LAUSR

Abstract Low viscosity engine oils have shown to be an effective solution to the fuel consumption reduction target, however, their potential is closely linked to the vehicle and engine design and to the real driving conditions. In this study the interaction between engine oil and driving conditions of two urban routes and one rural route in Spain and the United Kingdom has been put to test with the aim to evaluate their joint effect over fuel economy of a freight transport vehicle. In a first approximation, six different oil formulations, three of them belonging to the new API CK-4 and FA-4 categories and two with molybdenum-based friction modifier, were tested under stationary conditions with a medium-duty diesel engine. Followed by tests under real driving conditions of a freight transport vehicle, developed by means of computer simulations with an adjusted vehicle model, taking the fuel consumption maps of the six oil formulations, vehicle characteristics and the selected driving cycles as inputs to the model. Results of engine bench tests and simulations with oils of lower HTHS viscosity showed fuel consumption reduction values as expected. However unexpected results were found between the oils with molybdenum-based friction modifier added to their formulation.