Events & Fairs  |  Corporate  |  Bus 

Clean alternatives for the inner city: MAN Lion's City Diesel in EEV and Euro 6 MAN Lion's City CNG

Clean alternatives for the inner city: MAN Lion's City Diesel in EEV and Euro 6 MAN Lion's City CNG

  • MAN Truck & Bus offers four especially eco-friendly alternatives for city buses
  • Euro 6 technology for city buses premieres in Kortrijk
  • MAN realises Euro 6 optimised for consumption with SCRT system

At the Busworld 2011 in Kortrijk MAN Truck & Bus is showing its customers the entire bandwidth of environmentally friendly technologies for efficient city buses. What they have in common: they all combine particularly low pollutant emissions with excellent economy and are based on components that have proven themselves over many years of operation in MAN engines. The Busworld Kortrijk sees MAN presenting Euro 6 technology for diesel-powered city buses for the very first time. On show is a two-axle MAN Lion's City with a D2066 LUH engine delivering 235 kW (320 hp), with integrated exhaust-gas aftertreatment and an on-board diagnostic system complying with the statutory requirements of the Euro 6 standard. The D0836 LOH and D2676 LOH engines on display and the SCRT system (Selective Catalytic Reduction Technology) are also examples of MAN's Euro 6 technologies. The Euro 6 engines shown are representative of the wide range of engines and components for city buses that MAN also offers to external customers such as bus and body builders.

EEV with MAN PURE DIESEL® technology: the economiser

City buses from MAN meet the requirements of the currently strictest exhaust-gas standard, EEV (Enhanced Environmentally-friendly Vehicle), without an additive (AdBlue®). They therefore do not need any special infrastructure and are based on a mature technology whose long maintenance intervals, high payload and long service life are compelling. City buses from MAN achieve the EEV standard thanks to cooled exhaust-gas recirculation in conjunction with an MAN CRTec® particulate filter. The abbreviation "CRT" stands for "continuously regenerating trap". This filter comprises an oxidation catalytic converter integrated into the silencer. A downstream surface particulate filter reduces the mass of the finest particles in the exhaust gas by up to 99 percent. By comparison with Euro 5, EEV vehicles have to reduce the particulate in the exhaust gas by 33 percent (from 0.03 to 0.02 g/kWh in the European Transient Cycle). Also stipulated is a 70 percent decrease in smoke opacity relative to Euro 5. The MAN CRTec® particulate filter captures 100 percent of visible soot particles – irrespective of exhaust-gas temperatures and thus also immediately after a cold start. Until Euro 6 comes into effect, EEV is the recognised standard with the toughest requirements in terms of the particulate emission of diesel vehicles. EEV vehicles are thus an environmentally friendly alternative for green zones in the inner city.

MAN Lion's City Hybrid: rigorous reduction of CO2 for the city

Since 2010, MAN Truck & Bus has been offering an innovative city bus for urban transport that puts the technology of tomorrow on the road today: the Lion's City Hybrid. Continual braking and pulling away from bus stops and traffic lights are the optimum conditions for the use of hybrid technology. While conventional buses convert their braking energy to heat, the MAN Lion’s City Hybrid stores that energy in ultracaps, transforming it into power for its two electric drive motors. Finely tuned energy management controls the energy flow and switches the diesel engine off when it is in overrun, for example, or when the vehicle is stationary. Auxiliary consumers such as the air-conditioning system are electrically operated, being powered by the energy storage on the roof. The hybrid city bus emits no exhaust gases while at the bus stop and is able to pull away again very quietly under purely electrical power. This technology ­package makes the Lion's City Hybrid the most efficient option when it comes to CO2 emission and a pioneer for the future of urban transport. The low-floor bus saves up to 30 percent on diesel and CO2 with its serial hybrid drive. In addition, thanks to the long periods during which the diesel engine - when not switched off entirely - operates in its ideal speed range, the MAN Lion's City Hybrid achieves even better exhaust gas figures than a normal EEV-compliant diesel vehicle.

