Exhaust temperature control

Abstract: An emissions control system for rich-burn internal combustion engines, said control system comprising: a. a reaction chamber for oxidation of exhaust gas fuel values, b. passive means to utilize reaction chamber effluent flow energy to mix cooling air into reaction chamber effluent to lower the temperature of said effluent. c. flame arrestor means to prevent ignition of flammable fuel-air mixtures external to the engine.

Description: This invention relates to an emissions control system including the features of the pre-characterizing portion of claim 1. Exhaust emissions from small internal combustion engines such as are used, e.g., for lawn mowers and small generator sets, are a significant source of atmospheric pollution by hydrocarbons and carbon monoxide. Such engines typically operate fuel-rich and therefore are particularly dirty as compared to an automotive engine, even if the latter is operated without a catalytic converter. Although automotive emissions are now controlled by use of catalytic converters, such conventional devices are not considered feasible for small engine use because of inherently large size, high cost and system complexity relating to the need for air addition and limitation of the temperature of exhaust gases and exposed converter surfaces to safe values. The high emission levels of typical small engines means that destruction of those emissions by oxidation results in a greater evolution of heat with a consequent higher converter temperature than for typical automotive catalytic converters. Further, small engine systems typically are much more exposed to gasoline spills and to operator contact, creating a hazard even with temperatures comparable to those for automotive catalytic converters. An emissions control system of the kind specified in the pre-characterizing clause of claim 1 is disclosed in WO 95/06193, this system including a circular reaction chamber partially filled with a catalytic substance, and passive air induction means in the form of an injection nozzle through which the exhaust from the engine is directed centrally into the reaction chamber. The oxidized exhaust gases leave the reaction chamber through an annular shroud of e.g. glass wool to provide sound muffling, cooling of the effluent and spark extinction. However, any such shroud alone cannot effectively reduce the temperature of the effluent as well as the surface temperature of the device whereas, due to the oxidization process, this temperature will considerably be increased as compared to the temperature of the untreated engine exhaust. EP 0 526 673 Al, on the other hand, discloses a vehicle muffler in which cooling air is admixed to the exhaust just prior to its leaving the muffler without any catalytic reaction having taken place. This in mind, the present invention aims at improving an emissions controle system as specified in the pre-characterizing clause of claim 1 so that hazards due to the high temperature created in either the effluent of the system and the external surfaces thereof are minimized without the need of complex, space consuming and expensive means. This aim is achieved, according to the invention, with an emissions control system as specified in claim 1. The dependent claims indicate adventageous additional design features thereof. According to the invention, additional air is admixed to the gases leaving the reaction chamber by second passive air induction means thus to cool the effluent of the system to safe values whereas the reaction chamber can be operated at a temperature high enough to bring about substantially complete oxidation of the engine exhaust. In this admixing of air use is made of the high velocity pulses of the hot reaction chamber exhaust flow. Still, in spite of the high temperature existing in and at the exit of the reaction chamber, surface temperatures as well are maintained at a safe level and ignition of any fumes in the ambient air is reliably prevented all around the system. This allows use of engines with the emissions controle system of the present invention even in hazardous locations such as coal mines. Typically, in any such case the temperature of the effluent of the system is reduced to a value not higher than about 600 degrees Kelvin. Thus, the present invention makes possible economic achievement of ultra-low emission levels of carbon monoxide and hydrocarbon even with very small internal combustion engines and in hazardous locations. The term "passive", as here applied to the system of the invention or its components, refers to such devices or components which do not require any moving parts. Thus, a conventional catalytic converter is a passive device whereas a converter system utilizing a mechanical air pump is not passive. In the following a preferred embodiment of an emissions controle system according to the present invention is described in more detail taking reference to the accompanying drawing. The single figure thereof is a more or less diagrammatic longitudinal section of the respective emissions controle system attached to an internal combustion engine. In the embodiment as shown the exhaust from a single cylinder gasoline engine 1 passes through an exhaust line 2, which serves as an air inductor nozzle, into a line 3, thereby entraining air from a shroud 11 through opening 4 in line 3. This air enters shroud 11 through a flame arrestor 13. The exhaust gas and the mixed in added air pass from line 3 into a reaction chamber and muffler 5 into contact with catalytic surfaces of swirler 9 resulting in virgorous recirculation and stable gas phase combustion. Contact of gases with the catalytic surfaces of baffle plate 10 aid flame stabilization. Hot combustion products exiting vessel 5 are directed by deflector 6 which serves as an air inductor nozzle, into the venturi duct formed by wall 7 thereby inducting air into duct 8 through flame arrestor screen 16 and mixing it with the hot exhaust. Gases exiting through the venturi duct formed by wall 7 are more than 200 degrees Celsius lower in temperature than the hot gases exiting reactor/muffler 5. Contact of entering gases with swirler 9 also serves to create a low pressure region near the muffler inlet and thus inhibit backflow of gases through the open end of line 3. Typically, muffler 5 is encased in insulation 17 to reduce the temperature of surfaces 12 to an acceptable level. Gases exit the venturi formed by wall 7 through flame arrestor 14 to contain any flame from ignition of fuel in air entering through arrestor 16. In place of the insulation, a double walled heat shield may be used to enclose the muffler assembly to contain the reaction heat and minimize risk of burns or fire. EXAMPLE I Fuel rich exhaust gas from a small Briggs and Stratton single cylinder gasoline powered spark ignition engine driving an electrical generator was passed through an exhaust pipe of conventional size discharging as an injector nozzle into a larger pipe and inducting air through the opening between the discharge nozzle and the outer pipe. The exhaust gases with entrained air were passed to a conventional Briggs and Stratton muffler which had been modified by the addition of a coating of a platinum catalyst to the internal baffle plate surfaces to ignite and stabilize thermal reactions in the muffler and by addition of fixed swirler vanes opposite the muffler inlet. Reacted effluent from the muffler was passed through a second nozzle into a venturi duct to entrain additional air to dilute and cool the effluent. Thermal reaction of the fuel values in the exhaust gases with the oxygen in the inducted air resulted in a muffler exhaust temperature at the muffler exit of 923 degrees Kelvin, or about 200 degrees Kelvin higher than the 718 degrees Kelvin exhaust temperature of a noncatalytic muffler at the same operating conditions. The diluted exhaust was reduced from 923 degrees Kelvin to 713 degrees Kelvin or slightly lower than the exhaust temperature for the standard muffler at the same engine operating conditions. Integrating the venturi duct into a full surrounding sheet metal muffler heat shield through which engine cooling air is ducted resulted in external surface temperatures below 550 degrees Kelvin and an exhaust gas temperature below 610 degrees Kelvin, i.e. much lower than that of the standard non-catalytic muffler. Thus, not only were emissions controlled with a simple system but exhaust and surface temperatures were below those for an engine without emissions control.

