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

High-quality data on average specific and absolute emissions from agricultural tractors are needed in calculations of environmental loads caused by different food production techniques and agricultural strategies, but the standards used to calculate these data are not adapted to agricultural conditions. Correct data on typical average engine loads are also important when optimizing engine control systems. The purpose of this work was to calculate average specific emission values in g kWh(-1) and average absolute emission values in g h(-1) for a 70 kW tractor using different methodologies and to compare the results. The results show that the average specific hydrocarbon (HC) and carbon monoxide (CO) emissions calculated by European and international standards are lower than the specific emissions calculated from the average use of a 70 kW tractor, especially for tractors partly used for low-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 indicates that results calculated according to a non-standardized five-point test cycle developed in Germany are more representative for all-round use of tractors in the 50-75 kW range than results from European and international standards. Further, the results show that it is not possible to design one set of weighting factors that gives representative results for all types of agricultural tractors and work operations. (C) 2001 Silsoe Research Institute.