Patent Application
20110183274
The present invention is related to a process for producing ageing gas, and in particular for producing ageing gas for ageing components related to an after-treatment of exhaust gas.
Motor vehicles with internal combustion engines are subject to emission laws which, nowadays, can only be complied with by using exhaust gas after-treatment systems which adjoin, and are connected to, the internal combustion engines in the exhaust gas line. The exhaust gas after-treatment systems have to have the service life which is specified by law. For the European Union, after the introduction of exhaust gas stage EURO 4, there is specified a durability in the form of a minimum driving performance of 100,000 km, whereas after the introduction of exhaust gas stage EURO 5, a durability in the form of a minimum driving performance of 160,000 km has been specified. For homologizing a vehicle (type approval), it is necessary to prove permanent durability of the respective exhaust gas after-treatment systems. For this purpose, there are permitted artificial ageing processes whose purpose it is to simulate, in the course of rig testing, wear and damage processes during the operation of a motor vehicle in the course of the vehicle service life.
For monitoring the durability of exhaust gas after-treatment systems during the operation of the vehicle, there are required On-Board-Diagnosis systems (OBD) which, when the exhaust gas limit values are exceeded, inform the driver of the faulty operation of the exhaust gas after-treatment systems. Said On-Board-Diagnosis systems are also tested for their efficiency during a type approval operation using artificially aged exhaust gas after-treatment systems.
The “ageing” of a catalyst refers to the diminishing efficiency of the exhaust gas after-treatment during operation, inter alia as a result of the destruction of the catalytically active layer. As a result of the reduction in the size of the active surface it is no longer possible for all emissions to be oxidised and reduced, so that the emissions behind the catalyst, which are released into the environment, increase. Ageing of the catalysts is substantially caused by two mechanisms which, depending on the point of operation, can occur together or even separately. Both mechanisms are also used for specifically ageing catalysts.
Catalysts are designed to operate at temperatures of 200 to 950° C. During this temperature range, the ageing process is very slow. When the temperature increases to a value in excess of 850° C., the ageing process is faster; it is referred to as the so-called thermal ageing, a process which intensifies rapidly if temperatures of more than 1000° C. are reached, with the active surfaces being reduced by sintering processes. At temperatures of 1400° C. and more the ceramic member melts, which leads to total destruction. This is normally indicated by a performance loss of the engine due to too high an exhaust gas pressure in the catalyst.
There are two types of catalyst poisoning. On the one hand, the active surface can be poisoned chemically by foreign substances, for example fuel or oil additives, which chemical poisoning, as a result of chemical reactions, partially destroys or reduces the catalytic surface. In addition, there occurs mechanical poisoning wherein the active layer is covered for example by lead and sulphur from fuel and oil, which also leads to the reduction of the catalytic surface.
To be able to obtain information on the degree of ageing of a catalyst, it is necessary to make an OSC measurement which serves to determine the oxygen storage capacity of a catalyst from which it is then possible to derive an ageing condition. The older the catalyst, the lower its storage capacity. OSC measurements are made in production vehicles and during artificial catalyst ageing processes.
The OSC measurement is carried out in the steady condition of the exhaust gas temperature and of the mass flow. For this purpose, the lambda signals are measured in front of and behind the catalyst. The engine or burner is operated in such a way that, within a short time, the exhaust gas abruptly changes from a rich mixture (lambda<1) to a lean mixture (lambda>1). The phase displacement between the signal in front of and behind the catalyst (after the change in lambda) is proportional to the oxygen stored in the catalyst.
In the course of the artificial ageing process using an ageing gas produced in a burner, it is possible to produce endurance and limit catalysts. In the case endurance catalysts use is made of ageing cycles whose ageing results are comparable to the catalysts aged in road traffic. Measurements to determine the damage to the catalyst to be tested are carried out at fixed intervals. These measurements then enable vehicle manufacturers to develop vehicle-specific catalysts in respect of structure, coating and service life. If optimum adjustment has been achieved, the catalyst can be used. In addition, further dynamic cycles like the standard test cycle or the ZDAKW cycle as specified by law can be used, with air and/or fuel being dynamically added in front of the catalyst for generating an exothermal reaction.
