Realism is the new Reality

What will WLTP and RDE bring?

The exhaust gas and fuel consumption figures for cars equipped with internal combustion engines depend to a very large degree on the testing method employed. Starting this fall, the European Union will also require road tests. The goal is to reduce the discrepancy between the test stand and actual driving.

In his closing sentence, the writer warns the reader: “The new consumption figures will not reflect actual fuel consumption; there will still be scope for confusion on this score.” The article, by Wolfgang Peters, appeared in the Frankfurter Allgemeine Zeitung back in fall 1995, and reported on the “New European Driving Cycle” (NEDC). It replaced the previously used Euromix standard. Saying goodbye to Euromix proved to be difficult for the automotive industry: in particular, high-performance engines with large displacement benefitted from the fact that during simulated driving on highways and superhighways, there was no acceleration. Conversely, consumer advocates welcomed the new cycle, pointing out that it came closer to reality. In practice, the laws of physics applied, then as now: in order to accelerate mass, you need energy. And to accelerate more mass—e.g. a heavier automobile— you need even more energy. Now, two decades later, it’s the NEDC that’s on the way out. Starting in fall 2017, the European Union wants fuel consumption figures for new cars to conform to the “Worldwide Harmonized Light-Duty Vehicles Test Procedure,” or WLTP. Initially, the new regulation will apply solely to vehicles that undergo type approval; a year later, manufacturers will have to list the consumption data for all new vehicles in accordance with WLTP norms. There’s no denying that the new cycle comes somewhat closer to reality on the road than the old one. For example, the average speed has been increased by about a third to around 47 km/h, the top speed to 131 km/h. In addition, the amount of time the car spends on the dynamometer has been increased from 20 minutes to half an hour. At first glance, it’s obvious that standard consumption will be significantly higher in the new cycle due to greater demands made on the engine. Furthermore, the number of shutdowns decreases, which a modern start-stop system would normally be able to take advantage of. Finally, special equipment will be taken into account in future, which results in greater driving resistances. But the conversion isn’t all that simple: certain points of the new measurement technique have exactly the opposite effect. For example, a cold engine in which the oil is still viscous, consumes an unusually large amount of fuel right after it starts. Since the WLTP lasts longer, the first few minutes become relatively less important. Moreover, the NEDC included only very abrupt stops, whereas the WLTP also features phases in which velocity declines gradually—ideal conditions for recovering the deceleration energy with the help of a 48-volt system.

Just how big the differences between the two cycles are for an identical vehicle remains a closely guarded secret at most carmakers. One exception: back in 2016, Opel announced that it would publish the consumption data for its most common engine-transmission combinations using both measurement techniques. For the experts, the results hardly came as a surprise: gasoline engines with a high specific output—like the gasoline-powered 1.6 l 147 kW—reveal a higher discrepancy in the compact Astra: in the NEDC—in combination with a six-gear standard transmission— fuel consumption comes to 6.1 l/100 km; in the WLTP it’s 10.0 l/100 km. Conversely, standard consumption of a Mokka X with a 1.6 l diesel engine (100 kW) and no special equipment is identical at 4.9 l/100 km. Because individual consumption for the customer won’t change anyway, it’s tempting to dismiss the whole business as a tedious obligatory exercise and move on to more important matters. That is, if it weren’t for one catch: the CO2 fleet target. Almost before we know it, in 2021, the limit will be 95 grams per kilometer. It’s true that the limit will be calculated individually for each manufacturer, depending on the weight of the actual vehicles sold. But, according to a forecast published by PA Consulting, premium models will account for around 100 grams in the fleet mix. Already in 2017, the European Commission plans to continue tightening the thumbscrews, and define a new limit to be attained no later than 2030. The experts expect the new limit for passenger cars to be 75 grams of COper kilometer, which would correspond to fuel consumption of 3.2 liters for gasoline and 2.8 liters for diesel per 100 kilometers.


