FALL/WINTER 2005-06 — Vehicle Systems
PSAT Assesses the Impacts of Combining a Hydrogen Internal Combustion Engine with a Fuel Cell System
Because of their high efficiency and low-emissions potential, fuel cell vehicles are undergoing extensive research and development. However, several major barriers must be resolved first to enable a hydrogen economy. Because fuel cell vehicles remain expensive, very few fueling stations are being built. To accelerate the development of a hydrogen economy, automotive manufacturers took an intermediary step by developing a hydrogen-fueled internal combustion engine (ICE). However, despite being less expensive, the hydrogen ICE offers a lower driving range because of its lower efficiency. A CTR study evaluated the impact of combining a hydrogen ICE with a fuel cell to maximize fuel economy yet minimize the cost and amount of onboard fuel to maintain an acceptable driving range.
CTR researchers performed a sensitivity analysis to assess the impact of hybridization degree and battery sizing. Once the reference vehicle was sized to accept 80% of the recoverable energy, two options were considered:
- Constant Hybridization. Both the electric motor and hydrogen-ICE power were kept constant. Consequently, when the fuel cell system power was increased, the battery power decreased, leading to a decrease in regenerative braking.
- Constant Battery Power. This case was used to evaluate the impact of the fuel cell system while maintaining constant battery power. To keep performance constant, both electric motor and hydrogen-ICE powers were recalculated, leading to different hybridization degrees.
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Impacts of Hybridization Degrees – Constant Hybridization Degree Case |
Simulation results demonstrated that introducing a fuel cell system with the hydrogen-ICE hybrid electric vehicle configuration significantly improved fuel economy. In addition, the degree of hybridization should be chosen to optimize regenerative braking and fuel cell use. The battery size should be carefully selected not only to recuperate most of the regenerative braking energy but also to minimize cost. As the use of fuel cell systems significantly increases cost and complexity, the trade-off between fuel economy and cost needs to be made.
The study demonstrated that the hydrogen-ICE hybrid electric vehicle is a viable alternative to accelerate the demand for hydrogen. This combination can be a solution to maximize fuel economy while minimizing cost and amount of on-board fuel to maintain an acceptable driving range.
The study details and results will be presented at the Society of Automotive Engineers (SAE) World Congress 2006.
Sponsor
U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, FreedomCAR and Vehicle Technologies Program
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