Real-World Measurement of Hybrid Buses’ Fuel Consumption and Pollutant Emissions in a Metropolitan Urban Road Network

Christos Keramydas,Kwok-Lam Ng,Carol Wong,Hok-Lai Wong,Ting-Shek Lo,Leonidas Ntziachristos,Georgios Papadopoulos

doi:10.3390/en11102569

Christos Keramydas, Kwok-Lam Ng + Show 5 more

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https://doi.org/10.3390/en11102569

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Abstract

This study investigates pollutant emissions and fuel consumption of six Euro VI hybrid-diesel public transport buses operating on different scheduled routes in a metropolitan urban road network. Portable emission measurement systems (PEMS) are used in measurements and results are compared to those obtained from a paired number of Euro V conventional buses of the same body type used as control over the same routes. The selected routes vary from urban to highway driving and the experimentation was conducted over the first half of 2015. The available emissions data correspond to a wide range of driving, operating, and ambient conditions. Fuel consumption, distance- and energy-based emission levels are derived and presented in a comparative manner. The effect of different factors, including speed, ambient temperature, and road grade on fuel consumption and emissions performance is investigated. Mean fuel consumption of hybrid buses was found 6.1% lower than conventional ones, from 20% lower up to 16% higher, over six routes tested in total. The mean route difference between the two technologies was not statistically significant. Air conditioning decreased consumption benefits of the hybrid buses. Decrease of the mean route speed from 15 km h−1 tο 8 km h−1 increased the hybrid buses consumption by 63%. Nitrogen oxides (NOx) emissions of the Euro VI hybrid buses were 93 ± 5% lower than conventional Euro V ones. Nitrous oxide (N2O) emissions from hybrid Euro VI buses made up 5.9% of total greenhouse gas emissions and largely offset carbon dioxide (CO2) benefits. The results suggest that hybrid urban buses need to be assessed under realistic operation and environmental conditions to assess their true environmental and fuel consumption benefits.

Highlights

Control of the environmental impacts of road transport is pursued by local authorities of metropolitan areas around the world to ensure the quality of urban living [1], protect public health [2] and mitigate associated costs [3]
Hybrid urban buses are considered as one such option, with the main reduction in costs expected from a decreased fuel consumption (FC) over conventional buses
∑j=i 1 ∑t=1 di,j,t where EFdi,k is the estimated emission factor (g km−1 ) for pollutant k and vehicle i; Ri is the total number of trips for vehicle i; Ti,j is the total duration (s) of the jth trip of vehicle i; ERi,j,k,t is the instantaneous emission rate of pollutant k during the tth second of the jth trip travelled by vehicle i (g s−1 ); and di,j,t is the distance travelled by vehicle i during the tth second of its jth trip

Summary

Introduction

Control of the environmental impacts of road transport is pursued by local authorities of metropolitan areas around the world to ensure the quality of urban living [1], protect public health [2] and mitigate associated costs [3]. The cost of transport comprises both externalities, i.e., congestion, accidents, environmental and health related costs [4,5], and direct costs for purchasing and operating the vehicle fleet [6] and maintaining road infrastructure [7]. Fuel consumption is the main direct cost element of urban transit fleet operation [8]. Hybrid urban buses are considered as one such option, with the main reduction in costs expected from a decreased fuel consumption (FC) over conventional buses. Powertrain simulation results indicate that both parallel and series hybrid systems can offer fuel economy benefits up to 45% over conventional buses [11,12,13,14]. Semercioglu et al [16]

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