The "free acceleration" method is widely applied
Emission testing is an important step in the process of testing vehicles using diesel engines to limit environmental pollution. Currently, many countries around the world apply the "free acceleration" test, which is to quickly accelerate the engine from idle to measure the amount of smoke emitted from the exhaust pipe.
This method is being used in many regions such as the European Union, the United States, Japan, South Korea, Australia and most Southeast Asian countries. In the US, the test is usually carried out according to the SAE J1667 technical standard; while in Europe, emission testing is within the framework of periodic vehicle inspection regulations.
According to a report by the International Transport Forum under the Organization for Economic Cooperation and Development, free acceleration tests are still maintained by many countries because they are low-cost, easy to implement and suitable for testing large numbers of vehicles.
Before conducting the measurement, the engine must reach a stable operating temperature. The car is kept standing and the gearbox is switched to an intermediate state for the engine to run unloaded. The registry inspector then pedals the entire accelerator pedal journey for the engine to accelerate quickly to maximum speed according to the manufacturer's design.
Measure smoke levels multiple times to ensure accuracy
During the testing process, the test is usually performed three to five times. After each acceleration, the measuring device will record the smoke clearance in a very short period of time, usually an average of about half a second. The final result is calculated by the average of valid measurements and then compared with the permissible limit according to each country's technical standards.
Mr. John German - senior expert at the International Council on Clean Transportation, said that free acceleration testing is widely used because it is simple but still has the ability to quickly detect diesel engines emitting smoke exceeding standards.
According to technical documents from the American Association of Automotive Engineers, if the engine is well maintained and the test is performed according to the correct procedure, rapid acceleration in a short time does not cause damage to the engine, because the maximum speed when unloaded is still within the safety limits designed by the manufacturer.
However, in case the engine has deteriorated or the turbocharging system has problems, the test may reveal potential malfunctions. Some countries have recently added more modern testing methods such as load testing on power test strips or exploitation of data from the integrated diagnostic system on the vehicle to assess emissions in actual operating conditions.
