Fuel and Technology Alternatives for Buses
Buses are the backbone of many public transport systems around the world. Until now, the baseline bus in most parts of the world has been a dieselpowered 12-m (40-ft) long bus. Now the spectrum of technology options for buses is increasing, both regarding vehicle technology (advanced diesel technology, hybridization, lightweight designs, etc.) and fuels (sulfur-free diesel, biofuels, synthetic fuels, gaseous fuels, etc.). CNG buses have been around for a while, and now several manufacturers are offering hybrid buses. The procurement or delivery of bus services is often handled by municipalities or the state in a centralized manner. As the service life of buses is as long as 20 years, solid data on the performance of new technology are needed.
Purpose and Objective
It is obvious that the spectrum of vehicle and fuel technologies is widening, not closing in. This poses a challenge to decision makers at all levels of decision making: governments, local authorities, and fleet operators. Both when setting policies and when procuring new vehicles, the following questions must be confronted:
- Which technology or fuel/technology combination gives the best overall energy efficiency?
- Which technology or combination yields the lowest overall greenhouse gas (GHG) emissions?
- Which technology or combination is best for reduced local emissions and improved urban air quality?
- Which option provides the best overall cost efficiency for reduction of GHG emissions as well as local emissions?
- Which clean fuel options can be implemented for existing vehicle fleets?
The objective of the task was to bring together the expertise of IEA’s transport-related implementing agreements to access reliable information on overall energy efficiency, emissions, and costs (both direct and indirect ) of various technology options for buses. The technology options vary with respect to engine technology, powertrain technology, and fuels. The outcome of the task will be unbiased and provide solid IEA-sanctioned data for use by policy- and decision-makers responsible for public transport using buses.
The project comprised four major parts: well-to-tank (WTT) assessment of alternative fuel pathways, assessment of bus end-use (tank-to-wheel, TTW) performance, and combination of WTT and TTW data into well-to-wheel (WTW) data and cost assessment, including indirect as well as direct costs. The project was a combination of cost and task sharing.
In vehicle and engine testing, the following fuels diesel and diesel substitutes were covered:
- conventional diesel fuel
- diesel fuels from unconventional fossil sources (natural gas, oil sandderived fuels)
- biodiesel fuels (methyl esters as well as hydrotreated vegetable oils)
The alternative fuels requiring dedicated vehicles covered were:
- methane (biogas/natural gas)
- additive treated ethanol
- di-methyl-ether (DME)
- United States
- IEA Bioenergy (European Commission, Germany, Finland)
- HEV (Canada, Switzerland)