This means that switching to the WLTP amounts to lowering the limit through the back door. According to the EU, this isn’t planned; far more, the idea is to implement conversion factors following a period of observation. In just a few years, ordinary car buyers will have forgotten the NEDC, just as they have the old Euromix. On the other hand, when they’re on the highway, from time to time they’ll probably overtake a vehicle with a large metal box mounted to the rear bumper. When a young child sitting on the backseat asks his father what it is, it could well result in a rather involved answer: “You know, a few years back there was a scandal. It turned out that there were a lot more toxic substances coming out of exhaust pipes than people thought. So they decided they wouldn’t test for toxic substances in lab experiments any more. Instead, they attached a miniature lab to the bumper that measured toxic emissions when the vehicle was actually driving down the road.” The fictional father will have done a pretty good job of outlining the history of RDE measurements. RDE stands for ’Real Driving Emissions’, and thus for a whole stack of new regulations that also come into force in fall 2017, which will be progressively tightened. These aren’t aimed at nontoxic CO2, but at classic pollutants, especially nitrogen oxide. The fact the RDE measurements take place in real traffic doesn’t mean that there aren’t rules for conducting these tests. For example, a valid test run has to include 16 kilometers each in town, on a rural highway, and on a superhighway. In the process, they have to climb up to 1,200 meters of cumulative elevation. The vehicle can be loaded with up to 90% of its total permissible carrying capacity. And to make sure the car isn’t just moving along at one speed, a dynamic specification exists that is calculated from mean acceleration and average speed. In unfavorable cases, these factors can add up. In future, new vehicles will be allowed to exceed the test stand value—for the time being still calculated in the NEDC—by a factor of just 2.1. During a subsequent phase that comes into force in 2020, a value will have to be maintained, plus the measurement tolerance of perhaps 50 %. The RDE regulations will at first apply only to Europe, though there is at least talk of introducing them in China starting in 2020. As for the WLTP, whose name suggests an aspiration for global validity, it will initially be confined to only a few regions. Starting in 2018, Japan plans to gradually replace the JCO8 test it has used until now with the WLTP.

New cycles—new opportunities?

When engine developers talk about the challenges the new Real Driving Emissions test is confronting them with, they draw a simple diagram: the x-axis represents the engine speed, the y-axis, the required performance. Then they put in lots of dots. With the NEDC test stand used up until now, the dots form a dense cloud in the lower left hand corner of the diagram. With the WLTP, due to be used starting in fall 2017, the cloud of dots is somewhat larger, and extends into the center. Conversely, the RDE tests lead to dots appearing practically everywhere. In effect, this will mean that future engines in all states of operation will be allowed to emit only a bare minimum of pollutants. Basically speaking, the technology necessary for this is available and offers specialist parts suppliers new opportunities for growth. It’s true that selective catalytic reduction (SCR) is available as an after-treatment technology—one that is highly effective in reducing nitrogen oxide emissions in diesel engines. On the other hand, all vehicle makers are striving to minimize consumption of AdBlue, an aqueous urea solution. As a result, reducing the volume of raw emissions produced by the engine remains important. Exhaust gas recycling (EGR) is a tried-andtested means of doing this. It’s possible to expand their operating spectrum, especially at low temperatures after a cold start, especially by employing wear-resistant electromechanical actuators. Investigations conducted at Rheinmetall Automotive reveal that a well-designed EGR system can reduce AdBlue consumption from three to one liter per thousand kilometers. For gasoline engines, future installation of particle filters on a massive scale has finally resolved the exhaust gas issue—the task at hand now is to reduce as far as possible the consumption gap vis-à-vis diesel. One way of doing this is exhaust gas recycling, which also works at high engine speeds and loads, when more fuel is often injected than is actually necessary for the combustion process. But at full throttle, the fuel cools the heat-stressed components, which can reach temperatures of over 1,000 degrees. The same effect can be achieved by channeling cooled exhaust gas into the combustion process. Accordingly, Rheinmetall Automotive sees developing high temperature-resistant EGR components— perhaps even with active cooling—to be a core R&D task. Furthermore, the new cycles will require electrification of the drive unit, starting with the 48-volt system and extending to a sporty plug-in hybrid. Because every time you step on the gas, both fuel consumption and emissions rise abruptly. This effect can be reduced when part of the power necessary for this derives from the electric system. Rheinmetall Automotive is benefitting from this trend too thanks to the electrification of auxiliary units such as coolant pumps or coolant compressors, which until now were mechanically driven.