Alessandra Perna

Assessment of Fuel Cell Performance Under Different Air Stoichiometries and Fuel Composition

The behavior of fuel cells (FCs) at steady state and during transients is an important factor both for control tuning and for performance assessment. In the technical literature, few papers deal systematically with FC characterization. In this paper, the performance characterization of a proton exchange membrane (PEM) FC is carried out using an experimental analysis. The experimental activity has been conducted in a test station, properly designed and able to test PEM FC stacks in the range of 500-2000 W. The laboratory test facility is equipped with a National Instruments CompactDAQ real-time data acquisition and control system running a LabVIEW software. The bench commands two mass flow controllers, regulating both fuel flow and air flow which are commanded via two Recommended Standard 232 ports. The temperature of the FC is regulated via a fan operated by a brushless motor drive. An electronic load is connected to the FC terminals. The main operating parameters, such as the air stoichiometric ratio and fuel composition, have been varied and measured, and their influence on the PEM FC behavior has been investigated under both steady-state and transient conditions.

Theoretical Analysis on the Autothermal Reforming Process of Ethanol as Fuel for a Proton Exchange Membrane Fuel Cell System

The purpose of this work is to investigate, by a thermodynamic analysis, the effects of the process variables on the performance of an autothermal reforming (ATR)-based fuel processor, operating on ethanol as fuel, integrated into an overall proton exchange membrane (PEM) fuel cell system. This analysis has been carried out finding the better operating conditions to maximize hydrogen yield and to minimize CO carbon monoxide production. In order to evaluate the overall efficiency of the system, PEM fuel cell operations have been analyzed by an available parametric model.

Steam power-plants fed by high pressure electrolytic hydrogen

The possibility to obtain hydrogen and oxygen at high pressure directly from electrolysis was recently demonstrated at a laboratory scale. At the same time the working pressure of direct steam generator prototypes is increasing. The scaling-up of these devices will make very interesting the production of nuclear or renewable hydrogen (and oxygen) and its use in advanced steam power-plants fed with stoichiometric hydrogen/oxygen mixtures. This is a long-term view, but it is possible to find an interesting application even in the near term. It is the nightly and seasonal storage of energy by means of hydrogen and its use in attached steam power-plants. In this case the thermal energy required at low temperature can be supplied by regeneration and coal, while the combustion of hydrogen and oxygen is employed only in the steam super-heating phases. It results in high steam temperatures, increased specific work and improved thermodynamic efficiency. Moreover the availability of the reactants directly at high pressure, allows to save energy usually needed for storage and to avoid the installation of large compression units.

A steam cycle with an isothermal expansion: the effect of flowvariation

Abstract In the present paper the steam cycle proposed by Spazzafumo has been again taken into consideration and the effectof the flow variation on the cycle performances has been investigated. The isothermal expansion with increasingflow causes a decrease in cycle efficiency due to the greater condenser losses and, at high superheated temperatures,to the impossibility of full recovering of the available heat at the end of the expansion. However, using part of thisheat for preheating the required hydrogen and oxygen, yields a significant increase in efficiency.

Parametric analysis of a steam cycle with a quasi-isothermal expansion

Using a hydrogen/oxygen steam generator it is possible to carry out many steam mixing re-heatings without increasing the complexity of a traditional steam power-plant: steam is not required to re-enter the boiler for each re-heating. An isothermal expansion could thus be approached by means of several adiabatic expansions and several steam mixing re-heatings. A theoretical investigation showed that an isothermal expansion could achieve high efficiency (up to 70% of HHV) when the waste heat at the turbine outlet is recovered for pre-heating water, hydrogen and oxygen. In a real plant the number of re-heatings that can be carried out, although high, is limited and we can therefore expect an efficiency drop which varies as a function of the number of re-heatings, the re-heating temperature and the maximum pressure. In order to evaluate real cycle performance, a numerical code, specifically created, was implemented.

Development of a system-level model for fuel cell power units operated with syngas

This paper deals with a system-level modelling for the performance prediction of power units based on fuel cells that are designed to work witha syngas or with a fuel that can contain CO, such as HT-PEMFCs, MCFCs and SOFCs. The model solves mass and energy balances and allows to estimate the polarization curves by applying mathematical equations that take into account the different type of fuel cell. The empirical coefficients of the model equations have been tuned by using available experimental data.

Measuring the PEM fuel cell performance in a versatile test station

In this paper the performance characterization of a PEM fuel cell has been carried out using an experimental analysis. The experimental activity has been conducted in a test station, properly designed and able to test PEM fuel cell stacks in the range 500−2000 W. The laboratory test facility is equipped by a National Instruments Compact DAQ real-time data acquisition and control system running LabView software. The bench commands two mass-flow controllers, regulating both fuel flow and air flow which are commanded via two RS232 ports. The temperature of the FC is regulated via a fan operated by a brushless motor drive. An electronic load is connected to the FCM. The main operating parameters, such as air stoichiometric ratio and fuel composition, have been varied and measured and their influence on the PEM fuel cell behavior has been investigated under both steady-state and transient conditions.

A Steam Cycle with Direct Combustion of Hydrogen and Oxygen and an Isothermal Expansion

A new thermodynamical cycle characterised from an isothermal expansion has been examined from a theoretical point of view. In the real cycle the isothermal expansion could be approached by means of mixing re-heatings. The high temperature steam for mixing is produced in a direct steam generator burning a stoichiometric mixture of hydrogen and oxygen. The theoretical analysis has shown that the reference cycle allows an efficiency very close to the efficiency of a Carnot cycle evolving between the same extreme temperatures. The ratio between the two efficiencies can approach 90%.