A comparison between different methods of calculating average engine emissions for agricultural tractors

High-quality data on average specific and absolute emissions from agricultu ral tractors are needed in calculations of environmental loads caused by di fferent food production techniques and agricultural strategies, but the sta ndards used to calculate these data are not adapted to agricultural conditi ons. Correct data on typical average engine loads are also important when o ptimizing engine control systems. The purpose of this work was to calculate average specific emission values in g kWh(-1) and average absolute emissio n values in g h(-1) for a 70 kW tractor using different methodologies and t o compare the results. The results show that the average specific hydrocarb on (HC) and carbon monoxide (CO) emissions calculated by European and inter national standards are lower than the specific emissions calculated from th e average use of a 70 kW tractor, especially for tractors partly used for l ow-load operations and front loading. When studying the absolute amount of emissions, the results instead show that nitrogen oxide (NOx) emissions are overestimated if calculated according to the standards. The study also ind icates that results calculated according to a non-standardized five-point t est cycle developed in Germany are more representative for all-round use of tractors in the 50-75 kW range than results from European and internationa l standards. Further, the results show that it is not possible to design on e set of weighting factors that gives representative results for all types of agricultural tractors and work operations. (C) 2001 Silsoe Research Inst itute.