COMPARISON OF OPERATING CHARACTERISTICS OF CONVENTIONAL, DIESEL-ELECTRIC AND HYBRID-ELECTRIC CITY BUSSES UNDER REAL WORLD URBAN DRIVING CONDITIONS

Basic operating characteristics of Conventional, Diesel-Electric (DE) and Hybrid-Electric (HE) city busses were compared under real world urban driving conditions. To perform the comparison, real-time operating data of the buses were collected on Campus-Return route of Sakarya Municipality. It was observed that although traction powers versus bus speeds indicated similarities for all the buses, engine powers versus bus speeds did not indicate the same similarities. The main difference was that while the engine powers of the conventional and DE buses increased steeply to their maximum with the increasing bus speed, the engine power of the HE bus increased gradually to its maximum. Traction, braking and engine energy traces of the buses indicated similar trends, also. While the traction and braking energy traces were quite similar, the engine energy traces were significantly different although the buses were driven on the same route. The engine energies per km travel for the HE, conventional and DE buses were 1.30, 1.55 and 2.08 kW-h/km, respectively. Compared to the engine energy of the HE bus, that of the conventional and DE buses are 20% and 60% higher, respectively. In addition, the engine energies were 1.29, 1.48 and 1.84 times higher than their respective traction energies for the HE, conventional and DE buses, respectively. The main reason for the lower energy consumption of the BE bus is that while the HE bus takes advantages of downhill and frequent stopand-go driving conditions by recovering the braking energy, the conventional and DE buses waste their braking energies.