Method for diagnosing diesel oxidation catalyst fault

Abstract

A method for diagnosing a diesel oxidation catalyst fault includes: obtaining an standard molar enthalpy of formation-revolution speed-load table; obtaining a revolution speed, a load, a temperature difference of front and rear exhaust pipes, and a casing temperature, obtaining an standard molar enthalpy of formation corresponding to the revolution speed and the load from the standard molar enthalpy of formation-revolution speed-load table, and calculating an actual formation enthalpy corresponding to the temperature difference of front and rear exhaust pipes and the casing temperature from the temperature difference of front and rear exhaust pipes and the casing temperature; calculating a standard reaction enthalpy from the standard molar enthalpy of formation and standard conversion efficiency; and diagnosing a diesel oxidation catalyst fault by comparing the actual formation enthalpy with the standard reaction enthalpy. The method is capable of realizing online fault diagnosis on a diesel oxidation catalyst without the disassembly of the diesel oxidation catalyst.

Claims

1. A method for diagnosing a diesel oxidation catalyst fault, comprising the following steps: step S1: obtaining a standard molar enthalpy of formation-revolution speed-load table; step S2: obtaining a revolution speed, a load, a temperature difference of front and rear exhaust pipes, and a casing temperature, obtaining a standard molar enthalpy of formation corresponding to the revolution speed and the load from the standard molar enthalpy of formation-revolution speed-load table, and calculating an actual formation enthalpy corresponding to the temperature difference of front and rear exhaust pipes and the casing temperature from the temperature difference of front and rear exhaust pipes and the casing temperature; step S3: calculating a standard reaction enthalpy from the standard molar enthalpy of formation and a standard conversion efficiency; and step S4: diagnosing a diesel oxidation catalyst fault by comparing the actual formation enthalpy with the standard reaction enthalpy.

2. The method according to claim 1, wherein the standard molar enthalpy of formation-revolution speed-load table is obtained through experiments conducted on a diesel oxidation catalyst in good condition.

3. The method according to claim 1, wherein the temperature difference of front and rear exhaust pipes and the casing temperature are measured by using a temperature sensor or a thermodetector, and the revolution speed and the load are obtained by using an electronic control unit (ECU).

4. The method according to claim 1, wherein the actual formation enthalpy ΔH.sub.online is calculated from the temperature difference ΔT of front and rear exhaust pipes and the casing temperature T.sub.1 according to the following formula:
ΔH.sub.online=C.sub.exhaustgasΔT+ζ.sub.mental-air(T.sub.1−T.sub.air) wherein C.sub.exhaustgas is a heat capacity of exhaust gas; ζ.sub.mental-air is a coefficient of heat exchange between a wall of a diesel oxidation catalyst and air; and T.sub.air is an air temperature in the vicinity of the wall of the diesel oxidation catalyst.

5. The method according to claim 1, wherein the standard conversion efficiency is calculated from the temperature difference of front and rear exhaust pipes and the casing temperature.

6. The method according to claim 5, wherein the standard conversion efficiency is obtained by querying a carrier temperature-standard conversion efficiency, wherein the carrier temperature T.sub.carrier is calculated by the following formula:
T.sub.carrier=(ΔT+0.5T.sub.1)/2.5 wherein ΔT is the temperature difference of front and rear exhaust pipes, and T.sub.1 is the casing temperature.

7. The method according to claim 1, wherein the standard reaction enthalpy standard is calculated by the following formula:
ΔH.sub.standard=Conv.sub.standard×ΔH.sub.ideal wherein Conv.sub.standard is the standard conversion efficiency, and ΔH.sub.ideal is the standard molar enthalpy of formation.

8. The method according to claim 1, wherein after the actual formation enthalpy and the standard reaction enthalpy are obtained, an instantaneous performance score is calculated; instantaneous performance scores under different working conditions are calculated and weighted to obtain an average performance score; and an overall performance of a diesel oxidation catalyst is obtained from the average performance score.

9. The method according to claim 8, wherein the instantaneous performance score F.sub.DOCT is calculated by the following formula:
F.sub.DOCT=ΔH.sub.online/ΔH.sub.standard wherein ΔH.sub.online is the actual formation enthalpy, and ΔH.sub.standard is the standard reaction enthalpy.

10. The method according to claim 8, wherein instantaneous performance scores near a particular working condition point are weighted to obtain a weighted instantaneous performance score-revolution speed-torque table; and the diesel oxidation catalyst fault is diagnosed based on the weighted instantaneous performance score-revolution speed-torque table.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart according to an embodiment of present disclosure.

(2) FIG. 2 is a schematic diagram according to an embodiment of present disclosure.

DETAILED DESCRIPTION

(3) The present disclosure will be described in detail below in conjunction with the accompanying drawings and a specific embodiment. The embodiment is carried out on the premise of the technical solution of the present disclosure. Details of the embodiment and a specific operation process are given, but the protection scope of the present disclosure is not limited to the following embodiment.

