Reduced complexity models for water management and anode purge scheduling in DEA operation of PEMFCs

In this work, the dynamic behavior of Fuel Cell operation under Dead-Ended Anode conditions is shown. A DEA can be fed with dry hydrogen, since water crossing through the membrane is sufficient to humidify the fuel. The reduced requirements for inlet humidification yield a system with lower cost and weight compared to FCs with flow-through or recirculated anodes. The accumulation of water and nitrogen in the anode channel is first observed near the outlet. A stratified pattern develops in the channel where a hydrogen-rich area sits above a depleted region and is stabilized by the effect of gravity. A model is presented which describes the dynamic evolution of a blanketing N2 front in the anode channel and a hydrogen starved region. Understanding, modeling, and predicting the front evolution can reduce the H2 wasted during purges, avoid over drying the membrane, and mitigate degradation associated with hydrogen starved areas

Experimental validation of equilibria in fuel cells with dead-ended anodes

This paper investigates the nitrogen blanketing front during the dead-ended anode (DEA) operation of a PEM fuel cell. Surprisingly the dynamic evolution of nitrogen and water accumulation in the dead-ended anode (DEA) of a PEM fuel cell arrives to a steady-state suggesting the existence of equilibrium behavior. We use a multi-component model of the two-phase one-dimensional (along-the-channel) system behavior to analyze and exploit this phenomenon. Specifically, the model is first verified with experimental observations, and then utilized for showing the evolution towards equilibrium. The full order model is reduced to a second-order ordinary differential equation (ODE) with one state, which can be used to predict and amalyse the surprising but experimentally observed steady state DEA behavior

Nitrogen front evolution in purged polymer electrolyte membrane fuel cell with dead-ended anode

In this paper, we model and experimentally verify the evolution of liquid water and nitrogen fronts along the length of the anode channel in a proton exchange membrane fuel cell operating with a dead-ended anode that is fed by dry hydrogen. The accumulation of inert nitrogen and liquid water in the anode causes a voltage drop, which is recoverable by purging the anode. Experiments were designed to clarify the effect of N-2 blanketing, water plugging of the channels, and flooding of the gas diffusion layer. The observation of each phenomenon is facilitated by simultaneous gas chromatography measurements on samples extracted from the anode channel to measure the nitrogen content and neutron imaging to measure the liquid water distribution. A model of the accumulation is presented, which describes the dynamic evolution of a N-2 blanketing front in the anode channel leading to the development of a hydrogen starved region. The prediction of the voltage drop between purge cycles during nonwater plugging channel conditions is shown. The model is capable of describing both the two-sloped behavior of the voltage decay and the time at which the steeper slope begins by capturing the effect of H-2 concentration loss and the area of the H-2 starved region along the anode channel

A Controllable Membrane-Type Humidifier for Fuel Cell Applications-Part I: Operation, Modeling and Experimental Validation

For temperature and humidity control of proton exchange membrane fuel cell (PEMFC) reactants, a membrane based external humidification system was designed and constructed. Here we develop and validate a physics based, low-order, control-oriented model of the external humidification system dynamics based on first principles. This model structure enables the application of feedback control for thermal and humidity management of the fuel cell reactants. The humidification strategy posed here deviates from standard internal humidifiers that are relatively compact and cheap but prohibit active humidity regulation and couple reactant humidity requirements to the PEMFC cooling demands. Additionally, in developing our model, we reduced the number of sensors required for feedback control by employing a dynamic physics based estimation of the air-vapor mixture relative humidity leaving the humidification system (supplied to the PEMFC) using temperature and pressure measurements. A simple and reproducible methodology is then employed for parameterizing the humidification system model using experimental data

Measurement of Liquid Water Accumulation in a Proton Exchange Membrane Fuel Cell with Dead-Ended Anode