CNG: the economical alternative drive technology of today

Natural gas and bio-gas are eco-friendly, economical, future-proof alternatives to conventional diesel power for urban bus companies that are able to use an existing infrastructure to supply them with gas. MAN Truck & Bus is the market leader in natural-gas-powered city buses and offers the Lion's City CNG in a large number of variants as a solo or articulated bus in lengths from 12 to 18.75 metres. The range of products also includes chassis for city and intercity buses and CNG engines from 162 to 228 kW (220 to 310 hp) for external customers.

A characteristic of natural gas is that it burns very cleanly by comparison with other fossil fuels, so that engines emit low levels of raw pollutants. The systemic advantage of natural gas: emissions from CNG engines are way below the limits set for EEV, currently the most stringent emission standard. The engines' exhaust gases are especially low in nitrogen oxides (NOx) and particulates, and that without any complex filtering technology or additives. CNG engines and buses from MAN can also be run on treated biogas, which makes operation CO2 neutral. Moreover, CNG buses are also particularly quiet because combustion in the gas-powered engine, like its petrol-driven counterpart, is initiated by spark plugs and is therefore very smooth. And on top of all that, MAN's gas-powered engines convince with their long maintenance intervals, are easy to service and can be fully diagnosed using MAN-Cats II.

Euro 6 city buses: technology for the exhaust standard of tomorrow

With effect from January 1, 2014 all newly registered vehicles must comply with the Euro 6 exhaust-gas standard. The development of commercial vehicles that meet the requirements of Euro 6 poses an enormous challenge to the manufacturers, whose aim is to offer the customer efficient, reliable vehicles. At the Busworld in Kortrijk, MAN Truck & Bus is already presenting the technology required. The Euro 6 version of the MAN Lion's City shows illustrates how this technology is integrated into a city bus. With its Euro 6 diesel engines D2066 LUH (235 kW / 320 hp / 1,600 Nm), as mounted inside the exhibition bus, as well as the engines D0836 LOH (213 kW / 290 hp / 1,100 Nm) and D2676 LOH (353 kW / 480 hp / 2,300 Nm), MAN is giving a glimpse of what future units will offer in the way of performance. The newly developed, compact SCRT filter is an exhibit of its own at the fair. Together with the new engines, expanded vehicle electronics and the new AdBlue supply, it forms a part of the Euro 6 system.

Customers will be able to order the Euro 6 diesel version of the MAN Lion's City in the course of 2012 for delivery at the beginning of 2013. MAN is thus ready for the demand from municipal bus companies wanting to put Euro 6 buses into service in good time. The Lion's City with D2066 LUH engine being shown at the fair is the representative of the full range of MAN city buses being introduced for Euro 6. It meets the very highest emission requirements for inner city applications and is at the same time exceptionally economical. Touring coaches in the Euro 6 standard will be presented at the IAA 2012 and will also be on the market from 2013 on.

Euro 6 from MAN: proven components, new architecture

MAN has already been using the key technologies necessary for Euro 6 - EGR (exhaust-gas recirculation) and SCR (Selective Catalytic Reduction) - in commercial vehicles with great success for several years. SCR technology, for example, has been installed as standard in trucks since 2005. The MAN particulate filter technology CRTec was introduced in the year 2000. On this foundation, MAN will consolidate these tried and tested technologies and coordinate them optimally with each other for Euro 6. As far as the Euro 6 technology being shown by MAN at the Busworld Kortrijk 2011 is concerned, this means that the Euro 6 engines are also distinguished by dynamic characteristics, power and torque correspond to the EEV-compliant engines. A further reduction in fuel consumption was an extremely important goal for the developers.

