IMGP1016 © by marko8904
During the approval phase for cars, automobile companies are required to comply with the regulations in the NEDC (New European Driving Cycle) established by directive EU 91/441/EC.
This regulation calls for a series of tests that must be uniform and repeatable. To guarantee that they can be repeated, the tests are performed not on roads or a track but on dynamometric rollers in a laboratory at a controlled and constant temperature and humidity, therefore examining only a reduced and insignificant range of use.
Inside these labs urban and extra-urban cycles are simulated. The test has an overall duration of just a few minutes for a simulated distance of 11 km. The average speed for the urban cycle is 19 km/h and the maximum speed is 50 km/h for a total simulated distance of 4.052 km while the extra-urban test speed, on a simulated distance of 6.955 km, is 62 km/h with a maximum of 120 km/h so any distance on the highway is not taken into consideration.
Since the car is not in motion, there is no force generated by air friction which is calculated, approximately, through algorithms by the bench used for the test. The NED test doesn’t take into consideration many important aspects, which are those that create the greatest amount of harmful emissions, like the full load (accelerator pushed to the floor) and movements from one regime to the other, which are called transients in technical jargon as they actually occur, but only by simulating constant negative and positive acceleration.
I think it is logical to ask if the test, as it is performed today, is truly representative of real use or if it is too limited. How many times during daily use, for example, do we manage to accelerate and slow down in a constant manner? Another significant point is found in the specialised press where fuel consumption data obtained during road tests differ from those declared by the manufacturer and always ending up as being greater. Fuel consumption is directly proportional to automobile emissions so, given the difference between the data declared and obtained, it is obvious that there are also differences regarding emissions.
Using the test as it is conceived today, we can’t understand how the car truly behaves regarding emissions. With the electronics that run the engine nowadays, it is easy to make a harmful level of emissions for an automobile at 10 km/hour fall within the norm – just program the controller so the air/fuel mixture is “lean” and that’s it.
So then, what purpose do anti-pollution regulations have? Why during the approval phase do they not call for more complete tests that examine a greater number of situations which are closer to true automobile use?
Paolo Camerin
