Improving energy efficiency of heavy-duty vehicles: A systemic perspective and some case studies

Today's advanced market economy relies in logistic operations that are both reliable and timely. Road transport is a major contributor to this daily logistics, but also a major consumer of fossil fuels, hence producing a lot of carbon emissions. Furthermore, most of the technologies recently introduced to cut down fuel use and emissions in passenger cars are not practical in heavy trucks running long-distances. This paper focuses on how to more systematically address the energy process and gives some case-examples of progress made in real-world HDVs. Several studies at VTT have been addressing energy use in HDVs. It has become evident that for real improvements in energy efficiency, the complete vehicle must be taken into consideration. We must have better understanding of the factors influencing the energy demand, and not just how to make engines more fuel efficient. For that purpose a break-down of energy use in a heavy truck-trailer combination has been made. The objective for this approach was to give proportions for the various contributors for the energy use, and be able to assess, what kind of progress in each field could be possible. Apart from the holistic and systemic approach, we need metrics to measure the energy consumption in such a way that the results reflect real-world situation as good as possible. Using a chassis dynamometer capable of taking a full-size vehicle and replicating its on-road driving operations has proven to be an excellent tool in terms of precision and repeatability of the results. Adding also road gradient (uphill/downhill) simulation further enhances the realism, and improves the accuracy how closely the duty-cycle is reflected in engine speed/load sequence compared to on-road driving. Eventually, this match is the measure for the success of the method. In case studies several areas of energy use has been addressed, and the potentials for savings in real-use has been determined. These include e.g., choice of tyres for optimum rolling losses without compromising safety and most recently aerodynamic improvements for the complete truck-trailer combination for reduced drag. The paper will portray the achievable energy savings identified in these studies. Test results demonstrate that energy efficiency of heavy trucks can be improved, but for a long-standing and substantial impact the complete design of the vehicle should be viewed from the energy efficiency perspective.