IE912331A1

IE912331A1 - An exhaust gas duct with a filter for suspended particles¹and a regenerating burner

Info

Publication number: IE912331A1
Application number: IE233191A
Authority: IE
Original assignee: Zeuna Staerker Kg
Priority date: 1990-08-07
Filing date: 1991-07-03
Publication date: 1992-02-12
Also published as: EP0470361A1; PL291333A1; HU912392D0; HUT61819A; FI913568A0; CS245291A3; NO913053D0; DE4025017A1; DE4025017C2; TR25558A; FI913568A; MC2283A1; PT98580A; NO913053L

Abstract

In an exhaust system of a combustion engine which contains a particle filter (12) and a burner (11) for regeneration of the filter, an arrangement is proposed, in which the fuel for the burner is oxidised in a number of stages. The fuel is first sprayed with atomising air (53) into a mixing pipe (41) and there ignited and mixed with primary combustion air (40). A part of the still uncombusted fuel is combusted by residual oxygen from exhaust (16a) entering into the combustion chamber (21). Finally the remainder of the uncombusted fuel is completely combusted on leaving the combustion chamber (21) by the residual oxygen of the exhaust (16b) flowing around the flame pipe (15). The burner operation is regulated during the regeneration phase by changing the quantity of fuel, the primary air quantity being kept constant.

Description

An Exhaust Gas Duct with a Filter for suspended Particles and a regenerating Burner.

The invention relates to an exhaust gas duct for an internal combustion engine comprising a filter for suspended particles and a burner for regeneration of the filter with the burner opening into the exhaust gas duct upstream from the filter in terms of the direction of flow of the exhaust gas.

An exhaust gas system of this type has been described in the US patent 4,615,173, in the case of which a filter for suspended particles is arranged in a section of an exhaust gas duct and in which a burner opens into the exhaust gas duct upstream from the filter at an acute angle. The fuel mixed with the atomizing air and the primary combustion air in the burner is ignited by means of a spark plug and finally flows in a more or less completely burned condition obliquely into the exhaust gas duct.

The hot gas is thereby mainly contacted by the exhaust gas on one side, as yet unburned fuel being oxidized with residual oxygen from the exhaust gas.

In this known arrangement there is no intimate mixing of the hot gas with the exhaust gas. Furthermore the oxidation of unburned fuel with residual oxygen occurs relatively close to the input of the filter so that jets of flame may entail local overheating and consequently damage to the filter.

One object of the present invention is to improve upon an exhaust gas system of the type initially mentioned in such a manner - 2 that there is a complete combustion and an effective mixing of the exhaust gas with the hot gas.

In order to achieve these and/or other objects the present invention provides an exhaust gas duct for an internal combustion engine having a filter for suspended particles and a burner for regeneration of the filter, the burner having an opening into an exhaust gas duct upstream from the filter in the direction of flow of the exhaust gas, at least the combustion chamber of the burner being arranged within the exhaust gas duct and during operation being arranged within the flowing exhaust gas and the combustion chamber is so designed that the exhaust gas is able to be mixed in stages with the hot gas from the burner.

Thereafter the exhaust gas and the hot gas flow together without making contact on one side as is the case in the prior art, and instead the exhaust gas is able to flow around and therefore in a homogeneous form for mixing with the hot gas, the stage-by-stage mixing ensuring a complete mixing effect of the two gases.

This leads to the further advantages that a substantial part of the unburned fuel is oxidized even in an early stage by the residual oxygen so that adjacent to the filter if anything only small, that is to say short, jets of flame will be produced.

Accordingly it is possible for the burner to be located comparatively close to the filter. Owing to the stage-by-stage mixing of the exhaust gas it is furthermore possible to exclude the danger of the burner flame being blown out.

Preferably a first part of the exhaust gas is mixed within the combustion space with the hot gas and a further part is mixed with it outside the space so that the available burner space may also be utilized for mixing. On the other hand it is possible for the burner flame to be blown out by the exhaust gas flowing into the burner space. The design of the invention mentioned above takes this problem into account by a compromise solution to the effect that on the one hand the amount of mixing space does not have to be increased and on the other hand the division means that the flow into the combustion chamber may be respectively metered or controlled in order to prevent the burner flame from being blown - 3 35 out.

