How to Test Vehicle Exhaust Emissions?
4 Answers
There are three methods for testing exhaust emissions: 1. Method One: Simple Transient Driving Mode. The equipment for this method mainly includes a chassis dynamometer, exhaust sampling system, five-gas analyzer, gas flow analyzer, and automatic detection control system. The 'Simple Driving Mode' test simulates on-road driving conditions with load, covering various operating conditions such as acceleration, deceleration, constant speed, and idling, accurately reflecting the exhaust emission characteristics during actual driving. The transient driving mode can overcome the inability of other methods to detect oxygen sensor faults in fuel-injected vehicles, thereby improving the detection of exhaust emission defects. It can measure three pollutants: carbon monoxide, hydrocarbons, and nitrogen oxides. 2. Method Two: Filter Paper Smoke Method. This method involves running a diesel engine at idle speed, rapidly pressing the accelerator pedal to the floor, maintaining it for 4 seconds, and then releasing it. Under this condition, carbon smoke from a specified length of exhaust column is extracted from the exhaust pipe, and the degree of blackening of a clean filter paper is determined using a photoelectric method. 3. Method Three: Diesel Vehicle Loaded Deceleration LUGDOWN Method. This method tests smoke levels at three load conditions: maximum power point, 90% of the maximum power corresponding speed, and 80% of the maximum power corresponding speed. During the test, the sampling probe is inserted into the vehicle's exhaust pipe to a depth of at least 400mm. The test data includes wheel power, engine speed, and exhaust smoke level.
Vehicle exhaust emissions testing is divided into annual inspections and routine self-checks. For annual inspections, you need to go to designated stations authorized by the vehicle management office. They use professional exhaust gas analyzers by inserting a probe into the exhaust pipe to read data. The staff will ask you to rev the engine a few times to maintain RPM, measuring CO, HC, and NOx concentrations. Personally, I observe the exhaust pipe color—blue smoke indicates oil burning, black smoke suggests a rich air-fuel mixture, and white smoke means checking the coolant. If you smell a pungent odor when revving the engine in neutral, there’s a high chance of exceeding emission standards. For older cars, remember to warm up the engine before testing, as the catalytic converter is less efficient when cold. Always choose certified inspection stations with national-standard equipment—those roadside shops offering simplified tests are unreliable, and their data can be off by a factor of two.
Last time I went to the inspection station for an emissions test, the process was quite straightforward. First, the car was driven onto the roller test bench, where the technician connected the exhaust collection pipe and linked it to the computer equipment. When measuring the emission values at idle, he instructed me not to press the accelerator. Then, during the high-load condition test, it was necessary to rev the engine to 2500 RPM and hold it steady. The most critical part was checking whether the catalytic converter had failed, as the instrument would directly display the HC compound values. It's advisable to replace the air filter and spark plugs beforehand, as their aging can lead to incomplete combustion. Diesel vehicles also require an additional test for exhaust opacity, and a reading exceeding 5% means failure. Avoid testing when the engine is cold, as insufficient engine temperature can result in falsely high data.
Exhaust emission testing primarily focuses on four key indicators: Excessive carbon monoxide (CO) indicates incomplete combustion, often caused by clogged air filters or faulty oxygen sensors. High hydrocarbon (HC) levels suggest unburned fuel leakage, commonly due to aged spark plugs or ignition coil issues. A sharp increase in nitrogen oxides (NOx) typically points to catalytic converter failure. Particulate matter testing is especially critical for diesel vehicles. Many testing stations now employ infrared spectroscopy methods, delivering results within 10 minutes. For routine maintenance, inspect the inner walls of the exhaust pipe - heavy carbon buildup indicates poor combustion efficiency. For China VI compliant vehicles, it's recommended to check OBD data streams every six months, which proves more reliable than random exhaust emission tests.
