade, and the reduction of nitrogen oxides in the exhaust.
Another object is to provide such a construction wherein the bypass duct extends in heat exchange relationship through the customary hotspot of the inlet system and terminates within the induction conduit in direction to discharge hot exhaust gases upstream against the flow of the fuel-air mixture in the induction conduit and also against the usual throttle valve,
thereby to provide simple,'economical and effective means for accomplishing the foregoing as well as for preheating the throttle and simultaneously cooling the exhaust gases in the bypass duct below the fuel ignition temperature, and for diluting the fuel-air mixture with substantially incombustible exhaust gases to lower the combustion temperature in the engine and thereby reduce the formation of nitrogen oxides during the combustion process.
Another and more specific object is to provide such an exhaust recycling system wherein the restriction for the bypass duct is adjacent the latters upstream end within the environment of the hot exhaust gases at temperatures appreciably greater than 700 F. and spaced from the hotspot to minimize heat loss thereto. Such a construction is particularly suitable for use with fuels containing lead additives to improve combustion characteristics.
The resulting lead oxides in the exhaust exist in a vapor phase at temperatures above approximately 700 F. The latter temperature is well below the exhaust temperature available but is somewhat higher than the usual temperature of the hotspot, which is continually cooled by impingement of the comparatively cold inlet fuel and air mixture and the vaporization of liquid fuel droplets within the mixture. Accordingly, by locating the bypass restriction within the environment of the hot exhaust gases, the temperature of the bypass restriction will preferably be maintained above 800 F. and the exhaust gases containing lead oxide vapors will pass readily through the hot restriction without condensing thereat. If any lead oxides do condense and deposit within a cooler portion of the bypass duct downstream of the restriction with respect to the direction of the bypass flow, these deposits will be within an enlarged portion of the bypass duct and will be relatively harmless. For this reason also the bypass duct will be comparatively short, so that the portion thereof exposed to the comparatively cool inlet fuel and air mixture will only be as long as necessary to assure cooling of the hot exhaust gases sufficiently to prevent ignition of the inlet fuel and air mixture.
By virtue of the foregoing, communication will exist at all times between the exhaust and inlet systems and a portion of the hot exhaust gases will be directed against the throttle valve to prevent or minimize carburetor icing during fast idling of a cold engine when ice formation is most likely to occur. The downstream opening of the bypass duct opposing the flow of the inlet mixture will be shielded by the throttle valve at the idle and part open positions, but will be exposed in the manner of a pitot opening to approximately the full velocity pressure of the inlet mixture at wide open throttle, whereby the bypass flow may be effectively reduced at wide open throttle. By suitably determining the size of the bypass restriction, the bypass flow will be contained approximately within the limits of more than five percent and less than 25 percent, and usually about 15 percent of the total exhaust gases when the throttle is partially open and the effective pressure differential between the ends of the bypass duct corresponds to cruising or part throttle acceleration conditions.
In addition, within the range from idle to light or moderate load conditions, the total fluid flow through a fixed bypass or recycling orifice of the type comprising the present invention increases at any given engine speed with increasing engine load. For example in a conventional automobile engine, the pressure downstream of the throttle varies roughly in the neighborhood of from one-half atmosphere during idling to approximately one atmosphere at wide open throttle, while the exhaust pressure simultaneously varies roughly from one to two atmospheres. These factors compensate for the increasing combustion temperature with increasing load and result in a desirable increase in the effectiveness of the exhaust recycling through the fixed bypass restriction with increasing load or acceleration.
As the engine load or acceleration decreases and the speed increases to the cruising condition, the combustion temperature and the pressure differential across the fixed bypass restriction, as well as the total quantity of exhaust gases, decrease and the rate of exhaust recycling declines for improved fuel economy, again as desired because less recycling is required to maintain the combustion temperature below the level at which nitrogen oxide formation is objectionable. As the pressure differential between the inlet and exhaust headers increases with increasing load, the effective resistance of the fixed restriction to the recycling flow increases because the flow rate varies approximately as the square root of the pressure differential. Thus at wideopen throttle, the proportion of the total exhaust gases that is recycled is somewhat less than the proportion recycled at partially open throttle. This factor also is as desired because the customary excess fuel enrichment at wide open throttle in cooperation with the recycled exhaust gases is adequate to prevent overheating during the combustion process and reduce the formation of nitrogen oxides to the tolerable level.