In accordance with a further development of the invention for the entry of the exhaust gas in the wall of the combustion chamber a series of guide openings is provided, through which the entering exhaust gas is so guided that its flows within the combustion chamber adjacent to the wall thereof. In the case of a cylindrical combustion chamber the flow of exhaust gas will be in a spiral with a pronounced axial component and will mix with a circumferential part of the hot gas flow. As yet unburned fuel in the central part of the hot gas will then remain unoxidized until it leaves the combustion chamber and it will only be burned with the second part of the exhaust gas. The secondary combustion outside the combustion space may, given a suitable design of the device, be so reduced that despite there only being a small intermediate space between the burner and the filter local overheating of the filter is prevented, It is convenient for the exhaust gas duct adjacent to the combustion chamber to be so designed that the exhaust gas may be passed in a spiral around burner. This simultaneously makes possible cooling of the combustion chamber, the desired spiral flow adjacent to wail of the first fraction of the exhaust gas in the combustion space and an improved, thorough mixing of the exhaust gas and of the hot gas outside the combustion space.

The mixing of the gases outside the combustion chamber may in accordance with a further development of the invention be promoted by back pressure, guide and/or deflecting means. The turbulence of the exhaust gas is preferably produced adjacent to the exit for the hot gas. For this purpose the deflecting or, respectively, back pressure devices are arranged as near as possible to the outlet openings for the hot gases.

Devices in the form of back pressure baffles may advantageously simultaneously be utilized in order to secure the burner in the exhaust gas duct and in this case will be suitably designed for this purpose.

The initially mentioned object of the invention is also to be attained by an exhaust gas duct with a suspended particle filter - 4 and a burner for the regeneration of the filter, in the case of which the burner opens into the exhaust gas duct upstream from the filter in the direction of flow of the exhaust gas and the burner is equipped with an atomizing nozzle, which opens into a mixing duct for which a primary air supply guide means is so arranged that the primary air enters tangentially into the mixing duct and the primary air guide means is fitted with a check valve.

In this case the primary combustion air is so introduced into the mixing duct that it promotes the atomization of the fuel.

With the aid of guide inserts it is in this respect possible in addition to cause recycling of the fuel-air mixture into the mixing duct.

Highly efficient atomization and mixing leads to efficient combustion in the front part and reduction in the size of the fuel droplets so that it is possible to counteract the formation of large flame jets when the hot gases contact the residual oxygen from the exhaust gas. By suitably metering the supply of primary air it is possible to further control and to optimize the course of combustion and more particularly post-combustion.

By having a check valve in the primary air duct it is possible to prevent a reversal of the direction of flow into the supply duct when there is an increased back pressure in the exhaust gas system.

In accordance with a further development of the invention the burner is so designed that the oxidation of the fuel takes place before the same is injected and until combustion is completed in stages, that is to say firstly by mixing in primary air and then by step-by-step mixing in of exhaust gas.

The invention further relates to a method for the regulation of a burner for the regeneration of a suspended particle filter, which is arranged in the exhaust gas duct of an internal combustion engine, the quantity of fuel for the burner being regulated in accordance with given parameters and the supply of the primary air being maintained constant.

The method in accordance with the invention is, characterized in that the quantity of primary air is so - 5 predetermined that it is just sufficient to ensure complete combustion at the given, minimum fuel supply setting.

The fuel supply is preferably so regulated that the burner is supplied when starting up with a rate of fuel which makes possible a rapid increase in the temperature of the hot gases up to the temperature of the exhaust gas. Then the quantity of the fuel is so regulated that there is a smooth increase in the temperature of the exhaust gas upstream from the filter. This is intended to prevent sudden temperature changes in the filter and its surroundings.

The supply of fuel is preferably performed intermittently using known means.

The adjustable minimum quantity of fuel is set so as to maintain an pilot flame, which is reset if the fraction of residual oxygen in the exhaust gas is low, that is to say under 6 to 8%.

This will for instance be the case when the engine is running under full load. Accordingly the setting of the minimum quantity of the fuel may be performed in a way dependent on the position of the governor rod of the internal combustion engine. The setting of the minimum fuel supply rate may also be done using an oxygen sensor which responds to the residual oxygen level in the exhaust gas upstream from the burner. Furthermore the quantity of fuel is made dependent on the operation of the engine in such a manner that the exhaust gas temperature is maintained constant upstream from the filter after reaching the particle ignition temperature. The parameters for regulation may in this case be the speed of the engine, the temperature of the exhaust gas from the engine and the like. Preferably the regulation is performed in a way dependent on the temperature just upstream from the filter. This parameter includes the effect of the burner.

