KR101055838B1 - Temperature Prediction Device and Method of SCR Catalyst - Google Patents

Abstract

The present invention is to accurately predict the temperature of the SCR catalyst by temperature modeling considering the latent heat of evaporation due to the injection of aqueous urea (Urea) in the SCR (Selective Catalytic Reduction) catalyst mounted on a diesel vehicle.

The present invention detects engine control information including fuel injection amount when the engine is turned on, detects the exhaust gas temperature flowing into the SCR catalyst, and predicts the catalyst temperature rise and the convective heat transfer loss due to the inflow of the exhaust gas. , Modeling the latent heat loss of evaporation according to the injection flow rate of the aqueous urea solution, and applying the temperature rise and convective heat transfer losses predicted in the above process to predict the SCR catalyst temperature.

Therefore, the exact amount of ammonia required is calculated and the injection of the aqueous urea solution is thus controlled to provide the effect of increasing the NOx purification efficiency.

SCR catalyst, temperature modeling, latent heat of evaporation, urea solution

Description

Apparatus and method for predicting temperature of SCR catalyst {APPARATUS AND METHOD FOR TEMPERATURE ESTIMATION OF SELECTIVE CATALYTIC REDUCTION}

The present invention relates to a SCR (Selective Catalytic Reduction) catalyst mounted on a diesel vehicle, and more particularly, to an SCR catalyst for accurately predicting the temperature of the SCR catalyst by temperature modeling considering the latent heat of evaporation due to the injection of urea solution. The present invention relates to a temperature predicting apparatus and a method.

Vehicles with diesel engines are subject to various types of post-treatment to remove harmful substances such as NOx, CO, THC and Particulate Matters (PM) contained in the exhaust gas in accordance with the tightened emission regulations in North America and Europe. The device is mounted.

The post-treatment unit is located close to the engine and performs DOC (Diesel Oxidation Catalyst), which performs Non-Methane HydroCarbons (NMHC) conversion function, Diesel Particulate Filter (DPF), which collects particulate matter, and purifies NOx through reduction. SCR catalysts are included.

The SCR catalyst uses ammonia (NH ₃ ) as a reducing agent for purifying NOx, and has an advantage in that the reaction between NOx and ammonia is promoted even in the presence of oxygen as well as excellent selectivity to NOx.

SCR catalyst is a dosing module disposed at the front end to maintain NOx purification performance above a certain level. NH ₃ ) is obtained and occluded and purified by reacting the occluded ammonia with NOx.

The chemical conversion of the aqueous urea solution is as follows.

(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂

The chemical reaction of ammonia (NH ₃ ) and NO x obtained and occluded as described above is as follows.

4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O

4NH ₃ + 2NO ₂ + O ₂ → 3N ₂ + 6H ₂ O

8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O

2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ O

The relationship between the temperature of the SCR catalyst and the ammonia adsorption amount is that the adsorption proceeds slowly when the temperature of the SCR catalyst is low and that adsorption proceeds rapidly when the temperature is high.

Therefore, in order to determine the ammonia adsorption amount of the SCR catalyst, the temperature of the SCR catalyst is extracted by using a temperature sensor installed at the front and rear of the SCR catalyst under the assumption that there is no temperature difference inside the SCR catalyst, The extracted temperature information was applied to predict the possible amount of ammonia occlusion according to the volume of SCR catalyst and to determine the target amount of ammonia occlusion.

The injection amount of the aqueous urea solution was determined according to the difference between the target ammonia storage amount and the current ammonia storage amount of the SCR catalyst.

Recently, the method of predicting the temperature of the SCR catalyst through modeling has been applied, except for the temperature sensor installed at the front and rear of the SCR catalyst for cost reduction.

However, when urea aqueous solution is injected to the SCR catalyst (A) through the dosing module to obtain ammonia, as shown in FIG. 3, the cooling effect is caused by the latent heat of evaporation of the SCR catalyst. The phenomenon that temperature becomes lower than state (B) occurs.

Since the temperature modeling method of the conventional SCR catalyst does not consider the cooling effect of the SCR catalyst due to the latent heat of evaporation during the spraying of the urea solution, the prediction of the temperature for the SCR catalyst is inaccurate. There is a problem of lowering the purification efficiency of the catalyst.

In addition, the injection amount of the urea aqueous solution is not precisely controlled, there is a disadvantage in that the emission is unstable due to overproduction or underproduction of ammonia.

The present invention has been invented to solve the above problems, the object of which is to accurately predict the temperature of the SCR catalyst by temperature modeling considering the latent heat of evaporation according to the injection of urea aqueous solution provides safety in the control of ammonia storage amount, NOx It is to improve the purification rate to provide emission stabilization.

