Background  

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 diesel-powered 12-meter or 40-foot-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 (sulphur-free diesel, biofuels, synthetic fuels, gaseous fuels, etc.). Some manufacturers are already offering hybrid buses, while others are just in the phase of launching hybrids. The procurement or delivery of bus services is often handled by municipalities or states in a centralized manner. As the service life of buses is as long as 20 years, solid data are needed on the performance of the new technologies.

Purpose and Objectives

The objective of the project is to bring together the expertise of International Energy Agency’s (IEA’s) transport-related implementing agreements (seven in all) to generate information on the overall energy efficiency, emissions, and costs of various technology options for buses. Here technology options cover variations in engine technology, power train technology (including hybridization), and fuels. The outcome of the task will be to produce unbiased and solid IEA-sanctioned data for policy- and decision-makers responsible for public transport using buses. Three of the Implementing Agreements — Advanced Motor Fuels, Bioenergy, and Hybrid and Electric Vehicles — contribute with actual funding to the project. All transport-related Implementing Agreements are expected to contribute by producing condensed technology outlooks for their respective technologies.

Activities

The project encompasses a combination of desk studies and actual measurements on conventional and new types of buses. Thus the project is divided into two main parts, WTT (well-to-tank) fuel pathway analysis and TTW (tank-to-wheel) vehicle performance. For the well-to-tank studies, experts at Argonne National Laboratory (Argonne), Natural Resources Canada (NRCan), and VTT Technical Research Centre of Finland are cooperating to evaluate and filter data for the chosen fuel alternatives.

Environment Canada (EC) and VTT are carrying out chassis dynamometer emissions testing on buses to establish TTW performance. The testing is carried out using dynamic driving cycles representative for buses. EC covers North American vehicle technology and VTT European vehicle technology. In addition, there are two supplementary experimental activities. The consulting company AVL MTC of Sweden has conducted on-board emissions measurements on buses. von Thünen Institute in Germany has carried out detailed analysis of fuel effects on emissions, including unregulated emission components, by using a test engine installed in an engine dynamometer.

The WTT data and the TTW for the various fuel/powertrain combinations will be combined into overall well-to-wheel (WTW) data. The French energy agency ADEME (Agency for Environment and Energy Management) is responsible for cost assessments of the alternative pathways and will address both direct as well as indirect (environmental) costs.

The work on fuel pathways, as well as the vehicle measurements, are approaching completion. Analysis of the total WTW pathways (as well as costs) has commenced.

Results

Fuel Pathways

For the WTT analysis, three different methodologies were applied: the GREET model (developed by Argonne National Laboratory), the GHGenius model (developed by Natural Resources Canada), and the methodology presented in the European Union Renewable Energy Directive 2009/28/EC (developed by VTT). The simulation results using the GREET model and the values according to the European Union Renewable Energy Directive (RED) are already available. A description of these two methodologies has been written. Both the GREET model the RED methodology yield results for greenhouse gas emissions, and in addition, the GREET model also accounts for six criteria pollutants. The work based on use of the GHGenius model is in the final phase.

A description of the general principles of the WTT analysis based on life cycle assessment (LCA) has been written, in which the GREET and the GHGenius models and the European Union RED methodology are compared to each other, with an emphasis on highlighting the most important differences between these calculation methods. Some challenges and open questions related to the WTT assessment of biofuels (e.g., indirect land use change issues) also are addressed in the text. To provide some perspective regarding the uncertainty and the variation of the WTT results, a literature review of 25 LCA studies of 14 different biofuel chains has been conducted. This review shows significant variations in the WTT results.

Vehicle and Engine Testing

Both EC and VTT have carried out a significant number of vehicle tests. The variables include the following:

• Type of drive train (conventional vs. hybrid).
• Emissions certification class (three sets of regulations for North America as well as Europe, from the late 1990s to current emissions regulations).
• Diesel vehicles and alternative fuel vehicles (natural gas, ethanol, dimethylether [DME]).
• Alternative diesel fuels (conventional diesel fuel, various biofuel options and synthetic fuels from natural gas and oil sands).
• Test cycle (North American, European, and Japanese test cycles).

So far, EC has tested six vehicle platforms: four conventional diesel vehicles and two diesel hybrids. The fuel matrix comprises 13 different fuels (including ultra-low sulphur diesel, oilsands-derived diesel fuel, canola methyl ester, soy methyl ester, tallow/waste fry oil methyl ester, and hydrotreated vegetable oil [HVO]). More than 60 vehicle/fuel/test cycle combinations have been run.

VTT has tested nine vehicles: four conventional diesel vehicles, two diesel hybrids, and three alternative fuel vehicles (natural gas, ethanol, DME). The DME vehicle was a prototype truck that was simulated as a bus on the chassis dynamometer. At VTT, the full diesel fuel test matrix covers 11 different fuels (including ultra-low sulphur diesel, gas-to-liquid [GTL], rapeseed methyl ester, Jatropha methyl ester, and hydrotreated vegetable oil). Some 100 combinations have been tested already. Figures 1 (fuel consumption) and 2 (particulate emission) show the spread in performance for European vehicles.

von Thünen Institute carried out an in-depth emissions analysis using a Euro III certified heavy-duty diesel engine. The test fuels were diesel, 100% rapeseed methyl ester, 100% Jatropha methyl ester, and 100% HVO. Among otherobjectives, particulate mutagenicity was analyzed.

Time Schedule

All testing will be completed by June 2011. A final report is scheduled for November 2011.

Future Plans

The work on fuel pathways within the bus project gave a launching point for the new Advanced Motor Fuel (AMF) activity on life cycle analysis, Annex XL (40), “LCA of Transportation Fuel Pathways.” In addition, the WTT data of the bus project will be used in another AMF activity, Annex XLIII (43), “Performance Evaluation of Passenger Car Fuel and Powerplant Options.”