Consumption of Diesel exhaust fluid (DEF) of agricultural tractor engines using selective catalytic reduction (SCR) system

EU Stage IIIB and Stage IV and EPA Tier IV interim and Tier IV emission regulations for Diesel engines equipping agricultural tractors establish criteria to reduce nitric oxide (NO) and particulate matter (PM) in the exhaust gas. To comply with these emission regulations manufacturers adopt 2 alternative technical solutions: exhaust gas recirculation (EGR) + Diesel particulate filter (DPF) or selective catalytic reduction (SCR) converter. SCR requires to inject a Diesel exhaust fluid (DEF) made of an aqueous solution of 32.5% of urea into a catalytic converter located in the exhaust system to reduces NO emission. The paper examine the effectiveness of a procedure to estimate the DEF consumption during the power-take-off (pto) tests on a tractor equipped of SCR system. In accordance with results of the investigation reliable mean DEF consumptions, for any of the engine operating points to be checked during pto tests, are obtained with, at least, 2 minutes measurements. The DEF consumption recorded at the pto test on the tractor ranged between 4.3 and 7.9% of the fuel consumption, that are higher than the 2 to 4% of the fuel consumption claimed by manufacturers for tractors in real operation conditions.