Modelling study of vehicle electrification topologies for GHG emissions reduction and fleet planning

In response to the increasingly strict regulations on reducing greenhouse gas (GHG) emissions since the evolving environmental concerns, the demand for developing alternative powertrain architectures to replace conventional vehicles with internal combustion engines is raising. This work has carried out a systematic study on various vehicle powertrains and has developed a flexible vehicle modelling platform with consideration of different powertrain topologies as a novel tool to study GHG emissions for vehicles. Additionally, the analysis of the GHG emissions was based on the whole fuel cycle in the well-to-wheels (WtW) scope based on a comprehensive study on different supply pathways of fuel or electric energy production. Aiming at building a bridge to link the knowledge of vehicle powertrain technology from the engineering side to the GHG emissions study from the social science perspective, this study has developed a method for evaluating the impact of vehicle electrification by various scenarios on GHG emissions reduction for vehicle fleets.

The developed vehicle modelling platform was in modular design, aiming to adapt to various vehicle classes and driving cycles and to enable easy implementation of the developed powertrain models. Powertrain topologies combined vehicle models in this study include traditional internal combustion engine vehicles (ICEV) fuelled with fossil fuels, battery electric vehicles (BEV), fuel cell vehicles (FCV), internal combustion engine-battery hybrid electric vehicles (ICE-HEV) in series and parallel hybrid mode, and fuel cell-battery hybrid electric vehicles (FC-HEV). A concept of hybridization rates was introduced to define the power flow between the powertrain components for vehicles with hybrid powertrain configurations.

The model is capable to operate either in forward-facing simulation to work out fuel or energy consumption and emissions characteristics, or in backward-facing to achieve powertrain components sizing on certain design targets of vehicles. From this, it has conducted comparable analysis for powertrain transformation from various topologies for vehicles. The model was validated based on commercial vehicle data, test data from references and a road test from a cooperative project.

The vehicle GHG emissions study was carried out based on fuel/electric energy consumption of the vehicles that output from the vehicle model, combined with the study on the GHG emissions characteristics of the fuel or electric energy produced from different pathways. Fuel and energy sources considered include fossil fuels, electricity and hydrogen. In addition to the resources and the production methods of the energy sources, factors such as transportation and storage of the product were also taken into consideration.

A method of evaluating regional GHG emissions production from a fleet of vehicles that benefited from vehicle electrification solutions was presented in this study. Taking the EU passenger vehicles as an example, it has investigated the passenger vehicles emissions changes on vehicle fleet electrification solutions, with consideration of factors such as changes in vehicle amount and travelling distance against time and various energy sources supply pathways. Moreover, taking the Leeds city council vehicle fleet as an example, the scenario of a local vehicle fleet consisting of various vehicle classes was discussed.