Fuelcell hybrid locomotives: applications and benefits

Abstract

Led by Vehicle Projects LLC, an international industry government consortium is developing a 109-tonne, 1.2-MW fuelcell-powered road-switcher locomotive for commercial and military railway applications. As part of the feasibility and conceptual-design analysis, we have analyzed the potential benefits of a hybrid powerplant in which fuelcells comprise the prime mover and a battery or flywheel comprises the rechargeable auxiliary power device. Potential benefits of a hybrid powerplant are (1) enhancement of transient power and hence tractive effort, (2) regenerative braking, and (3) reduction of capital or recurring costs. Generally, tractive effort of a locomotive at low speed is limited by wheel adhesion and not by available power. Enhanced transient power is therefore unlikely to benefit a switcher locomotive but could benefit applications, such as subway trains with all axles powered, requiring high acceleration. In most cases, the benefits of regenerative braking in locomotives are limited. For low-speed applications such as switchers, both the available kinetic energy and the effectiveness of DC traction motors as generators are low. For high-speed heavy applications such as freight, the ability of the auxiliary power device to absorb a significant portion of the available kinetic energy is low. Moreover, the hybrid powerplant suffers a double efficiency penalty: losses occur in both absorbing and then releasing energy from the auxiliary device, result in a net storage efficiency of no more than 50% for current battery technology. Where the duty cycle peak power demand requires that a significant portion of the prime mover energy is cycled into auxiliary power device then a net increase in fuel consumption can result. Capital cost in some applications may be reduced. Based on recorded locomotive duty cycles and a cost model utilized in this project, hybridity can reduce fuelcell capital cost. However, because of the double efficiency penalty and increased powerplant complexity, we predict it will increase recurring costs such as fuel and maintenance. In particular, the choice of the optimum capital cost solution would increase the fuel consumption by as much as 20-40%. Moreover, for usual rail duty cycles, the weight and volume of the combined powerplant would be significantly increased. Based on this analysis, the consortium has decided to develop for this project a pure fuelcell road-switcher locomotive, that is, not a hybrid locomotive.