Obstacles Fall To Feasibility Of Hybrid Fuel Cell Vehicle

"The professors asked the class to solve the problem of hydrogen odorization," says Jamie Weston, graduate student in energy and geoenvironmental engineering. "We quickly came up with a solution and, took the rest of the course to develop our solution and follow the problems as far as we could."

The students -- Mike Sprague, Hui Long, Ramya Venkataraman, Patrick Flynn, Eric Wolfe and Weston -- are all in Penn State's Energy and Geoenvironmental Engineering program and took the hands-on fuel science class taught by Alan W. Scaroni, head and professor, Andre Boehman, associate professor, and Sarma V. Pisupati, associate professor in the department.

Hydrogen is a colorless and odorless gas. The U.S. government mandates that all flammable gases must, by law, have an odor. The chemicals used to add a smell to the gas, limit the possibility of using the hydrogen in a fuel cell because the chemicals often poison the cells.

"We came up with a simple system that removes the odorant with adsorbers and then tests to ensure that all the odorant is removed before sending the hydrogen to solid storage and fuel cell," says Weston.

Fuel cells convert the chemical potential of hydrogen and oxygen to electrical potential with heat and water without burning the hydrogen. For a fuel cell to work, the hydrogen must be ultra pure.

Another problem in the conceptualization of hybrid fuel cell vehicles is hydrogen storage. While hydrogen is easily stored as a compressed gas, safety concerns swayed the students to use a technically feasible solid storage method. The students chose a metal hydride system based on magnesium.

The hydrogen in the magnesium hydride is stable up to 554 degrees Fahrenheit, but once heated above that temperature, hydrogen gas is released. The five-passenger General Motors Precept electrical vehicle would require the energy from about 23 pounds of hydrogen to travel 500 miles, the researchers told attendees today (Aug. 19) at the 224th American Chemical Society annual meeting in Boston. The students designed their system for this 500-mile limit.

Fuel cells are not the sole energy source in this hybrid automobile. The battery stacks, which may be charged from an outlet in the garage or by the fuel cells are the primary source of power for short trips and in town driving. The batteries will also power the electric heating units that heat up sections of the magnesium hydride, once the battery stack is drained to a certain capacity. Excess energy from the fuel cells will also recharge the batteries.

"Batteries are now being reduced in size, so the weight of the batteries and the hydrogen fuel system will not make the car too heavy," says Weston. "Because most of the hydrogen is stored as a solid, the automobile may be as safe as today's cars."

The magnesium hydride fuel storage system is not combustible or pyrophoric, so the stored fuel will not burn or explode. Also, at any time in the system, only a small amount of hydrogen is present as a gas, never leaving enough enclosed hydrogen gas to explode. The fuel cell stack is separate from the rest of the system and well vented. In the case of an accident, mechanical sensors would shut off the hydrogen generation.