Limit catalysts, on the other hand, are aged until they reach the regionally fixed legal OBD emission limits. These limits are then used for establishing a control-technical model for the vehicle, which model is able to detect if the emission limits have been exceeded. For measuring the degree of ageing of the catalysts, the so-called OSC measurement is available at the burner test rig, just as it is in the vehicle.
When producing the OBD limit catalyst, the catalysts are aged for a certain period of time at a constant point of operation. For this ageing process, use is made of thermal ageing, the purpose of said ageing method being to age a catalyst to such an extent that it only just observes the OBD emission limit. Because, depending on its coating, each vehicle-specific catalyst behaves in a different way, the length of the ageing process cannot be foreseen, which is the reason why the ageing process is divided into intervals with subsequent OSC measurements in order to prevent the catalyst from drifting beyond the limit value and thus cannot be used if the ageing time is too long. In parallel to the OSC measurements, there is carried out an exhaust gas test in order to determine the emissions of the aged catalyst. For this purpose, the catalyst is taken from the test rig and built into the associated vehicle, with the measurement being carried out on a roller test rig in realistic surroundings (real engine with exhaust gas after-treatment system).
As the oxygen storage capacity and the emissions are connected to one another anti-proportionally, but as determining emissions is expensive, the OSC value serves as a measure for the emissions. This means that OBD limit catalyst ageing is used to determine the OSC value at which the emissions of the vehicle have limit values. At a later stage, in a production vehicle, it is then possible with the help of an OSC measurement, to detect a defective catalyst and non-observance of emission values.
The ZDAKW cycle was developed by the exhaust gas centre of the German automotive industry. It was developed in order to provide a standard test method for catalyst coatings. Said cycle substantially consists of a high-temperature phase involving five overrun fuel cut-offs and one poisoning phase with three temperature levels. When the thrust is disconnected, the fuel injection is briefly interrupted and, in parallel thereto, the exhaust gas mass flow is reduced. As a result, the catalyst is flushed with oxygen and a lambda value of approximately 8 is set. When subsequently intensifying the mass flow and re-starting the fuel injection, the lambda value is again increased to the set value of 1. The purpose of this process is to simulate the driving operation in cases of sudden deceleration and acceleration. During the poisoning phase, at a low temperature level, a somewhat richer mixture of the exhaust gas is guided via the catalyst, the result being that the catalytically active layer is reduced by chemical poisoning.
It is possible to simulate the process of ageing exhaust gas after-treatment systems, more particularly exhaust gas catalysts, on engine test rigs, but on the one hand it is expensive and on the other hand it is difficult to reproduce because engine ageing influences represent an influencing factor which cannot be calculated.
Therefore, there was developed a process and a device according to which ageing gas for aging exhaust gas after-treatment systems is produced in burners in which, depending on the individual case, Otto fuel or diesel fuel is burnt in certain simulation cycles whose purpose it is resemble the production of exhaust gas during vehicle operation. The respective operating cycles of the burners used must be able to simulate any interference like ignition failure and overrun fuel cut-off
From U.S. Pat. No. 7,140,874 B2 there is known a process and a device for testing exhaust gas catalysts which contain a burner which, in front of the combustion chamber, comprises a swirl plate which is provided with a central through-aperture into which fuel is injected by a fuel injection nozzle, and with circumferentially distributed boreholes through which the combustion air flows into the combustion chamber. At least some of said circumferentially boreholes, from the entry end to the exit end, extend with tangential components and radial components, which leads to a swirl of the combustion air at the entrance to the combustion chamber.
Producing said swirl plates is expensive, with optimum combustion being possible at only one single operating point of the burner, whereas the ageing cycles require several operating conditions because the ageing gas has to be provided with different temperatures and, optionally, also has to be produced with different combustion air conditions. More particularly, this applies if Otto fuel and diesel fuel is to be used in the same burner.
