“WLTP? A Race Against Time!”

Wherever Erik Pellmann goes, you can usually smell smoke. He is the DEKRA expert on emissions technology. In this interview, he takes us behind the scenes of the turbulent launch of the WLTP emissions cycle.

As a new standard, the measurement procedure should provide more realistic values ​​for pollutant emissions and consumption. Photo: Fotolia - fotohansel

As a new standard, the measurement procedure should provide more realistic values ​​for pollutant emissions and consumption. Photo: Fotolia – fotohansel

DEKRA solutions: Mr. Pellmann, has the automotive industry been too complacent about the launch auf WLTP?

Erik Pellmann: No, I don’t think so. One or two companies may have miscalculated, hoping for a longer transition period. This didn’t happen, because politicians showed no leniency following the emissions scandal. The Worldwide Harmonized Light Vehicles Test Procedure is extremely complex, which resulted in a lot of head-scratching and overtime for all concerned. I can assure you that everyone involved is giving it their all. But they’re also working at the limit.

What makes WLTP so complicated?

There are some 1,000 pages of test regulations. Not only do people need to understand it all, but they also need to clarify with all parties how certain things are meant and how details should be interpreted. After all, we need valid, legally compliant, and reproducible test procedures that are understood and used by everyone. The onus is not only on car manufacturers (who need to modify their processes), but also on testing equipment manufacturers, technical service providers such as DEKRA, and, last but not least, the official agencies connected with the German Federal Motor Transport Authority. With that in mind, a twelve-month implementation period amounts to a race against time. The size of the leap is clearly illustrated by a couple of dates. The first uniform emissions regulations for motor vehicles came into force in 1970 with Directive 70/20/EEC. The underlying principles of the New European Driving Cycle (NEDC) originate from 1992. Since then, there has been seismic change in terms of engine technology.

Erik Pellmann is Head of DATC*M2 Exhaust Emissions and Powertrain at DEKRA Automobil GmbH. Photo: Thomas Küppers

Erik Pellmann is Head of DATC*M2 Exhaust Emissions and Powertrain at DEKRA Automobil GmbH. Photo: Thomas Küppers

So what has changed on the test bench?

In order to conduct more realistic and relevant tests, the level of complexity on the test bench alone is virtually double that of the NEDC procedure. This means a new interpretation of the cycle, new marginal conditions, redefined procedures for calculating resistance, and higher speeds. More post-processing is also required whenever a new procedure is introduced; follow-up measurements are needed more often, as robust processes are developed empirically. What’s more, it is no longer the case that just one vehicle per type is tested. With WLTP, the best and worst version of each engine-transmission combination has to be tested, with the CO2 emission level calculated as an average between the two extremes. The emissions properties are then communicated as a worst-case scenario. In order to verify these algorithms, however, we have to perform spot checks to determine the accuracy of the imputed values — which means testing even more vehicles.


Why are there such big differences between manufacturers in terms of implementation?

Some manufacturers possibly have better control over their processes than others. And a high-volume manufacturer might have more than 260 engine–transmission combinations in their portfolio. That’s a lot of work.

How big is the difference between Euro 6 and Euro 6d-temp?

This is the most brutal leap of all time in terms of exhaust technology. Suddenly, I have to achieve optimum values for the particle number and for nitrogen oxide emissions under all conditions — both in the lab and on  the road.

And RDE is the icing on the cake?

Indeed. The rules of application for the Real Driving Emissions procedure were published at a late stage — and were an unknown quantity for all involved. Furthermore, the European Commission has set a tough challenge. The RDE rules of application stipulate that the particle limit and the NOx limit have to be met in the road test (with a permitted exceedance factor) with every single fuel available in the EU. Although these general Euro 6 limits have long been known, there was no mention of RDE. In practice, the PN limits are not feasible without a gasoline particulate filter and the latest engine control unit. Manufacturers who planned to solve this problem within the engine itself made a significant misjudgment and now have to catch up. In terms of diesel engines, it was necessary to fit the vehicles with SCR technology in combination with improved exhaust gas recirculation or with combinations involving Nox-storage catalytic converters. This is necessary in order to adhere to the stringent RDE nitrogen oxide requirements during normal driving.

From NEDC to WLTP and RDE

What does the new WLTP emissions measuring procedure entail, and what added benefits are offered by RDE measurements on the road?

The old procedure (NEDC)

The fundamental principles of the New European Driving Cycle date back to the 1970s. The test procedure measures fuel consumption and emissions over a 20-minute period. Critics argue that there is considerable scope for unrealistic optimizations, such as excessively high tire pressure, a disconnected battery, and low-friction oils. The procedure simulates a four-kilometer journey through a downtown area, as well as seven kilometers on country roads. In the old procedure, the vehicle accelerates very slowly and only reaches an average speed of 34 kmh.

The new procedure (WLTP)

WLTP stands for “Worldwide Harmonized Light Vehicle Test Procedure.” This new, Europe-wide standard aims to generate more realistic values for hazardous emissions and fuel consumption. To this end, the maximum and average speeds on the test bench have been increased, while the idle periods have been shortened. The test simulates a journey that is twice as long as that used for the NEDC. The vehicle travels and accelerates more quickly. Experts estimate that the values will be up to 25 percent higher.

Measurement method

First of all, the rolling and air resistance of the vehicle are precisely calculated. The vehicle is then driven through a standardized driving cycle during which the emissions are measured and, on this basis, fuel consumption is calculated. In the case of electric vehicles, battery consumption is measured.

Measurements on the road (RDE)

Even before the emissions scandal, the European Commission had decided to measure harmful emissions under real-life conditions on the road. The “Real Driving Emissions” primarily serve to check the accuracy of the laboratory values.

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