A detection method for gasoline vehicle three-way catalytic converter based on exhaust gas secondary catalysis

Abstract

The present invention discloses a method for detecting three-way catalytic converters of gasoline vehicles based on secondary catalysis of exhaust gas. During the whole vehicle emission detection process of gasoline vehicles, a small amount of exhaust gas is diverted from the exhaust tail pipe outlet of the vehicle, and the diverted exhaust gas is heated by an electric heater, and then subjected to secondary catalysis by a reference catalyst, and the exhaust gas composition and concentration after the secondary catalysis are detected by emission analysis equipment. If the exhaust gas emissions after the secondary catalysis still do not meet the emission regulatory limit requirements, it is determined that the original exhaust conditions of the engine do not meet the working requirements of the catalyst. The present invention can identify whether the excessive emissions of the whole vehicle are caused by the three-way catalytic converter. The method is simple and the detection efficiency is high, which provides technical method support for the implementation of the automobile emission inspection and maintenance (IM) system. The present invention is also suitable for secondary detection of exhaust gas of vehicles burning alternative fuels such as CNG and LPG.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile detection, and in particular to a detection method for a three-way catalytic converter of a gasoline vehicle based on secondary catalysis of exhaust gas. Background Art

[0002] The gasoline mixture is fully combusted within the engine, theoretically producing carbon dioxide and water. Currently, relying solely on in-engine gasoline purification technology cannot achieve near-zero emissions. The engine's raw emissions still contain a certain amount of incomplete combustion products, such as hydrocarbons (CmHn), carbon monoxide (CO), and nitrogen oxides (NOx) (NO + NO2) generated by high-temperature combustion. To meet modern emissions regulations, gasoline vehicles must use a three-way catalytic converter, which further converts these three major exhaust pollutants into water and carbon dioxide through a catalytic reaction.

[0003] To ensure that in-use vehicle emissions meet regulatory requirements, countries around the world have implemented regular vehicle emissions inspections for gasoline vehicles. For example, my country conducts annual inspections of in-use vehicles in accordance with the "Emission Limits and Measurement Methods of Pollutants from Gasoline Vehicles (Dual Idle Method and Simple Operating Condition Method)" (GB18285-2018). Because vehicle emissions are determined by both the engine's raw emissions and the performance of the three-way catalytic converter, factors such as the engine's fuel supply, air intake, ignition system, electronic control calibration, and oxygen sensor can all contribute to abnormal vehicle emissions. For vehicles found to have excessive emissions, existing testing methods cannot determine whether the catalytic converter is the cause.

[0004] The "substitution elimination method" can decouple this issue: replace the catalytic converter with a quality-matched, original catalyst that meets the vehicle's original design for the vehicle. If emissions still exceed the standard after retesting, the catalytic converter quality issue can be ruled out. This method is theoretically feasible, but replacing the catalytic converter and retesting every vehicle with excessive emissions would significantly reduce testing efficiency and waste manpower and resources.

[0005] To this end, this paper proposes a gasoline vehicle three-way catalytic converter testing method based on secondary exhaust catalysis. This method does not make any modifications to the vehicle's exhaust system. During vehicle emissions testing, a small amount of exhaust gas is diverted from the vehicle's tailpipe outlet and passed through a reference catalytic converter for secondary catalysis. The composition and concentration of the diverted exhaust gas after secondary catalysis are used to determine the quality compliance of the gasoline vehicle's installed catalytic converter.

[0006] Figure 1 This section explains the impact of post-catalytic converters on exhaust emissions. The subscripts CAT1 and CAT2 represent the currently installed catalyst and the baseline catalyst for post-catalytic converters. Regarding exhaust gas conditions that influence catalyst performance evaluation, T represents exhaust temperature, A / F represents air-fuel ratio, and SV represents catalyst space velocity.

[0007] Comparing the exhaust inlet conditions of the existing and baseline catalysts: Regarding exhaust temperature, since the baseline catalyst is installed after the vehicle's tailpipe outlet, exhaust temperature losses along the way cause the exhaust inlet of the downstream benchmark catalyst to be even lower, hindering the catalytic reaction. Regarding the exhaust air-fuel ratio, the reduction reaction is more efficient when the exhaust at the inlet of the existing catalyst is rich, causing the exhaust to lean, and vice versa. In other words, the air-fuel ratio at the inlet of the downstream benchmark catalyst is always more favorable for the catalytic reaction. Regarding air velocity, since the flow rate of the diverted exhaust can be freely and reasonably controlled, it has no effect on the baseline catalyst.

