A fleet of four Mercedes-Benz station wagons powered by a gasoline-hydrogen mixture have been in service here on a field test for six months in a West German project to beat the practical problems of hydrogen as an automotive fuel.
Hydrogen has been billed as the ideal fuel for the 21st Century when oil stocks run low. It causes no pollution. When it burns with oxygen it leaves pure water as the only residue.
For Daimler-Benz research engineers working on the hydrogen project, the chief obstacle has been the difficulty of carrying adequate fuel on board a vehicle to give it a range comparable to a purely gasoline-powered car.
Since October, doctors on emergency duty in West Berlin have been making calls using the four Mercedes 280 station wagons, which are fitted with combined gasoline-and-hydrogen-powered motors.
Daimler-Benz had its first experimental hydrogen-powered vans on the road in 1974. What is new in the Berlin project is the idea of a hydrogen-petrol mix, allowing for smaller fuel tanks than in hydrogen only cars.
Fuels Are Mixed
The 184 brake-horsepower engines are fitted with electronic fuel injection systems which mix the two fuels according to the load on the motor. At idle the motors run on pure hydrogen, with the gasoline ratio rising as the power output increases.
Daimler-Benz sees a major advantage for the hybrid motor in stop-start driving in city traffic, which makes West Berlin, a city hemmed in East Germany, ideal for the field test.
The experimental cars revealed many bugs early in the test.
"On their first use in October, 1984, the autos were often out of action because of minor defects," said Gerd Von Essen, manager of the emergency doctor service using the cars in its fleet.
During the early stages of the trial, each of the four cars averaged only two days a month in full running order.
"Often it was only minor defects like water in the electronics or a wet fuse," Von Essen said.
By March many of the bugs had been ironed out and the vehicles were roadworthy an average 14 days a month, although it was already clear that the cars would not achieve the 28,000 miles running that was planned at the beginning of the field test.
The other reason the cars will not run the full experimental distance was that their range proved well under the 108 miles expected. Early in the test the cars ran out of fuel after 50 miles. With modifications, the range has been increased to 75 to 80 miles, Von Essen said.
Drivers are able to do without hydrogen power when the fuel is unavailable. A push button switches the car to full gasoline power.
Specially trained filling attendants take 20 minutes to transfer hydrogen into the vehicles' tanks, which hold 65 cubic yards of hydrogen measured at normal pressure.
Hens Tretter, who runs West Berlin's only hydrogen filling station, said he had had no major problems handling the fuel, except that his pumps froze on cold winter days. Hydrogen is safer than gasoline, he said, because it could not ignite if sprayed on hot exhaust pipes.
Tank Wouldn't Explode
Filling involves compressing hydrogen power into the gas storage system where it soaks up the gas like a sponge, unlike a pressure vessel, this tank would not explode if the car crashed.
In operation, the stored material is heated, releasing the gas which is then piped to the engine.
Automotive experts do not rate the Berlin cars or any other developments as yet viable to go into commercial production.
Not only are the systems still unreliable, but hydrogen is still far more expensive than gasoline or diesel. The hydrogen being used in the Berlin test is converted from town gas at an absorber plant and costs five times as much as the equivalent amount of gasoline.