H2—O2 (air) fuel cells are well known in the art and have been proposed as a power source for many applications. There are several different types of H2—O2 fuel cells including acid-type, alkaline type, molten-carbonate-type and solid oxide type. So-called PEM (proton exchange membrane) fuel cells [a.k.a. SPE (solid polymer electrolyte) fuel cells] are of the acid-type, potentially have high power and low weight, and accordingly are desirable for mobile applications such as electric vehicles. PEM fuel cells are well known in the art, and include a “membrane electrode assembly” or MEA comprising a thin, proton transmissive, solid polymer membrane-electrolyte having an anode on one of its faces and a cathode on the opposite face. A plurality of individual cells are commonly bundled together to form a PEM fuel cell stack.
In PEM fuel cells hydrogen is the anode reactant or fuel and oxygen is the cathode reactant or oxidant. The oxygen can either be in a pure form as O2 or air as O2 admixed with N2.
For vehicular applications, it is desirable to use a liquid fuel such as a low molecular weight alcohol (e.g. methanol or ethanol), or hydrocarbons (e.g. gasoline) as the fuel for the vehicle owing to the case of on board storage of liquid fuels and the existence of a nationwide infrastructure for supplying liquid fuels. However, such fuels must undergo chemical conversion processes to release the hydrogen content thereof for fueling the fuel cell. The initial process is accomplished in a reformer that provides thermal energy as needed to catalyst mass and yields a reformate gas comprising primarily hydrogen, carbon monoxide, and carbon dioxide.
The heat required to produce hydrogen varies with the electrical demand put on the fuel cell system at any given point in time. Accordingly, the heating source for the reformer must be capable of operating over a wide range of heat outputs. Heating the reformers with heat generated from either a flame combustor or a catalytic combustor is known. The present invention relates to an improved flame combustor intake system, and the integration thereof with a fuel cell system in which a single given volume is utilized to perform two different operations, one during start-up and the other during normal operation.
The acceptance of fuel cells by vehicle owners will be governed, in part, by their experience with vehicles powered by internal combustion engines. Consumers have grown accustomed to the relatively quick starting times of engines. Thus, one challenge facing fuel cell designers is to provide a similar relatively quick start up time for fuel cells. This is made difficult by the relatively high operating temperature of some of the components within fuel cells such as the primary reactor within the fuel processor.
In order to reduce the start up time required to heat the catalyst to its light off temperature (between 150° C. to 250° C.), it is known to use a thermal combustor. Unfortunately, such thermal combustor systems require a separate chamber for the combustion reaction, increasing the mass, cost and size of the fuel cell system.
Accordingly, a need exists in the art of fuel cells to develop a low-cost thermal combustor system for preheating the catalyst in an autothermal reformer with reduced mass and volume.