Under the proposed scheme, Connexxion, one of the main Dutch public transport companies, will operate more than 20 hydrogen internal combustions engine buses manufactured by the bus builder MAN Nutzfahrzeuge and its subsidiary NEOMAN Bus. The buses will be fueled from a Shell combined gasoline-hydrogen service station—the first in the Netherlands. The station is expected to be built and the buses operational by 2009. The same service station will also sell conventional fuels to the public.

The five-year project will evaluate public reaction as well as the reliability and economics of using hydrogen to fuel public transport in major urban areas. It will also help to establish technical standards for operating hydrogen fuel outlets.

The Rotterdam project follows a successful three-year trial in Amsterdam, where Shell Hydrogen together with partners worked on the infrastructure and operation of three fuel-cell hydrogen buses. In addition to being the country’s second largest city and one of the main ports in Europe, Rotterdam offers an opportunity to capitalize on a well-developed existing hydrogen infrastructure for industrial applications.

MAN Nutzfahrzeuge AG and NEOMAN Bus GmbH are members of the HyFLEET: CUTE project that began earlier this year. (Earlier post.) MAN will supply a total of 14 two-axle MAN Lion’s City buses with hydrogen combustion engines to the Berlin Transport Authority (Berliner Verkehrsbetriebe—BVG), where they will be tested in practical operation until the end of the project in early 2009. The first buses arrived at BVG on 1 June.

For the HyFleet:CUTE project, MAN is deploying two configurations of hydrogen combustion engines—reflecting second- and third-generation development—with identical displacement (12.8 liters), bore and stroke. The first engine (H 2876 UH, representing the second generation) is naturally aspirated with external mix formation, and uses sequential port injection at 5 bar with lambda <1. It produces power output of 150 kW and torque of 750 Nm.

The second engine (H 2876 LUH 01, representing the third generation) is turbo-charged with direct injection (internal mixture formation) at 10 bar. The engine has a rated output of 200 kW and torque of 1,000 Nm.

Both engines achieve emissions well below all EU exhaust-gas limits fixed for the future:

• NO_x: 0.2 g/kWh (Euro 5 = 2.00)
• HC: 0.04 g/kWh (Euro 5 = 0.46)
• PM: 0.005 g/kWh (Euro 5 = 0.02)

Emissions of carbon monoxide are below the level of detection (all figures according to the European Stationary Cycle ESC).

To prevent incandescent explosion, backfiring into the intake pipe and knocking in the naturally-aspirated version, MAN reduced the compression ratio to 8.5 : 1 and uses sequential multi-point hydrogen port injection using electromagnetically actuated valves.

Through slight oversaturation of the fuel/air mixture with hydrogen it was possible to minimize the emissions of NO_x in a downstream catalytic converter. This patented process reduces NO_x, for example, by more than 95%.

Whereas the first generation of the hydrogen engine (used in earlier trials in Berlin) was controlled by the Bosch Motronic M 3.3, the latest variant uses the ME7-GAS1, which is also used in natural-gas engines. The exhaust manifold is water-cooled because of the high combustion temperatures.

The turbo-charged, third-generation engine is based on the current D 2876 generation of diesel engines. The main innovation are special valves that allow the direct injection of hydrogen into the cylinder at a low pressure of about 10 bar to prevent backfiring.

Exhaust-gas turbocharging increases the amount of air in the engine, which in turn permits operation in lean-mix conditions. The aim is to achieve lambda values above 2, which will lead to low NO_x emissions. This again means that exhaust-gas cleaning will not be necessary.

The lean mixture also makes it possible to raise the compression ratio to 12 : 1; in this way and with partial dethrottling in partial load mode considerable consumption advantages can be achieved compared with the naturally-aspirated engine.

Depending on the pressurized storage system used, the operating ranges can be up to 300 km (186 miles), another figure that makes bus operation on scheduled routes a realistic proposition.

Resources:

• MVV Consulting: Experiences from using hydrogen in public transport