Search Results

This paper presents a computational investigation of the effect of ambient conditions (temperature and relative humidity) on the performance of a polymer electrolyte membrane (PEM) fuel cell stack with an open-cathode manifold. It uses the annual climate data of Abu Dhabi as a case study. The objective is to develop a better fundamental understanding of the fuel cell's performance in the hot arid environment. Such an understanding will be beneficial in improving the fuel cell design for mobile applications. The mathematical model used in this study comprises of three components: the fuel cell stack, the fan and the ambient. The model considers two-phase flow and conservation of mass, momentum, species and energy in the ambient and PEM fuel cell stack, as well as conservation of charge and a phenomenological membrane and agglomerate model for the PEM stack.

This paper presents a computational investigation of the effect of engine exhaust gas modulations on the performance of an automotive catalytic converter during cold starts. The objective is to assess if the modulations can result in faster catalyst light-off conditions and thus reduce cold-start emissions. The study employs a single-channel based, one-dimensional, non-adiabatic model. The modulations are generated by forcing the variations in exhaust gases air-fuel ratio and gas compositions. The results show that the imposed modulations cause a significant departure in the catalyst behavior from its steady behavior, and modulations have both favorable and harmful effects on pollutant conversion during the cold-starts. The operating conditions and the modulating gas composition have substantial influence on catalyst behavior.

This paper presents a computational investigation of the effect of space velocity on the dynamic performance of an automotive catalytic converter. The objective is to develop a better fundamental understanding of the converter's performance under actual driving conditions. The study employs a single-channel based, one-dimensional, non-adiabatic model. The transient effects are considered by modulating the air-fuel ratio and compositions of the exhaust gases entering the catalyst. The results elucidate the role of space velocity in determining the catalyst behavior under transient conditions. At high space velocities, the catalyst performance is relatively more influenced by imposed transients.

Engine exhaust systems need to undergo continuous modifications to meet increasingly stricter regulations. In the past, much of the design and engineering process to optimize various components of engine and emission systems has involved prototype testing. The complexity of modern systems and the resulting flow dynamics, and thermal and chemical mechanisms have increased the difficulty in assessing and optimizing system operation. Due to overall complexity and increased costs associated with these factors, modeling continues to be pursued as a method of obtaining valuable information supporting the design and development process associated with the exhaust emission system optimization. Insufficient kinetic mechanisms and the lack of adequate kinetics data are major sources of inaccuracies in catalytic converters modeling.

Automotive exhaust emission regulations are becoming progressively stricter due to increasing awareness of the hazardous effects of exhaust emissions. The main challenge to meet the regulations is to reduce the emissions during cold starts, because catalytic converters are ineffective until they reach a light-off temperature. It has been found that 50% to 80% of the regulated hydrocarbon and carbon monoxide emissions are emitted from the automotive tailpipe during the cold starts. Therefore, understanding the catalytic converter characteristics during the cold starts is important for the improvement of the cold start performances This paper describes a mathematical model that simulates transient performances of catalytic converters. The model considers the effect of heat transfer and catalyst chemical reactions as exhaust gases flow through the catalyst. The heat transfer model includes the heat loss by conduction and convection.