The burner or, respectively, the burning rate thereof is consequently regulated within regeneration periods in a way dependent on the operation of the engine in order more particularly to achieve a constant temperature of the exhaust gas passing through the filter, such temperature being selected to be between 600 and 700° C. The switching over to the minimum fuel rate owing -βίο a low level of the residual oxygen in the exhaust gas does however have priority.

The initiation of the regenerating phase may be performed in accordance with known methods, for instance in accordance with the pressure differential at the filter. Regulation on the basis of the particle field emission characteristics to calculate the quantity of particles produced in the period of time and which starts a regeneration phase when a predetermined value is reached, is however to be preferred.

In accordance with one possible design of the invention the end of the regeneration phase may be in accordance with the temperature downstream from the filter. In this respect the fuel supply for the burner is turned off on reaching a temperature of 500° C downstream from the filter and after the elapse of an additional time. The burner operation to be continued after reaching approximately 500° C serves for the complete oxidation of the soot retained in the filter. The time, which lasts for 3 minutes, or under low load condition is longer, is regulated in accordance with the speed of the internal combustion engine.

The accompanying drawing shows one possible embodiment of the invention diagrammatically in the form of a section of an exhaust gas duct.

The section of the exhaust duct 10 has a regenerating burner 11 and a particle filter 12 in it. Into this part there opens an exhaust gas duct section 13 so as to be tangential to the following exhaust gas duct section 14, in which a flame duct 15 of the burner 11 is coaxially arranged. In this design the exhaust gas 16 is guided to move spirally in an annular space 17 surrounding the flame duct 14 before reaching the filter 12.

The flame duct 15 is provided in one circumferential plane with guide openings 20, which are regularly spaced over the periphery. A part 16a of the exhaust gas passes through these guide openings 20 into the combustion space 21 defined by the flame duct 15. The guide openings 20 are so designed that the incoming gas fraction 16a spins in a spiral adjacent to the wall of the combustion space 21 and thus mixes only with the marginal part of - 7 the hot gas 22 from the burner. This is intended to be prevent the hot gas flame 22 being blown out by exhaust gas 16a entering the combustion space 21. If desired a plurality of rows of guide openings may be provided in the flame duct 15.

The residual part 16b of the exhaust gas 16 flows around the flame duct 15 and passes to a baffle plate 25 arranged perpendicularly to the axis of the flow and which is provided with passages 26, by which the second exhaust gas fraction 16b is caused to become turbulent after passing through the same (at 27). The turbulence 27 is produced adjacent to the hot gas 28 emerging from the flame duct 15. For the emergence of the hot gas from the combustion chamber 21 radial outlet openings 29 are provided, which are distributed in at least one plane adjacent to periphery of the flame duct 15 with a regular spacing. The end face 30 of the flame duct 15, which extends parallel to the inlet surface 31 of the filter 12, is sealed off.

The above described exhaust gas and hot gas system described entails step-by-step oxidation of the fuel introduced into the burner 11. The number of the oxidation stages may be multiplied along the axis of the hot gas flow 22 if the exhaust gas 16 is introduced through a plurality of rows of openings and mixed with the hot gas 22 in a plurality of stages.

In addition to the residual oxygen from the exhaust gas 16 the burner 11 is fed with primary air 40. The primary air and the residual exhaust gas oxygen lead to a complete combustion in the burner 11 at every operating load of the internal combustion engine producing the exhaust gas 16. For this purpose the burner 11 is provided with a mixing duct 41, into which the primary air supply 42 enters tangentially. Fuel-air mixture passes from the atomizing nozzle 45 into the mixing duct 41. The primary air 40 aids in the atomization of the fuel 46 and causes spin of the fuel-air mixture 46 within the mixing duct 41. Recycling of the air fuel mixture ignited within the mixing duct 41 may be caused by internal guiding members in order to ensure complete use of the oxygen available in the mixing space 47 and a fine atomization of the fuel.

Oxidation in one or more further stages of as yet unburned - 8 fuel takes place in the combustion space 21 with the above mentioned introduction of the first exhaust gas part 16a.

