Effect of auxiliary usage on bus CO2 emissions through vehicle simulation

Zacharof N., Özener O., Özkan M., Gezer O., Broekaert S., Fontaras G., ...More

24th Transport and Air Pollution Conference, 30 March - 01 April 2021, pp.1

  • Publication Type: Conference Paper / Full Text
  • Page Numbers: pp.1
  • Yıldız Technical University Affiliated: Yes


Road passenger transportation needs are estimated at 3000 billion p-km in the EU annually. Passenger vehicles include cars and motorbikes for personal transportation and buses for collective transportation. There have already been regulations (Regulation (EC) 443/2009) to reduce the fuel consumption and CO2 emissions from passenger cars as they comprise the highest share of vehicles in terms of absolute numbers. Although heavy-duty vehicles, namely trucks and buses, comprise a relatively low share of about 4% of the vehicle fleet, they are responsible for about 25% of the road emissions, out of which about 7.5% is attributed to buses. Respective measures to reduce CO2 emissions for buses are to be evaluated by 2022, while measures are already being implemented for rigid and tractor-trailer trucks that transfer goods (Regulation (EU) 2019/1242).

Under the heavy-duty certification scheme, CO2 emissions from trucks are calculated from vehicle simulations through the Vehicle Energy Consumption calculation Tool (VECTO), capable also of simulating buses. Buses as heavy-duty vehicles share similar technical characteristics with trucks such as engine and gearbox models and could be highly customizable. However, there are several differences as buses need to accommodate people and create a pleasant cabin atmosphere during the trip. This leads to increased use of auxiliaries that has been found to be at ~16% of the total energy use compared to the 5% of the trucks.

This difference highlights the need to assess the usage of auxiliaries under different operating conditions properly. The current study investigated the auxiliary usage by making use of the VECTO advanced auxiliaries module. The development of the model was based on on-road measurements that were performed with a city bus over a real-world route in Istanbul. Subsequently, the effect of the auxiliaries on fuel consumption was investigated by creating scenarios with varying environmental conditions over one year. The results were compared with the reference environmental conditions in Europe and it was found that they diverge between 2% and 7%. The investigation showed that VECTO has potential beyond the type-approval procedure. It could be utilized to simulate vehicles for future fleets in public transportation by considering the local environmental characteristics.