Fuel impact on the aging of TWC’s under real driving conditions

Abstract

The impact of different fuels, gasoline, two ethanol–gasoline blends (E5, E85) and compressed natural gas (CNG), as well as lubricating oils on the aging behavior of Three-Way-Catalysts (TWCs) has been investigated with six state-of-the-art passenger cars over 40,000km under real world driving conditions. For the study, all vehicles have been equipped with identical TWCs. During the investigation all relevant engine and vehicle operational parameters have been recorded. Exhaust gas measurements on a chassis dynamometer have been performed every 10,000km.After 40,000km, the surface of the TWCs has been analyzed by means of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The investigations revealed significant P, Ca, Zn and partly Mg depositions on the wash coat layer of the catalyst inlet area, rapidly decreasing along the catalyst channels towards the outlet.The SEM images showed strongest ash depositions for the vehicles that had higher oil consumptions. Cracks and partly ablation of the wash coat at the inlet area of all TWC’s have been identified strongly differing from vehicle to vehicle. Strongest damages have been encountered on the catalysts of the vehicles fuelled by the ethanol blends.However, no emission deterioration of the vehicles could be determined over the New European Driving Cycle (NEDC) even after 40,000km. In contrast, emission increase was ascertained over the more realistic Common Artemis Driving Cycle (CADC), which involves considerably higher space velocities of the exhaust gases through the catalysts. The vehicles using ethanol fuel blends, and having the severe damages on their wash coat layers showed the strongest emission deterioration. In contrary, vehicles with the thickest ash layer on the catalysts did not exhibit significant emission increase.