China has been testing the exhaust emissions of in-use vehicles for 20 years, and the current testing methods have been difficult to keep up with the needs of environmental protection in some big cities in China. The more advanced "simple working condition test method" abroad strongly attracts us. This paper summarizes and introduces the traditional detection methods and their disadvantages, the policies, standards and development status of simple working conditions in foreign countries and China.

First, why should we test the exhaust of vehicles in use?

Since 1980s, the number of cars in China has increased rapidly, and the air pollution caused by motor vehicles has been increasing, especially in big cities, which has aroused widespread public concern.

Successful experience abroad shows that effective control of automobile pollution needs to start from two aspects. First, implement new car emission regulations to control the emission level of pollutants from the beginning of new cars; Second, do a good job in the supervision of vehicles in use and implement the vehicle emission detection/maintenance system (I/M system). The former is the premise of low pollution of motor vehicles, and the latter is to ensure that motor vehicle emissions are in a normal state.

It is very important to detect the emissions of in-use vehicles for the following reasons:

In order to ensure that the vehicles in use are in good technical condition and find out those vehicles with high emissions, China has implemented an annual inspection of exhaust gas, and those that fail to meet the standards can be repaired and maintained before driving.

Second, the country's current detection methods

In China, the annual inspection system is implemented for in-use automobile exhaust detection. The commonly used detection methods are gasoline vehicle idling method (or double idling method) and diesel vehicle free acceleration smoke method. They all belong to the no-load detection method, and the test price is cheap and the test method is simple and fast.

1. Idle speed detection method for gasoline vehicles

What is idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle idle. When the car warms up steadily after starting, there is a red light at the intersection, and when there is traffic jam, the car idles. Idle speed detection is mainly used for vehicles in use. For new cars, it is mainly used for testing in the workshop after the new car is off the assembly line.

Test method The engine is accelerated from idle speed to 0.7 rated speed, held for 60 seconds, and then reduced to idle speed. Insert the sampling probe into the exhaust pipe, keep it at 15s, and then start reading the highest and lowest values within 30s, and take the average.

The characteristics of idle speed detection can only reflect the no-load emission of vehicles at idle speed. At this time, the engine is lean in oxygen and rich in combustion, mainly producing CO and HC, with little or no nitrogen oxides. The operation is convenient and fast, and the price is cheap. It is widely used in vehicle annual inspection in testing field, road inspection in environmental protection department and vehicle maintenance in repair shop. Help the environmental protection supervisor and vehicle maintenance personnel to judge whether the engine is in normal working condition.

See table 1 for the normal emission range of vehicles. It can be seen that the standard restrictions are very loose. If the emission is close to or exceeds the standard, it means that the engine is seriously deviating from normal combustion. Should be overhauled and maintained as soon as possible.

Idle speed detection method The traditional idle speed measurement method has great limitations. In recent years, in order to monitor the deterioration of automobile emissions caused by the wear of carburetor nozzle or the reduction of catalyst conversion efficiency, double idle speed measurement method has been widely used in some countries. The measurement method of double idle speed is also formulated in ISO3929 standard. In order to meet the needs of our country, GB/T 3845-93 "Determination of Exhaust Pollutants of Gasoline Vehicles (Idle Speed Method)" lists the double idle speed determination procedure of ISO3929 in Appendix C for reference by local environmental protection systems. On this basis, Beijing issued the emission standard of pollutants for gasoline vehicles at double idle speed on 1994.

For EFI vehicles equipped with three-way catalytic converter, a five-gas analyzer is needed to give the air excess coefficient (λ) by measuring the O2 content in the exhaust gas. When the engine is at high idle speed, λ shall be1.00 0.03 (or the range specified by the manufacturer).