WLTP vs NEDC : comparing doesn’t help!

Created in 1973, the NEDC test was designed to imitate european road conditions in a reproducible way in order to provide an objective comparison between the different cars on the market, rather than to determine accurate and realistic consumption levels. It was developed based on a theoretical driving model consisting of acceleration and coasting phases. This model accounts for the performance of cars at the time, which was quite modest compared with that of contemporary cars. An example to illustrate this: a 1980 Porsche 911 had around 200hp and a top speed of nearly 230 km/h – the same figures as a contemporary Mercedes 220 diesel which, in 1978, reached the unprecedented speed of 135 km/h with its valiant 60hp engine! Moreover, when European pollutant emission standards were introduced in 1992, the NEDC was naturally used to carry out emission tests as it was already in place.

Transition to WLTP : the VW affair as a detonator

Indeed, the NEDC was so removed from reality that its application had almost become a fiction. Only by driving in a sort of “safety” mode could one hope to obtain the same levels as those measured in the laboratory. Driving on the road in normal or somewhat dynamic traffic conditions, motorists automatically exceeded the test results by using “off-test” engine functionality. This meant we were polluting and consuming as we saw fit – and with the law’s blessing!

It was based on this observation, admittedly distressing, that certain manufacturers such as VW took certain liberties, to the point of using techniques offered by modern electronics to detect whether the car was in NEDC test mode (ambient temperature, acceleration and speed profile, etc. thanks to a variety of sensors that track vehicle performance). From there it became simple, and very tempting, to programme engine software à la carte: one setting to easily pass the NEDC test and others that used the engine’s full capacities (i.e., the famous “sport mode” button provided by certain carmakers) without worrying about pollution limits. I rest my case!  When the scheme was exposed, every claim and its opposite was made by politicians and the media, who understood little about the situation. They chose to demonize the diesel engine, an easy target to blame for pollution, although this “cheating” applied equally to petrol engines. In short, diesel is now “persona non grata” in many cities while modern diesel engines can meet standards just as successfully as petrol engines. But that’s another story…

Is the WLTP test more accurate?

In order to correct the shortcomings of the NEDC test and provide more realistic conditions, the new WLTP test was created.

In practice:

• the acceleration phases are more intense,
• the speed levels reached are faster,
• the distances covered longer,
• with fewer stopping periods.

These WLTP test conditions enable all to simulate a driving experience more in line with reality. As logic would dictate, consumption and emission levels rose by 15 to 20% depending on the cars tested. This does not make things easier for manufacturers, who will have to comply with the CO₂ limit of 95 g/km by 2020, or be charged with a fine of 95 euros per additional gram for each car sold! If we multiply this amount by the number of cars sold, it is no wonder manufacturers prefer to invest in the development of hybrid and electric cars.

Test WLTP : all this for what?

The Euro 6d-Temp standard has been in force since September 2017 for new vehicle type approvals and will apply to all new registrations as of September 2018. Does this mean that adequate measures have been taken to limit CO₂ and pollutant emissions? Nothing could be more uncertain, as the blind witch-hunt led by politicians and the media has further encouraged the use of petrol engines, which – based on a law of thermodynamics – consume on average between 20 to 30% more than their diesel counterparts. Add to this the fact that the new car market has seen sales of SUVs (larger and heavier than classic cars) explode in the past several years, resulting in a 20 to 30% increase in consumption. In the end, when we know that fuel consumption and CO₂ emissions are directly proportional, it is clear that driving SUVs with petrol engines means increasing consumption, and therefore CO₂ emissions, by nearly 50%.

And so one might wonder: what is the logic behind all this? Could it be that, under the pretext of protecting the planet from “evil” diesel engines, governments are lining public purses by selling more petrol while levying CO₂ taxes on both drivers and manufacturers? We can rightly raise the question…