For this reason, the most important success factor in the Euro 6 development was unifying two goals with opposed physical principles: the reduction of NOx and the reduction of fuel consumption and consequently of CO2 emission. MAN has been able to reduce the fuel consumption of its engines continually over the past few years, while at the same time meeting the ever more stringent requirements regarding nitrogen oxide reduction. For the leap from Euro 5 / EEV to Euro 6, the MAN developers have optimised injection and combustion with regard to consumption and production of particulate. In the course of the series-production and field tests, exact data on consumption has been and continues to be collected. MAN expects the consumption of its Euro 6 city buses to be at least as low as that of the EEV models. An additional benefit of such combustion is the smaller amount of particulate in the exhaust gas.

By comparison with the Euro 5 standard, Euro 6 requires a reduction of 80 percent in NOx emissions, from 2 g/kWh to 0.4 g/kWh. MAN Truck & Bus achieves this with a combination of controlled exhaust-gas recirculation and an SCR catalytic converter for exhaust-gas aftertreatment. Dividing the workload between the two systems, EGR and SCR, is the optimum solution for low fuel consumption paired with low AdBlue® consumption. Operating in the engine itself, EGR enables a consumption that is optimised for low raw emissions of NOx. This in turn enables low AdBlue® consumption for NOx reduction in the SCR system. It is the combination of EGR + SCR that makes for effective NOx reduction in the classic city bus cycles. MAN's concept is distinguished by low fuel consumption, low AdBlue® consumption and high reliability.

Compared with Euro 5, the particulate mass has to be reduced by a further 66 percent. In addition, Euro 6 stipulates for the first time a limit on the number of particles. This limit can only be achieved by using a CRT particulate filter, which practically leads to a reduction of particulate mass by more than 90 percent, compared to Euro 5. This is why MAN has combined an SCR catalytic converter with a closed particulate filter including a sensor to form the SCRT system, whose compact dimensions enable it to fit neatly into the silencer. The entire Euro 6 technology is integrated into the city bus in such a way that not a single seat is lost relative to the EEV-compliant diesel bus. To a large extent, MAN's engineers were even able to retain the weight advantage of MAN city buses with MAN PURE DIESEL® technology: the extra weight of the Euro 6 system compared with EEV is around 150 kg.

The reduction in nitrogen oxide emissions required by Euro 6 is roughly as much as in all five previous stages of the Euro standard together. In Euro 6, the systems will for the first time have to continuously monitor compliance with limit values in operation ("in-use compliance"). The expanded requirements regarding the in-use monitoring of NOx necessitate new, more complex vehicle electronic systems and sensor.

Central components of Euro 6 technology in the MAN city bus

The central components for Euro 6 are, on the engine side, common-rail- injection, cooled and controlled exhaust-gas recirculation and two-stage turbocharging. These are followed by exhaust-gas aftertreatment by an SCR system with integrated oxidation catalytic converter plus CRT filter (Continuous Regenerating Trap). Electronic sensors permanently monitor the absorption capacity of the particulate filter. Also integrated into the SCRT system is the sensor monitoring NOx.

Common-rail injection has been standard at MAN since 2002, the Euro 5, EEV and Euro 6 engines are already equipped with third-generation CR systems. Only today's CR systems with their fully-variable injection control enable the physics balancing act required in order to deal with nitrogen oxides, particulate and consumption at every operating point. The development engineers designed the common-rail injection for Euro 6 so that injection pressures are up to 1,800 bar, the same as in Euro 5/ EEV engines. The most important of the Euro 6 engine's key components, the fundamentally new combustion design, burns diesel fuel at higher temperature and is thus more economical.

With regard to turbocharging, Euro 6 employs a combination of two-stage turbocharging with primary cooling and intercooling of the boost air. Two robust turbochargers in a compact supercharging module regulate the inlet air and boost pressure in two stages, and consistently use the energy contained in the exhaust gas. The high-pressure stage, a small exhaust turbocharger with waste gate, ensures speedy build-up of boost pressure and thus high pulling-away torque in the lower load and engine-speed range. Even at low engine speeds the high air ratio is produced that is required for combustion with low particulate content. In the upper load and engine-speed range, the low-pressure stage ensures the necessary amount of air and is characterised by especially high efficiency, resulting in very good fuel consumption and combustion with low particulate levels. This turbocharging strategy not only helps the Euro 6 engines also produce the pulling power at all engine speeds for which MAN is renowned, it is also consciously based on two separate rugged and reliable turbochargers instead of a single, more complex turbocharger with variable turbine geometry.