[0008] In summary, if a small amount of exhaust is diverted from the vehicle's tailpipe outlet and a secondary catalytic system is installed, the exhaust inlet temperature of the baseline catalyst will undoubtedly be lower than that of the existing catalyst. If exhaust temperature is compensated by heating to negate temperature losses along the exhaust path, the pollutant conversion efficiency of the two-stage catalytic system consisting of the existing catalyst and the baseline catalyst should be no less than that achieved by replacing a vehicle with an original catalyst that meets the vehicle's original design and is of qualified quality, as envisioned in the aforementioned "elimination and substitution method." In other words, using a secondary exhaust catalytic method, the objectives of the aforementioned "elimination and substitution method" can be achieved without modifying the vehicle's exhaust system. Summary of the Invention

[0009] The purpose of the present invention is to effectively identify whether the vehicle's existing catalytic converter meets emission control requirements in combination with vehicle emission inspection without changing the vehicle's original exhaust system.

[0010] To achieve the above-mentioned purpose, one embodiment of the present invention provides a method for detecting a three-way catalytic converter of a gasoline vehicle based on secondary catalysis of exhaust gas.

[0011] The following steps are involved:

[0012] (A) An exhaust gas sampling device is connected to the exhaust tailpipe outlet of the vehicle to introduce the vehicle exhaust gas into the diversion pipe; the diversion sampling device is used to control the flow rate of the diverted exhaust gas, with the goal of making the air velocity of the reference catalyst the same as the air velocity of the currently installed catalyst; for the steady-state working condition of the vehicle, a fixed flow rate can be used for diversion; for the variable working condition cycle of the vehicle, a proportional diversion sampling should be used. The steady-state working condition method of the present invention is as follows Figure 2 shown.

[0013] (B) The diverted exhaust gas is heated to a temperature that reaches or exceeds the exhaust inlet temperature of the currently installed catalyst.

[0014] (C) The vehicle under test is operated under the specified operating conditions, and the emission concentration of the entire vehicle and the diverted exhaust gas after secondary catalysis is measured simultaneously.

[0015] (D) When the emissions of the inspected vehicle do not meet regulatory requirements, the assessment is made in conjunction with the emission concentration of the diverted exhaust gas after secondary catalysis. If the emission concentration of any controlled pollutant component in the diverted exhaust gas after secondary catalysis exceeds the regulatory limit, the engine's original emissions are deemed unqualified. If the emission concentration of any controlled pollutant component in the diverted exhaust gas after secondary catalysis all meet the regulatory limit, the engine's original emissions are deemed qualified, but the performance of the currently installed catalyst is unqualified.

[0016] Preferably, the reference catalyst has the same activity type (oxidation type, three-way type, etc.) as the currently installed catalyst, and has the same or better catalyst light-off temperature, air-fuel ratio window and oxygen storage performance.

[0017] Preferably, the vehicle emission test is performed at a low to medium speed, and the actual air velocity of the currently installed catalyst is lower than 1 / 2 of the design value.

[0018] In summary, the present invention has the following advantages:

[0019] 1. The present invention can be combined with vehicle emission testing to determine the performance compliance of the three-way catalytic converter without any disassembly or modification of the exhaust system of the tested vehicle, which can significantly improve the testing efficiency.

[0020] 2. The present invention determines whether the original exhaust conditions of the vehicle meet the working requirements of the catalyst through the actual effect of the benchmark catalyst, without relying on theoretical calculations.

[0021] 3. Taking into account the impact of secondary catalysis on the evaluation by increasing the volume of the catalyst (reducing the air velocity), the present invention recommends the use of low vehicle speed (i.e., low engine exhaust flow) operating conditions so that the catalyst air velocity does not become the main factor affecting the conversion efficiency, thereby maximally eliminating the impact of the secondary catalysis test results on the performance judgment of the existing catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the effect of secondary catalysis on tail gas emissions in the background art;

[0023] Figure 2 It is a schematic diagram of the test operation cycle of the steady-state working condition method. DETAILED DESCRIPTION

[0024] The present invention provides a method for detecting a three-way catalytic converter of a gasoline vehicle based on secondary catalysis of exhaust gas, comprising the following steps:

[0025] (1) A collection device is installed on the exhaust tail pipe of the entire vehicle and is used to connect with the exhaust tail pipe of the entire gasoline vehicle to ensure that there is no exhaust leakage.

[0026] (2) Wrap the selected reference catalyst coating carrier with a cushion layer and properly install it in the secondary catalytic system housing, ensuring that the cushion layer is tightly wrapped and the diverted exhaust gas does not leak to the downstream through the gap between the housing and the carrier.