Claims: An emissions control system for the exhaust of an internal combustion engine (1), the system comprising: a reaction chamber (5) for oxidation of exhaust gas fuel values contained in said exhaust from said engine (1), said reaction chamber comprising a catalyst to stabilize termal combustion, passive air induction means (2, 11) utilizing exhaust flow energy for induction of air into the exhaust gas entering the system, duct means (3) for transferring said exhaust gas together with said inducted air into said reaction chamber (5), and cooling and flame arrestor means (6, 7; 14) at the outlet of the system, characterized in that said reaction chamber (5) is designed to operate at a temperature in excess of 800 degrees Kelvin and includes heat insulation means (17) to reduce external surface temperature, that cooling means separate from flame arrestor means (14) at the outlet of the system comprise second passive air induction means (6, 7) utilizing reaction chamber effluent flow energy for induction of air into the reaction chamber effluent to lower the temperature of said effluent by at least 200 degrees Kelvin, and that additional flame arrestor means (13, 16) are provided at the air intake of either said first and said second air induction means (2, 11; 6, 12). The system of claim 1 wherein said reaction chamber (5) comprises recirculation inducing means for inducing recirculation of the gases flowing through said reaction chamber, said recirculation inducing means preferably comprising a swirler (9) and/or a baffle plate (10). The system of claim 2 wherein said catalyst is formed by catalytic surfaces of said swirler (9) and/or said baffle plate (10) substantially spaced from the walls of said reaction chamber (5). The system of any one of the preceding claims wherein said second air induction means (6, 7) comprise a venturi duct (7) into which said reaction chamber effluent flow is directed by a nozzle (6). The system of any one of the preceding claims wherein said second air induction means (6, 7), same as the reaction chamber (5), include heat insulation means (17) to reduce external surface temperature. The system of any one of the preceding claims wherein said heat insulation means (17), at least in part, consist of a double-walled heat shield. The system of any one of the preceding claims wherein at least said reaction chamber (5) is integrated into a muffler of said engine (1). The system of claim 7 wherein engine cooling air is conducted through said muffler. The system of any one of the preceding claims wherein the hot gases of either the engine exhaust and the reaction chamber effluent are prevented from impinging any external walls of the system.

Inventors: PFEFFERLE WILLIAM C, PFEFFERLE, WILLIAM C.
Applicants: PFEFFERLE WILLIAM C, PFEFFERLE, WILLIAM C.
Application year: 1995
Main classification: F01N3
IPC codes: F01N3, F02B1, F01N7, F01N1