Combustion is complete at the latest at the end, which is remote from the atomizing nozzle 45, of the flame duct 15, when the hot gas 28 emerges from the flame duct 15 and mixes with the residual oxygen 16b.

The burner is put into operation as required during operation of the internal combustion engine. For operation of the burner 11 there is a regulator 50, which operates a fuel valve 51 and a primary air valve 52 in accordance with the degree of filling of the filter 12. The commencement of the regenerating phase may be caused in accordance with the back pressure in the exhaust gas duct 14, the pressure differential upstream from and downstream from the filter 12, the time of operation of the internal combustion engine and/or other parameters. A method is recommended in which the particle emission characteristics are taken into account. The emission of particles may be estimated in conjunction with the speed of rotation or, respectively, the loading of the internal combustion engine. On the basis of these characteristics and the load-dependent times of the operation it is possible to estimate the load on the filter. On attaining a maximum load value burner operation is commenced by opening the fuel nozzle 51 and the primary air nozzle 52. In order to regulate the operation of the burner the primary air rate is maintained constant at a predetermined value, while the supply of fuel is regulated in accordance with the operation of the internal combustion engine.

The regulation of the fuel rate comprises firstly allowing the passage of a major starting or initial quantity, which together with the atomizing air 53 is injected from the atomizing nozzle 45 into the mixing space 47, where it is ignited and mixed with the primary air 40. The increased fuel rate is dependent on the exhaust gas temperature as measured at the commencement of the regeneration phase. For this purpose a temperature sensor 60 is provided in the exhaust gas duct 14 upstream from the filter 12 whose output signals go to the regulator 50. The increased initial rate serves to rapidly boost the temperature of the hot gas 22 - 9 produced to the exhaust gas temperature obtaining.

The following heating up phase for the exhaust gas 16 takes place gradually until a temperature of approximately 700 C is attained. Slow heating up is intended to avoid thermal stresses and consequent damage in the exhaust gas system and more particularly in the filter 12. When the desired particle combustion temperature has been attained the regulation of the supply of the fuel is continued in a way dependent on the signals from the temperature sensor 60 so that a temperature is maintained which is as constant as possible.

The above described regulating system also involves a monitoring of the quantity of residual oxygen in the exhaust gas 16, by which the control of the supply of the fuel takes place in accordance with the residual oxygen, this having priority as a factor controlling the regulation of the fuel. It serves to ensure a complete combustion of the supplied fuel. The burner system is designed that the complete combustion takes place in stages, that is to say using the atomizing air 43, the primary air 40 introduced into the mixing duct, the oxygen of the exhaust gas 16a introduced into the flame duct and finally the residual oxygen from the fraction 16a of exhaust gas mixed outside of the combustion space 21, one after the other. The secondary combustion air from the exhaust gas is thus included in the combustion process. During full load operation of the internal combustion engine producing the exhaust gas 16 the exhaust gas will only have a small quantity of the residual oxygen so that any increased quantity of fuel would not be burned if there is a need for a higher temperature. In order to avoid periods with incomplete combustion of the fuel, the fuel supply is reduced in a manner independent of the instantaneous requirement to a minimum quantity as long as the level of the residual oxygen is below the predetermined limit. This limit is dependent on the design of the complete burner system and the quantity of primary air dependent thereon. As a rule the system is so set that in the case of a residual oxygen level of less than 6 to 8% the fuel is reduced to a value, which is just sufficient to maintain a pilot flame. Since in this case practically no oxygen - 10 is available from the exhaust gas, the quantity 40 of the primary air is so set that in conjunction with the minimum quantity of the fuel it ensures a complete combustion. It is only after an increase of the residual oxygen that the system is set for resumption of normal regulation.

For the limitation, that is taken as a priority, of the quantity of fuel it is possible to provide a regulation system which is linked with a governor rod of the internal combustion engine. Accordingly this provides a direct indication of full load operation and such signal is processed via the regulator 50. This regulation may however also take place in a way dependent on the signals from an oxygen sensor 55, which for instance is arranged at the exhaust gas inlet into the exhaust gas duct 14, in which the burner 11 is arranged.

