Process and system for detoxicating the exhaust gases of an internal combustion engine

Abstract

For detoxicating the exhaust gases of an internal combustion engine an in-series arrangement of a first reactor and an oxidizing reactor is provided with the exhaust line of the engine along with an oxygen measuring element and structure for producing two additional air streams fed to the exhaust line. The first reactor reduces the nitrogen oxides in the exhaust gas and the second or oxidizing reactor oxidizes the hydrocarbons and the carbon monoxide in the exhaust gas. The oxygen measuring element is mounted to the exhaust line and regulates the mass ratio of air to fuel on the suction side of the engine. The first additional air stream is injected into the exhaust pipe in the flow direction upstream of the oxygen measuring element. The quantity of this air stream is regulated and corresponds to the fuel throughput of the engine so that when the oxygen measuring element measures a stoichiometric mixture (.lambda.=1) a slightly rich air-fuel mixture (.lambda. .apprxeq.0.98-0.99) is supplied to the engine.BACKGROUND OF THE INVENTIONThe present invention relates to a process and system for detoxicating the exhaust gases of an internal combustion engine, the exhaust pipe of which contains an in-series arrangement of a first reactor for reducing the nitrogen oxides in the exhaust and a second reactor for oxidizing the hydrocarbons and the carbon monoxide in the exhaust. This process operates with a first control system which regulates the mass ratio of air to fuel on the intake side of the engine as a function of the quantity measured by an oxygen measuring element disposed in the exhaust pipe and with at least a second control system which controls the injection of supplementary air into the exhaust pipe in the direction of flow upstream of the oxidizing reactor.With exhaust gas detoxicating systems of this type comprising two bed catalysts, to obtain satisfactory reduction of the nitrogen oxides NOx, the air-fuel mixture supplied to the engine should be slightly richer (.lambda.<1) than a stoichiometric mixture (.lambda.= 1). By using this slightly richer mixture (slight air deficiency), the combustion temperature in the engine is kept relatively low which counteracts oxygen formation and provides a better drive performance as less misfiring and other disturbing phenomena are produced in the course of combustion when the position of the accelerator is altered rapidly. This slightly richer mixture can be ignited more easily. On the other hand, this produces an increase of carbon monoxide CO and hydrocarbons HC. These substances are thereafter oxidized in the oxidizing catalyst while air is added. The slightly richer mixture is also an advantage to the rapid heating of the oxidizing catalysts as these only operate satisfactorily after reaching a specific operating temperature which is largely dependent on the composition of the catalysts.Known detoxicating processes of the type described initially operate with a relatively rich air-fuel mixture on the intake side of the engine so that with the constantly varying characteristic values of the engine during operation of an internal combustion engine, it is possible to effectively prevent the engine from occasionally receiving too lean a fuel mixture, resulting in that the additional CO required of reducing NOx is not present. The disadvantage of these known systems is a relatively large, costly air pump for injecting large quantities of additional air into the exhaust pipe, a high efficiency loss and high fuel consumption.OBJECTS AND SUMMARY OF THE INVENTIONThe principal object of the present invention is to provide a detoxicating system of the type described initially by means of which a slightly richer air-fuel mixture (.lambda. = 0.98 - 0.99) is supplied to the engine, wherein measurements taken on the exhaust side of the engine are effected by an oxygen measuring element which changes its output voltage abruptly, in a manner known per se, when the air number .lambda. = 1, such that only this air number is utilized for an accurate measurement, and wherein the supplementary air is supplied by a relatively small pump.This and other objects are accomplished according to the present invention in that the supplementary air supply is divided into two streams and blown into the exhaust pipe, with a first stream being injected in the direction of flow upstream of the oxygen measuring element and being regulated at a quantity corresponding to the gas throughput of the engine so that with a measuring element measurement of a stoichiometric mixture (.lambda. = 1), a slightly richer air-fuel mixture (.lambda. .apprxeq. 0.98 - 0.99) is supplied to the engine, and with a partial stream of additional air being supplied upstream of the oxygen measuring element, such that a slightly weaker air-fuel mixture is initially detected by the measuring element. Thus, a slightly richer air-fuel mixture is supplied to the engine in correspondence with the first partial stream of additional air. Although the fuel consumption is only slightly higher than when .lambda. = 1, a reducing or oxidizing atmosphere will be sure to prevail in the catalysts.According to a feature of the invention, the supplementary air pump is driven by the engine and the first partial stream of supplementary air can be controlled, at least indirectly, in dependence on the pressure in the suction pipe downstream of the engine throttle valve.According to another feature of the invention the partial stream of additional air is regulatable as a function of the flow conditions in the exhaust line.Other objects, features and advantages of the present invention will be made apparent from the following detailed description of two preferred embodiments thereof provided with reference to the accompanying drawings which show three variants of the two embodiments.