It is therefore the objective of the present invention to provide a process and a device which, under stable operating conditions, provide ageing gases of different temperatures and which are also suitable for producing an ageing gas with different combustion air conditions under stable burner operating conditions.
The objective is achieved by providing a process of producing ageing gas for ageing components used for the after-treatment of exhaust gas, more particularly exhaust gas catalysts, in a burner which comprises a combustion chamber and at least one fuel injection nozzle, as well as a supply pipe for combustion air with means for generating swirl, with the swirl of the combustion air being set as a function of the selected combustion air radio By specifically pre-setting the swirl value of the combustion air, it is possible, in this way, to ensure a stable operation under different combustion air conditions at different process parameters—depending on the fuel used (Otto fuel or diesel fuel) or in accordance with the required exhaust gas temperature and/or the required exhaust gas composition.
The ageing gas is generated by burning a carbon containing fuel with combustion air in the burner. The composition of the ageing gas can be modified by adding additional gas and/or other substances, more particularly oil, to achieve as close as possible a similarity with natural engine exhaust gases. Additional gases can be added in a pure form from storage containers, i.e. gas cylinders. The ageing gas should have a temperature of >250° C., preferably >700° C. and, more particularly, 1000 to 1250° C., but optionally also <200° C.
The combustion air ratio can be varied in predetermined cycles in accordance with the test regulations. In this way, the exhaust gas after-treatment device can be provided with different ageing gas compositions and ageing gas temperatures in accordance with the load spectrum such as it corresponds to mixed operational conditions. By adjusting the parameters of the combustion air ratio as well as fuel quantities and air quantities, the exhaust gas after-treatment device can be subjected to cyclical thermal loads and thus experiences conditions such as they occur under actual driving conditions.
A typical ageing cycle is within a temperature range of 800 to 1250° C. It is also possible to achieve special ageing cycles in which the starting behaviour of the exhaust gas after-treatment device at the test rig is copied.
A particularly effective way of ensuring a stable burner operation, even under dynamic changes in the operating conditions, is achieved if the swirl of the combustion air is varied as a function of the changes in the combustion air ratio λ in the course of the production of the ageing gas.
It is particularly advisable if the swirl of the combustion air ratio of λ>1 (lean/stoichiometric) is set to be lower than at a combustion air ratio of λ<1 (rich combustion air ratio).
The flow of the combustion air (fresh air) fed into the burner must be mass flow controllable, more particularly by an external combustion air supply system.
It has been found to be particularly advantageous if the combustion air in an inner primary air flow of the combustion chamber is subjected to swirl and in an outer secondary air flow is supplied in a substantially swirl-free condition. More particularly, this applies if the at least one fuel injection nozzle is arranged centrally in the combustion chamber. An ignition device has to be arranged in the combustion chamber at some distance behind the fuel injection nozzle.
Furthermore, it is advantageous to vary also the supplied combustion air quantity in order to adapt same to the changed quantity of injected fuel without allowing excessive effects on the swirl. It is therefore proposed that the external secondary air flow can be throttled.
The fuel should be injected into the combustion chamber so as to be controllable in cycles at a high pressure in excess of 20 bar.
According to an advantageous embodiment it is proposed to add ageing gas in an internal return flow in the burner near the at least one fuel injection nozzle of the combustion air. For this purpose, there has to be generated a Venturi effect in the central combustion air flow by means of which returned ageing gas can be sucked off near the fuel injection nozzle. This process variant is referred to as primary exhaust gas and ageing gas return.
In order to avoid any disadvantageous effect on the ageing gas temperature, the primary ageing gas return flow is also reduced when the secondary air flow is throttled.
In order to ensure stable, uniform combustion processes in the combustion chamber, it is proposed according to a preferred process that the axial position of the burner flame is detected for example by means of a maximum temperature and that, if the burner flame moves towards the rear, the swirl of the combustion air is increased and that the swirl of the combustion air is reduced when the burner flame moves towards the front.
When simulating the exhaust gas return such as it occurs in an engine in order to achieve improved exhaust gas values, it is proposed according to a further special type of process that conditioned ageing gas is added in the combustion chamber to the ageing gas originally produced in the burner.