Another object is to provide an exhaust recycling system as described wherein a bypass control valve plunger extends obliquely to the flow of the inlet mixture into the downstream opening of the bypass duct and through the latters upstream restriction to close the same, and wherein operation of the plunger is responsive to the position of the throttle valve, so that the plunger is normally withdrawn from the upstream restriction to open the latter, but is moved into the upstream restriction to close the same when the throttle valve is at either its idle or wide open position.
The plunger operating mechanism preferably comprises pressure responsive means responsive to the pressure at the customary distributor vacuum advance port which opens into the inlet header adjacent and at the high pressure side of the leading edge of the usual blade type throttle valve when the latter is at its idle position. The high pressure at this port when the throttle valve is at either its idle or wide open position is transmitted to the pressure actuated means to move the plunger through the upstream restriction of the bypass duct to close the same and at the same time to maintain the restriction free of exhaust deposits.
By virtue of this construction, the bypass duct may be located to extend through the hotspot directly below the throttle valve. The oblique plunger will extend through the sidewall of of the inlet header to its operating means out of the flow path of the inlet mixture.
Other objects of this invention will appear in thefollowing description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic fragmentary cross-sectional view through an automobile engine induction systems showing a bypass duct for recycling exhaust gases.
FIG. 2 is a similar view showing a modification.
FIGS. 3, 4 and 5 show three other modifications embodying a bypass control valve.
It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, an application of the present invention is illustrated in FIG. 1 by way of example with an automobile engine 9 having a carburetor 10 providing the inlet fuel-air induction conduit 11, which comprises the upstream portion of an inlet header [2 for supplying a combustible fuel and air mixture to the engine cylinders 13, FIG. 3. The carburetor 10 may comprise any conventional type which has the usual air inlet at the upstream end of the induction conduit II, the usual fuel metering system and nozzles or jets for supplying idle and operating fuel to the conduit ll during various operating conditions and for enriching the fuel supply during acceleration and wide open throttle, and the usual automatic choke (including choke valve 11a) and thermostatic means for controlling idle enrichment and fast idle operation during cold starting conditions. An example of such a carburetor is illustrated by way of example in Ball Pat. No. 2,966,344, so that the foregoing conventional features disclosed in the latter patent are incorporated herein by reference and are not described in detail.
The downstream portion of the induction conduit ll comprises the customary throttle body 16 containing the conventional butterflytype throttle valve 14. The inlet fuel-air mixture is conducted via the headers or manifolds 12a and 121;, comprising extensions of the header 12, to the left and right banks of cylinders 13 respectively in timed relation by operation of the inlet valves 18a. After combustion of the fuel-air mixture above the pistons 15, the exhaust gases are conducted in timed relationship by operation of the exhaust valves 18!) to the exhaust manifolds or headers 17, which discharge through a muffler to the atmosphere.
The left and right manifolds 17 are connected by a crossover conduit 19 which conducts the hot exhaust gases into heat exchange relationship with portion 20 of the wall of the inlet header 12. The wall portion 20 extends transversely to the direction of flow of the inlet mixture and is commonly referred to as the hotspot" which preheats the inlet mixture and enhances vaporization and mixing of liquid fuel droplets.
A thermostatically controlled valve 21 in one header 17, FIG. 4, controls the flow of hot gases in the crossover conduit 19 to expedite heating of the hotspot 20 during the engine warmup period and to prevent overheating during operation of the engine under load. The structure described thus far may also be conventional.
Associated with the throttle valve 14 and extending through the hotspot 20 is a restricted nozzle 22 which extends directly from the exhaust crossover conduit 19 and has an orifice or restriction 23 at its lower or upstream end opening flush with the interior of conduit 19. Thus nongaseous combustion products cannot readily enter and accumulate within the nozzle 22 and clog the bypass system. Where the exhaust contains appreciable quantities of materials that tend to form gummy residues upon cooling, as for example in giving up heat to the hotspot 20, these residues have less tendency to deposit within the hot passage 19 than in the cooler stem of the nozzle 22 which is cooled by the inlet fuel and air mixture.
The nozzle 22 is directed toward and terminates adjacent the throttle valve 14 when the latter is at its idle position shown and directs a jet of exhaust gases in opposition to a jet of inlet gases flowing through a restricted opening 30 in valve 14. The opening 30 may comprise part of the idle air supply for the engine, especially during fast idle, and is dimensioned with respect to the dimensions of the exhaust bypass duct system to substantially block exhaust recirculation when the throttle valve 14 is at its warm idle position shown.
