CH716216A1 - System for injecting a liquid into a pipe. - Google Patents

Abstract

The invention relates to a system for injecting a liquid into a line, preferably for injecting a liquid reducing agent into an exhaust line of an internal combustion engine, the system comprising a gas pump (11), a liquid pump (21), an injector (50), one of the liquid pump liquid line (40) leading to the injector and a gas line (10) leading from the gas pump to the injector, a controllable shut-off valve (25) being arranged in the liquid line or within the injector to synchronize a liquid flow to the injector or through the injector to be able to release and block, and / or wherein the injector has a central liquid outlet opening for delivering a liquid jet into the line, which is surrounded by a ring formed by one or more gas outlet openings, the one or more gas outlet openings being designed, a conical to the Axis of the liquid to form the tapering gas curtain.

Description

The invention relates to a system for the functional injection of a liquid into a line, preferably for injecting a liquid reducing agent into an exhaust line of an internal combustion engine.

When injecting a liquid reducing agent into an exhaust line of an internal combustion engine, the technical challenge is the conditioning of the liquid or the reducing agent with the aim that this is present in the line in the smallest possible droplet size and homogeneously over the shortest possible distance over the flow cross-section is distributed and the deposition of droplets is ideally completely avoided.

For the reduction of nitrogen oxides in exhaust gases from internal combustion engines, the technique of selective catalytic reduction (SCR) has become known, with a liquid urea solution being injected into the exhaust gas flow as a reducing agent. This technology has been widespread in road vehicles for many years, especially in heavy commercial vehicles and also in the non-road sector, e.g. B. in use in mobile machines.

Internal combustion engines for mobile work machines and devices not intended for road traffic, which have been produced since 01.01.2019, must meet Regulation (EU) 2016/1628 of the European Parliament and of the Council in their scope. As a result, off-road diesel engines whose mechanical output power is greater than 560 kW now also have to comply with certain exhaust gas limit values; i.a. for nitrogen oxides, better known as NOx. Therefore, there is now a need for devices with which higher quantities of reducing agent can be fed into the exhaust gas aftertreatment in a functional manner. Conventional injection systems cannot provide the significantly larger reducing agent injection quantities of around 30 kg urea solution per hour, which are often required for the particularly large - to be more precise, the particularly powerful - diesel engines, which are now also subject to exhaust gas legislation. This is because scaling the existing systems does not lead to a functional reducing agent injection. For this reason, several injection systems with separate reducing agent injectors are currently used in parallel for the exhaust gas aftertreatment of a correspondingly powerful diesel engine. However, this is not only disadvantageous for reasons of cost, but also leads to non-optimal placement of injection points, at least for an injector, increased maintenance effort and increased susceptibility to errors.

The object of the invention is to provide a robust generic system which is suitable to be able to properly inject the correspondingly high amounts of reducing agent for the exhaust gas treatment, as is the case for today's correspondingly powerful diesel engines.

Against this background, the invention relates to a system for the functional injection of a liquid into a line, preferably for injecting a liquid reducing agent into an exhaust line of an internal combustion engine, the system being a gas pump, a liquid pump, an injector, one of the liquid pump to the injector has leading liquid line and a gas line leading from the gas pump to the injector. According to the invention it is provided that a controllable shut-off valve is arranged in the liquid line or within the injector in order to be able to release and block a liquid flow to the injector or through the injector in time, and / or that the injector has a central liquid outlet opening for dispensing a liquid jet has the line which is surrounded by a ring formed by one or more gas outlet openings, wherein the one or more gas outlet openings are designed to form a gas curtain tapering conically towards the axis of the liquid jet.

The gas curtain is preferably formed from several individual gas jets which emerge from individual punctual gas outlet openings of the injector. Alternatively, an annular outlet slot can be provided. It is preferred that all jets or segments of the gas curtain converge at the same point on the axis of the liquid jet.

The check valve can be designed so that it is closed when there is no activation and is only opened or remains open by activation. Alternatively, the shut-off valve can be designed in such a way that it is open when there is no activation and is only closed or remains closed by activation. Such a shut-off valve is preferably used, which changes between the two open and closed states as quickly as possible. In an idealized view, which neglects the transition states between the closing and opening of the shut-off valve and the short-term transient reducing agent volume flows, which are caused by this and the interruption of the injection, the time curve of the injected reducing agent volume flow resembles a so-called pulse width Modulated signal, better known as PWM signal in its abbreviation.

