Auxiliary Power Units: Fuel Cells

Abstract

The expression auxiliary power unit (APU) originated from aircraft, where such units based on relatively small gas turbines deliver electrical power and heat independent of the main engines. They operate preferably on the ground. At present, this expression is used more generally, and owing to economical and ecological reasons, APUs are attracting increasing interest for different mobile applications including passenger cars, trucks, buses, and marine units. Particularly, the independent operation allows, in a number of cases, the shutdown of the main engine(s) at stillstand of the automobile, thereby avoiding the idling of the engine. During this period, the APU delivers power and heat, which means an improvement of the system’s efficiency. Encouraged by the progress made in the performance of fuel cells, an increase in R&D activity for an early application in APUs is observed. Different potential APU applications with their specific operating conditions and the required fuel cell performances are discussed and relevant technological approaches together with the present state of development are explained.