Description

Claims

1. A process for detoxicating the exhaust gases of an internal combustion engine having an exhaust line containing in series a first reactor for reducing nitrogen oxides and a second reactor for oxidizing hydrocarbons and carbon monoxide, and an oxygen measuring element connected to the exhaust line comprising the steps of:

a. regulating the mass ratio of air to fuel on the suction side of the engine as a function of the measured quantity of the oxygen measuring element;

b. injecting additional air into the exhaust line upstream of the oxidizing reactor in the form of a first and second air stream, the first one of which is injected in the exhaust flow direction upstream of the oxygen measuring element, and

c. regulating the first air stream at a quantity corresponding to the gas throughput of the engine, so that when the measuring element measures a stoichiometric mixture a slightly rich air-fuel mixture is supplied to the engine.

2. A process as defined in claim 1, wherein the internal combustion engine further has a pump which supplies, at least in part, the two air streams, the process further comprising:

d. driving the pump at an rpm corresponding to the rpm of the engine.

3. A process as defined in claim 1, wherein the internal combustion engine further has a suction pipe and a throttle valve mounted within the suction pipe, and wherein the step of regulating the first air stream is accomplished, at least indirectly, as a function of the pressure in the suction pipe downstream of the throttle valve.

4. A process as defined in claim 1, wherein the step of regulating the first air stream is accomplished as a function of the flow conditions in the exhaust line.

5. A system for detoxicating the exhaust gases of an internal combustion engine having a suction pipe, a throttle mounted within the suction pipe and an exhaust line containing in series a first reactor for reducing nitrogen oxides and a second reactor for oxidizing hydrocarbons and carbon monoxide, the system comprising:

a. a first control system including an oxygen measuring element connected to the exhaust line which regulates the mass ratio of air to fuel on the suction side of the engine as a function of the measured quantity of the oxygen measuring element;

b. a second control system including means for injecting additional air into the exhaust line upstream of the oxidizing reactor in the form of a first and second air stream through a first and second line, respectively, with the first air stream being injected in the exhaust flow direction upstream of the oxygen measuring element;

c. an air valve; and

d. a control line for connecting the air valve to the suction pipe, whereby the opening cross-section of said air valve corresponds to the pressure within the suction pipe, wherein:

i. said air valve is also connected to at least one of the two air lines; and

ii. said first air stream is regulated by said air valve and at least indirectly as a function of the pressure in the suction pipe downstream of the throttle valve at a quantity corresponding to the fuel throughput of the engine so that when the measuring element measures a stoichiometric mixture a slightly rich air-fuel mixture is supplied to the engine.

6. The system as defined in claim 5, wherein the means of said second control system includes an air pump and means connecting the air pump to the engine for driving the air pump at an rpm corresponding to the rpm of the engine.

7. The system as defined in claim 5, further comprising:

e. a throttle, wherein:

i. said throttle is disposed in the second air line; and

ii. said air valve is disposed in the first air line such that the cross-sectional area of flow of the first air stream is reduced as the vacuum pressure in the suction pipe increases.

8. The system as defined in claim 5, further comprising:

e. a throttle, wherein:

i. said throttle is disposed in the first air line; and

ii. said air valve is disposed in the second air line such that the cross-sectional area of flow of the second air stream is increased as the vacuum pressure in the suction pipe increases.

9. The system as defined in claim 5, wherein said air valve comprises a three-way valve which controls the distribution of additional air to form the first and second air streams, the total flow cross-sectional area thereof being preferably constant.

10. The system as defined in claim 5, further comprising:

e. a bypass, wherein:

i. said first air stream is regulated as a function of the flow conditions in the exhaust line;

ii. the oxygen measuring element is disposed in the bypass; and

iii. the bypass branches off from the exhaust line upstream of the reactors.

11. The system as defined in claim 10, wherein the bypass discharges into the suction pipe preferably in the flow direction upstream of the throttle valve.

12. The system as defined in claim 10, further comprising:

f. a compensating storage element, wherein:

i. said storage element is formed as a cross-section enlargement of the first air line; and

ii. said storage element compensates for exhaust pulses.

13. The system as defined in claim 10, further comprising:

f. a Venturi nozzle, wherein:

i. said first air stream discharges into said Venturi nozzle; and

ii. said Venturi nozzle is disposed in said bypass in the flow direction upstream of the oxygen measuring element.

14. The system as defined in claim 13, further comprising:

g. a throttle disposed in the first air line.

15. The system as defined in claim 10, wherein said air valve comprises a three-way valve which controls the cross-sectional flow passage of the second air stream as a function of the pressure in the exhaust line.

16. The system as defined in claim 15, wherein said air valve includes a diaphragm which is acted on on one side by the pressure in the exhaust line and on the other side by the pressure of the additional air.