If, for example, half of the maximum possible reducing agent supply is required, the shut-off valve is opened to 50% of a cycle and the shut-off valve is closed during the remaining 50% of the cycle - for better understanding of the text, neglecting the transition states. There is one opening and one closing operation of the shut-off valve per cycle. Exceptions only exist if there is no reducing agent at all or the maximum reducing agent supply is available. As long as the first-mentioned case is present, the shut-off valve clearly remains permanently closed; in the second case permanently open.

The controllable shut-off valve is preferably an electrically controlled lifting armature valve, an electronic control or regulation being preferably used. Such a control or regulation is carried out taking into account certain operating parameters, e.g. the exhaust gas temperature, the speed-torque operating point of the internal combustion engine, etc., as well as other parameters that can be present, for example, as application-specific fixed values.

In one embodiment, the system has a pressure relief line which is branched off from the liquid line between the liquid pump and the shut-off valve, wherein a pressure relief valve is arranged in the pressure relief line which is designed to open when a threshold pressure is reached in the liquid line and to allow the drainage of liquid from the liquid line through the overpressure line. The system can have a liquid reservoir which is connected to the liquid pump on the suction side and into which the overpressure line preferably leads.

The liquid pump and the gas pump can be driven by a common motor. The two pumps can for example be arranged on the same shaft. The motor is preferably an electric motor, for example a brushless direct current motor.

[0013] The angle of incidence of the conically tapering gas curtain can be between 25-60 °, preferably between 30-50 ° and more preferably between 35-45 °. The ring formed by the one or more gas outlet openings is preferably a circular ring. The angle of incidence is preferably identical at all angular positions of the circular ring.

In one embodiment, the liquid outlet openings and the gas outlet openings on the one hand and the liquid pump and the gas pump on the other hand are designed relative to one another so that the flow rate of the atomizer gas through the gas outlet opening or the gas outlet openings is greater than the flow rate of the liquid through the liquid outlet opening. The ratio is 10: 1 to 25: 1, more preferably 15: 1 to 22: 1 and in particular 17: 1 to 20: 1. The pumps and their drive motors are preferably optimized for their respective stationary operating point. The two pumps are particularly preferably coordinated with one another in such a way that they can be driven jointly by the same motor. If the latter is implemented, the shared motor is optimized for its stationary operating point.

Exemplary opening dimensions and pump designs and the ultimately fixed operating points of the pumps can be such that the flow rate of the liquid through the liquid outlet opening is between 5-15 m / s, preferably 7-10 m / s and more preferably between 8-9 m / s and / or that the flow velocity of the gas through the gas outlet opening or the gas outlet openings is between 100-200 m / s, preferably 150-200 m / s and more preferably between 160-180 m / s. The values refer to the mean value of the speed distribution.

The injector can have at least six and preferably at least eight gas outlet openings. The gas outlet openings can be distributed equally spaced on the ring formed by them. The point of convergence of the conically tapering gas curtain can be located at a distance of 0.5-10 mm, preferably 1-5 mm and more preferably 1.5-2.5 mm from the liquid outlet opening.

The design parameters described have proven to be optimal in tests for effective atomization with the above-mentioned comparatively large amounts of liquid to be injected. In the context of the system according to the invention, optimal atomization should meet the following criteria. (1) The liquid introduced may only be present in small droplets. The maximum size of these droplets should not exceed approx. 30 µm (SMD). (2) The liquid introduced must have as homogeneous a distribution as possible over the flow cross-section after a short run. (3) Reality must correspond as closely as possible to the idealization that not even the smallest amounts of the liquid introduced should settle and form deposits.

In one embodiment it can be provided that the drilling depths of the gas outlet openings in the range of between 0.5-5 mm, preferably in the range of between 0.5-3 mm and more preferably in the range of between 1-2.5 mm lie. In the design described, this represents a good compromise between the lowest possible pressure loss on the one hand and the best possible jet formation on the other.

