Optimal Powertrain Sizing of Series Hybrid Coach Running on Diesel and HVO for Lifetime Carbon Footprint and Total Cost Minimisation

Abstract

This article aims to calculate, analyse and compare the optimal powertrain sizing solutions for a long-haul plug-in series hybrid coach running on diesel and hydrotreated vegetable oil (HVO) using a co-design optimisation approach for: (1) lowering lifetime carbon footprint; (2) minimising the total cost of ownership (TCO); (3) finding the right sizing compromise between environmental impact and economic feasibility for the two fuel cases. The current vehicle use case derived from the EU H2020 LONGRUN project features electrical auxiliary loads and a 100 km zero urban emission range requiring a considerable battery size, which makes its low carbon footprint and cost-effective sizing a crucial challenge. Changing the objective between environmental impact and overall cost minimisation or switching the energy source from diesel to renewable HVO could also significantly affect the optimal powertrain dimensions. The approach uses particle swarm optimisation in the outer sizing loop while energy management is implemented using an adaptive equivalent consumption minimisation strategy (A-ECMS). Usage of HVO fuel over diesel offered an approximately 62% reduction in lifetime carbon footprint for around a 12.5% increase in overall costs across all sizing solutions. For such an unconventional powertrain topology, the fuel economy-focused solution neither achieved the lowest carbon footprint nor overall costs. In comparison, CO2−cost balanced sizing resulted in reductions close to the single objective-focused solutions (5.7% against 5.9% for the CO2 solution, 7.7% against 7.9% for the TCO solution on HVO) with lowered compromise on other side targets (CO2 reduction of 5.7% against 4.9% found in the TCO-focused solution, TCO lowering of 7.7% against 4.4% found in the CO2-focused solution).

A Review of Fuel Cell Powertrains for Long-Haul Heavy-Duty Vehicles: Technology, Hydrogen, Energy and Thermal Management Solutions

“…Table 1 lists some of the market-launched and upcoming HD FCEV truck, coach and city bus use cases [67]. With propulsion solely supported by the electric drive, an optimised size is dependent on maximising traction efficiency and on the scope and trend of possible regenerative braking events in the intended driving profile as shown in the LONGRUN project [68]. With its major contribution to powertrain losses, the FCS is usually sized to efficiently satisfy just above the average power requirements of the vehicle while assuring high operating efficiency.…”

“…Such a sizing preference of the industry can also be reasoned considering the technology maturity, costs of key powertrain components, and the FCS efficiency curve suited for low-mid load range operation. If the powertrain sizing objective is to minimise environmental impact while improving economic feasibility, a sole focus on FCEV H 2 fuel efficiency may not be the best approach considering the importance of different hydrogen production pathways (well-to-tank impact) and components production impact on lifetime CO 2 emissions and costs [68]. To promote the adoption of fuel cell technology in the European heavy-duty sector, the STASHH project funded by Fuel Cells and Hydrogen 2 Joint Undertaking will develop an open standard for sizing, interfacing, controls and testing protocols of fuel cell modules towards lowering TCO, market entry threshold while promoting mass production and reliability [69].…”

“…Verbruggen et al have shown the advantage of using a tandem combination of two identical or differently sized eDrives while aiming for better overall traction efficiency [100]. The electric drive is not only responsible for providing traction efforts, but can also recuperate kinetic and potential energy of the moving vehicle during braking and down-hill descends, which can be particularly beneficial for the HDVs due to the combination of heavy weight, highway speeds, mountainous or interurban transient driving conditions and should be taken into account for the right sizing of the eDrive [68,101]. Hub-mounted eDrives can simplify drivetrain packaging while adding modularity for changing applications using planetary gear sets with multi-speed reductions.…”