EP2655821A1

EP2655821A1 - Internal combustion engine and method for operating same

Info

Publication number: EP2655821A1
Application number: EP11799638.9A
Authority: EP
Inventors: Rolf Miebach; Stephan Schraml; Markus Müller
Original assignee: Deutz AG
Current assignee: Deutz AG
Priority date: 2010-12-22
Filing date: 2011-12-16
Publication date: 2013-10-30
Also published as: WO2012084156A1; DE102010055548A1

Abstract

The invention relates to an internal combustion engine (1), comprising at least one exhaust pipe (2), at least one burner and/or evaporator (3), at least one metering device (4), at least one regulating or control unit (5) and a fuel supply unit (6) in communication with the burner and/or evaporator (3), and at least one SCR catalyst (10).

Description

Internal combustion engine and method for operating the same

DESCRIPTION

The invention relates to an internal combustion engine and a method for operating the same.

Such internal combustion engines or processes are known, for example, from DE 10 2005 039 630 A1. This is disadvantageous in that you always additional reducing agent such. B. NH ₃ must carry.

The invention has for its object to provide an internal combustion engine with evaporator device or a method for operating such an internal combustion engine with evaporator device in an exhaust system, in particular in front of an SCR catalyst, which manage without additional reducing agent. This object is achieved in that a delivery device for an evaporative liquid is inserted into the exhaust pipe of a burner. The corresponding method is characterized in that the burner provides a basic thermal power, the lower limit of which is predetermined by the provision of a sufficient amount of energy for the vaporization of an amount of vapor liquid introduced into the exhaust gas line. The embodiment of the invention is characterized in that the evaporator device can be used for any liquid to be evaporated. In the case that the liquid is a fuel, it is preferably the same fuel, for example diesel fuel, which is also injected with the supply device of the burner. In principle, however, it is also possible to use a gaseous fuel, for example natural gas, to operate the burner. The separate introduction of the additional burner Stoffs on the introduction device has the advantage that in contrast to the prior art, for example, a required amount of fuel for a process must not be supplied through the supply device of the burner, but downstream of the burner, a subset of the total required fuel as "secondary fuel quantity" is supplied , This secondary fuel quantity is then finally processed in a completely controlled manner and / or burned. The corresponding possible method variants are explained below in connection with the dependent method claims. In a further development of the invention, an orifice of the introduction device in the exhaust pipe has an atomizing nozzle, in particular a pressure atomizing nozzle or an air atomizing nozzle. With the Druckzerstäuberdüse the evaporating liquid is atomized only by the pressure of the evaporating liquid. Alternatively, the introduction device can also be designed as an air Stromzerstäuberdüse. The Luftstromzerstäuberdüse is operated so that the evaporation liquid is introduced with a small amount of air into the exhaust pipe. If the evaporative liquid is fuel, for example, during normal operation of an air atomizing nozzle, 20 l of air / min. and 2 cm ³ / min. Fuel to be supplied to provide an ignitable fuel-air mixture, while with the invention operated Luftstromzerstäuberdüse up to 100 cm ³ / min. Fuel to be promoted. Such a rich fuel-air mixture is not primarily ignitable. In a further embodiment, a venturi device is arranged in the exhaust gas line in the region of an opening of the introduction device. This causes a rapid mixing of the successive partial flows of exhaust gas and vaporized liquid. In a further embodiment of the invention, the burner with the combustion chamber, the exhaust pipe and the introduction device are integrated in a housing and the housing is adapted to the exhaust pipe. Thus, a construction unit is provided which can be attached to various exhaust pipes. In this case, the housing can ideally be designed such that, when used on an internal combustion engine, it is preferably connected to the exhaust gas system near the engine, for example directly behind the exhaust manifold or an exhaust gas turbocharger of the internal combustion engine. can be built. In a further embodiment, the exhaust pipe protrudes with at least one outlet into the exhaust pipe. This ensures a good mixing of the coincident gas streams. For this purpose, the exhaust pipe is preferably concentrically introduced into the exhaust pipe so that the outlet from the exhaust pipe in the flow direction of the process exhaust stream, so for example, the engine exhaust gas flow is arranged. As a result, an increase in the flow rate of the process exhaust gas is achieved, which ensures rapid mixing of the gas mixture of burner exhaust gas and vapor (vaporized evaporation liquid) with the process exhaust gas. As a result, ignition of the gas mixture can be prevented even if the process exhaust gas contains oxygen. In order to further prevent the occurrence of chemical reactions in the area of the initiation, appropriate aids which support this can be provided. Such possible aids are, for example, a plate or a cone, which are arranged in front of the outlet of the exhaust pipe, wherein the cone tip is aligned with the outlet of the exhaust pipe. It is also provided, in addition to or as an alternative to further increasing the flow velocity in the region of the outlet, to provide a flow constriction in the exhaust pipe, for example in the form of a venturi or venturi. In other words, a possible reaction of the treated with evaporating liquid burner exhaust gas to be quenched with the process exhaust gas. In a further development of the invention, a process exhaust gas leading gas conducting device opens into the exhaust pipe. As a result, process exhaust gas is supplied to the burner exhaust gas and the vaporous liquid. Thereby, the burner exhaust gas is controlled cooled (at a supply in the flow direction before the mouth of the