Against the background mentioned at the beginning, the invention also relates to a mobile work machine with an internal combustion engine and an exhaust pipe leading away from the internal combustion engine, an injection system according to the invention being arranged on the exhaust pipe in order to functionally supply a liquid reducing agent, preferably a urea solution from a suitably filled tank injected into the exhaust pipe. The internal combustion engine can be a diesel engine with a displacement of, for example, greater than 15, greater than 20 or even greater than 25 liters.

The invention further relates to a method for operating an injection system according to the invention or a mobile work machine according to the invention, the system being operated with constant operation of both pumps by a clocked control of the shut-off valve so that liquid is pulsed through the liquid outlet opening.

[0021] The timing is preferably constant. In one embodiment, the clocking frequency can be between 0.5-5 Hz, preferably between 2-4 Hz and more preferably between 2.5-3.5 Hz.

[0022] The injected liquid is preferably a liquid reducing agent, for example a urea solution. The nebulizer gas is preferably air.

The operation of the pumps and the design of the connections and outlet openings are preferably coordinated with one another so that the flow speeds or speed ratios of gas and liquid mentioned above in connection with the description of the system according to the invention are achieved during an injection phase.

Suitable absolute pressures of the liquid before exiting the injector can be between 1.2-3 bar, preferably between 1.3-2 bar and more preferably between 1.4-1.6 bar. The delivery rate of the liquid during an injection phase can be greater than 20 kg / h, preferably greater than 25 kg / h and more preferably about 30 kg / h or more. Delivery rates for the atomizer gas can be 1-6 kg / h, preferably 2-5 kg / h, and more preferably 2.5-4 kg / h, in particular based on a liquid delivery rate of about 30 kg / h. The resulting average droplet size should be a maximum of 30 µm (SMD).

As mentioned, the fundamentally new approach of the system according to the invention is that - apart from the transition states, i.e. the start of an injection and the termination of an injection - the injector is always operated at a single operating point. Of course, an injector optimized for this operating point is preferably used. A transient phase of a reducing agent injection is present during the transition states. However, these transient processes are reproducible when the shut-off valve is opened. The same applies when the shut-off valve is closed. As explained in detail above, the adaptation to the respective instantaneous reducing agent requirement is achieved via a discontinuous, pulsed reducing agent supply.

In the previously known systems, however, there is an injection quantity that is continuously adapted to the requirement. As a result, a sufficiently good mixture formation must always be achieved over the entire bandwidth, starting from the smallest injection quantities up to the maximum quantity. And precisely this disadvantage is avoided by the system according to the invention and the method according to the invention.

Further details and advantages of the invention emerge from the exemplary embodiment described below with reference to the figures. In the figures show: <tb> <SEP> FIG. 1: a schematic representation of the principle of selective catalytic reduction; <tb> <SEP> FIG. 2: a circuit diagram of an embodiment of an injection system according to the invention; <tb> <SEP> FIG. 3: a sectional view through the injector of an embodiment of an injection system according to the invention; and <tb> <SEP> FIG. 4: a schematic representation of the liquid atomization which occurs as a result of the injection via an injector as shown in FIG.

FIG. 1 shows a schematic representation of the principle of selective catalytic reduction.

An exhaust pipe 101 extends from the internal combustion engine 100 to a catalytic converter 102. Here, the exhaust gases from the internal combustion engine 100 reach the catalytic converter 102 by means of the exhaust gas line 101. So that the catalytic converter 102 can effectively reduce the nitrogen oxides contained in the exhaust gas An additive in the form of finely atomized reducing agent 103 is added to the exhaust gas. For this purpose, an injection system E is located on exhaust line 101, which includes an injector 50, via which a reducing agent can be fed into exhaust line 101 between internal combustion engine 100 and catalytic converter 102 in exhaust line 101. The injector 50 is connected to a tank 22 by means of a reducing agent supply line 20 and to an air-sucking compressor 11 by means of an atomizing air line 10. With the aid of device E, reducing agent can be finely atomized and injected into the exhaust gas flow of exhaust gas line 101. The reducing agent 103 is mixed with the exhaust gas flow so that the nitrogen oxides in the exhaust gas can be effectively reduced in the catalytic converter 102.

Figure 2 shows a circuit diagram of an embodiment of an injection system E according to the invention. The system has an air pump 11 (a compressor) arranged on an atomizing air line 10 and a reducing agent pump 21 arranged on a reducing agent line 20, which are based on a common motor 30 via the common Axis 31 can be operated. The motor 30 is a brushless DC motor.

