Influence of vehicle and battery ageing and driving modes on emissions and efficiency in Plug-in hybrid vehicles

Plug-in hybrid electric vehicles (PHEVs) can operate in both charge-depleting (CD) and charge-sustaining (CS) modes offering flexibility to users and potentially playing a critical role in the transition path towards the transport decarbonisation. This study assesses the impact of vehicle and battery ageing on PHEV emissions, energy and fuel consumption, through two approaches: detailed laboratory testing of a representative gasoline PHEV and fleet-wide real-world data analysis. After 47,000 km and two years of driving the aged vehicle exhibited higher CO, NOx, and THC emissions, and lower particle number (PN) emissions due to improved filter efficiency. Laboratory tests revealed a 7 % increase in CD CO₂ emissions, a 2.2 % reduction in all electric range, and a 4.8 % decline in battery capacity, indicating battery degradation. Meanwhile, CS CO₂ emissions and energy consumption decreased by 2.1 % and 2.8 %, respectively, possibly due to reduced drivetrain friction losses. A fleet-wide analysis of over 1,900 similar PHEVs registered in the European market uncovered a significant gap, up to 3.5 times, between official and real-world CO₂ emissions, complicating efforts to assess long-term ageing effects. Annual distance driven correlated with increased real-world CO₂ emissions and a decrease in electric drive share (EDS), indicating insufficient battery charging during longer trips. Over two years, PHEVs driven primarily in electric mode showed 5 % higher CO₂ emissions, pointing to the possible impact of battery ageing, while those driven mainly in conventional mode saw emissions decrease by 2 %. These findings provide novel insights into how PHEV performance evolves with age, offering critical data for researchers and engineers to better address emissions and battery durability standards as vehicles age.