Bavarian municipal utility Augsburger Stadtwerke aims to make its entire local public transport operation CO2-neutral by 2017, and buses fuelled with renewable natural gas (biomethane) are leading the way. The Augsburg-based public utility buses serving the city have been running on environmentally friendly natural gas for many years and switched to 100-percent renewable natural gas in 2011. Now it is adding 13 new-model Mercedes-Benz Citaro NGT (Natural Gas Technology) buses to its fleet.
On 11 December 2015, Tammo Voigt, Head of Local Public Transport Fleet Sales at the Mercedes-Benz Bus and Coach unit, handed over the symbolic key for the first delivered Citaro natural-gas bus featuring new engine technology to Ernst Schäfer, Head of the Bus Workshops at Augsburger Stadtwerke.
Augsburg is Germany’s first city to have an almost completely CO2-neutral bus fleet in service on its roads. The new Citaro NGT with natural-gas engine sets standards in terms of environmental friendliness and comfort. It is approved for the use of renewable natural gas to DIN 51624 (Automotive Fuels – Compressed Natural Gas – Requirements And Test Methods) without restriction and discernibly undercuts the noise level of its diesel-engined counterpart. Depending on the driving status, its noise emissions are up to 4 dB(A) lower, which corresponds to the subjectively perceived noise level almost being cut by half.
Both factors – low CO2 emissions and low noise level – predestine the new Citaro NGT specifically for service in busy inner cities and for serving residential areas or old-town districts with high numbers of tourists like Augsburg.
This version of the articulated gas-powered bus has 43 seats and standing room for a further 108 passengers.
New M 936 G gas engine
At the heart of the new Citaro NGT is the Mercedes-Benz M 936 G natural-gas engine. With a displacement of 7.7 l, it is currently the most compact natural-gas engine in its class and weighs just 747 kg including the precatalyst.
The natural-gas engine is based on the OM 936 turbodiesel engine. The vertically installed six-cylinder in-line mono-fuel engine runs on compressed natural gas or biogas. It has an output of 222 kW (302 hp) at 2000 rpm while delivering a peak torque of 1200 Nm consistently from 1200 to 1600 rpm. In many instances, it undercuts the Euro VI emission limits by a considerable margin. These figures, in combination with its impressive power delivery, put the single-stage turbocharged engine on a par with its diesel-powered counterpart. In the main transmission range, performance and torque characteristics remain consistent from idle speed to around 1500 rpm. Above this, the natural-gas engine actually delivers a slight advantage in terms of power and torque. Only from an engine speed exceeding 2000 rpm is the diesel engine superior to the natural-gas engine – levels that an urban bus does not reach in real-world scenarios.
At the same time, the natural-gas engine from Mercedes-Benz raises the bar for environmental friendliness particularly high, because the CO2 emissions of a natural-gas engine are up to ten percent below those of a diesel engine. Using renewable natural gas to power the bus makes the carbon footprint even better because in that case a natural-gas bus becomes virtually CO2 neutral.
Augsburg on the move
Augsburger Stadtwerke’s fleet of 89 buses, all powered by natural gas, clocks up around 4 million kilometres a year. The bus route network in Augsburg itself covers 137 kilometres and has 281 bus stops with 668 stopping places. Natural-gas buses first took to the road in Augsburg as far back as 1995, and the fleet has been running entirely on renewable natural gas since 2011. Stadtwerke Augsburg received the 2012 ADAC Mobility Prize in recognition of its environmental commitment and active contribution to inner-city air pollution control. The ADAC, Germany’s automobile association, has awarded its Mobility Prize for innovative transportation achievements and approaches in Bavaria every year since 2001.