The lines 10 and 20 lead from an air intake opening 12 or a reduction tank 22 provided with an air filter 13 to an injector 50 which will be described in more detail below. The injector 50 opens into the exhaust pipe 101 of an internal combustion engine.

With reference to the circuit diagram, a controllable shut-off valve 25 in the form of a plunger valve is arranged in the reducing agent line 20 between the reducing agent pump 21 and the injector 50. In a real implementation, the shut-off valve is located significantly closer to the reducing agent outlet opening 52 with regard to the flow path length. Depending on the system design, the shut-off valve 25 can be located in the injector 50. However, a certain distance or other measures are necessary so that the shut-off valve 25 is not overheated by the hot exhaust gas. A pressure accumulator 26 for reducing agent and a pressure sensor 27 are also located on the reducing agent line 20 between the reducing agent pump 21 and the check valve 25, but this is only optional and not necessary. In accordance with the general convention of a circuit diagram, the arrangement shown, the branching of the pressure accumulator 26, the branching of the pressure sensor 27 and the shut-off valve in relation to the direction of supply of the reducing agent from the reducing agent pump 21 to the injector 50 merely depicts the sequence.

Between the reducing agent pump 21 and the blocking valve 25, an overpressure line 40 branches off from the reducing agent line 20 and opens into the reducing agent reservoir 22 or into the suction area of the reducing agent pump 21. An overpressure valve 41 is arranged in the overpressure line 40 and is designed to release the overpressure line 40 as soon as the reducing agent reaches a pressure level in the line path between the reducing agent pump 21, shutoff valve 25 and overpressure valve 41 which exceeds a threshold value. This is typically the case when the shut-off valve 25 remains closed for a certain period of time during operation and the reducing agent pump 21 continues to be operated as intended. Such behavior is present as desired when the SCR device E only requires a low reducing agent feed rate. In such a situation, the shut-off valve 25 is in shut-off mode for a much longer period of time and only for a very short period of time in the open state, whereas the reducing agent pump 21 operates at the same delivery rate as in the case of the maximum reducing agent requirement.

In the atomizer air line 10, a memory 16 for compressed air is provided, which is also only optional and would not be necessary.

Figure 3 shows sectional views through the injector 50 of the system shown in Figure 2, once as an overview (left) and once enlarged (right).

On the one hand, the injector 50 has a central outlet opening 52 for emitting a reducing agent jet, which is connected to the reducing agent line 20. In addition, the injector 50 has an annular space 53 arranged around the reducing agent line 20 or the reducing agent outlet opening 52, which is connected to the atomizing air line 10 and ends at a cone-shaped orifice 54 with a row of air outlet openings 51 distributed in a circle around the reducing agent outlet opening 52. The aperture 54 is shaped such that the axes of the air outlet openings 51 are at a certain angle of incidence α to the axis of the reducing agent outlet opening 52, as will be explained in more detail in the discussion of FIG. 4 below.

Finally, FIG. 4 shows a schematic representation of the atomization of liquid by an injector 50 as shown in FIG. 3. The round viewing window is not a cross-sectional view through the exhaust pipe 101, but the representation is a longitudinal section based on the direction of exit of the Reducing agent from the injector 50, that is to say ultimately a view from the same perspective as in FIG. 3.

In this illustration it is easy to see how the compressed air jets 151 exiting the air outlet openings with the angle of incidence α of 40 °, for example, conically approach the reducing agent jet 152 emerging from the reducing agent outlet opening 51 and impinge on it at an atomization point Z. The reducing agent jet 152 is thus atomized into small droplets, which have a maximum size of 30 µm (SMD), and the finely atomized reducing agent 103 is distributed homogeneously over the flow cross-section after a short distance of the exhaust pipe 101. In addition, the accumulation of reducing agent in the exhaust gas path , ie largely avoided in the exhaust line 101 and the components of the exhaust gas aftertreatment system. The distance L between the atomization point Z, corresponding to the point of convergence of the conically tapering reducing agent jets 152 and the reducing agent outlet opening 52 can be, for example, 2 mm.

