A strategy of estimating fuel concentration in a direct liquid-feed fuel cell system

Fuel control is one of the most pressing topics to achieve a self-sustainable direct liquid-feed fuel cell system, such as a direct methanol fuel cell (DMFC), and enhance its overall efficiency. In a DMFC system, sensing the methanol concentration generally serves as the basis of the fuel control strategies. This paper proposes a three-dimensional measurement space and constant concentration surfaces (CCS) to develop an algorithm of estimating fuel concentration in a liquid-feed system, which embraces the following merits: (1) it measures only three quantities or indices that correlate with the fuel concentration. The indices can be chosen as current, voltage, temperature, or other quantities that are easily acquired in an operating fuel cell system. The estimation can be accomplished without interrupting the operation of the system, (2) it estimates the fuel concentration in a three-dimensional measurement space; hence it is suitable for situations when one or more operating conditions are varying, (3) it can be performed as a sensor-less approach that requires no additional methanol sensors, thus consuming the less system power, and (4) it is particularly suitable for small and hand-held applications.