Fuel Cell Propulsion for Urban Duty Vehicles – Bavarian Fuel Cell Bus Project

R. Wurster, M. Altmann, Ludwig-Bölkow-Systemtechnik GmbH [LBST], Daimlerstr. 15, D-85521 Ottobrunn
D. Sillat, Linde AG, Werksgruppe Technische Gase, Seitnerstr. 70, D-82049 Höllriegelskreuth
H.-J. Drewitz, Ch. Gruber, MAN Nutzfahrzeuge AG, P. O. Box 500620, D-80976 München
K.-W. Kalk, MAN Technologie AG, P. O. Box 1347, D-85751 Karlsfeld
A. Hammerschmidt, W. Stühler, Siemens AG, KWU BSZ 2, P. O. Box 3220, D-91050 Erlangen
E. Holl, Siemens AG, VT 51, P. O. Box 3240, D-91050 Erlangen

Published at the 12^th World Hydrogen Energy Conference, Buenos Aires, Argentina, June 1998

1. ABSTRACT

Following a feasibility study [2, 3] and a detailed specification phase, the realization of a fuel cell city bus prototype was started in autumn 1996 [1]. The project is a joint development effort of Siemens, MAN and Linde, which receives a 50 % funding by the Bavarian State Ministry for Economic Affairs, Transport and Technology [BStMWVT] in the context of the Hydrogen Initiative Bavaria [4, 5].

An MAN low-floor bus will be equipped with the components for a fuel cell drive system. The PEM fuel cell is developed by the power generation division of Siemens. Four fuel cell modules deliver a total electrical output of 120 kW to the two electric motors, which are linked by a summation gearbox by the Siemens Transportation Systems Division. MAN Technologie AG is responsible for the compressed hydrogen storage system allowing for a driving range of more than 250 km, while Linde AG takes care of the hydrogen periphery and delivers the hydrogen for the test operation scheduled for the beginning of the year 2000. Project coordination is done by Ludwig-Bölkow Systemtechnik GmbH.

The project is divided into four phases. The conceptual design phase is scheduled to last until the end of 1997. The partly overlapping system integration phase will end in the first quarter of 1999. The subsequent test and commissioning phase will prepare the test operation at the beginning of 2000 with a bus operator yet to be defined.

2. INTRODUCTION

In 1994, a group of interested Bavarian industry started work on fuel cell propulsion for city buses and urban delivery vehicles. A feasibility study was carried out and detailed specifications were elaborated by LBST [2, 3] in collaboration with the industry partners funded by the Bavarian State Ministry for Economic Affairs, Transport and Technology [BStMWVT]. In late 1996, the realization of a fuel cell city bus prototype was started by Siemens Power Generation (KWU), Siemens Transportation Systems, MAN Nutzfahrzeuge, MAN Technologie and Linde. The project receives a 50 % funding by BStMWVT in the context of the Hydrogen Initiative Bavaria [4, 5]. It is coordinated by LBST.

The construction of the prototype fuel cell bus will last until next year followed by a test and commissioning phase. Test operation is planned to start in early 2000 with a bus operator yet to be defined.

3. THE FUEL CELL BUS

The project status presented here is of February 1998 [1].

3.1 The concept

A conventional low-floor city bus will be equipped with a fuel cell system delivering electricity to an electric drive train. The hydrogen is stored on-board the vehicle in compressed gaseous form. Figure 5 shows a schematic of the bus; table I summarizes its technical data.

3.2 The bus

An MAN low-floor city bus will be adapted to fuel cell propulsion. The fuel cell system will be housed at the rear of the vehicle The 12 m fuel cell bus named NL 163 BZ will have a maximum total weight of 18t.

In addition to housing the various components of the fuel cell drive, the main bus design work is the choice and design of the auxiliary power consumers normally hydraulicly driven, e.g. brakes, doors etc. Here, everything will be electrically driven.

3.3 The fuel cell

The fuel cell system will be a PEM (proton exchange membrane) fuel cell manufactured by Siemens Power Generation (KWU). It consists of four modules each delivering 30 kW rated output power at a voltage level of 400 V at maximum output. The operating parameters are: 60° C operating temperature, 1.5 bar (abs.) air operating pressure, air ratio 2. The hydrogen consumption at rated output is 8 kg/h.