introduction), in the form that enough power for evaporation of the evaporating liquid is still provided, but its ignition (if the evaporative liquid is fuel) is prevented. The supply can also take place in the region of the mouth or in the flow direction behind the mouth. By suitable choice of the described auxiliaries, the chemical reactions of the evaporating liquid with the burner exhaust gas and / or the process exhaust gas can be promoted or prevented as may be required. In particular by influencing the Temperature in the region of the introduction device, it is possible to produce by reactions of the evaporative liquid with the burner exhaust gas targeted substances that support desired reactions in the subsequent catalysts. In a further embodiment, the exhaust aftertreatment device comprises a nitrogen oxide selectively catalytically reducing catalyst and / or an oxidation catalyst and / or at least one particle filter. Each of the catalysts or the catalyst particle filter systems can be operated with the evaporation device according to the invention alone or in any desired combination, as will be explained in detail below in connection with the method of operation. The present invention includes an evaporator unit having the property of converting diesel fuel into other (ideally short chain) hydrocarbons, this particular HC mix providing high NOx conversion rates on the downstream SCR catalyst as illustrated in FIG. The constructive embodiments described above are used to implement the following described further embodiment of the invention Betreibungsverfahrens useful. Thus, the burner is operated in a lambda range of 0.75 to 1.75, preferably 1. Furthermore, the burner is designed such that it can be operated in a power range up to 20 kW, preferably up to 15 kW and very preferably up to 5 kW. It is an object of the invention to operate the burner with the lowest possible power, because then in particular the required air conveyor for the supply of (combustion) air can be relatively easily configured. Furthermore, by the inventive method in a general form evaporating liquid (optionally with the direct addition of a subset of process exhaust gas) is evaporated by the burner exhaust gas and passed together with the burner exhaust gas and the total amount of process exhaust gas in the exhaust gas aftertreatment device to cause the provided there SCR reaction. When used in conjunction with internal combustion engines, which are operated with diesel fuel and in which the evaporative liquid is fuel, this is fed together with the burner exhaust gas and the process exhaust via the exhaust pipe an oxidation catalyst and a subsequent particulate filter and in the Oxidized catalyst and / or oxidized in a catalytically coated particulate filter. A particular advantage of this refinement is that the oxidation reaction therefore takes place only in the oxidation catalyst and consequently the temperatures required for regeneration of the particulate filter are only generated here. If, as is the case with the system described in the prior art, the injected fuel would already be ignited at the point of introduction into the exhaust pipe, this would be associated with a higher thermal load on the entire exhaust system and considerable heat losses would have to be compensated by larger fuel quantities become. In the oxidation catalyst, for example, a temperature of up to 650 ° C is generated by the oxidation of the vaporized fuel, which is needed for the regeneration of particulate filters. In a further embodiment of the invention, different vapor liquids, in particular fuel, can be introduced into the exhaust pipe via one or more introduction devices. With only one introduction device, the supply of the evaporative liquid is alternately controlled via a corresponding switching device, while in two existing introduction devices, the switching device is not needed. Also in this case normally takes place an alternate supply of vaporized liquid. This alternating supply can be advantageously used, for example, if the oxidation catalyst is a general-purpose vanadium-containing catalyst in particular, which is also suitable for assisting the selective catalytic reduction of NO x. In this case, the oxidation catalyst is alternately used for different functions. Of course, it is also possible to provide an oxidation catalyst and, separately, a catalytic converter for selective catalytic reduction of NOx. In a further refinement of the method, a partial amount of the fuel quantity introduced and vaporized as evaporating liquid is oxidized with the release of heat within the exhaust gas line and / or the location of the merging with the process exhaust gas. As a result, the total thermal power can be increased so far with a minimum set burner power that a safe commissioning of a catalyst takes place. In order to start its activity, that is to say a catalytic reaction of the For example, if an evaporated fuel had to start, an oxidation catalytic converter must reach a predetermined minimum temperature, for example 300 ° C. This temperature is achieved by summing the burner output and the power generated by the burned subset. In a further embodiment, the oxidized subset of the evaporated fuel quantity is kept at least approximately constant independently of the total amount of fuel evaporated. In this case, it is further envisaged to end the partial conversion after exceeding a limit quantity of the partially converted fuel quantity and to evaporate the total fuel mass as a whole. These different effects are achieved by strictly controlling the combustion air ratio in the burner and / or strictly controlling the amount of atomizing air supplied to the air jet atomizing nozzle in the case of using an air jet atomizing nozzle. Further influencing factors are the location of the attachment of the inlet of the introduction device and the supply of a partial amount of process exhaust gas (for cooling the burner exhaust gas and consequently the evaporative liquid), also taking into account the supply location. An alternative embodiment provides an internal combustion engine with an exhaust gas aftertreatment device, which consists in the flow direction of the exhaust gas of the following components:

Burners having an evaporator device for generating heat and for providing substances, which substances in the subsequent catalysts support desired reactions, from an SCR catalyst for the selective catalytic reduction of nitrogen oxides and optionally an oxidation catalyst and a particle filter or a catalytic converter. lytically coated particulate filter.

The said substances are produced by evaporation of an evaporating liquid. The substances are produced by evaporation and by chemical reactions of the evaporative liquid with the burner exhaust gas and / or the Process exhaust or the exhaust gas of the internal combustion engine (VKM) generated.

The vaporization liquid preferably consists of the same fuel that is also injected with the supply device of the burner. The vaporous liquid is diesel fuel or biodiesel fuel. The generated substances are used in an SCR catalyst for the selective catalytic reduction of nitrogen oxides. The SCR catalytic converter is followed by an oxidation catalytic converter in the flow direction of the exhaust gas.

The oxidation catalyst is followed by a particle filter or a catalytically coated particle filter in the flow direction of the exhaust gas.

If the vaporization liquid is the same fuel that is also injected with the supply device of the burner, it is oxidized in the oxidation catalyst and / or in a catalytically coated particle filter and thus generates the temperatures required for regeneration of the particle filter, preferably in such a way that always a catalytically coated filter is included in the exhaust tract. In an alternative embodiment, an uncoated filter is provided.

Further advantages of the invention are listed below:

- There are high NOx conversion rates can be displayed.

There is no need to provide a second resource. A special HC mix is provided from entrained diesel fuel through the burner / evaporator unit. Burner / evaporator acts as a reformer.

- There is no costly infrastructure (tank, dosing module, pump, heating of the equipment, diagnosis (OBD), etc ..) necessary.

Good miscibility and uniform distribution can be represented.

There is no crystallization in the exhaust system. Further advantageous embodiments of the invention are described in the drawings, in which the embodiment of the invention shown in the figure is described in more detail. 1 shows a burner-A steam generator unit with SCR catalyst

Figure 2 shows the experimental setup for sampling the vaporized

Diesel fuel

FIG. 3 shows the exemplary temperature profile before / after DOC during a thermal regeneration of the DPF

Figure 4 shows the chemical composition of the gas sample at the time of the maximum secondary fuel amount

FIG. 1 shows an internal combustion engine 1 with an exhaust tract 2. In the exhaust tract 2 protrudes a housing 15 in which a burner or an evaporator 3 and a metering device 4 are arranged. The burner and / or the evaporator 3 are preferably operated with the same fuel or evaporator material, in particular diesel fuel. The burner and / or evaporator 3 and the metering device 4 arranged in the flow direction are connected to the control or control unit 5. The fuel supply unit 6, which supplies fuel to both the burner and / or evaporator 3 and the metering device 4, is connected to the control unit 5. The burner and / or evaporator 3 has an air supply unit 7, which is connected to the control or control unit 5. Downstream of the housing 15, an SCR catalytic converter 10 is arranged in the exhaust tract 2. In the flow direction in front of the SCR catalytic converter 10, a pressure or temperature measuring sensor 8 is arranged. A pressure or temperature measuring sensor 9 is installed in the flow direction of the exhaust gas after the SCR catalyst 10. The pressure or temperature measuring sensors 8, 9 are connected to the control or control unit 5. In the flow direction in front of the SCR catalyst 10, an air mass sensor 1 1 is arranged, which is connected to the control or control unit 5. Detailed burner evaporator unit