[0027] (3) Use the flow control valve to adjust the flow of the diverted exhaust gas through the reference catalyst so that the air velocity of the reference catalyst is consistent with the air velocity of the catalyst currently installed on the vehicle being tested.

[0028] (4) Start the exhaust gas heater and adjust the heating control unit so that the exhaust temperature at the inlet of the reference catalyst is not lower than the exhaust temperature at the inlet of the installed catalyst. If the exhaust temperature at the inlet of the installed catalyst is unknown, ensure that the exhaust temperature at the inlet of the reference catalyst is above 500°C to ensure efficient secondary catalysis.

[0029] (5) Install a split exhaust gas analysis device downstream of the reference catalyst to measure the composition and concentration of the split exhaust gas.

[0030] (6) Operate the vehicle according to the gasoline vehicle emission test conditions. Taking the current GB18285-2018 "Gasoline Vehicle Pollutant Emission Limits and Measurement Methods (Dual Idle Method and Simple Operating Condition Method)" as an example, the ASM5025 operating condition is preferred.

[0031] (7) Simultaneously collect vehicle emission results and emission test results after secondary catalysis by the benchmark catalyst. The secondary catalytic exhaust data obtained by the split exhaust analysis equipment is synchronously corrected based on the atmospheric pressure, temperature and humidity conditions of the vehicle emission test.

[0032] (8) When the emissions of the whole vehicle exceed the relevant emission regulations, compare the exhaust emission results after the secondary catalytic reaction. If the exhaust emissions after the secondary catalytic reaction meet the regulatory limits, the original emission problem of the engine can be ruled out, and it can be determined that the performance of the catalyst installed on the whole vehicle does not meet the emission control requirements; if the exhaust emissions after the secondary catalytic reaction still do not meet the emission regulations, it can be determined that the original exhaust conditions of the engine do not meet the working requirements of the catalyst.

Claims

1. A method for detecting a three-way catalytic converter for a gasoline vehicle based on secondary catalysis of exhaust gas, characterized by: During the whole vehicle emission test of gasoline vehicles, a small amount of exhaust gas is diverted from the vehicle's exhaust tail pipe outlet, and an electric heater is used to make the diverted exhaust gas reach the reaction temperature required by the catalyst. The diverted exhaust gas is then secondary catalyzed by the reference catalyst. The composition and concentration of the diverted exhaust gas after the secondary catalysis are used to determine the quality compliance of the catalyst currently installed on the gasoline vehicle.

2. The method for detecting a three-way catalytic converter for a gasoline vehicle based on secondary catalysis of exhaust gas according to claim 1, characterized in that: A small amount of exhaust gas is diverted out at the vehicle's exhaust tailpipe outlet. The volume flow rate of the diverted exhaust gas is determined based on the volume of the reference catalyst. The goal is to make the exhaust air velocity of the reference catalyst equal to the exhaust air velocity of the currently installed catalyst.

3. The method for detecting a three-way catalytic converter for a gasoline vehicle based on secondary catalysis of exhaust gas according to claim 1, characterized in that: The diverted exhaust gas is heated so that the temperature of the diverted exhaust gas at the inlet of the reference catalyst is not lower than the exhaust gas temperature at the inlet of the currently installed catalyst.

4. The method for detecting a three-way catalytic converter for a gasoline vehicle based on secondary catalysis of exhaust gas according to claim 1, characterized in that: The benchmark catalyst is a small-sized catalyst sample that conforms to the original design of the vehicle, and the performance of the benchmark catalyst should be regularly checked using standard gas to ensure that the catalytic performance of the benchmark catalyst meets the original design requirements of the vehicle.

5. The method for detecting a three-way catalytic converter for a gasoline vehicle based on secondary catalysis of exhaust gas according to claim 1, characterized in that: The exhaust gas composition and concentration after secondary catalysis are tested simultaneously with the vehicle emission test.

6. The method for detecting a three-way catalytic converter for a gasoline vehicle based on secondary catalysis of exhaust gas according to claim 1, characterized in that: When the emissions of the entire vehicle exceed the relevant emission regulations limit requirements, compare the exhaust emission results after secondary catalysis. If the exhaust emissions after secondary catalysis meet the regulatory limit requirements, the original emission problem of the engine can be ruled out, and it can be determined that the performance of the catalyst currently installed on the vehicle does not meet the emission control requirements; if the exhaust emissions after secondary catalysis still do not meet the emission regulations limit requirements, it is determined that the original exhaust conditions of the engine do not meet the working requirements of the catalyst.

Images