According to an aspect of the present invention, there is provided an apparatus for predicting temperature of an SCR catalyst, comprising: an SCR catalyst for purifying NOx by reacting occluded ammonia with NOx; A temperature sensor installed at a front end of the dosing module to detect a temperature of the exhaust gas; A NOx sensor installed at the rear of the SCR catalyst; It includes a control unit that predicts the temperature rise and convective heat transfer loss of the SCR catalyst by modeling, predicts the latent heat loss due to the injection amount of the urea aqueous solution, and then applies the temperature rise and the convective heat transfer loss to predict the temperature of the SCR catalyst.

In addition, the SCR catalyst temperature prediction method according to an embodiment of the present invention, detecting the engine control information including the fuel injection amount when the start-up, detecting the exhaust gas temperature flowing into the SCR catalyst; Modeling the catalyst temperature rise and the convective heat transfer losses due to the inflow of exhaust gas; Modeling the latent evaporative heat loss according to the injection flow rate of the urea aqueous solution and applying the temperature rise and convective heat transfer loss predicted in the above process to predict the SCR catalyst temperature.

By the above-described configuration, the present invention provides reliability in ammonia storage amount control by predicting the correct temperature of the SCR catalyst, and stabilizes the emission by maximizing the NOx purification rate.

In addition, accurate temperature prediction of the SCR device provides precise injection control of the aqueous urea solution for ammonia production, so that excessive or under-generation of ammonia does not occur to keep the emission stable.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

The present invention can be embodied in various different forms, and thus the present invention is not limited to the embodiments described herein.

1 is a view schematically showing a temperature predicting apparatus of an SCR apparatus according to an embodiment of the present invention.

The present invention is a power source engine 2 and exhaust pipe 6, SCR catalyst 10, temperature sensor 12, NOx sensor 14, dosing module 20, mixer 22, urea tank 30 , A pump 32, a supply line 34, a pressure sensor 36 and a control unit 40.

The SCR catalyst 10 is made of V ₂ O ₅ / TiO ₂ or Pt / Al ₂ O ₃ or zeolite, and is disposed at a predetermined position of the exhaust pipe 6 connected to the engine 2 as a power source. Ammonia is obtained from the urea injected from the dosing module 20 and occluded, and NOx is purified by reacting the occluded ammonia with NOx.

The temperature sensor 12 is disposed in front of the dosing module 20 to detect the temperature of the exhaust gas flowing into the SCR catalyst 10 and provide information about the temperature to the controller 40.

The NOx sensor 14 is disposed at the rear end (outlet side) of the SCR catalyst 10 to detect the amount of NOx contained in the exhaust gas purified through the SCR catalyst 10 and provide the information to the controller 40.

The dosing module 20 injects an urea solution for generating ammonia for occlusion in the SCR catalyst 10 by operating an injector under the control of the controller 40.

The mixer 22 is disposed between the dosing module 20 and the SCR catalyst 10 to collide the particles of the urea solution injected through the dosing module 20 to split the particles, thereby spraying the exhaust gas and the injected particles. The urea particles are evenly mixed to improve the uniformity in the SCR catalyst 10.

The urea tank 30 accommodates the urea solution and forms an even pressure set in the supply line 34 by the driving of the pump 32 mounted therein, so that the SCR catalyst 10 is operated when the dosing module 20 is operated. At the front of the spray urea aqueous solution at high pressure.

The pressure sensor 36 detects the pressure formed in the supply line 34 and provides information about the pressure to the control unit 40 so that the set pressure can be maintained at all times while the engine 2 is kept on starting. do.

The controller 40 predicts the temperature rise and convective heat transfer loss of the SCR catalyst 10 through modeling, predicts the latent heat loss of evaporation according to the injection amount of the urea aqueous solution, and then applies the temperature rise, convective heat transfer loss, and latent heat loss of evaporation. The temperature of the SCR catalyst 10 is estimated.

The controller 40 controls the temperature rise of the SCR catalyst 10 to determine the flow rate of the exhaust gas flowing into the SCR catalyst 10, the pressure of the SCR catalyst 10, the temperature of the exhaust gas flowing into the SCR catalyst 10, and the SCR catalyst. The temperature of (10) is predicted by modeling, and the convective heat transfer loss is estimated by modeling by applying the convective heat transfer coefficient, the surface area of the SCR catalyst 10, the temperature of the SCR catalyst 10, and the outside air temperature.