To influence the ageing gas temperature to which the exhaust gas after-treatment systems are subjected, the returned ageing gas can be cooled and dried. This process variant is referred to as secondary exhaust gas return and secondary ageing gas return.
The percentage of the secondary ageing gas return flow of the burner, more particularly, is varied as a function of the required ageing gas temperature. The ageing gas of the secondary ageing gas return flow is added in the burner preferably in the form of an annular sheath flow.
The conditioned ageing gas can be taken from a main ageing gas pipeline behind the components for the exhaust gas after-treatment or from a bypass ageing gas pipeline which bypasses said components.
According to a further embodiment it is proposed that to the ageing gas produced in the burner, there is added cold- or hot-conditioned returned ageing gas behind the burner or before entering the exhaust gas after-treatment components. In this way, too, it is possible to influence the temperature of the ageing gas entering the exhaust gas after-treatment system. The above-described process variant is referred to as tertiary exhaust gas return or ageing gas return.
Oil and/or fuels and/or foreign gas and/or air, such as, age-related, they occur in the course of engine combustion with increasing wear, can be added in front of the catalyst to the ageing gas of the secondary and/or tertiary exhaust gas return flow or to the exhaust gas, the advantage being the reproducibility of said process stages when producing the ageing gas as a function of time, i.e. as a function of the cycles of the production of ageing gas.
The inventive process is particularly advantageous in that it is possible to simulate the overrun fuel cut-off of an internal combustion engine in that the fuel supply to the burner is interrupted and that, to re-start the combustion chamber, there is set a combustion air ratio of λ<1 (rich fuel mixture) in combination of a very high swirl rate of the primary air flow, which results in very good ignition conditions, so that the cut-off phases can be observed in a very controlled way. Also, with the objective of reducing the mass flow, exhaust gas can be guided through the catalyst in the bypass. To control the mass flows, it is possible to use suitable exhaust gas flaps. In addition, it is possible to age a plurality of catalysts in parallel and to control the mass flows by suitable exhaust gas flaps. Furthermore, if exhaust gas manifolds are provided, the temperature of the individual partial mass flows can be set by a measured exhaust gas return and/or by individual exhaust gas flaps.
The invention comprises a process of ageing components for the exhaust gas after-treatment, more particularly exhaust gas catalysts by subjecting same to ageing gas which is produced in accordance with the above-described conditions. Artificial ageing of the entire exhaust gas after-treatment system takes place in such a way that hot ageing gas with C-, HC- and/or NOx-containing components is produced in a burner and guided through the exhaust gas after-treatment system, wherein the hot ageing gas subjects the exhaust gas after-treatment components for the after-treatment of C-, HC- and/or NOx-containing components to the same loads in the same way as engine exhaust gas naturally produced under actual driving conditions.
Furthermore, the invention comprises a burner for producing ageing gas for the ageing of components for the after-treatment of exhaust gas, more particularly exhaust gas catalysts, which burner comprises a combustion chamber with a combustion chamber axis and at least one fuel injection nozzle and a combustion air supply line which comprises swirl generating means which are adjustable in the sense of changing the swirl intensity of the combustion air. Said swirl generating means can be adjusted from the outside without having to remove the burner in order to preset the swirl intensity or adjust the swirl intensity during operation. Said adjustment can take place in accordance with pre-programmed combustion cycles and/or within the framework of control processes.
More particularly, the swirl generating means of the combustion air supply line are circumferentially distributed swirl blades which are arranged radially relative to the combustion chamber axis and which are pivotable on journals. They preferably engage one single rotatable adjusting ring which cooperates with the swirl blades.
According to a preferred embodiment there is provided an annular plate or funnel which is arranged in the combustion air supply flow in front of the fuel injection nozzle and which divides the combustion air flow into an inner primary air flow and an outer secondary air flow, with the swirl generating means preferably being positioned in the primary air flow. More particularly, it is the combustion air flow positioned near the fuel injection nozzle which has to be provided with a variable swirl, whereas the outer secondary air flow which optionally constitutes a greater volume flow percentage remains substantially swirl-free.
