Analysis of a Diesel Passenger Car Behavior On-Road and over Certification Duty Cycles

Precise, repeatable and representative testing is a key tool for developing and demonstrating automotive fuel and lubricant products. This paper reports on the first findings of a project that aims to determine the requirements for highly repeatable test methods to measure very small differences in fuel economy and powertrain performance. This will be underpinned by identifying and quantifying the variations inherent to this specific test vehicle, both on-road and on Chassis Dynamometer (CD), that create a barrier to improved testing methods. In this initial work, a comparison was made between on-road driving, the New European Drive Cycle (NEDC) and World harmonized Light-duty Test Cycle (WLTC) cycles to understand the behavior of various vehicle systems along with the discrepancies that can arise owing to the particular conditions of the standard test cycles. The engine controller of a 2.0L diesel vehicle with active de-NOx and a particulate filter (DPF) has been monitored over 13,700km of driving. The engine speed/torque operating points showed that both the NEDC and WLTC fail to capture the complete static and dynamic usage observed on the road, and are ill-equipped to capture any driver to driver variations. A cyclic analysis of the DPF is proposed, showing up to 70% variation in soot loading at the point of regeneration. This variation can be explained by the controller waiting for favorable driving conditions for regeneration. NEDC and WLTC are poor cycles for capturing DPF effects as the former presents insufficient engine powers to trigger and the later insufficient time to complete a regeneration event. Along with understanding the general contrasts between standard CD cycles and road conditions, this is a key finding for the project overall as understanding and managing DPF loading and regeneration will enable improvements to be made in test precision.