The basic design of the engine and stroke and bore have not changed. Similarly, there have been no modifications to the dimensions or arrangement of the engine cooling system.

Cooled exhaust-gas recirculation (EGR) has been in series production at MAN since 2000. EGR combined with the cooling of the recirculated exhaust gas creates a lower temperature of the fresh air/exhaust mix in the cylinder – even in combustion, fewer nitrogen oxides are produced. Thanks to EGR control with its lambda probe, the optimal EGR rate is set for each operating point of the engine even in dynamic conditions. That guarantees especially high efficiency and economical diesel consumption.

The newly developed SCRT system used for exhaust-gas aftertreatment combines an SCR catalytic converter with an oxidation catalytic converter and a closed, electronically controlled surface particulate filter. The particulate filter component has already seen duty in EEV-compliant city buses (CRTec® filter, Continuously Regenerating Trap). The system is fully integrated into the Euro 6 rear silencer. Also new is the arrangement of the tanks: the diesel and AdBlue® tanks on the MAN Lion's City are located on the right side of the vehicle, with the 20-litre AdBlue tank placed next to the diesel tank for ease of operation. Its cap is coloured blue to prevent any confusion. AdBlue® has a freezing point of minus 11.5 degrees Celsius. For this reason the tank, the supply lines and the AdBlue® dosing module can be heated, ensuring that exhaust gases are properly cleaned even at low ambient temperatures.

The Euro 6 legislation means that on-board diagnosis has to provide several more functions; the electronics now has to permanently monitor the emission values. In the event of a fault, OBD informs the driver by means of a warning indicator. In addition and independently thereof, Euro 6 legislation stipulates an NOx control system ("Anti-Tampering"). This system monitors the SCR system, checking that it is supplied with AdBlue® in the specified amount and quality. If this is not the case, a warning is initially output to the driver. In a second step, this leads to a reduction of torque, and in a third step to a speed restriction. For the first time, the measured values must comply with the "Worldwide Harmonized Duty Cycles", which means i.e. also from a cold start and during light-loading operation. Moreover, the system must be guaranteed to have a service life of 700,000 kilometres or seven years. This shows clearly just how comprehensive the development and product requirements for Euro 6 vehicles are.

Simplified, the SCRT system functions as follows. First, an oxidation catalytic converter with a highly efficient precious-metal coating converts the limited constituents of the exhaust gas, HC and CO, to harmless CO2 and H20. The nitrogen oxides are also largely converted from NO to NO2. The surface particulate filter (CRT) that follows traps up to 99 percent of the particulate mass present in the exhaust-gas stream. The soot particles trapped in the CRT filter are burned using the NO2 produced beforehand or converted to CO2. The soot loading on the particulate filter and thus the effectiveness of the filter are electronically monitored by a sensor. This information is also fed to the vehicle's service interval indicator. The maintenance interval is influenced by the operating conditions, which are detected by the sensors. The on-board electronic system then informs the driver as to the state of the filter. Continuing the process, with the help of the injected reducing agent AdBlue® the SCR catalytic converter reduces the amount of nitrogen oxide to below the Euro 6 limit of 0.4 g/kWh.

The SCR process enables a combustion design producing low levels of particulate at high combustion temperatures. This made it possible for MAN's engine designers to also realise consumption-optimised combustion. With the help of the additive AdBlue®, selective catalytic reduction reduces the nitrogen oxides that are formed. This harmless reducing agent is injected ahead of the SCR catalytic converter as required. The last element that the exhaust-gas flows through is an ammonia-blocking catalytic converter. This converts any residual amounts of the NH3 (ammonia) formed in the SCRT catalytic converter into nitrogen and water.