However, it is proposed furthermore that there are provided means for controlling the volume of the combustion air flow, which means, more particularly, can act on the outer secondary air flow. The means for controlling the volume flow of the combustion air flow are provided in the form of a ring which is arranged concentrically relative to the fuel injection nozzle and which comprises adjustable apertured diaphragms.
For detecting the axial position of the burner flame inside the combustion chamber there can be provided one or more special sensors, more particularly temperature sensors which are arranged so as to be distributed along the length of the combustion chamber.
Further design characteristics consists in that inside the combustion chamber there is concentrically arranged a flame pipe which ends in front of the end of the combustion chamber and which, near the fuel injection nozzle, comprises circumferentially distributed exit apertures for returning primary ageing gas. To ensure that the latter is guided into an independent return flow, it is proposed that the exit apertures in the flame pipe are positioned in a flame pipe portion which is narrowed nozzle-like and arranged behind the fuel injection nozzle, with a Venturi effect occurring in the primary combustion air flow.
A further advantageous embodiment consists in that inside the burner sheath, there is provided a mixing pipe which is arranged concentrically relative to the combustion chamber axis, which, together with the burner sheath, forms an annular chamber to which there is connected a supply port for conditioned returning ageing gas and which extends beyond the length of the flame pipe and, behind the end of the flame pipe, comprises circumferentially distributed exit apertures for the conditioned ageing gas. This embodiment, more particularly, serves for adding secondary returned conditioned ageing gas as described above in connection with the various processes.
The invention comprises a system for artificially ageing exhaust gas catalysts and exhaust gas after-treatment systems which are subjected to ageing gas produced in a burner, into which system there is inserted a burner according to one of the previously mentioned embodiments.
Such a system consist of the following components: air supply line, fuel supply line, burner with mixing device, ageing pipeline for the exhaust gas after-treatment components to be aged and an ageing gas return line.
The air supply line is used to supply the burner with combustion air for the purpose of producing, together with the fuel, an ignitable mixture at a later stage. Fresh air is sucked in via an air filter, which fresh air is compressed via a Roots compressor which is driven by an asynchronous motor. As a result of the pressure gradient relative to the ambient air at the exhaust gas chimney behind the exhaust gas after-treatment system, there occurs a mass flow in said direction. The asynchronous motor is speed-controlled via a frequency converter. Subsequently, the temperature of the compressed combustion air can be cooled down via a counter flow heat exchanger. Behind the fresh air has passed through the air filter, a hot film air mass sensor (HFM) measures the mass flow which is controlled via a subsequently arranged throttle valve. The quickly controlling throttle valve is essential because the Root compressor is too inert for achieving the rapid mass flow variations required for the various cycles. In this way, the combustion air reaches the burner head with a certain mass flow and a certain temperature.
By means of a fuel pump, the fuel is pumped from a tank into the burner. A mass flow meter measures the fuel through-put. A counter flow heat exchanger cools the fuel which is not required. A high-pressure pump now increases the fuel pressure to 50 bar which is required for the injection valve.
Burner with Mixing Device
At the entry end, an entry manifold, also referred to as the burner head, forms the transition from the cold to the hot part of the system. At the exit end, the combustion chamber forms the transition to the exhaust gas after-treatment system via a flange.
For cooling the components in the mixing device, the two-shell entry manifold is cooled by cooling water sheath.
The mixing device substantially consists of the following components: air controlling unit with swirl device and diaphragm, injection nozzle with injection valve and flame pipe.
It is the purpose of the mixing device to mix the fuel and the combustion air in such a way as to produce a combustible mixture which is burnt in the flame pipe in order to provide, at the burner exit, an exhaust gas mixture which resembles the exhaust gases of an Otto engine or diesel engine.
