GENERATING NITROGEN DIOXIDE FOR USE WITH BURNER-BASED EXHAUST GAS REPLICATION SYSTEM

Abstract

Method for using a burner-based exhaust gas replication system (100) to generate exhaust gas containing nitrogen dioxide (NO2), comprising: Selecting a fluid that decomposes to form NO2 as one of its decomposition products; Heating the fluid and thereby generating NO2 the extent and duration of the heating are controlled in such a way as to achieve a desired degree of decomposition of NO2; Feeding NO2 into an exhaust stream of the test system (100); and Measuring the fluid before the heating step or measuring the NO2 supplied to the exhaust gas stream to provide a desired amount of NO2 in the exhaust gas stream; wherein a reservoir (21) is provided which contains the fluid that generates NO2, wherein the NO2 generating fluid is injected directly into a combustion zone of the burner (112).

Description

TECHNICAL AREA OF INVENTION

[0001] This invention relates to exhaust gas replication systems, such as systems for testing motor vehicle exhaust aftertreatment devices, and in particular to the generation of nitrogen dioxide for introduction into the exhaust gas stream generated by such systems. BACKGROUND OF THE INVENTION

[0002] In modern motor vehicles, exhaust aftertreatment systems remove potentially harmful gases and particles from engine exhaust. Examples include catalytic converters commonly found in gasoline-powered vehicles, as well as diesel oxidation catalysts, diesel particulate filters, and catalysts for selective catalytic reduction.

[0003] The desire for reduced vehicle emissions has led to a need for test systems that can quickly and cost-effectively evaluate and age exhaust aftertreatment systems. This allows for testing of both performance and durability.

[0004] Traditionally, exhaust aftertreatment systems were tested on engine test benches. However, burner-based systems are also used. One example of a burner-based system is the Exhaust Component Transient Operation Laboratory (ECTOLab™) developed by the Southwest Research Institute.

[0005] To test the various exhaust aftertreatment systems currently used for motor-driven vehicles, a burner-based test system must be able to replicate the exhaust gases produced by the engines. Two pollutants of interest are NO (nitrogen oxides) and NO₂ (nitrogen dioxide). Methods exist for the in-situ generation of NO by burning nitromethane / nitroethane, but a method for generating NO₂ is needed. In this context, JP H09-94437A, WO 2014 / 202509A1, CN 102095587A, and US 2008 / 0236134A1 represent the state of the art. BRIEF DESCRIPTION OF THE FIGURES

[0006] A more comprehensive understanding of the present embodiments and their advantages can be obtained by referring to the following description in conjunction with the accompanying figures, in which corresponding reference numbers indicate corresponding features, and wherein: Fig. 1 represents a burner-based test system for testing motor vehicle exhaust aftertreatment systems with an NO2 generation system according to the invention. Fig. 2 a first embodiment of a NO2 generation system for generating NO2 in the exhaust gas stream of the test system made of Fig. 1 represents. Fig. 3 a second embodiment of an NO2 generation system for generating NO2 in an exhaust gas stream of the test system Fig. 1 represents. Fig. 4 a variation of the NO2 production system from Fig. 3 represents. Fig. 5 and Fig. 6. Show how the NO2 production system consists of Fig. 4 can be used to control NO2 production by varying the flow rates of N2 and HNO3 into the decomposition reactor. Fig. Figure 7 illustrates how the NO2 production system consists of Fig. 4 can be used to control NO2 production by varying the residence time of HNO3 in the decomposition reactor. Fig. 8 that from the NO2 production system Fig. 4. The generated NO2:NOX ratio is represented as a function of the residence time within the decomposition reactor. DETAILED DESCRIPTION OF THE INVENTION

[0007] The following description refers to a method for simulating automotive exhaust gases in a burner-based test system. The method generates NO2 (nitrogen dioxide), a gaseous air pollutant composed of nitrogen and oxygen, and one of a group of related gases called nitrogen oxides or NOx.

[0008] This method enables the precise generation and control of NO2 in a burner-based test system. This allows the test system to generate a desired NO2:NOx ratio in its exhaust stream. Typically, the method is used to generate NO2 for testing automotive aftertreatment systems, but it could be used for any exhaust replication system where NO2 is required as a component to simulate engine exhaust.

