Promise kept: demonstrably lower fuel consumption with Euro VI-certified Mercedes-Benz Citaro and Setra ComfortClass

  • Promise kept and exceeded — Euro VI makes economic sense
  • Record Run Buses 2012: five buses, five days, 18,000 km
  • Citaro Euro VI: 8.5 per cent better fuel economy in Record Run
  • Setra ComfortClass S 515 HD: savings of 8.2 per cent in diesel fuel
  • Three Citaro buses in round-the-clock line service in Wiesbaden
  • Two Setra coaches completed 1800 km on motorways each day
  • Citaro Euro VI: ancillary components optimised in particular
  • Setra ComfortClass 500: outstanding aerodynamics
Stuttgart/Wiesbaden – The objective seemed impossible: a simultaneous reduction in fuel consumption and exhaust emissions while meeting Euro VI emission standards. In the Record Run Buses 2012 the new Euro VI-certified Mercedes-Benz Citaro urban regular-service bus and the new Setra ComfortClass 500 touring coach demonstrated that the two seemingly conflicting goals can be achieved at the same time. During the Record Run Buses 2012 the five buses covered a total distance of 18,000 kilometres under impartial supervision. The bottom line: the buses not only deliver on the promised fuel savings of four to six per cent (Citaro) and five to six per cent (Setra) but can even noticeably surpass these figures. Another insight gained from the Record Run Buses 2012: Euro VI can also pay off economically.
Record Run Buses 2012: five buses, five days, 18,000 km
The five buses completed a demanding round-the-clock program between 22 and 26 October 2012. Loaded at 50 per cent of the payload with a realistic 3.2 t of ballast, the three Mercedes-Benz Citaros each covered a distance of about 1400 km in demanding urban traffic. The two high-deck touring coaches of the Setra ComfortClass 500 travelled about 9000 km each in long-distance trips on public roads.
The urban traffic in Hesse’s capital Wiesbaden (Citaro) and trips between Leipzig and Hamburg as well as trips in the quadrangle formed by the cities of Leipzig/Sangershausen, Schweinfurt, Hof and Bautzen (Setra) presented challenging routes for the five buses.
Citaro Euro VI: 8.5 per cent better fuel economy in Record Run
The Mercedes-Benz Citaro came to the starting line in three versions: The new Euro VI-certified model with the also new Mercedes-Benz OM 936 h engine and a displacement of 7.7 litres and a rated power output of 220 kW (299 hp) faced the directly comparable Euro V-certified predecessor models with OM 906 hLA engine (6.4 litres displacement, rated power output 210 kW/286 hp) as well as with OM 457 hLA engine (220 kW/299 hp). Transmissions, final drive ratios and tyres were identical in each case.
With a fuel consumption of 38.7 l/100 km the new Euro VI-certified Citaro turned in an excellent performance in the Record Run Buses 2012 in light of the difficult route. It considerably outperformed its predecessors, which are known to be economical, by 3.6 l/100 km or 8.5 per cent. This means the Euro VI-certified Citaro not only delivers on the brand promise of fuel savings of three to five per cent but can even significantly surpass these figures. Assuming an annual mileage of 60,000 km it also relieves the burden on the environment by 5700 kg in CO2 emissions at the same time.
The fuel savings translate into a surprising economic equation: assuming an annual mileage of 60,000 km and current fuel prices of about 1.25 euros per litre (excluding VAT), the new Euro VI-certified Citaro saves about 2700 euros in costs for diesel fuel annually. The additional expense for the new Euro VI-certified Citaro is worthwhile not only because the vehicle pays for itself after about four years but also due to the predicted higher value retention.
The conclusion to be drawn from the Record Run Buses 2012: the move to Euro VI not only significantly lowers the fuel consumption and emissions of the Mercedes-Benz Citaro; Euro VI also pays off economically.
Setra ComfortClass 515 HD: savings of 8.2 per cent diesel fuel
The results for the new Setra ComfortClass 500 are similar. Here a Euro VI-certified S 515 HD of the ComfortClass 500 with the new Mercedes-Benz OM 470 engine and a rated power output of 315 kW (428 hp) rolled up to the starting line. The in-house opponent was the directly comparable S 415 GT-HD ComfortClass 400 predecessor model with the previous OM 457 LA engine and an identical power output of 315 kW (428 hp). This duel also featured identical gear and final drive ratios as well as tyres. Both buses were fully loaded to the maximum permissible gross vehicle weight of 18 tonnes.
