Method for diagnosing diesel oxidation catalyst fault

This patent application claims the benefit and priority of Chinese Patent Application No. 202010706538.X filed on Jul. 21, 2020, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.

The present disclosure relates to the field of power machinery and engineering, and in particular, to a method for diagnosing a diesel oxidation catalyst (DOC) fault.

Diesel engines are widely used in the fields of transportation, agricultural machinery and engineering machinery due to excellent power performance and fuel efficiency. However, the exhaust gas emitted by diesel engines contains a lot of pollutants that are not completely combusted, such as carbon monoxide (CO), hydrocarbons (HCs), and carbonaceous particles (C), causing severe pollution to the atmospheric environment and posing a serious threat to the health of residents. A diesel oxidation catalyst (DOC) is capable of oxidizing CO, HCs and part of carbonaceous particles into carbon dioxide and water that are harmless to humans, and thus serves as a necessary technical means for diesel engines to meet current emission regulations.

The DOC can effectively reduce carbon monoxide and hydrocarbons in diesel engine exhaust gas. In modern diesel engines, porous honeycomb ceramics are usually used as a DOC carrier. There are many parallel channels in the carrier, so that the exhaust gas entering from the inlet is divided into a plurality of parts to pass through the channels. During this process, the exhaust gas comes into sufficient contact with the walls of the channels, so that CO and HCs undergo complete oxydoreduction reaction with oxygen in the presence of a noble metal catalyst applied on the walls and thus are converted into carbon dioxide and water. In this way, the exhaust gas is purified.

During the working process of the DOC, desorption and failure of the catalyst may occur due to the heat released by the oxydoreduction reaction, the scouring of high-speed exhaust gas and the adhesion of emissions. Consequently, the expected purification effect cannot be achieved. Therefore, it is important to evaluate the real-time performance of the DOC.

An objective of the present disclosure is to provide a method for diagnosing a diesel oxidation catalyst fault in order to overcome the defects of the prior art as described above.

The objective of the present disclosure can be achieved by the following technical solution:

A method for diagnosing a diesel oxidation catalyst fault includes the following steps:

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;

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

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

The standard molar enthalpy of formation-revolution speed-load table may be obtained through experiments conducted on a diesel oxidation catalyst in good condition.

The temperature difference of front and rear exhaust pipes and the casing temperature may be measured by using a temperature sensor or a thermodetector, and the revolution speed and the load may be obtained by using an electronic control unit (ECU).

The actual formation enthalpy ΔH online may be calculated from the temperature difference ΔT of front and rear exhaust pipes and the casing temperature T 1 according to the following formula:

Δ H online =C exhaustgas ΔT+ζ mental-air ( T 1 −T air )

where C exhaustgas is heat capacity of exhaust gas; ζ mental-air is a coefficient of heat exchange between the wall of the diesel oxidation catalyst and air; and T air is an air temperature in the vicinity of the wall of the diesel oxidation catalyst.

The standard conversion efficiency may be calculated from the temperature difference of front and rear exhaust pipes and the casing temperature.

The standard conversion efficiency may be obtained by querying carrier temperature-standard conversion efficiency, where the carrier temperature T carrier is calculated by the following formula:

T carrier =(Δ T+ 0.5 T 1 )/2.5

where ΔT is the temperature difference of front and rear exhaust pipes, and T 1 is the casing temperature.

The standard reaction enthalpy ΔH standard may be calculated by the following formula:

Δ H standard =Conv standard ×ΔH ideal

where Conv standard is the standard conversion efficiency, and ΔH ideal is the standard molar enthalpy of formation.

After the actual formation enthalpy and the standard reaction enthalpy are obtained, an instantaneous performance score may be calculated. Instantaneous performance scores under different working conditions may be weighted to obtain an average performance score. The overall performance of the diesel oxidation catalyst may be obtained from the average performance score.

The instantaneous performance score F DOCT may be calculated by the following formula:

F DOCT =ΔH online /ΔH standard

where ΔH online is the actual formation enthalpy, and ΔH standard is the standard reaction enthalpy.

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

Compared with the prior art, the present disclosure has the following advantages:

(1) During traveling or parking of a vehicle, the engine operates under a particular working condition. The temperature difference of front and rear exhaust pipes and the casing temperature are measured, and the actual formation enthalpy is compared with the standard reaction enthalpy under this working condition corresponding to the standard molar enthalpy of formation obtained through experiments conducted on a DOC in good condition. Thus, the evaluation of the performance of the DOC is achieved. Besides, online fault diagnosis can be performed on the DOC without the disassembly of the DOC as long as the engine operates under a particular working condition.

(2) The revolution speed and the load can be obtained by the ECU without addition of extra devices. The temperature difference of front and rear exhaust pipes and the casing temperature can be measured by using the temperature sensor or the thermodetector, which is simple and easy to operate with low cost.

(3) The overall performance of the DOC may be obtained based on the average performance score, and a diesel oxidation catalyst fault may be predicted based on the weighted instantaneous performance score-revolution speed-torque table.

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

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

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.

Embodiment

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

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;

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

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

Specifically,

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).

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

The actual formation enthalpy ΔH online is calculated from the temperature difference ΔT of front and rear exhaust pipes and the casing temperature T 1 according to the following formula:

Δ H online =C exhaustgas ΔT+ζ mental-air ( T 1 −T air )

where C 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 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 air is an air temperature in the vicinity of the wall of the diesel oxidation catalyst, which does not change significantly relative to T 1 during the operation of the engine and can be regarded as a constant value within an error range.

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

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 carrier is calculated from the temperature difference of front and rear exhaust pipes and the casing temperature according to the following formula:

T carrier =(Δ T+ 0.5 T 1 )/2.5.

The standard reaction enthalpy ΔH standard is calculated by the following formula:

Δ H standard =Conv standard ×ΔH ideal

where Conv standard is the standard conversion efficiency, and ΔH ideal is the standard molar enthalpy of formation.

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 DOCT is calculated by the following formula:

F DOCT =ΔH online /ΔH standard

where ΔH online is the actual formation enthalpy, and ΔH standard is the standard reaction enthalpy.

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.

For example, after 1000 s, the average performance score is

F DOC _ = ∑ i = 0 1000 ⁢ ⁢ F DOCT - i / 1000 ,

where F DOCT-i is the instantaneous performance score under working condition i. For a particular working condition point p, a region thereof is: n i ∈[1000,1050], T i ∈[200,205], where n i is an engine revolution speed under working condition i, and T i is an engine torque under working condition i; and the weighted instantaneous performance score is F DOC-p =ΣF DOCT-i /N(i), (n i ∈[1000,1050], T i ∈[200,205]), where N(i) is a total number of samples within the range of the working condition point. The F 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 DOC is less than 0.8, there may be a diesel oxidation catalyst fault.