Do Fuel Cell Topics Belong In A Combustion Course?

Combustion technologies are responsible for a lion’s share of the country’s electric power production and virtually a hundred percent of the conversion of fuels to power in the transportation sector. In spite of this domination, there is a growing competition from cleaner, more efficient energy technologies and a demand for distributed power generation. This is an area of engineering in which fuel cells are beginning to play a noticeable role. Fairly often combustion and fuel cells are referred to as opposing and quite different technologies. For example, one of the most reputable Thermodynamics textbooks emphasizes that the chemical reactions in fuel cells are “not a combustion process.” Despite the differences, a careful inspection of the topics associated with fuel cells surprisingly reveals a great deal of parallels with combustion. The traditional sequence of topics in a combustion course proceeds from stoichiometry thru the second law to the Gibbs function and to the chemical equilibrium of combustion products. This coverage of material allows a straightforward extension into the thermochemistry of fuel cells with the derivation of the Nernst equation. This equation contains important fuel cell operating parameters, such as temperature and pressure. For example, the temperature affects the ideal voltage of a fuel cell, while partial pressures are responsible for fuel utilization. Along the same lines, both pressure and temperature influence the product outcome in combustion. Fuel cell topics also include fuel-reforming applications. Depending on the operating temperature, fuel cells utilize internal or external reforming. There are three main technologies of fuel reforming. First, partial oxidation is a combustion process where fuels are burned in fuelrich conditions. Second, steam reforming and the water-gas shift reaction are chemical reactions already common in combustion textbooks. Third, thermal autoreforming is a combination of the two methods. All of them present an excellent opportunity to expand students’ experiences with relevant chemical equilibrium homework problems as well as course projects. The authors fully agree that fuel cell reactions are not combustion. Nevertheless, the similarity of the underlying theories and applications is undeniable. This paper will introduce a way of interweaving fuel cell topics in a combustion course. This is especially beneficial in a curriculum that is not ready or does not have room for a full course on fuel cells.