3.4 The electric drive

The bus will be propelled by two asynchronous motors transmitting their power to the rear axle via a summation gearbox and a cardan shaft. The electric motors have a maximum output of 75 kW each. A pulse-controlled inverter will transform the DC current from the fuel cell for the electric motors.

3.5 The hydrogen storage

The hydrogen will be stored in compressed gaseous form in 9 cylinders at a pressure of 25 MPa. The composite materials cylinders with an inner aluminum liner have a total capacity of about 1.53 m³ [approx. 30 kg of H₂]. This will give the bus an operating range of more than 250 km.

4. ENVIRONMENTAL BENEFITS

In the assessment of the environmental benefits of fuel cell vehicles, the analysis of the full fuel cycles, i.e. from cradle to grave, from bore hole to tailpipe, is of major importance. Energy efficiency and carbon dioxide emissions are not only important in the operation of a vehicle, but also in the production, delivery and conditioning of the fuel itself. This is especially true for renewable fuels thus showing their full potential for solving the global warming and resources problems.

Other problems associated with road transportation are summer smog/ ozone and in general air quality especially in urban areas. Here, zero emission fuel cell drives lead to a substantial improvement. But in analogy to the energy efficiency/ CO₂ analysis, local emissions of the fuel production and distribution also have to be taken into account. For heavy duty vehicles like buses, nitrous oxides and particulate emissions are the most important and critical emissions for urban air quality.

In collaboration with the project partners, LBST has analyzed full fuel cycles based on a detailed study carried out in 1995/96 in collaboration with German automotive industry [6].

The analysis of fuel production and distribution has been carried out using the GEMIS tool [7, 8]. In addition to the analysis tool, GEMIS also provides data on a variety of energy chains, processes, scenarios etc. with different levels of sophistication and detail. For this analysis, several new energy chains and processes, especially those for hydrogen and methanol production, were incorporated by LBST. Energy efficiency and emission data are based on manufacturer information and on other studies and inventories.

Seven different combinations of propulsion systems and fuels have been analyzed:

1. diesel internal combustion engine, no exhaust gas catalyst; low sulfur diesel

2. internal combustion engine; compressed natural gas

3. hydrogen fuel cell drive; compressed hydrogen production by natural gas steam reforming

4. hydrogen fuel cell drive; liquid hydrogen production via electrolysis from Canadian hydro power

5. methanol fuel cell drive, onboard methanol steam reformer; methanol production from natural gas

6. hydrogen fuel cell drive; compressed hydrogen from biomass farming and steam reforming

7. methanol fuel cell drive, onboard methanol steam reformer; methanol production from wood

The seven fuel chains have been assigned to different time horizons depending on their technical and commercial maturity. The indicated years are not to be taken as predictions of the commercial availability, but are rather intended to give a qualitative ranking of short-term (0 to 5 years), mid-term (5 to 10 years) and long-term (10 years and up) options:

0 to 5 years: diesel (1), natural gas (2).

5 to 10 years: fuel cell + hydrogen from natural gas (3), fuel cell + hydrogen from Canadian hydropower (4), fuel cell + reformer + methanol from natural gas (5)

10 years + : fuel cell + hydrogen from biomass (6), fuel cell + reformer + methanol from wood (7)

A 12 m low-floor city bus has been chosen as vehicle for the comparison. Energy consumption of some of the vehicle/ fuel combinations has been simulated using the so-called „Linie 66" driving cycle, a synthetic driving cycle for city buses in the city of Munich. For other options, the fuel consumption has been estimated based on simulations of similar vehicle concepts and on experience of the bus manufacturer MAN Nutzfahrzeuge. Emissions have been estimated based on projected emission standards for Europe (EURO 3).

The results for the full fuel cycles are shown in figures 1 through 4. The data used in the analysis have to be taken as conservative estimates for the non-conventional options.

Figure 1 shows the energy consumption of the various options in units of kWh/100 km (diesel has an energy content of roughly 10 kWh/l). Over the whole fuel chain, only the „hydrogen from natural gas fuel cell vehicle" (3) and the „hydrogen from biomass farming fuel cell vehicle" (6) are about as energy efficient as the diesel vehicle. The other vehicles are less energy efficient.

