Abstract
Keywords: hybrid vehicle, alternative fuel vehicle, well to wheels, CO2 emissions, simulation
The preponderance of alternatively fuelled vehicles makes it necessary to have a method of making straightforward comparisons of emissions to conventional vehicles. 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 diesel or gasoline powered. Alternative fuelled vehicles, where these vehicles may run either partially or wholly off electricity, or through 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 also be considered 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 covers manual and automatic transmission conventional, hybrid and electric vehicle architectures. An extension to this model now 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.
There is considerable variability 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 Well-to-Wheels analysis.
This new and comprehensive method allows a fairer comparison between currently available technologies such as electric, hybrid, plug-in hybrid, bio-fuel and conventional vehicles on a well-to-wheels basis, in terms of CO2 emissions.