[0009] For illustrative purposes, the NO2 generation procedure is described in connection with its use with a burner-based ECTO-Lab test system. As described in the background, the ECTO-Lab test system is used for aftertreatment testing and can accommodate full-size catalysts from light gasoline engines to large, heavy diesel and natural gas engines. It is a multi-fuel, burner-based system designed to replicate the exhaust conditions produced by internal combustion engines. The ECTO-Lab system can simulate lean and stoichiometric exhaust conditions using gasoline, diesel, natural gas, or propane fuels. It meets the testing requirements for a wide range of full-size aftertreatment catalysts and equipment.

[0010] However, the invention can be used with any burner-based automotive test system that requires nitrogen dioxide in its exhaust stream.

[0011] Fig. Figure 1 shows a burner-based test system suitable for use with the present invention. System 100 is designed to simulate engine exhaust gases with respect to temperature and flow rate. As described below, System 100 has a NO2 generation system 30 capable of providing a desired amount of NO2 in the exhaust gas stream.

[0012] As mentioned in the background, one example of such a system is the ECTO-Lab™ system, developed by the Southwest Research Institute. Exhaust gas conditions are generated by computer control, allowing for various combinations of flow rate, temperature, and concentrations of exhaust gas components.

[0013] A burner 112 combusts a hydrocarbon fuel, such as gasoline or natural gas, thereby producing an exhaust stream. A wide range of air-fuel ratios can be used. A blower 111 is used to generate the desired airflow into the burner 112.

[0014] A heat exchanger 113 enables the control of the exhaust gas temperature supplied by system 100. A typical range of outlet temperatures for system 100 is between 400 and 1200 degrees Celsius.

[0015] An exhaust pipe 119 directs the exhaust gases to an exhaust aftertreatment unit 120, which is being tested. An oil injector allows oil to be injected into the exhaust pipe 119.

[0016] This feature of System 100 is important for the aging of various exhaust aftertreatment systems. A secondary air injector makes it possible to inject a specific amount of fresh air into the exhaust pipe 119.

[0017] In this example, device 120 is a catalyst for selective catalytic reduction (SCR). Testing the SCR catalyst is of particular interest because a desired NO2:NOx ratio must be achieved at the front of the catalyst to simulate its use in a vehicle.

[0018] A Controller 130 allows the System 100 to implement programmable aging cycles. Parameters that influence the exhaust gas flow and content, such as exhaust gas temperature, flow rate, air-fuel ratio, secondary air and oil injection, can be varied. Although in Fig. Not shown in Figure 1, System 100 has suitable valves, injectors, and other mechanisms to achieve these controls. Inlet lines for oil injection and secondary air injection are located in Fig. 1 shown, although they are not necessarily used for NO2 production purposes.

[0019] Controller 130 can include the various control functions described below, or these functions can be implemented with separate controllers.

[0020] Most System 100 units have a modular design that allows components to be added to the base burner and heat exchanger. The System 100 can be modified as needed to simulate stoichiometric or lean-burn multi-fuel engines and to fully replicate transient exhaust trails.

[0021] Fig. Figure 2 shows a first embodiment of a NO2 generation system for generating NO2 in an exhaust gas stream of the test system 100. In this embodiment, NO2 is produced by combustion in the burner 112.

[0022] Reservoir 21 contains a fluid that produces NO2 when burned. Using measuring instrument 25, a desired quantity of this fluid is measured into burner 112, where it burns together with the "normal" burner fuel. The NO2-producing fluid can be injected directly into the combustion zone of the burner.

[0023] Nitric acid is an example of an NO2-generating fluid. Nitric acid (HNO3) is known to decompose thermally or through exposure to light according to the equation 4HNO3 → 2H2O + 4NO2 + O2. Nitric acid can be used in aqueous form to reduce any potential corrosive effects on equipment and personnel.

[0024] The extent of decomposition and the decomposition products may require precise temperature and O2 control, both of which can be integrated into a closed-loop control scheme of System 100.

[0025] Fig. Figure 3 represents a non-claimed example of an NO2 generation system 30 for generating NO2 in an exhaust gas stream from test system 100. In this method, NO2 is generated outside of system 100 and introduced into the exhaust gas stream of system 100, directly into the exhaust gas line 119.