With the aid of the system according to the invention, a sufficient amount of urea solution can be injected into the exhaust pipe in a robust manner in a robust manner in the case of large systems. Due to the good mixture formation and the small droplet diameter, the system can and can also be used at low exhaust gas temperatures of around 160 ° C, for example. It is known to the person skilled in the art that injection of reducing agent at temperatures that are too low leads to deposits, so-called deposits, of the reducing agent, which must be avoided at all costs. An expensive sensor for measuring the reducing agent pressure can be dispensed with. As is known to those skilled in the art, a suitable sensor for this is particularly expensive because it must be designed in such a way that the sensor is not destroyed by the freezing of the reducing agent, because an aqueous urea solution that freezes at -11 ° C is typically used as the reducing agent. The design of the pumps and, above all, the condition of the injector can be optimized to a stationary value and the system can react very quickly to changes in the setpoint value in the reducing agent dosage.

Claims (13)

1. System for injecting a liquid into a line, preferably for injecting a liquid reducing agent into an exhaust line of an internal combustion engine, the system comprising a gas pump, a liquid pump, an injector, a liquid line leading from the liquid pump to the injector and one from the gas pump to the injector has leading gas line, characterized, that a controllable shut-off valve is arranged in the liquid line or within the injector in order to be able to release and block a liquid flow to the injector or through the injector in rhythm, and / or that the injector has a central liquid outlet opening for the discharge of a liquid jet into the line, which is surrounded by a ring formed by one or more gas outlet openings, wherein the one or more gas outlet openings are designed to form a gas curtain that tapers conically towards the axis of the liquid jet. 2. System according to claim 1, characterized in that the system has an overpressure line which branches off from the liquid line between the liquid pump and the shut-off valve, wherein a pressure relief valve is arranged in the overpressure line which is designed to open when a threshold pressure is reached in the liquid line to open and to allow the drainage of liquid from the liquid line through the overpressure line. 3. System according to one of the preceding claims, characterized in that the liquid pump and the gas pump are driven by a common motor. 4. System according to one of the preceding claims, characterized in that the angle of incidence of the conically tapering gas curtain is between 25-60 °, preferably between 30-50 ° and more preferably between 35-45 °. 5. System according to one of the preceding claims, characterized in that the liquid outlet openings and the gas outlet openings on the one hand and the liquid pump and the gas pump on the other hand are designed relative to one another in such a way that the flow rate of the atomizer gas through the gas outlet opening or the gas outlet openings is greater than the flow rate of the liquid through the liquid outlet opening is preferably 10 to 25 times as large, more preferably 15 to 22 times as large and in particular 17 to 20 times as large. 6. System according to one of the preceding claims, characterized in that the injector has at least six and preferably at least eight gas outlet openings and / or that the gas outlet openings are equally spaced on the ring formed by them. 7. System according to one of the preceding claims, characterized in that the convergence point of the conically tapering gas curtain is at a distance of 0.5-10 mm, preferably 1-5 mm and more preferably 1.5-2.5 mm from the liquid outlet opening is located. 8. Mobile work machine with an internal combustion engine and an exhaust pipe leading away from the internal combustion engine, characterized, that a system according to one of the preceding claims is arranged on the exhaust pipe in order to inject a liquid reducing agent, preferably a urea solution, from a correspondingly filled tank into the exhaust pipe. 9. The method for operating a system according to one of claims 1-7 or a mobile work machine according to claim 8, characterized, that the system is operated with constant operation of both pumps by a clocked control of the shut-off valve in such a way that liquid is released in a pulsed manner through the liquid outlet opening. 10. The method according to claim 9, characterized in that the pulse widths can be changed by a corresponding control of the shut-off valve, preferably by an electrical control of the shut-off valve. 11. The method according to claim 10, characterized in that the pulse widths can be determined by a regulation or control, the determination taking into account certain operating parameters e.g. the exhaust gas temperature, the speed-torque operating point of the internal combustion engine, etc., as well as other parameters that can be present as application-specific fixed values, for example. 12. The method according to claim 10 or 11, characterized in that the pulse width, i. E. the length of time in which a liquid reducing agent is dispensed via the liquid outlet opening or the length of time in which the shut-off valve is open, the greater the higher the setpoint delivery rate of the liquid reducing agent. 13. The method according to any one of claims 9 to 12, characterized in that the injected liquid is a liquid reducing agent, preferably a urea solution, and / or that the atomizer gas is air.