F2008-09-038
Simulation Framework for Well to Wheels Analysis of Hybrid Electric Vehicles
The preponderance of alternatively fuelled vehicles makes straightforward comparisons of emissions to conventional vehicles difficult. For conventional vehicles, only CO2 emissions from tank to wheels are measured by vehicle testing and certification agencies. The well to tank CO2 emissions are broadly similar for diesel and gasoline fuels and therefore conventional vehicles can already be compared fairly, whether they be diesel or gasoline powered. Alternative fuelled vehicles, where these vehicles may run either partially or wholly off electricity, or may use conventional engines fuelled on bio-fuels, make accounting for CO2 emissions in the full well to wheels analysis necessary, in order to compare to conventional vehicles. This in turn means that the conventional oil refining well to tank route must be considered also for conventional vehicles. A flexible simulation package, WARPSTAR [1], has been developed which considers the tank to wheel vehicle CO2 emissions, for a wide range of hybrid vehicle architectures. This simulation package also includes manual and automatic transmission conventional vehicle, and electric vehicle, architectures. An extension to this model allows the well to tank portion of the supply chain, for conventional and alternatively fuelled vehicles, to be accounted for, in terms of CO2 emissions. This allows a well to wheels consideration for concept hybrid electric vehicles and production vehicles run over real-world drive cycles, rather than just from published certification figures. The different routes available to produce electricity to recharge hybrid vehicle batteries are explored, with the differing impact on CO2 production. In these calculations, CO2 from sources other than combustion of the fuel are considered, such as plant construction costs. The bio-fuels approach to reducing the CO2 impact of transportation is also explored where the CO2 absorbed by the growing crop is offset against the CO2 produced during combustion in the vehicle. There is considerable uncertainty in reported numbers for CO2 emissions for different electricity producing stations and for CO2 absorption by growing crops. In addition, there is no apparent agreement for which non-combustion processes should be included in a Wells-to-Wheels analysis. A discussion of this will be covered within the final paper. This comprehensive method allows us to fairly compare currently available technologies such as electric vehicles, hybrid vehicles, plug-in hybrid vehicles, bio-fuel vehicles and conventional vehicles on a well to wheels basis, in terms of CO2 emissions for published numbers. The framework is designed such that additional CO2 sources or sinks can be easily added, and actual values updated to maintain the applicability of the package.
[1] A. Walker, A. McGordon, G. Hannis, A. Picarelli, J. Breddy, S. Carter, A. Vinsome, P. Jennings, M. Dempsey, M. Willows, "A Novel Structure for Comprehensive HEV Powertrain Modelling", in IEEE VPP Conf., Windsor, UK, September 2006.
Poster presentation: Resources and ecology