After the exhaust gas has left the flame pipe, it is gradually cooled down by adding the cooled conditioned ageing gas of the secondary exhaust gas recirculation flow (EGR). By supplying the ageing gas laterally, a swirl flow occurs around the mixing pipe. Rebound plates and boreholes ensure that the colder returned ageing gas is pressed into the inside of the combustion chamber, so that, towards the rear, there is generated an ageing gas with an ever decreasing temperature. The exhaust gas temperature at the burner exit can additionally be influenced by adding specific amounts of air, with the mass flow which subsequently flows through the exhaust gas after-treatment system consisting of a fresh air mass flow, an EGR mass flow and a fuel mass flow.
By measuring the temperature in several places of the combustion chamber, it is possible to detect the position of the flame and to set the position of the flame by varying the swirl.
Ageing takes place between two flange connections. The first flange connection is directly behind the burner exit whereas the second flange connection is located in front of a particle filter. The flanges are arranged at a constant distance from one another, so that the catalysts to be treated can be adapted to the system in advance. As the geometry and exhaust gas line of the catalysts to be aged usually greatly differ from one another, said adaptation measures always have to be undertaken individually. As a rule, every catalyst is provided with connecting muffs in front of and behind the catalysts for lambda probes and with several threaded muffs for thermo elements and temperature sensors. Depending on the ageing capacity of the burner and the ageing gas requirements for the catalysts, two or more catalysts can be connected in parallel in the ageing path. For controlling the mass flow, at least one bypass line leading to the catalysts can be provided in the ageing path. Ageing gas return
The returning ageing gas flow removes part of the exhaust gas mass flow in front of the exhaust gas chimney to mix same again in a cooled condition with the original ageing gas. For this purpose, the hot ageing gas is guided over a counter flow heat exchanger which cools same down to 40° C. The cooled ageing gas is guided over a cyclone separator for the purpose of filtering out the liquid phase after the cooling process. Now the mass flow of the returned ageing gas is determined via a hot film air mass sensor (HEM), to be able to control same via an adjoining throttle valve and a Roots compressor, Finally, the cooled ageing gas reaches the burner where, via the mixing pipe, it is added to the hot, originally produced ageing gas.
Preferred embodiments of an inventive burner and of an inventive system for artificially ageing exhaust gas catalysts are illustrated in the drawings and will be described below.
The inner annular projection at the carrier flange 15 carries a cylindrical flame pipe 23 which, in respect of length, substantially extends along the first portion 16 of greatest diameter of the burner sheath 12. Inside the flame pipe 23 there are provided two rows of recirculation apertures 24 for a primary ageing gas circulation which will be explained at a later stage.
An ageing gas return pipe (port) 26 which, at a short distance behind the entry flange 13, ends in an annular chamber 27 between the burner sheath 12 and the additional guiding pipe 21, is attached to the burner sheath 12. Said ageing gas return pipe 26 serves to return the secondary ageing gas.
At the entry end in front of the flame pipe 23, there is connected a mixing device 25 with a fuel injection nozzle 31 and a air controlling device 32. The air controlling device 32 comprises an adjustable swirl device and an adjustable throttle diaphragm for the combustion air, which two devices will be explained at a later stage. In front of the burner 10 there is provided an air supply manifold 34 which is connected thereto by an attaching flange 33 and which comprises an inner jacket 35 and an outer jacket 36 between which there is formed a shell-type chamber 38 for cooling water. In addition to the attaching flange 33, the air supply manifold 34 comprises an entry flange (not shown here). Further details of the parts mentioned latterly are given in the following Figures.