In order to comply with the emissions legislation from 201 1, the exhaust aftertreatment system (EATS) will consist of either an EGR in combination with DPF and upstream DOC or an SCR system to reduce nitrogen oxides. For the thermal regeneration of the DPF under all environmental and operating conditions, a two-stage burner is provided.

The burner evaporator unit will be described. For the required heat generation in two stages, the system works as follows:

1st stage: Atmospheric diesel burner

2nd stage: diesel evaporator The thermal performance of the first stage is designed so that the DOC's light-off temperature of about 300 ° C, which serves as a catalytic burner for the thermal regeneration of a DPF, in the entire engine map in all environments - and operating conditions is achieved. In the first burner stage, the atmospheric diesel burner is operated stoichiometrically with a turbulent premix flame, the flame stabilization being achieved by means of a swirl flow and a recirculation vortex. The mixture formation takes place with a Luftzerstäuberdüse, which is used at the same time for the swirl generation within the combustion chamber. The design of the atomizer nozzle and the dimensioning of the combustion chamber allow the operation of the diesel burner in a power range of 8 to 15 kW. An electric air pump with speed control provides the required combustion air. To determine the air mass flow, a hot film sensor is used. The air supply to the burner is designed so that on the one hand the ignition components are cooled and on the other hand, a combustion air preheating is realized, which ensures an increase in combustion stability. In contrast to a burner head cooling with cooling water can be achieved in this case that the complete burner power is available for heating the exhaust gas and is not dissipated via the coolant. The fuel is supplied by means of an extended metering module, wherein an additional metering valve is installed for the fuel supply of the first burner stage.

The ignition system of the burner consists of two main components. Centrally to the swirl atomizing nozzle, a glow plug for the evaporation of the fuel is arranged and in the combustion chamber rear wall two spark plugs are installed, which allow a continuous spark ignition. With this configuration, a reliable ignition can be realized even with highly unsteady engine operation and in extreme cold weather conditions down to -25 ° C as well as for biodiesel mixtures up to 30%.

In the second stage diesel fuel is metered into the exhaust gas of the first stage, so that it evaporates in the very hot oxygen-poor exhaust gas, but is hardly oxidized. For this purpose, an evaporator tube is installed directly at the burner outlet, which is dimensioned so that the spray injected sufficient residence time for complete evaporation is available, thus allowing an ideal treatment for the catalytic oxidation. Spray generation is assisted by air to generate the necessary fine droplets. At the exit from the burner's evaporator tube, the burner gas is mixed with the engine exhaust gas and the subsequent oxidation of the vaporized hydrocarbons in the DOC. The metering amount of the second stage serves as a control variable for the regeneration temperature. In the present design, a sufficiently large drop surface and residence time of the droplets in the evaporator tube are available to process about 150 g of diesel fuel per minute. The main advantage of the complete evaporation of the diesel fuel in the second burner stage is that on the one hand vaporized diesel fuel has very good transport properties. In this case, without further application onsaufwand realize very different pipe guide. On the other hand, a homogeneous distribution of hydrocarbons on the catalyst surface is guaranteed. This leads to very low radial temperature gradients in the catalyst, which has a positive effect on the thermo-mechanical loading of the catalyst and thus on the durability.

