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Technical Paper

Assessing and Modeling Direct Hydrogen and Gasoline Reforming Fuel Cell Vehicles and Their Cold-Start Performance

This paper analyzes fuel economy benefits of direct hydrogen and gasoline reformer fuel cell vehicles, with special focus on cold-start impacts on these fuel cell based vehicles. Comparing several existing influential studies reveals that the most probable estimates from these studies differ greatly on the implied benefits of both types of fuel cell vehicles at the tank-to-wheel level (vehicle-powertrain efficiency and/or specific power), leading to great uncertainties in estimating well-to-wheel fuel energy and/or greenhouse gas (GHG) emission reduction potentials. This paper first addresses methodological issues to influence the outcome of these analyses. With one exception, we find that these studies consistently ignore cold-start and warm-up issues, which play important roles in determining both energy penalties and start-up time of fuel cell vehicles. To better understand cold-start and warm-up behavior, this paper examines approaches and results based on two available U.S.
Technical Paper

Evaluating Commercial and Prototype HEVs

In recent years, vehicle manufacturers have made great progress in developing and demonstrating commercially available and prototyped hybrid electric vehicles (HEVs). These vehicles include commercially available gasoline hybrid cars (Toyota Prius and Honda Insight) and Partnership for the Next Generation Vehicle (PNGV) diesel hybrid prototypes (Ford Prodigy, GM Precept, and DaimlerChrysler ESX3). In this paper, we discuss tested and claimed fuel benefits and performance of these commercial and prototyped HEVs relative to conventional vehicles (CVs) that are otherwise similar to these HEVs, except for hybridization. We also describe a reverse-engineering approach to de-hybridize or “conventionalize” these five existing commercial and prototyped HEVs. Because these commercial and prototyped HEVs represent a variety of technological choices, configurations, and development stages, this analysis gives us in-depth knowledge about how each of these vehicles achieves high efficiency.
Technical Paper

Hybrid Options for Light-Duty Vehicles

Hybrid electric vehicles (HEVs) offer great promise in improving fuel economy. In this paper, we analyze why, how, and by how much vehicle hybridization can reduce energy consumption and improve fuel economy. Our analysis focuses on efficiency gains associated solely with vehicle hybridization. We do not consider such other measures as vehicle weight reduction or air- and tire-resistance reduction, because such measures would also benefit conventional technology vehicles. The analysis starts with understanding the energy inefficiencies of light-duty vehicles associated with different operation modes in U.S. and Japanese urban and highway driving cycles, with the corresponding energy-saving potentials.
Journal Article

Analysis of Input Power, Energy Availability, and Efficiency during Deceleration for X-EV Vehicles

The recovery of braking energy through regenerative braking is a key enabler for the improved efficiency of Hybrid Electric Vehicles, Plug-in Hybrid Electric, and Battery Electric Vehicles (HEV, PHEV, BEV). However, this energy is often treated in a simplified fashion, frequently using an overall regeneration efficiency term, ξrg [1], which is then applied to the total available braking energy of a given drive-cycle. In addition to the ability to recapture braking energy typically lost during vehicle deceleration, hybrid and plug-in hybrid vehicles also allow for reduced or zero engine fueling during vehicle decelerations. While regenerative braking is often discussed as an enabler for improved fuel economy, reduced fueling is also an important component of a hybrid vehicle's ability to improve overall fuel economy.