Abstract
The World-wide harmonised Light-duty Test Cycle (WLTC) was developed internationally for the determination of pollutant emission and fuel consumption from combustion engines of light-duty vehicles. It replaced the New European Driving Cycle (NEDC) used in the European Union (EU) for type-approval testing purposes. This paper presents an extensive comparison of the WLTC and NEDC. The main specifications of both driving cycles are provided, and their advantages and limitations are analysed. The WLTC, compared to the NEDC, is more dynamic, covers a broader spectrum of engine working states and is more realistic in simulating typical real-world driving conditions. The expected impact of the WLTC on vehicle engine performance characteristics is discussed. It is further illustrated by a case study on two light-duty vehicles tested in the WLTC and NEDC. Findings from the investigation demonstrated that the driving cycle has a strong impact on the performance characteristics of the vehicle combustion engine. For the vehicles tested, the average engine speed, engine torque and fuel flow rate measured over the WLTC are higher than those measured over the NEDC. The opposite trend is observed in terms of fuel economy (expressed in l/100 km); the first vehicle achieved a 9% reduction, while the second – a 3% increase when switching from NEDC to WLTC. Several factors potentially contributing to this discrepancy have been pointed out. The implementation of the WLTC in the EU will force vehicle manufacturers to optimise engine control strategy according to the operating range of the new driving cycle.
Highlights
Light-duty vehicles powered by internal combustion engines have been tested for exhaust emissions and fuel consumption since the late 60s
The performance characteristics of two vehicles tested in the wide harmonised Light-duty Test Cycle (WLTC) and New European Driving Cycle (NEDC) are analysed and compared, with a special emphasis on engine speed, engine torque, and fuel consumption
Engine speed and non-negative torque measured over both driving cycles are presented in Figure 3
Summary
Light-duty vehicles powered by internal combustion engines have been tested for exhaust emissions and fuel consumption since the late 60s. The ideal driving cycle should comply with the following requirements [2, 3]; be practical (easy to execute in a laboratory) and provide full repeatability and reproducibility, and statistically represent diverse real-world driving conditions. The NEDC is not complicated, easy to drive, as it contains only steady-state modes and ensures good repeatability. It has been highly criticised for not representing real-world vehicle operation [4, 5]. The imperfections of driving cycles contribute to the growing discrepancy between results of laboratory and on-road testing of emission and fuel consumption of vehicles [6, 7]
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