(4) Embodiment

(5) This embodiment provides a method for diagnosing a diesel oxidation catalyst fault, including the following steps:

(6) step S1: obtaining an standard molar enthalpy of formation-revolution speed-load table;

(7) step S2: obtaining a revolution speed, a load, a temperature difference of front and rear exhaust pipes, and a casing temperature, obtaining an standard molar enthalpy of formation corresponding to the revolution speed and the load from the standard molar enthalpy of formation-revolution speed-load table, and calculating an actual formation enthalpy corresponding to the temperature difference of front and rear exhaust pipes and the casing temperature from the temperature difference of front and rear exhaust pipes and the casing temperature;

(8) step S3: calculating a standard reaction enthalpy from the standard molar enthalpy of formation and standard conversion efficiency; and

(9) step S4: diagnosing a diesel oxidation catalyst fault by comparing the actual formation enthalpy with the standard reaction enthalpy.

(10) Specifically,

(11) the standard molar enthalpy of formation-revolution speed-load table is laboratory measurements obtained through experiments conducted on a diesel oxidation catalyst in good condition. The revolution speed and the load are obtained by using an electronic control unit (ECU).

(12) The temperature difference of front and rear exhaust pipes and the casing temperature is measured by using a temperature sensor or a thermodetector.

(13) The actual formation enthalpy ΔH.sub.online is calculated from the temperature difference ΔT of front and rear exhaust pipes and the casing temperature T.sub.1 according to the following formula:
ΔH.sub.online=C.sub.exhaustgasΔT+ζ.sub.mental-air(T.sub.1−T.sub.air)
where C.sub.exhaustgas is heat capacity of exhaust gas, which may be regarded as a constant value within temperature and composition variation ranges in a diesel engine after-treatment system; ζ.sub.mental-air is a coefficient of heat exchange between the wall of the diesel oxidation catalyst and air, which is a constant value; and T.sub.air is an air temperature in the vicinity of the wall of the diesel oxidation catalyst, which does not change significantly relative to T.sub.1 during the operation of the engine and can be regarded as a constant value within an error range.

(14) In this embodiment, the standard conversion efficiency T.sub.carrier is calculated from the temperature difference of front and rear exhaust pipes and the casing temperature according to the following formula:

(15) The standard conversion efficiency is obtained by querying carrier temperature-standard conversion efficiency that is measured through experiments in a laboratory. The carrier temperature can be calculated by several approaches, such as by using a DOC heat transfer model or by averaging. In this embodiment, the carrier temperature T.sub.carrier is calculated from the temperature difference of front and rear exhaust pipes and the casing temperature according to the following formula:
T.sub.carrier=(ΔT+0.5T.sub.1)/2.5.

(16) The standard reaction enthalpy ΔH.sub.standard is calculated by the following formula:
ΔH.sub.standard=Conv.sub.standard×ΔH.sub.ideal
where Conv.sub.standard is the standard conversion efficiency, and ΔH.sub.ideal is the standard molar enthalpy of formation.

(17) After the actual formation enthalpy and the standard reaction enthalpy are obtained, an instantaneous performance score is calculated. Instantaneous performance scores under different working conditions are weighted, i.e., averaged in this embodiment, to obtain an average performance score. The overall performance of the diesel oxidation catalyst is obtained from the average performance score. The instantaneous performance score F.sub.DOCT is calculated by the following formula:
F.sub.DOCT=ΔH.sub.online/ΔH.sub.standard
where ΔH.sub.online is the actual formation enthalpy, and ΔH.sub.standard is the standard reaction enthalpy.

(18) Instantaneous performance scores near a particular working condition point are weighted to obtain a weighted instantaneous performance score-revolution speed-torque table. A diesel oxidation catalyst fault is predicted based on the weighted instantaneous performance score-revolution speed-torque table.

(19) For example, after 1000 s, the average performance score is

(20) $\stackrel{\_}{F_{\mathrm{DOC}}}=\underset{i=0}{\overset{1000}{.Math.}}{F}_{\mathrm{DOCT}-i}/1000,$
where F.sub.DOCT-i is the instantaneous performance score under working condition i. For a particular working condition point p, a region thereof is: n.sub.i ∈[1000,1050], T.sub.i ∈[200,205], where n.sub.i is an engine revolution speed under working condition i, and T.sub.i is an engine torque under working condition i; and the weighted instantaneous performance score is F.sub.DOC-p=ΣF.sub.DOCT-i/N(i), (n.sub.i∈[1000,1050], T.sub.i∈[200,205]), where N(i) is a total number of samples within the range of the working condition point. The F.sub.DOC-p near each working condition point is calculated to obtain the instantaneous performance score-revolution speed-torque table. If the average performance score F.sub.DOC is less than 0.8, there may be a diesel oxidation catalyst fault.