The termination of the regeneration period may for instance be caused in accordance with the temperature 62 following the filter. A temperature 62 at this point of approximately 500° C is a signal for the completion of the oxidation of the particles retained in the filter 12. In order to complete oxidation the burner is further operated for a period of for some minutes. It is recommended that this time be set and varied in accordance with the speed of rotation of the engine or, respectively, with load operation in such a manner that the time is extended in the case of a low load. If the internal combustion engine is operating under full load when a temperature of 500° C is detected, then approximately 3 minutes will be sufficient in order to complete oxidation of the particles. In the case of light load operation this time will be extended to 5 or 6 minutes.

Claims

1. An exhaust gas duct for an internal combustion engine comprising a filter for suspended particles and a burner for regeneration of the filter with the burner opening into the exhaust gas duct upstream from the filter in terms of the direction of flow of the exhaust gas, at least the combustion chamber of the burner being arranged within the exhaust gas duct and during operation being arranged within the flowing exhaust gas and the combustion chamber is so designed that the exhaust gas is able to be mixed in stages with the hot gas from the burner.

2. An exhaust gas duct as claimed in claim 1, wherein the wall of the combustion chamber is provided with guide openings through which a first exhaust gas fraction is able to flow into the combustion chamber and within the combustion chamber is able to flow adjacent to the wall of the combustion chamber and a further fraction of the exhaust gas is able to be mixed with the hot gases outside the combustion chamber.

3. An exhaust gas duct as claimed in claim 1 or in claim 2, wherein adjacent to the combustion chamber the exhaust gas duct is so designed that the exhaust gas is able to be guided around the burner and in the flow path of the second exhaust gas fraction at least one back pressure and/or deflecting means is arranged for deflecting and swirling the exhaust gas.

4. An exhaust gas duct for an internal combustion engine comprising a filter for suspended particles and a burner for regeneration of the filter with the burner opening into the exhaust gas duct upstream from the filter in terms of the direction of flow of the exhaust gas, said burner being fitted with an atomizing nozzle, which opens into a mixing duct and a primary air supply means is so associated with the mixing duct that the primary air enters the mixing duct tangentially and the means supplying the - 12 primary air is fitted with a check valve.

5. An exhaust gas duct as claimed in any one of the preceding claims, wherein the burner is so designed that the oxidation of the fuel until completion of the combustion takes place by sequential mixing of primary air and then stage-by-stage mixing of exhaust gas.

6. A method of regulating a burner for the regeneration of a particle filter which is positioned in the exhaust gas duct of an internal combustion engine, the quantity of fuel for the operation burner being regulated in a way dependent on the predetermined parameters and the supply of primary air being maintained constant and the filter the quantity of primary air is so set that it is just sufficient to ensure complete combustion at the predetermined minimum fuel supply setting.

7. A method as claimed in claim 6, wherein the regulation of the fuel is so designed that on starting up the burner is supplied with a large amount of fuel in order to rapidly increase the temperature of the hot gas to the exhaust gas temperature of the filter then the quantity of fuel is so regulated that there is a gradual increase in the gas temperature upstream from the filter until the particle oxidation temperature is reached.

8. A method as claimed in claim 6 or claim 7, wherein the supply of fuel is intermittent.

9. A method as claimed in any one of the preceding claims 6 through 8, wherein in the case of a low fraction of residual oxygen in the exhaust gas the quantity of fuel for the burner is reduced to the predetermined level in order to maintain a pilot flame and the regulation takes place in accordance with the position of the governor rod of the internal combustion engine.

10. A method as claimed in any one of the preceding claims - 13 6 through 9, wherein the quantity of fuel is regulated in accordance with the temperature in the exhaust gas flow, and preferably the exhaust gas temperature, upstream from the filter.

11. A method as claimed in claim 6, wherein the regenerating phase is commenced in accordance with the particle characteristics of the internal combustion engine.

12. A method as claimed in claim 6, wherein the regenerating phase is terminated in accordance with the temperature downstream from the filter

13. A method as claimed in claim 12, wherein on reaching a temperature of approximately 500° C downstream from the filter and after the end of a time dependent on the load of the internal combustion engine the regeneration phase is terminated.

14. An exhaust gas duct as claimed in claim 1 substantially as described hereinbefore with reference to and as illustrated in the accompanying drawing.

15. A method of regulating a burner for the regeneration of a particle substantially as described hereinbefore with reference to and as illustrated in the accompanying drawing.

16. An exhaust gas duct according to any preceding claim substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

17. A method of regulating a burner according to any preceding claim subtantially as hereinbefore described to and as illustrated in the accompanying drawings.