by Paul Abelson, technical editor
Early in 2001, then Freightliner CEO Jim Hebe demonstrated a fuel cell prototype in one of his Freightliner trucks. Today, Jim Hebe is not in the trucking industry. Neither are fuel cells. I cannot speak for Jim’s future (I will miss his exciting press events. He was always good for a quote.), but I do know Jim was right. In the future of trucking, we will have fuel cells.
There is a revolution underway in our industry. While long-haul truckers are getting used to major amenities in their cabs (TVs, refrigerators, microwaves, stereos, etc.), electricity to power these devices is in short supply. Most drivers idle their engines to run their alternators. Already severely restricted in many jurisdictions because of local ordinances, idling may be dealt its terminal blow by the new engine emission regulations.
Idling not only wastes fuel and creates emissions, it affects engine wear and performance. In the not-too-distant future, we can expect to see engine warranties limited by hours of operation, not miles traveled. Who would want to waste warranty time generating electricity if there are alternatives?
Present alternatives include fuel-fired heaters, deep-cycle and higher capacity batteries, and on-board electrical generators with small diesel engines to produce current. Plug-in shore power is still rare, and there are many questions about its future. Long term, the most promising development is the fuel cell. It can generate needed current without noise, without vibration, without exhaust and pollution, and with minimal fuel consumption.
What is a fuel cell? In simplest terms, it is an electrical storage device that, like a battery, uses a chemical reaction to release energy. Like batteries, fuel cells can be recharged. A conventional battery converts lead and sulfuric acid to lead sulfate and water (and releases electrons in the process). A fuel cell combines hydrogen and oxygen to create water and releases a supply of electrons. A single cell in a lead-acid truck battery produces two volts, and six cells are used inside the case to give us 12 volts. The most promising fuel cell technology for mobile applications — the proton exchange membrane fuel cell (PEMFC) — produces about 0.7 volts. To reach useable voltage levels, fuel cells must be combined to form a “fuel cell stack.”
The PEMFC can draw its oxygen from the air, but it needs a source of hydrogen to react with it. Depending on the application, that source can be pure liquid hydrogen (used on the original Freightliner prototype) or any hydrocarbon such as methane gas, methyl alcohol, gasoline or diesel fuel. City bus demonstrators, using PEMFCs to drive electric propulsion motors, have no problem putting several tanks of liquid hydrogen on the roof. They are part of the design, and the bus is back in the yard for refueling every day. Automobiles and trucks do not always return to their domiciles, so we will want a fuel available on the road. For us, that’s diesel. But to work in a fuel cell, diesel must be extra clean and virtually free of sulfur. By the time fuel cells are ready to be mounted on trucks, it will be.
A reformer is needed to get the hydrogen from diesel fuel. The reformer strips carbon from the hydrogen and combines it with oxygen to form carbon dioxide gas. The hydrogen is taken to the fuel cell and combined with oxygen to create electric current.
There are other fuel cell technologies under development, all of which combine hydrogen and oxygen. They all generate large amounts of heat, as much as 1,800 degrees Fahrenheit.
Fuel cell technology on trucks?
Here’s where fuel cell technology needs to be before it will be commercially feasible on trucks. The targets for development of a fuel cell, which engineers expect to be demonstrated in three to five years, are:
Power output: 5 kilowatts
Weight: 50 kg, or about 110 lbs.
Volume: 50 liters or about the size of a stack of two-liter pop bottles, five across by five high, including insulation, reformer, stacks and insulation.
Temperature: cool enough to keep your hand on top of the box.
Cost: to be competitive with generator sets on a per-kilowatt basis.
Life: four years continuous operation before replacing stacks, at 15 percent of initial price.
When these targets are met later in this decade, fuel cells will open a new era in truck design and driver amenities. Fuel cells have the potential to make the “More Electric Truck” (see article on the DOE Essential Power Workshop on page 62 of this issue) the most fuel-efficient and most comfortable transport vehicle ever imagined.