[0026] A reservoir 27 stores an NO2-producing fluid, such as nitric acid. The NO2-producing fluid is fed into a decomposition reactor 28, where it is heated to a desired temperature for a desired duration to produce NO2. To increase the reaction rate, a decomposition catalyst can be used in the reactor 28. Additionally or alternatively, an inert surface promoter, such as Raschig rings made of glass or ceramic, can be used.

[0027] A controller 29 has a measuring instrument, such as a mass flow meter, to measure the flow of gaseous NO2 into the exhaust line 119 of system 100. The controller 29 can be installed on either side of the reactor 28. The controller 29 also regulates the temperature of the reactor 28. The residence time of the NO2-generating fluid in the reactor 28 can be controlled by measuring the flow rate into the reactor 28 as described below.

[0028] The NO2 injection point can be located anywhere downstream of the burner 112 and upstream of the aftertreatment unit 120. Typically, the injection point is located a sufficient distance upstream of the unit 120 to ensure mixing and thus the uniformity of the NO2 in the exhaust gas mixture. If desired, the line 29a, which carries the NO2 to the exhaust gas line 119, can be heated.

[0029] Fig. Figure 4 represents a non-claims example of the NO2 production system, which is a variation of the system of Fig. 3. In system 400, HNO3 and nitrogen (N2) are stored in corresponding reservoirs 41 and 42. The N2 is used as a carrier gas to achieve uniform and repeatable NO2 formation in the decomposition reactor 45.

[0030] Carrier gases other than nitrogen can be used, such as ambient air or carbon dioxide. Other suitable carrier gases include all non-radioactive noble gases such as helium, neon, argon, krypton, and xenon.

[0031] Both fluids have associated measuring instruments, such as mass flow meters, 41a and 42a, which measure the respective fluids flowing into the decomposition reactor 45. The reactor 45 includes a heater and possibly a reduction catalyst and surface promoter. As with system 30, a controller 49 regulates the temperature of reactor 45. It also controls the measuring instruments 41a and 41b to regulate the residence time of HNO3 and N2 in the reactor.

[0032] Fig. Figure 5 shows how the system 400 can be used to control NO2 production by varying the flow rates of N2 and HNO3 into reactor 45. Using measuring instruments 41a and 42b, the individual flow rates can be varied. In an example experiment, the sum of the HNO3 and N2 flow rates was kept at a constant value of 36.0 l / min, and the individual flow rates were varied. The decomposition reactor 45 was maintained at a temperature of 550 °C. Under these conditions, all the nitric acid is decomposed. The flow rate of HNO3 can be varied to obtain a desired NO2 concentration or NO2:NOx ratio.

[0033] Fig. Figure 6 shows how the decomposition is affected by lower temperatures in decomposition reactor 45. In the example experiment from Fig. 6. The decomposition reactor 45 was cooled to 400 °C. As in Fig. In step 5, a constant total flow rate of HNO3 and N2 was maintained at 36.0 l / min, and the HNO3 and N2 flow rates were varied individually. By lowering the temperature of decomposition reactor 45, the NO2:NOx ratio can be increased to a value of >95%. The NO2 and NO+NO2 plots overlap. At lower temperatures, the NO2:NOx ratio has a wider control range in the exhaust gas stream, even though nitric acid also enters the exhaust gas stream.

[0034] Fig. Figure 7 illustrates how the decomposition is influenced by the residence time of HNO3 in decomposition reactor 45. In this example experiment, the flow rate of HNO3 was kept constant at 30.2 g / min, and the N2 flow rate was progressively increased. Decomposition reactor 45 was maintained at 550 °C. By increasing the N2 flow rate in this way, the residence time of HNO3 in decomposition reactor 45 was progressively reduced, and the effect on the NO2:NOx ratio was quantified.

[0035] Fig. 8 represents the NO2 production system Fig. Figure 4 shows the NO2:NOx ratio generated as a function of the residence time in decomposition reactor 45. These data show that increasing the residence time of HNO3 within decomposition reactor 45 leads to a decreased NO2:NOx ratio when the decomposition reactor was kept at 550 °C.

[0036] The data described above show that a suitable decomposition reactor temperature and HNO3 residence time must be selected if a high NO2:NOx ratio is to be achieved while simultaneously reducing HNO3 breakthrough.

