Patent ID: 8097370

Claim:
A method of operating a direct oxidation fuel cell (DOFC) system comprising at least one fuel cell assembly including a cathode and an anode with an electrolyte positioned therebetween, a source of liquid fuel in fluid communication with an inlet of said anode, an oxidant supply in fluid communication with an inlet of said cathode; and a liquid/gas (L/G) separator in fluid communication with outlets of each of said anode and cathode for: (1) receiving unreacted fuel and liquid and gaseous products of selected electrochemical reactions at said cathode and anode, and (2) supplying said unreacted fuel and liquid product to said inlet of said anode, comprising the steps of: determining a fuel efficiency value of said DOFC system during operation by using an electronic control unit (ECU), utilizing the ECU to determine and control oxidant stoichiometry of said DOFC system at an appropriate value in response to the determined fuel efficiency value, periodically or continuously determining said fuel efficiency value and utilizing same for periodically or continuously determining and controlling said oxidant stoichiometry value, utilizing a sensor for measuring an output current of said DOFC system, utilizing said appropriate oxidant stoichiometric value for controlling a rate of supply of said oxidant to said cathode of said at least one fuel cell assembly, and utilizing as said ECU a programmed computer adapted for: (1) indirectly determining a current density equivalent of a liquid fuel crossover rate of said fuel cell assembly, utilizing a stored mathematical relationship between the current density equivalent of the liquid fuel crossover rate of said fuel cell assembly and output current density of said fuel cell assembly; and (2) utilizing said indirectly determined current density equivalent of said liquid fuel crossover rate and said measured current output for determining said fuel efficiency value.