The operation and accumulation of liquid water within the cell structure of a polymer electrolyte membrane fuel cell (PEMFC) with a dead-ended anode is observed using neutron imaging. The measurements are performed on a single cell with 53 square centimeter active area, Nafion 111-IP membrane and carbon cloth Gas Diffusion Layer (GDL). Even though dry hydrogen is supplied to the anode via pressure regulation, accumulation of liquid water in the anode gas distribution channels was observed for all current densities up to 566 mA cm-2 and 100% cathode humidification. The accumulation of liquid water in the anode channels is followed by a significant voltage drop even if there is no buildup of water in the cathode channels. Anode purges and cathode surges are also used as a diagnostic tool for differentiating between anode and cathode water flooding. The rate of accumulation of anode liquid water, and its impact on the rate of cell voltage drop is shown for a range of temperature, current density, cathode relative humidity and air stoichiometric conditions. Neutron imaging of the water while operating the fuel cell under dead-ended anode conditions offers the opportunity to observe water dynamics and measured cell voltage during large and repeatable transients

Coordination of Converter and Fuel Cell Controller

Abstract-Load-following fuel cell systems depend on control of reactant flow and regulation of DC bus voltage during load (current) drawn from them. To this end, we model and analyze the dynamics of a fuel cell system equipped with a compressor and a DC-DC converter. We then employ modelbased control techniques to tune two separate controllers for the compressor and the converter. We demonstrate that the lack of communication and coordination between the two controllers entails a severe tradeoff in achieving the stack and power output objectives. A coordinated controller is finally designed that manages the air and the electron flow control in an optimal way. Our results could be used as a benchmark of achievable fuel cell performance without hybridization

Reducing Cyclic Dispersion in Autoignition Combustion by Controlling Fuel Injection Timing

Abstract-Model-based control design for reducing the cyclic variability (CV) in lean autoignition combustion is presented. The design is based on a recently proposed control-oriented model that captures the experimental observations of CV. The model is extended here to include the effect of the fuel injection timing, which is an effective way of influencing the combustion phasing. This model is only stable for certain amounts of residual gas. For high amounts, runaway behavior occurs where the combustion phasing occurs increasingly earlier. For low amounts, a cascade of period-doubling bifurcations occurs leading to chaotic behavior. This complex dynamics is further complicated with significant levels of noise, which creates a challenging control problem. With the aim at controllers feasible for on-board implementation, a proportional controller and a reduced-order state feedback controller are designed, with feedback from the combustion phasing. The controllers are evaluated by simulations and the results show that the CV can be significantly reduced, in an operating point of engine speed and load, for a wide range of residual gas fractions

Extremum seeking control for soft landing of an electromechanical valve actuator,

Abstract Many electromagnetic actuators su er from high velocity impacts. One such actuator is the electromechanical valve actuator, recently receiving attention for enabling variable valve timing in internal combustion engines. Impacts experienced by the actuator are excessively loud and create unnecessary wear. This paper presents an extremum seeking controller designed to reduce the magnitude of these impacts. Based on a measure of the sound intensity at impact, the controller tunes a nonlinear feedback to achieve impact velocities of less than 0:1 m=s while maintaining transition times of less than 4:0 ms. The control strategy is implemented with an eddy current sensor, to measure the valve position, and a microphone.

Reducing Cyclic Dispersion in Autoignition Combustion by Controlling Fuel Injection Timing

Abstract-Model-based control design for reducing the cyclic variability (CV) in lean autoignition combustion is presented. The design is based on a recently proposed control-oriented model that captures the experimental observations of CV. The model is extended here to include the effect of the fuel injection timing, which is an effective way of influencing the combustion phasing. This model is only stable for certain amounts of residual gas. For high amounts, runaway behavior occurs where the combustion phasing occurs increasingly earlier. For low amounts, a cascade of period-doubling bifurcations occurs leading to chaotic behavior. This complex dynamics is further complicated with significant levels of noise, which creates a challenging control problem. With the aim at controllers feasible for on-board implementation, a proportional controller and a reduced-order state feedback controller are designed, with feedback from the combustion phasing. The controllers are evaluated by simulations and the results show that the CV can be significantly reduced, in an operating point of engine speed and load, for a wide range of residual gas fractions