DEKRA-certified tests: Mercedes-Benz HD trucks cut fuel consumption 22% in 20 years while meeting more stringent emissions rules; VECTO
Despite drastically more stringent emission standards for nitrogen oxides and particulates, the fuel consumption of Mercedes-Benz heavy trucks has been reduced by 22% over the last 20 years, according to the results of a comparative test drive certified by the test organization DEKRA.
The August 2016 testing by commercial vehicle magazine Lastauto Omnibus (LaO) compared the latest generation of the Mercedes-Benz Actros long-distance truck compared to the basic model of 1996—a Mercedes-Benz from the SK model series and therefore one of the last representatives of the pre-Actros era. The model 1844 was certified according to the Euro II standard valid in 1996, and was therefore allowed to emit 7 grams of NOx per kilowatt hour (kWh) while staying within the limiting value of 0.15 g/kWh for particulate matter. The number and size of the soot and other particles was not prescribed.
|Left to right: Mercedes-Benz SK 1844 Euro II (model year 1996), Mercedes-Benz Actros 1846 Euro III (model year 2003), Mercedes-Benz Actros 1845 Euro VI (model year 2016). Click to enlarge.|
The second test vehicle, an Actros 1846 (production year 2003) was certified according to emission standard Euro III, with 5 grams of NOx per kilowatt hour (kWh) and 0.10 g/kWh of particulate mass.
The latest-generation Euro VI Mercedes-Benz Actros 1845 was the third test vehicle. A current Euro VI Actros betters the old Euro II limits by 94.3% (NOx, present limit 0.4 g/kWh) and 96% (0.01 g/kWh) for particulate mass, though today’s measuring conditions are far more stringent.
This reduction in fuel consumption has resulted in savings of more than 50 million tons of CO2 by Mercedes-Benz trucks in Europe since 1996. This calculation is based on the following: sales of around one million Mercedes-Benz trucks in the segment of long-distance transport in Europe between 1996 and today, as well as a conservative estimate for the annual mileage of 75,000 km per vehicle, and a service life of eight years. The current fuel consumption per 100 km measured during the certified DEKRA test run for the years 1996, 2003 and 2016 is extrapolated on a linear basis for the other years.
Against a background of drastically reduced emission levels in the traditional pollutant categories, the actual on-the-road consumption for the test covering 1,536 kilometres (954 miles) on very demanding topography with a test weight of 40 tons showed the following results over an identical route and distance:
- The 20 year-old Mercedes-Benz SK (model 1844) reached a figure of 40.8 l/100 km (5.76 mpg US);
- The Actros 1846 Euro III consumed 37.4 l/100 km (6.28 mpg US); and
- The current Euro VI Mercedes-Benz Actros 1845 31.9 l/100 (7.37 mpg US).
The test was structured according to the principles which LaO test manager Frank Zeitzen has defined for all on-road fuel consumption and vehicle mileage measurements. These include test vehicles that have been identically prepared as far as possible, and highly experienced truck test journalists at the wheel. The test drivers took turns behind the wheel after each test round, and the semi-trailers were changed every day.
This ensured that the trailers being towed were used the same number of times with each tractor unit. This eliminates differences in rolling characteristics. The semi-trailers were identically loaded and had the same tires.
For this three-generations comparison, three box semitrailers were loaded to an identical 32 tons and fitted with the same tires. So as to reflect progress made in rolling characteristics as well, the basic Mercedes-Benz SK 1844 truck from 1996 was shod with the then very popular Michelin XZA/XDA tyres in size 295/80-22.5. The second test truck, the Actros 1846 (from 2003) was fitted with tires from the Michelin Multiway family, in size 315/70-22.5 still current today. The latest-generation Actros 1845 Euro VI was fitted with factory-fresh Michelin tires in size 315/70-22.5.
Where the mileage of the test vehicles is concerned, the new Actros Euro VI was at a slight disadvantage. With just over 8,000 km on the odometer, it was not yet quite run-in. The best fuel economy thanks to minimized resistances within major assemblies is normally to be expected after around 50,000 km. The Actros 1846 Euro III (from 2003) used in the test was thoroughly run-in at 55,000 km. The 20 year-old basic vehicle, the Euro II Mercedes-Benz SK 1844 dating from 1996, had an odometer reading of 610,000 km.
LaO test manager Zeitzen prescribed the same driving style with exact requirements for himself and the other two test drivers, Michael Kern and Vassilis Daramouskas. The cruising speed and overshoot/undershoot times for downhill and uphill gradients were defined and monitored by the recording personnel. Conventional cruise control was used to ensure a consistent cruising speed for the two older trucks. In the latest Actros this was taken care of by the Predictive Powertrain Control (PPC) system.
All in all, six measuring rounds of 256 km were taken on the Lastauto Omnibus test circuit. The test drivers changed vehicles after each measuring run, and the 32-tonne trailers were also exchanged in accordance with the assigned driver. Every evening the vehicles were refueled under precise, temperature-compensated conditions.
Although the precise fuel consumption levels in such a three-generations comparison will be different on other test routes, nNo great differences are to be expected in the relative figures.
VECTO test procedure. To ensure even better comparability of actual fuel consumption by trucks in future, Europe’s truck industry has agreed to develop a measuring cycle. The test procedure intended to achieve this is called VECTO (Vehicle Energy Consumption Calculation Tool). Here too, the major input data are measured and subsequently processed using a calculation tool officially provided by the European Commission.
The test course to be used has been defined as representative of European long-distance operations in a very involved process. For example, the aerodynamic drag of every single cab variant of a truck model has been measured on the road by independent test organizations.
The same applies to the rolling resistance of tires. Here too, the tire manufacturers have had to demonstrate the rolling characteristics of their product lines, i.e. different sizes, substructures and tread patterns, in extensive road tests. Where the powertrain consisting of the engine, transmission and drive axle(s) is concerned, as in the case of the cab, it is the vehicle manufacturer who must deliver.
The VECTO test procedure is currently being finalized in the official committees of the European Union, and will first be used for the most important truck segments (long-distance and distribution) in the summer/autumn of 2018.