As valve 14 progressively opens with increasing engine load, the opposing jets from nozzle 22 and orifice 30 move out of alignment, the effective pressure differential across orifice. 30 decreases, and the pressure differential across the restriction of nozzle 22 increases, all to the end of increasing the bypass flow or exhaust recirculation from conduit 19 into conduit ll. Also during part throttle opening, the upper open end of nozzle 22 is protected by throttle valve 14 from the dynamic or velocity pressure of the inlet gases. At wide open throttle, dotted position, the upper end of nozzle 22 is exposed to the inlet velocity flow in the manner ofa pitot tube, thereby to oppose and reduce the exhaust recirculation.
The nozzle 22 is suitably secured removably to the hotspot 20, as for example by the screw connection shown and preferably is formed from stainless steel to resist corrosion and fouling and, by virtue of the construction shown will ordinarily serve properly for'many thousands of miles. In the event of eventual plugging of the restriction 23, or in the event it is IOIO26 OHI desirable to change the latters dimensions to accommodate changing operating conditions for the engine, the nozzle 22 may be removed and replaced through the riser portion of header 12 when the carburetor and throttle body 26 are removed.
For operation during normal cruising conditions, the fixed restricted orifice 23 is dimensioned to enable controlled recycling of a portion of the exhaust gases into the inlet header 11 to pass at least five percent and not more than 25 percent of the total exhaust gases, depending upon the specific engine and its operating conditions. In the usual situation effective reduction of nitrogen oxides in the exhaust is accomplished by recycling approximately 15 percent of the exhaust gases as aforesaid, preferably through several nozzles 22, each arranged in the manner of the nozzle shown where a multiple barrel carburetor is involved.
ln climatic regions where icing is a problem, each nozzle 22 may be extended into proximity with its associated throttle valve 14 by means of the low resistance tubular stem or stand pipe shown having a length depending upon the specific geometry and location of the portion of the hotspot through which it extends. Each bypass duct 22 may thus have the same resistance to gas flow. The flow of the hot exhaust gases through the hotspot 20 and nozzle 22 facilitates preheating of the hotspot 20 and throttle valve 14 to assure vaporization of the inlet mixture and the prevention of ice formation adjacent the edges of the throttle valve 14. Simultaneously the recycled exhaust gases are cooled below the ignition temperature of the combustible inlet mixture. To this end the nonle 22 is preferably of heat conducting material and is sufficiently long to achieve the necessary heat transfer from the exhaust gases to the hotspot and inlet mixture. Also by directing the exhaust gases oppositely to the flow of the inlet mixture, improved breaking up, dispersion and vaporization of liquid fuel droplets are achieved with consequent improved mixing of the combustible inlet gases and uniform predictable combustion characteristics within the cylinders 13.
Where the condensation of exhaust matter would otherwise be particularly objectionable, as for example with certain fuels containing lead additives, the structure of FIG. 2 may be employed, wherein a comparatively short stainless steel nozzle 22a is screwed into the hotspot 20 coaxially with the inlet conduit 11 directly below the throttle valve 14. An enlargement or bolthead 24 of the nozzle 22a has a hexagonal exterior to facilitate assembly and removal of the nozzle 220 as described above in regard to FIG. 1 and also serves as a stop to locate the restriction 23 at a predetermined position below the hotspot 20 and within the environment of the hot exhaust gases within passage 19. Thus heat loss from the region of the restriction 23 to the cooler hotspot 20 is reduced and the temperature at the restriction 23 will approximate the temperature of the hot exhaust gases within passage 19 which is customarily maintained well above the temperature at which lead contaminants in the exhaust precipitate. Also by virtue of the comparatively short length of the nozzle 22a, cooling of the head 24 by the inlet fuel and air mixture is likewise reduced, and the temperature of the head 24 may be maintained at approximately the temperature of the hotspot 20, such that fouling of the nozzle 22a and its restriction 23 is rendered nominal with many fuels and is less objectionable in any event, as compared to conventional bypass conduits employed for exhaust recycling.
Except for the feature of the opposed jets shown in FIG. 1, the nozzle 22a operates substantially in the manner of nozzle 22, the restriction 23 being dimensioned to maintain the amount of exhaust recycling within the desired range described above. Also as described above, the throttle l4 shields the upper opening of nozzle 22a from the inlet flow of fuel and air during idle and part throttle operation to enable a progressive increase in the exhaust bypass flow with increasing pressure in conduit 19 resulting from increasing engine load,
and to decrease the bypass flow with the consequent decreasing exhaust pressure in passage 19 as the engine attains its cruising speed for any given partthrottle opening at wide open throttle the nozzle 22a is exposed to the full velocity pressure of the inlet fuel and air to inhibit exhaust recycling.
