Dazo Water Fuel Technology

1.2.1.1 Solid Oxide Fuel Cell APUs

Like PEM fuel cells, solid oxide fuel cells (SOFCs) are galvanic cells that directly produce electricity from hydrogen and oxygen through an electrochemical reaction. However, SOFCs are constructed of different materials and use a different chemical reaction from PEM fuel cells.
SOFCs operate at much higher temperatures than PEM fuel cells – between 1,100 °F and 1,800 °F.

When combined with a small fuel reformer they can also use diesel fuel or gasoline vapors as fuel, eliminating the need to carry hydrogen gas onboard.

In an SOFC, the electrolyte is not a plastic-like material as it is in a PEM cell; it is a ceramic material made of a solid metal oxide, usually zirconia oxide. This electrolyte does not need to be coated with an expensive platinum catalyst as in a PEM cell. As with a PEM fuel cell, the major by-products of the reactions inside the cell are electricity, water, and heat. See Figure 6. Also see Appendix A for a more detailed description of the construction of SOFCs and the chemical reactions that take place inside the cells.

 

Unlike a PEM cell, an SOFC does not need to be fueled with pure hydrogen gas. Because SOFCs operate at such high temperature and because oxygen ions are transferred through a solid oxide electrolyte material—not hydrogen ions—SOFCs support automatic “reforming” of gaseous hydrocarbon fuels like methane (natural gas) within the device. Reforming is the chemical process of separating the hydrogen from the carbon atoms in a hydrocarbon fuel (see Section 1.4). Diesel fuel and gasoline vapors can not be internally reformed by an SOFC, but can be used to fuel an SOFC if it is combined with a relatively simple fuel reformer/processor.
 

When using diesel fuel, the “reformate” produced by the fuel processor and introduced as the fuel at the anode of the SOFC will include hydrogen, nitrogen, carbon monoxide, and CO2. The exhaust from the SOFC will also include CO2 and nitrogen, as well as water and waste heat.
SOFCs operate at much higher temperatures than PEM fuel cells—between 1,100 °F and 1,800 °F—so the waste heat created during operation is also at a higher temperature and can, therefore, more easily be put to use, for example, to heat the interior of a vehicle as is typical of the waste heat from an ICE.
 

There are at least fifteen companies that have demonstrated prototype or commercial SOFC systems (HARC, 2004). Most of these systems are small, producing from 200 watts to 25 kilowatts of power. Several manufacturers are developing low-power systems specifically for use as an auxiliary power unit (APU) on commercial trucks (DELPHI, 2005)
Truck APUs are used to provide electrical power and sometimes heat to power truck accessories such as cabin lighting, air conditioning, and heating. Most often used with sleeper berth-equipped, truck-tractors they allow these loads, which are normally supplied by the truck’s main engine, to be supplied even when the main engine is off.

Without an APU, many long-haul truckers end up idling their main engines for eight hours a day or more while resting in the sleeper-berth. This practice is wasteful and results in unnecessary harmful exhaust emissions. Testing by the U.S. Environmental Protection Agency has shown that a commercial truck’s main engine typically consumes about one gallon of fuel per hour while idling, while a properly sized ICE APU will burn only about one fifth as much (EPA, 2002). The use of an APU instead of main engine idling can therefore save a truck operator money and reduce pollution at the same time.
 

In comparison to an ICE APU, an SOFC APU could be more efficient, smaller and lighter, quieter, and produce fewer exhaust emissions (DELPHI, 2005). Because an SOFC with a fuel processor can be fueled directly with diesel fuel, there would be no need to carry compressed hydrogen on the vehicle (see Section 1.4).