Travelling a distance of 7000 km with an average fuel consumption of 21.0 litres/100 km the new ComfortClass S 515 HD also turned in an outstanding economic performance. It outperformed the fuel-efficient comparison model by 1.9 l/100 km or 8.2 per cent.
In light of the prediction of five to six per cent in fuel savings it must be noted for the Setra touring coach as well: promise kept and in the Record Run Buses 2012 even surpassed.
Crunching the numbers also pays off in the case of the Setra ComfortClass 500: given the current fuel price of around 1.50 euros a litre and an annual mileage of 100,000 km it saves the operator about 2850 euros in fuel costs, at 180,000 km the savings amount to more than 5000 euros a year. The respective reductions in CO 2 emissions are around 5000 kg and 9000 kg a year. It goes to show: Euro VI is a worthwhile investment not only with regard to protecting the environment and conserving resources; Euro VI also makes economic sense.
Five buses in five-day major efficiency test
Start and finish line for the three Mercedes-Benz Citaros and the two Setras of the ComfortClass 500 was Wiesbaden, the capital of the German state of Hesse. The run started at 1 p.m. on October 22. 
With the exception of two refuelling stops each day, the five buses operated around the clock for five days straight.
Three Citaros in round-the-clock urban regular service in Wiesbaden
For the urban bus comparison the new Euro VI-certified Mercedes-Benz Citaro competed as a standard bus against its predecessors with comparable power output. In each case power was transferred by the fully automatic ZF Ecolife torque converter transmission. Also identical was the final drive ratio of i=5.771.
All Citaros operated in line service on the demanding route 17 in Wiesbaden. It traverses the city centre of Hesse’s capital including the pedestrian zone and outlying areas.
To ensure realistic operating conditions, the test buses followed the urban buses in regular service at a significant distance. They also maintained a significant distance between each other. The elevation change along Route 17, which is 18.6 km long, is over 400 metres. The buses completed 17 round trips each day and stopped at each bus stop where the buses were lowered using the kneeling function and the passenger doors were opened.
Two Setras completed 1800 km on motorways each day
In the touring coach comparison the Euro VI-certified Setra ComfortClass S 515 HD competed against its Euro V-certified Setra S 415 GT-HD ComfortClass 400 predecessor with identical engine power output. The two-axle high-deck touring coaches each measure a little over 12 metres in length. The ComfortClass 515 HD coaches were powered by the OM 470 engine with 315 kW (428 hp). Its OM 457 predecessor in the ComfortClass 415 GT-HD had the identical power output. The touring coaches were equipped with the Mercedes GO 250-8 PowerShift (ComfortClass 500) respectively the Mercedes GO 240-8 PowerShift transmission. Their gear ratios were identical as was the final drive ratio of i=3.583 of both high-deck coaches.
The touring coaches also used Wiesbaden as the starting point, in this case for a trip to Leipzig. From there they made an 8881-km daytime loop from Leipzig via Erfurt, Schweinfurt, Bayreuth and Dresden to Bautzen and back. At night the two Setras drove a 922-km route from Leipzig via Potsdam to Hamburg and back.
The touring coaches travelled a distance of just over 1800 km a day. Some 90 per cent of the distance was driven on motorways, the remaining ten per cent on main and country roads. The vehicles travelled at the legal speed limit of 100 km/h or 80 km/h whenever the traffic situation permitted such speeds.
Identical conditions, technology and refuelling stops monitored
In addition to the transmissions and the final drive ratios, the loads as well as the tyre brand and tread depth were also identical within each respective model series. All buses had been broken in at the start of the Record Run Buses 2012 with around 10,000 km on the odometer. The Record Buses 2012 were driven by skilled test drivers as well by trainers from Omniplus Ecotraining. Each shift, a crew of two drivers manned each of the five buses. These crews changed buses every day. The buses were operated in two shifts around the clock. In addition, the drivers for the Record Run Buses 2012 on route 17 in Wiesbaden received briefings from driving instructors of the transport authority.
The test vehicles and their operations were monitored by Dekra, an independent specialist automotive organisation. The engineers sealed all components relevant to fuel consumption as well as the fuel tanks, and monitored all refuelling stops. In addition, the load was checked and sealed. All refuelling stops were at the same filling stations in Wiesbaden or Leipzig and even at the same pumps. Even the position of the vehicles at each pump was defined.