FIGS. 3, 4 and 5 show modifications of the present invention wherein the exhaust flow through the bypass nozzle is controlled by a valve mechanism responsive to the position of the throttle valve 14. In FIG. 3 a stainless steel nozzle 22!) similar to the nozzle 22 or 22a but provided with an upwardly enlarging conical opening 31 underlies valve 14. A reduced diameter rod or valve element 32a of a reciprocable plunger 32 extends obliquely to the inlet flow of the fuel-air mixture in parallel supported relationship along the conical wall of opening 31, so as to be insertable into the restricted orifice 23. The upper portion of the plunger 32 extends through a bore 33 in the wall of header 12 to a pressure actuated valve'operating mechanism remote from the flow of the inlet mixture.
The plunger 32 extends axially through a tubular guide 34 in closely fitting relationship and is secured at its upper end to a flexible diaphragm 35 that divides a housing 36 into upper and lower pressure chambers 37 and 38 respectively. The guide 34 screws into the exterior of bore 33, supports housing 36 at its outer end, and opens into the chamber 38. The latter also opens to the atmosphere via duct 39 which may communicate with a source of clean fresh air, as for example at the downstream side of the conventional carburetor air filter. By virtue of the close fit between the plunger 32 and tubular guide 34, a high resistance annular leakage path 39 amounting in essence to a seal is provided between the chamber 38 and the inlet header l2 downstream of throttle valve 14. A coil spring 40 seated between an upper portion of the housing 36 and diaphragm 35 urges the latter and plunger 32 downward for normally restricting or closing the orifice 23 by insertion of the rod or valve portion 32a thereinto.
The chamber 37 is connected by means of a duct 41 with the customary vacuum advance duct 42 which connects the distributor vacuum advance port 43 with the customary vacuum actuated mechanism 44 for advancing or retarding the ignition spark distributor in accordance with varying engine operating conditions. The port 43 opens as is customary adjacent and at the upstream or high pressure side of the upper leading edge of the blade of throttle valve 14 when the latter is at its idle position shown. Accordingly when the throttle valve 14 is at either the idle position illustrated by solid lines or the wide open position illustrated by dotted lines, the resulting high pressure at port 43 substantially balances the atmospheric pressure in chamber 38 and enables spring 40 to urge plunger 32 downward to restrict or close orifice 23 and at the same time clear the latter of any deposits that might have formed during cold operation of the engine, for example. During part throttle operation, the pressure at port 43 will gradually decrease as the throttle valve 14 opens from the idle position, whereby the reduced pressure at port 43 is conducted via conduits 42 and 41 to chamber 37 to withdraw plunger 32 and open orifice 23, as illustrated by the dotted position, FIG. 4. Simultaneously, as the throttle valve opens from the idle position, the resulting reduction in pressure at port 43 is communicated to mechanism 44 to actuate the latter to advance the spark distributor in accordance with customary practice.
The nozzle 22b in other respects is substantially the same as nozzle 22 or 22a and is releaseably secured within the hotspot 20 coaxially with the inlet conduit 1]. The latter is not shown to scale in the schematic drawings and will ordinarily be appreciably oversize with respect to the maximum diameter of the nozzle head 24 to enable installation of the nozzle 22b through the riser portion of the header 12 when the carburetor and throttle body are removed as above described.
FIG. 4 shows a similar structure where the operating parameters for rod valve 320 are modified to close orifice 23 only during idle operation. Instead of the spring 40, a spring 40a is employed within chamber 38 between a lower portion of housing 36 and diaphragm 35 to urge the latter upwardly and normally hold the plunger 32 at the open position of orifice 23 as shown. The annular space 39a between plunger 32 and bore 33 and also tubular guide 34 is enlarged with respect to the corresponding space 39 of FIG. 3 to provide an annular passage communicating freely between chamber 38 and the inlet header 12 downstream of throttle I4. Accordingly, when the latter is at the idle position, the low pressure downstream of the throttle 14 is communicated to chamber 38 to move diaphragm 35 and plunger 32 downwardly and insert the valve extension 32a into the orifice 23 to close or restrict the latter, dotted position FIG. 4.
During part open throttle operation of the engine, the pressure at port 43 and the pressure downstream of throttle valve I4 will tend to be the same, so that spring 40a will move diaphragm 35 upwardly to open the orifice 23. At wide open throttle, a similar situation will prevail and plunger 32 will remain at the open position shown. Also the nozzle 22b will no longer be shielded from the flow of the inlet fuel-air mixture, so that this flow will oppose and partially reduce the bypass flow of exhaust gases into the header 12, thereby to prevent undue dilution of the combustible mixture when maximum power is required. On the other hand, the upward flow of the hot exhaust gases provide effective means for enhancing the mixing and vaporization of liquid fuel droplets with the inlet air to enable increased power at wide open throttle.