[0037] The decomposition of nitric acid to NO₂ and its other products can be complete (100% conversion) even at low temperatures, such as as low as 200 °C and 1 atm. If the nitric acid is given sufficient time to decompose, complete decomposition can occur at even low temperatures, such as as low as 120 °C.

[0038] Using the methods described above, the test system is capable of achieving a desired NO2:NOx ratio at the upstream end of an exhaust aftertreatment system, such as an SCR catalyst. No oxidation catalyst is required. An example of a suitable NO2:NOx ratio for testing an SCR catalyst is 0.5.

[0039] Further embodiments are described below to facilitate understanding of the invention: Embodiment 1. Method for using a burner-based exhaust gas replication system to generate exhaust gas containing nitrogen dioxide (NO2), comprising: Selecting a fluid that decomposes to form NO2 as one of its decomposition products; Heating the fluid and thereby generating NO2; the extent and duration of the heating are controlled in such a way as to achieve a desired degree of decomposition of NO2; Feeding the NO2 into an exhaust stream of the test system; and Measuring the fluid before the heating step, or measuring the NO2 supplied to the exhaust gas stream in order to supply a desired amount of NO2 to the exhaust gas stream. Embodiment 2. Method of embodiment 1, wherein the fluid is nitric acid. Embodiment 3. Method of embodiment 1, wherein the heating step is carried out in a decomposition reactor with a reduction catalyst. Embodiment 4. Method of embodiment 1, wherein the feeding step is carried out using a heated line. Embodiment 5. Method of embodiment 1, wherein the desired amount of NO2 is a proportion of an NO2:NOx ratio. Embodiment 6. Method of embodiment 1, further comprising the use of nitrogen as a carrier gas for the fluid. Embodiment 7. Improved burner-based exhaust gas replication system, wherein the exhaust gas replication system has an exhaust duct that carries an exhaust gas stream as a product of the test system, wherein the improvements include: a decomposition reactor that is operational to receive a fluid that decomposes to produce NO2 as one of its decomposition products and to heat the fluid and thereby produce NO2; a controller that can be operated in such a way that the amount and duration of heating can be controlled to achieve a desired degree of NO2 decomposition; a line for supplying the NO2 from the decomposition reactor into the exhaust gas stream of the test system; and a measuring instrument upstream or downstream of the decomposition reactor that can be operated in such a way that a desired amount of NO2 is introduced into the exhaust gas stream. Embodiment 8. Test system of embodiment 7, wherein an exhaust aftertreatment device is installed on the exhaust line for testing, and wherein the line supplies the NO2 upstream of the exhaust aftertreatment device. Embodiment 9. Test system of embodiment 7, wherein the measuring instrument is located upstream of the decomposition reactor, and wherein the controller regulates the duration of the heating by controlling the measuring instrument and thereby the residence time of the fluid in the decomposition reactor. Embodiment 10. Test system of embodiment 7, wherein the fluid is nitric acid. Embodiment 11. Test system of embodiment 7, wherein the decomposition reactor has a reduction catalyst. Embodiment 12. Test system of embodiment 7, wherein the line is heated. Embodiment 13. Test system of embodiment 7, wherein the desired NO2 quantity is a proportion of an NO2:NOx ratio. Embodiment 14. Test system of embodiment 7, wherein the decomposition reactor is further capable of acquiring nitrogen as a carrier gas for the fluid.

Claims

[1] Method for using a burner-based exhaust gas replication system (100) to produce exhaust gas containing nitrogen dioxide (NO2), comprising: Selecting a fluid that decomposes to form NO2 as one of its decomposition products; Heating the fluid and thereby generating NO2 the extent and duration of the heating are controlled in such a way as to achieve a desired degree of decomposition of NO2; Feeding NO2 into an exhaust stream of the test system (100); and Measuring the fluid before the heating step or measuring the NO2 supplied to the exhaust gas stream to provide a desired amount of NO2 in the exhaust gas stream; wherein a reservoir (21) is provided which contains the fluid that generates NO2, wherein the NO2 generating fluid is injected directly into a combustion zone of the burner (112). [2] The method of claim 1, wherein the fluid is nitric acid. [3] Method according to any of the preceding claims, wherein the desired amount of NO2 is a proportion of an NO2:NO x -relationship is.

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