Abstract
We report an algorithm for real time controlling quantity and methanol concentration of the fuel of a DMFC. The MEA voltage decay coefficients [e1, e2], and I-V-T, M'-I-T, and W'-I-T curves (where I is the current, V the voltage, T the temperature, and M' and W' the methanol and water consumption rates, respectively) of n fuels with specified methanol concentrations CM,k (k= 1, 2,…, n) are preestablished and form (I,V,T), (M',I,T), and (W',I,T) surfaces for each CM,k. The in situ measured (I,V,T)u after voltage decay correction is applied to the n preset (I,V,T) surfaces to estimate CM,u (the CM corresponding to (I,V,T)u ) using an interpolation procedure. The CM,u is then applied to the n preset (M',I,T) and (W',I,T) surfaces to estimate cumulated “methanol” and “water” consumed quantities. Thus in a real time system, the CM and total quantity of fuel can be controlled using the estimated CM,u and cumulated “methanol” and “water” consumed quantities. In this thesis, (1) by modifying Chiu and Lien constant concentration surfaces approach, we developed a sensor-less algorithm for estimating methanol concentration of fuel; (2) developed an approach for evaluating the consumption rate of water and methanol, thereby determining the in-situ consumed quantity of liquid fuel in an operating DMFC system. We also carried out experiments to validate the proposed approach on a stack of 32-cells for both the steady-state and dynamic operating conditions. Thus the algorithm is suitable for fuel control management of portable DMFC systems.