FIG. illustrates a structure which operates substantially in the manner described with respect to FIG. 3, except that in place of the high resistance annular leakage path 39 relied upon in FIG. 3 to separate chamber 38 from the inlet header 12, a flexible sealing diaphragm 45 is provided to partition chamber 38 into upper chamber 38a and lower chamber 38b, the former being in communication with the atmosphere via duct 39 as described above. This structure avoids the necessity of maintaining close tolerances between the tubular guide 34 and plunger 32 and provides a positive seal to prevent fluid flow between chamber 38b and header 12.
Iclaim: I. In an internal combustion engine adapted to use a gasoline fuel containing a lead additive,
B. an exhaust header for discharging the hot combustion products from said engine and having a wall portion comprising a hotspot exposed to the flow of said fuel-air mixture in said inlet header to heat said mixture, A. an inlet header for conducting a fuel-air inlet mixture into said engine for combustion therein, C. and means for effectively inhibiting the formation of oxides of nitrogen during said combustion by limiting the combustion temperature comprising a bypass duct for conducting hot exhaust gases from said exhaust header into said inlet header, said bypass duct extending through said hotspot in heat transfer relationship to facilitate heating thereof and having I. one end opening into said exhaust header at a location within the hot exhaust gases and spaced from said hotspot,
2. a second end opening into said inlet header, and
3. a restriction in said bypass duct adjacent the opening of said one end within said hot gases and spaced from said hotspot to reduce heat loss thereto from said restriction to obtain a temperature at the latter above the precipitation temperature of lead contaminants in said exhaust gases.
2. In the combination according to claim I, said hotspot extending transversely to the flow of said fuel-air mixture in said inlet header for impingement of said mixture thereagainst.
3. In the combination according to claim 1, the second end of said bypass duct opening into said inlet header in an upstream direction with respect to the flow of said mixture to direct a stream of hot exhaust gases in opposition to said flow to enhance mixing and vaporization of said mixture.
4. In the combination according to claim 3, a throttle valve in said inlet header upstream of said one end and movable between idle and wide open positions, said second end opening into said inlet header at a location increasingly exposed to the opposing flow of said mixture as said throttle valve moves to its wide open osition.
5. In the com matron according to claim I, a throttle valve in said inlet header movable between idle and wide open positions, said restriction comprising a restricted orifice in said bypass duct, and normally open valve means responsive to the position of said throttle valve for restricting said orifice when said throttle valve is adjacent either its idle or wide open position.
6. In the combination according to claim I, said restriction being spaced within said exhaust header from said hotspot sufficiently to maintain an operating temperature at said restriction above 700 F.
7. In the combination according to claim I, said bypass duct having a comparatively short length on the order of magnitude of the wall thickness of said hotspot and extending directly through said hotspot and terminating within said inlet header proximate the surface of said hotspot exposed to said inletv mixture.
8. In the combination according to claim 7, said bypass duct being comparatively resistance free to the flow of exhaust gases therethrough downstream of said restriction.
9. In the combination according to claim 7, the opening of said bypass duct enlarging downstream of said restriction.
10. In the combination according to claim 9, a throttle valve in said inlet header movable between idle and wide open positions, a valve plunger within said inlet header movable obliquely within the enlarging downstream opening of said bypass duct, and means responsive to the position of said throttle valve for normally maintaining said plunger out of said restriction and for moving said plunger into said restriction when said throttle valve is adjacent either its idle or wide open position.
11. In the combination according to claim I, the opening of said bypass duct enlarging conically downstream of said restriction, a throttle valve in said inlet header movable between idle and wide open positions, a valve plunger reciprocable along the conical surface of the conically enlarging opening of said bypass duct and within said restriction to reduce the opening of the latter, and plunger operating means responsive to the position of said throttle valve for normally maintaining said plunger out of said restriction and for moving said plunger into said restriction when said throttle valve is adjacent either its idle or wide open position.
12. In the combination according to claim 11, said second end of said bypass duct opening into said inlet header at a location shielded from the opposing flow of said mixture by said throttle valve when the latter is at its idle position and exposed to said opposing flow when said throttle valve moves to its wide open position.
13. In the combination according to claim 11, said bypass duct being located centrally with respect to the flow of said mixture downstream of said throttle valve, said plunger having a remote end out of said flow, and said plunger operating means engaging said remote end to operate said plunger.