An Experience with a DPF Retrofitted at the Exhaust of an Euro II Urban Bus Engine

Nitrogen dioxide (NO2) and particulate matter (PM10) are the most critical pollutants in urban areas and their EU limit values, as air quality standard, are often overcome. NOx and PM10 are the most critical emissions from Diesel engines and there is a big interest in the development and implementation of after-treatment systems for their reduction. Diesel Particulate Filters (DPF) are commercially available today. In this experimental work some ESC tests have been performed with an Euro II urban bus Diesel engine equipped with a passive DPF system DPXTM by Engelhard. Regulated emissions have been measured and the NO2/NOx ratio has been evaluated. Particulate matter emissions have been characterized by using different techniques: gravimetry, opacimetry, filter smoke meter, photoacustic soot sensor and electrical low pressure impactor. DPXTM reduces PM emissions by at least 85%, it also strongly reduces the ultra fine particles but an increase of NO2 in the total NOx emission has been measured.