Comparative Evaluation of the Effect of Various Technologies on Light-duty Vehicle CO2 Emissions over NEDC and WLTP

Abstract

The paper presents the results of the effect of various fuel economy technologies on the certified CO2 emissions of light duty vehicles. The vehicles operate under two different driving cycles, namely the New European Driving Cycle (NEDC) and the Worldwide harmonized Light duty Test Procedure (WLTP), which is considered closer to real world driving and is going to be the new type approval test in the near future. The study focuses on the comparative evaluation of the effect of each technology on CO2 emissions under these two driving cycles. To this aim, simulation models for a number of passenger cars were developed and validated against test data, generated via a specifically developed test protocol. In order to cover a large share of the market, the European fleet was divided into a number of segments based on specific vehicle characteristics and technologies, and representative vehicles for each segment were chosen. In order to minimize flexibilities and sources of uncertainty, the models were developed according to a standardized modelling procedure, based on the development of a reference “template model”. AVL's Cruise was used as simulation platform. The various components and modules for each vehicle model, as well as the respective input parameters, were defined with the support of the respective OEMs. After gaining confidence in the simulation models for all the vehicles considered in the present work, additional technologies, such as start-stop, brake energy recuperation and different drivetrain configurations, were implemented in each model. Specific strategies have been defined for the implementation of individual technologies and, where needed, additional algorithms were developed in Cruise. The results show that the effect of each technology on CO2 emissions is different between NEDC and WLTP, owing to the different characteristics of each cycle. For example, the effect of start-stop on CO2 emissions is larger in NEDC, due to longer idling periods compared to WLTP. In this context, the results of this study can provide useful indications for the most effective fuel economy technologies under the new type approval procedure.