The buses were also equipped with instruments for measuring fuel consumption. Any movement of the five buses in the Record Run Buses 2012 could be monitored with the help of the FleetBoard telematics system.
Arrival at the finish line in Wiesbadenafter 18,000 km on 26 October 2012
All five buses crossed the finish line of the Record Run Buses 2012 in Wiesbaden at 2:00 p.m. on 26 October 2012. By that time the touring coaches each had covered a distance of some 7000 km, the urban regular-service buses each just shy of 1400 km.
Citaro and ComfortClass 500: maximum efficiency
The engineers from Daimler Buses employed all available means to achieve maximum efficiency of the Mercedes-Benz Citaro and the Setra ComfortClass 500. A multitude of measures counteract the inevitable added weight of the additional or larger components that the move from Euro V to Euro VI entails. For this reason the new ComfortClass 500 actually weighs less than the predecessor model. In spite of this, both buses were fully loaded with 18 tonnes.
The centrepieces of the drive system are the new BlueEfficiency Power engines. Both the in-line six-cylinder Mercedes-Benz OM 936 engine in the Citaro and the OM 470 engine in the Setra ComfortClass 500 are characterised by robustness, longevity and maximum cost-efficiency with regard to fuel, motor oil and AdBlue consumption as well as by long maintenance intervals. A distinctive trait of the engines is a high torque at very low engine speeds and an excellent throttle response. Both qualities are part of the prerequisites for successfully taking the place of the predecessor engines that to some extent had significantly more displacement – the keyword in this context is downsizing.
In addition to the drive system the development engineers carefully examined the ancillary components with an eye on fuel economy and longevity, for the Mercedes-Benz Citaro as well as for the Setra ComfortClass 500. Alternators, battery management, radiator fan and air compressor – these and other components play a major role in fuel consumption and in both model series were optimised down to the last detail.
Citaro Euro VI: ancillary components specifically optimised
Two distinctive features on the Euro VI-certified Citaro deserve special mention, both of which are major factors in an urban regular-service bus. A lowered entrance height reduces the amount of air needed for kneeling and consequently the amount of energy required. The second point concerns the energy management: free (without diesel injection) electricity generated in overrun mode is stored in dual-layer capacitors (supercaps) and is available the next time for acceleration. This relieves the burden on the alternators and consequently reduces fuel consumption.
Setra ComfortClass 500: outstanding aerodynamics
Outstanding aerodynamic properties are essential for the Setra ComfortClass 500 touring coach. From the rounded front with clipless blade wipers and optimised exterior mirrors to smooth flanks and the tapered rear with its separation edge, the aerodynamic efficiency of the ComfortClass 500 sets new touring coach benchmarks. The result is an outstanding drag coefficient of just 0.33. The drag is also reduced by a trick that is unmatched in the industry: at speeds of 95 km/h and above the bus is lowered by 20 mm.
Prediction: reduction in fuel consumption between four and six per cent
The development engineers of Daimler Buses expected these measures to add up to a reduction in fuel consumption of the Mercedes-Benz Citaro by four to six per cent as the result of the move from Euro V to Euro VI emission standards. For the switch from the Setra ComfortClass 400 to the new ComfortClass 500 the engineers expected a fuel economy advantage of five to six per cent for the new model. Under the real-life conditions encountered during the Record Run Buses 2012, these predictions were not only substantiated; the results actually significantly exceeded the predicted values.

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    Record Run Buses 2012: Arrival at the finish line in Wiesbaden after 18,000 km on 26 October 2012
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    Record Run Buses 2012: Arrival at the finish line in Wiesbaden after 18,000 km on 26 October 2012
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    Record Run Buses 2012: Arrival at the finish line in Wiesbaden after 18,000 km on 26 October 2012
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    Record Run Buses 2012: Arrival at the finish line in Wiesbaden after 18,000 km on 26 October 2012
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    Record Run Buses 2012: Mercedes-Benz Citaro
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    Record Run Buses 2012: Mercedes-Benz Citaro
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    Record Run Buses 2012: Mercedes-Benz Citaro
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    Record Run Buses 2012: Mercedes-Benz Citaro
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    Record Run Buses 2012: Mercedes-Benz Citaro
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    Record Run Buses 2012: Mercedes-Benz Citaro
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    Record Run Buses 2012: Mercedes-Benz Citaro
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    Record Run Buses 2012: Mercedes-Benz Citaro
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    Record Run Buses 2012: Mercedes-Benz Citaro
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