The principle used for carrying out the combustion process corresponds to that of a burner stabilised by swirl. From behind, the fresh air flows out of the cooled air supply manifold 34 into the mixing device 25 where the air flow is divided into an inner primary air flow and an outer secondary air supply. In the case of the primary air flow, the fresh air, on the inside, flows over the swirl device. Then, in front of the primary air supply borehole in the throttle diaphragm, the fresh air is mixed with the injected fuel, and the combustible fuel-air mixture reaches the flame pipe 23. In the case of the secondary air flow, the fresh air is guided around the swirl device and, via secondary air boreholes in the throttle diaphragm, flows into the flame pipe and envelops the fuel-air mixture, so that, during the combustion process, the edge regions, too, are supplied with oxygen and so that part of the ageing gas generated in the course of combustion is sucked back via the recirculation bores 24 in the flame pipe 23. By changing the aperture cross-section of the secondary air boreholes in the throttle diaphragm, it is possible, to variably and divisibly control the air quantity through the swirl device (primary air borehole) and around same (secondary air boreholes). As a result, the air flow speed at the exit of the mixing device 25 is changed, so that there occurs a vacuum at the recirculation boreholes 24 of the flame pipe 23. The recirculation boreholes 24 serve to stabilise the flame, and via the air circulation boreholes 24 ageing gas on the outside of the flame pipe 23 is sucked up (Venturi effect). In consequence, the ageing gas deposits itself from the outside like a jacket around the flame.
In
Details of the air controlling device 32 and its adjusting mechanism will be described with reference to the following Figures.
In
Between the two annular discs 51 and 52, there extends an initially cylindrical and then funnel-shaped annular sheath 61 which separates an inner primary combustion air flow ring from an outer secondary combustion air flow ring. Inside the annular sheath 61 and thus inside the inner primary combustion air flow ring there are positioned circumferentially distributed, adjustable swirl flaps 62 on radially arranged rotary journals 63 through which the inner primary combustion air flow ring can be influenced in respect of swirl, whereas the outer secondary combustion air flow ring can be adjusted by the adjustable apertured diaphragms 56 in respect of the volume flow quantity.
In
At the fuel supply unit 71 it is possible to identify a fuel tank 72, a fuel conveying pump 73 as well as a low-pressure fuel pump 74 and a high-pressure fuel pump 75 with an electric motor. A mass flow sensor 76 is arranged behind the low pressure fuel pump 74. A return loop extending parallel to the low-pressure fuel pump comprises a pressure regulating valve 77 and a fuel re-cooling device 78. The returning loop extending parallel to the high-pressure pump 75 comprises a pressure regulating valve 79 and a fuel re-cooling device 80.
At the combustion air supply line 81 it is possible to see an air filter 82 and a mass flow sensor 83 which are followed by a throttle flap 84 and a Roots compressor 85 with a frequency-controlled electric motor. Behind the compressor 85 there is positioned a charge air cooler 86 in front of the entrance to the burner 10.
When fuel and combustion air are supplied by the means 71, 81 as mentioned, the burner 10, when ignited by an ignition device, produces ageing gas which can pass through exhaust gas catalysts 91, 92 and a diesel particle filter 95, and the exhaust gas catalysts, for example, can be TWC- or DOC- or SCR- or CDPF-catalysts and can be arranged parallel relative to one another.
The main ageing line 100 is divided into two ageing gas branch lines 115, 116 leading to the exhaust gas catalysts 91, 92 and a centrally positioned ageing gas bypass line 119. The branch lines contain setting valves 93, 94 in front of the catalysts 91, 92 and setting valves 117, 118 behind the catalysts in which the mass flows can be divided, i.e. set so as to be of equal size. In the bypass line 114, there is provided a metering valve 120 and a switching valve 121 which can be used to control the size of the bypass flow and thus the mass flows leading to the catalysts. The branch lines 115, 116 and the bypass line 119 are combined again to form the main ageing gas line 100 in front of the theses particle filter 95. The controllable burner 10 is used to run through certain operating cycles which serve to effect standard ageing of the exhaust gas catalysts 91, 92 and optionally of the diesel particle filter 95.
The line diagram can be used analogously for treating further parallel catalysts.
The main flow of the after-treated ageing gas is discharged from the main ageing gas line 100 via an exhaust gas chimney 101, while a partial flow, via a secondary return line 98, returns secondary ageing gas after-treated as exhaust gas to the burner 10. Optionally, via a secondary ageing gas bypass line 114, ageing gas can be branched off behind the burner 10 and in front of the exhaust gas after-treatment system and returned in the form of secondary ageing gas to the burner. At the entry to the return line 98, there is arranged a regulating valve 122 for the exhaust gas after-treated ageing gas, and in the return line 114, there is positioned a regulating valve 124 for the non-after-treated ageing gas by means of which the composition of the secondary ageing gas can be varied. In the return line 98 for the secondary ageing gas, there is arranged an exhaust gas heat exchanger 102 as well as a condensate separator 103 with a controllable outlet valve 104. The condensate separator 103 is followed by a mass flow sensor 105 which, in turn, is followed by a throttle flap 106 and a Roots compressor 107 which is driven by a frequency-controlled electric motor.