Introducing renewable fuels however reduces the priority in the importance of energy efficiency in the fuel production and supply chain. Carbon dioxide emissions are of much more concern as they cause global warming. Other trace gases contributing to the greenhouse effect are methane (CH₄) and laughing gas (N₂O). Based on CO₂ equivalence factors of 21 for methane and 310 for N₂O (atmospheric lifetime in both cases: 100 years), the CO₂ equivalent has been calculated indicating the global warming potential of the different vehicle concepts. Results are shown in figure 2. CO₂ absorbed from the atmosphere by the biomass used for fuel production have been subtracted from the CO₂ emissions during fuel production and fuel consumption in the respective fuel chains. Here it is obvious that even though some of the renewable fuel chains are not as energy efficient as diesel, the former have a by far greater potential of reducing greenhouse gases than any increase in conventional fuel efficiency. This is to a large extent due to the fact that propulsion systems for buses are already very energy efficient; the case for passenger cars is somewhat different. This shows that only the introduction of renewable fuels is able to significantly reduce the greenhouse effect caused by duty vehicles. Nevertheless, also the „hydrogen from natural gas fuel cell bus" offers slight improvements compared to a diesel bus. Technical development will probably increase the advantage of this vehicle concept further.

Figure 3 shows that emissions of nitrous oxides responsible for ozone formation can be reduced by a variety of alternative fuel/ vehicle concepts. Already compressed natural gas drives can reduce the nitrous oxide emissions by a factor of four. Most of the fuel cell drive/ fuel combinations have the potential to reduce these emissions by another factor of four. However, the NO_x emissions of diesel engines might be reduced by future reducing catalyst converters (Denox catalyst converter). Ozone formation is a regional problem. Therefore, also nitrous oxide emissions of fuel production and distribution in the region of consumption have to be taken into account.

Another problem for local air quality especially caused by duty vehicles are particulate emissions in discussion as causing lung cancer. Here also, a variety of alternatives to diesel vehicles offer substantial improvements, but also filter systems for diesel vehicles are presently being developed (see figure 4). Particulate emissions are mainly a local problem especially in urban areas. So the particulate emissions in the fuel production and supply chain might not have as negative an effect as those stemming from bus operation.

5. CONCLUSION AND OUTLOOK

The analysis of full fuel cycles shows that the fuel cell drive for city buses offers significant environmental improvements compared to diesel internal combustion engines. This refers to emissions of greenhouse gases as well as to local emissions of trace gases. The main improvement with regard to the global warming problem can nonetheless only be achieved if renewable fuels are introduced.

Since the beginning of this project, fuel cell propulsion for vehicles has made a dramatic development. Almost every big car manufacturer of the world is developing prototype fuel cell vehicles; many of them have announced to commercialize fuel cell passenger cars around 2005.

In case the production costs of fuel cells including the necessary periphery can be brought down to competitive levels, which can only be achieved by mass production as envisaged for fuel cell passenger car production, fuel cell drives can also be cost competitive in city buses.

Acknowledgements

All partners would like to express their thanks to the Bavarian State Ministry for Economic Affairs, Transport and Technology for funding this project.

REFERENCES

[1] HyWeb: http://www.HyWeb.de/FCBus

[2] LBST: Machbarkeitsuntersuchung zu Brennstoffzellenantrieben für städtische Nutzfahrzeuge, Ludwig-Bölkow-Systemtechnik Gmbh et al., 1995 (Feasibility study on fuel cell propulsion for urban duty vehicles; in German)

[3] LBST: Feasibility study on fuel cell propulsion for urban city buses and delivery trucks, Proceedings of the 11^th World Hydrogen Energy Conference, Stuttgart, Germany, June 1996

[4] BStMWVT: Developing hydrogen-based power technologies, Count N. Stillfried, Bavarian State Ministry for Economic Affairs, Transport and Technology, Proceedings of the 11^th World Hydrogen Energy Conference, Stuttgart, Germany, June 1996

[5] WIBA: http://www.wiba.de (in German)

[6] LBST: Fortschrittliche Antriebskonzepte für Stadtbusse und Verteilerfahrzeuge mit niedrigsten Emissionen; Stufe 1, Ludwig-Bölkow-Systemtechnik GmbH et al., Juni 1996 (Advanced propulsion concepts for city buses and distribution vehicles with lowest emissions; stage 1; in German)

[7] Fritsche: Gesamt-Emissions-Modell-Integrierter-Systeme Version 2.0, Endbericht, U. Fritsche et al., Öko-Institut Darmstadt, 1992

[8] GEMIS: GEMIS 2.0, U. Fritsche et al., Öko-Institut Darmstadt, 1992

TABLE I Technical Data