Gas composition of vaporized diesel fuel

Investigations have shown that the evaporation of diesel fuel in the hot atmosphere of the burner exhaust gas leads to altered chemical properties of the diesel fuel, which must be taken into account by the catalyst technology. Mainly here partial oxidation and short-chain cracking products of the diesel fuel could be found. A completely platinum-free palladium-based coating can achieve a cost reduction in the noble metal loading of the catalyst. An increase in nitrogen dioxide emissions (N ₂ 0), which is known from platinum-containing coatings, has not been found, which allows the use of this technology for indoor and underground use. Based on these findings, a detailed analysis of the vaporized diesel fuel was conducted. For this purpose, during the thermal regeneration of a DPF in engine operation, various gas samples are taken with a gas sampling tube ("gas mouse") by passing the sample gas stream over the gas sampling tube according to FIG. 2 of the FTIR exhaust gas analyzer. For the investigation, a 6.2 l diesel engine (TCD 2012 L06) of the EU HIB exhaust gas level was operated stationary in the partial load range (1650 rpm, 260 Nm). Based on an engine exhaust temperature of 285 ° C, the temperature could be increased to 405 ° C before DOC after connecting the first burner stage. The target temperature of 650 ° C. after DOC could, according to FIG. 3, be achieved by means of three ramp-shaped secondary fuel quantities. The temperature before DOC was kept stable at 405 ° C except for the last sector. Here was during the max. Secondary fuel quantity a temperature decrease of approx. 18 ° C before DOC measured. This is due to the cooling of the burner exhaust gas of the first stage, since a high evaporation enthalpy is required for the evaporation of large quantities of diesel fuel of the second burner stage.

In addition to the FTIR analysis, gas samples were chemically analyzed. By means of gas chromatography it was possible to determine the gas composition in v% [I Γ ¹ ] for the various gas samples produced during regeneration in the liquid gas analysis according to DIN 51 619. Furthermore, in a natural gas analysis according to DIN EN ISO 6974-3 hydrocarbon components, ie exclusively FID relevant components, could be detected in w% [kg kg ^"1 ] .The following table shows the result of the chemical composition of the gas sample at the time of the maximum Secondary fuel quantity is shown, which leads to a target temperature of 650 ° C. before DOC at this operating point From the table in Figure 4 it can be seen that in the vaporized diesel fuel mainly short-chain alkenes (ethene, propene) and alkynes (ethyne) are found The proportion of ethene in the total gas composition is only 0.12 v% [I Γ ¹ ], but this component has a content of 31.5 w% [kg kg ^"1 ] within the detectable hydrocarbons.

reference numeral

1 internal combustion engine

2 exhaust tract

3 burners and / or evaporator

4 metering device

5 control unit

6 fuel supply unit

7 air supply unit

8 pressure or temperature measuring sensor in front of the SCR catalytic converter

9 Pressure or temperature measuring sensor downstream of the SCR catalytic converter

10 SCR catalyst

11 air mass sensor

14 mouth of the introduction device

15 housing

Claims

Internal combustion engine and method for operating the same APPARATUS

1. Internal combustion engine (1), comprising an exhaust gas aftertreatment device in the exhaust tract (2), at least one burner and an evaporation device (3), at least one SCR catalyst (10) for the selective catalytic reduction of nitrogen oxides and / or an oxidation tion catalyst and / or a particulate filter and / or a catalytically coated particulate filter.

2. Internal combustion engine according to claim 1,

characterized in that it comprises at least one air supply unit (7) and / or an air mass sensor (11).

3. internal combustion engine according to claim 1 or 2,

characterized in that it comprises a diesel particulate filter (12) and / or an oxidation catalyst (13).

4. internal combustion engine according to one or more of the preceding claims,

characterized in that the fuel is a gaseous or liquid fuel.

5. Internal combustion engine according to one or more of the preceding claims,

characterized in that the vaporising liquid is a liquid fuel or other liquid.

6. internal combustion engine according to one or more of the preceding claims,

characterized in that the air supply unit (7) is connected to the control device (5) by means of a line for data exchange.

7. internal combustion engine according to one or more of the preceding claims,

characterized in that the air mass sensor (1 1) in the flow direction of the air in front of the air supply unit (7) is arranged.

8. Internal combustion engine according to one or more of the preceding claims,

characterized in that the air mass sensor (11) in the flow direction of the air after the air supply unit (7) is arranged.

9. internal combustion engine according to one or more of the preceding claims,

characterized in that the fuel is a gaseous or liquid fuel.

10. Internal combustion engine according to one or more of the preceding claims,

characterized in that in particular the mouth of the introduction device (14) in the exhaust pipe (2) has a spray nozzle, in particular a Druckzerstäuberdüse or a Luftstromzerstäuberdüse and / or a Venturieinrichtung.

11. internal combustion engine according to one or more of the preceding claims,

characterized in that the burner (3), the exhaust pipe (2) and the metering device (4) are integrated in a housing (15) and the housing (1) is adapted to the exhaust pipe (2).

12. A method for operating an internal combustion engine, characterized in that a device according to one or more of the preceding claims is used.