In front of the return line 98, before same enters the burner 10, there branches off a return branch line 99 which, behind the burner, ends in the main ageing gas line 100; the point of entry is connected to a mixer 96 and can serve for returning the so-called tertiary ageing gas. In the return branch line 99, there is arranged a controllable shut-off valve 109. A mixer 108 can be used for adding to the tertiary ageing gas a liquid such as oil or fuel or foreign gases for each of which there are provided branch lines 112, 113 leading to the mixer 108 with controllable inlet valves 110, 111. In front of the return branch line 99 there branches off an ageing bypass line 123 which, in the bypass leading to the main ageing gas line, bypasses the mixer 96 and is divided into two branch lines 125, 126 for cooled and conditioned ageing gas, which each lead into ageing gas branch lines 115, 116 leading to the exhaust gas catalysts 91, 92. Into each of the branch lines 125, 125 there are inserted regulating valves 127, 128 which are used for measuring the added cooled ageing gas and by means of which the ageing gas temperature in the exhaust gas catalysts can be influenced, more particularly lowered.
There can be seen a burner 10 which is enveloped by an insulating jacket 50 and which is followed by and connected to two exhaust gas catalysts 91′, 92′ connected in series, as well as a diesel particle filter 95. The main ageing gas line 100 ends in an exhaust gas chimney 101. From said main line there branches off a return line 98 in which there is arranged an ageing gas re-cooling device 102 which is followed by a condensate separator 103 with an outlet valve 104, which, in turn, is followed, in the return line 98, by a mass flow sensor 105 and a throttle flap 106. Behind the throttle flap 106, in the line 98, there can be seen a Roots compressor 107 which can be driven by a frequency-controlled electric motor. Following the Roots compressor, the return line 98 laterally ends in the burner 10 in the starting region of the combustion chamber. While the fuel supply system is not shown in this Figure, it is possible, of the air supply system 81, to see the air filter 83, the throttle flap 84, the Roots compressor 85 drivable by a frequency-controlled electric motor and the charge air cooler 86.
The OSC measurements are carried out in the steady condition of the exhaust gas temperature and in mass flows. For this purpose, lambda signals are measured in front of and behind the catalyst. The burner is now supplied with fuel in such a way that, within a short time, the exhaust gas abruptly changes from a fatty mixture (lambda<1) to a lean mixture (lambda>1), with the curve aimed at being represented by the curve “Nominal lambda”. The phase displacement between the before-catalyst signal “lambda before cat” and the after-catalyst signal “lambda after cat” is proportional to the oxygen stored in the catalyst.
The catalyst measured here still has a high oxygen storage capacity. It can clearly be seen that the lambda value after the catalyst (lambda after cat) increases more slowly than the lambda signal before the catalyst (lambda before cat) and only seconds later reaches its maximum value. A limit catalyst, on the other hand, shows a different behaviour. Shortly after the maximum value of the lambda signal of the sensor in front of the catalyst has been reached, the lambda value at the sensor behind the catalyst would reach maximum values. Both lambda signals would increase nearly simultaneously.
The high temperature phase of a duration of 600 seconds is passed through 48 times. The poisoning phase of a duration of 30 minutes is passed through 8 times. The entire cycle lasts 96 hours. The complete cycle corresponds to a driven distance of 80,000 km.
It is to be understood that various modifications are readily made to the embodiments of the present invention described herein without departing from the scope and spirit thereof. In addition, Accordingly, it is to be understood that the invention is not limited by the specific illustrated embodiments, but by the scope of appended claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP08/06982 | 8/26/2008 | WO | 00 | 4/5/2011 |