When the accurate temperature of the SCR catalyst 10 is predicted through the modeling as described above, the amount of ammonia occlusion is calculated according to the above, and the injection amount of the urea aqueous solution is controlled through the dosing module 20.

Referring to the operation of predicting the temperature of the SCR catalyst in the present invention that includes the function as described above are as follows.

When the engine of the diesel vehicle according to the present invention is started on, the controller 40 detects information such as fuel injection amount from various sensors not shown, and detects information of the temperature sensor 12 installed at the front end of the dosing module 20. The temperature of the SCR catalyst 10 estimated from the temperature of the exhaust gas flowing into the SCR catalyst 10 and the temperature of the exhaust gas is determined (S101).

Thereafter, the controller 40 flows in the exhaust gas flow rate flowing into the SCR catalyst 10 calculated from the fuel injection amount, the pressure of the SCR catalyst 10 and the SCR catalyst 10 detected by the temperature sensor 12. The temperature rise of the SCR catalyst 10 is modeled by applying the temperature of the exhaust gas and the estimated temperature of the SCR catalyst 10 (S102).

The convective heat transfer loss of the SCR catalyst 10 is modeled by applying the convective heat transfer coefficient, the surface area of the SCR catalyst 10, the temperature of the SCR catalyst 10, and the outside temperature (S103).

In addition, the control unit 40 models the latent heat loss of evaporation according to the injection flow rate of the urea solution (S104), and then applies the temperature rise, the convective heat transfer loss, and the latent heat loss of evaporation to predict the correct temperature of the SCR catalyst 10. Next, the amount of ammonia occlusion according to the temperature of the SCR catalyst 10 is calculated, and the injection amount of the urea aqueous solution is controlled through the dosing module 20 (S105).

Therefore, the calculation of the required amount of ammonia to which the accurate temperature information of the SCR catalyst 10 is applied, and the injection control of the aqueous urea solution are performed to increase the purification efficiency of the NOx to keep the emission stable.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It is included in the scope of rights.

1 is a view schematically showing an apparatus for predicting a temperature of an SCR catalyst according to an embodiment of the present invention.

2 is a flowchart illustrating a temperature prediction procedure of an SCR catalyst according to an embodiment of the present invention.

3 is a graph showing the temperature change according to the injection of the urea aqueous solution of the SCR catalyst.

<Explanation of symbols for the main parts of the drawings>

2: engine 6: exhaust pipe

10: SCR catalyst 12: temperature sensor

14: NOx sensor 20: dosing module

22: mixer 30: urea tank

40: control unit

Claims (5)

SCR catalyst for purifying NOx by reacting the ammonia occluded with NOx; A temperature sensor installed at a front end of the dosing module to detect a temperature of the exhaust gas; A NOx sensor installed at the rear of the SCR catalyst; A control unit for estimating the temperature rise and convective heat transfer loss of the SCR catalyst, predicting the evaporation latent heat loss according to the injection amount of the urea aqueous solution, and predicting the temperature of the SCR catalyst by applying the temperature rise and the convective heat transfer loss and the latent heat loss of evaporation; SCR catalyst temperature prediction apparatus comprising a. The method of claim 1, The controller models the temperature rise by applying the flow rate of the exhaust gas flowing into the SCR catalyst, the pressure of the SCR catalyst, the temperature of the exhaust gas flowing into the SCR catalyst, and the temperature of the SCR catalyst, A convective heat transfer coefficient, the surface area of the SCR catalyst, the temperature of the SCR catalyst, and the outside air temperature are applied to model the convective heat transfer loss. Detecting start-up of engine control information including fuel injection amount, and detecting exhaust gas temperature flowing into the SCR catalyst; Modeling the catalyst temperature rise and the convective heat transfer losses due to the inflow of exhaust gas; Modeling the latent heat loss of evaporation according to the injection flow rate of the aqueous urea solution and predicting the SCR catalyst temperature by applying it to the predicted temperature rise and convective heat transfer loss; Temperature prediction method of the SCR catalyst comprising a. The method of claim 3, wherein The prediction of the catalyst temperature increase may be performed by modeling the exhaust gas flow rate estimated from the fuel injection amount, the pressure of the SCR catalyst, the temperature of the exhaust gas flowing into the SCR catalyst, and the temperature of the SCR catalyst estimated from the exhaust gas temperature. SCR catalyst temperature prediction method. The method of claim 3, wherein The prediction of the convective heat transfer loss is predicted by modeling by applying the convective heat transfer coefficient, the surface area of the SCR catalyst, the temperature of the SCR catalyst estimated from the exhaust gas temperature, and the outside air temperature.

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