Current industry trends in both powertrain electrification and vehicle drag reduction point towards reduced peak and average power demands from the internal combustion engine in future long-haul class 8 vehicles. Downsizing the engine displacement to match these new performance requirements can yield a benefit in drive cycle efficiency through reduced friction and improved cruise load efficiency. Downsizing by reducing cylinder count avoids the heat loss and friction penalties from reduced per-cylinder displacement and could allow a manufacturer to continue to leverage the highly optimized combustion system from existing heavy-duty engines in the new downsized offering.
The concept of this study is to leverage powertrain electrification and the improvement trends in vehicle aerodynamics and rolling resistance to develop a fuel economy focused, downsized heavy duty diesel powertrain for future long-haul vehicles utilizing a reduced cylinder count. Powertrain performance requirements were backwards calculated from vehicle performance metrics and the required power and torque computed while assuming future vehicle aerodynamic and driveline efficiencies and chassis rolling resistance values.
This study explores an 8.5 liter 4 cylinder heavy duty diesel utilizing a P1 48v hybrid architecture, electric exhaust gas recirculation (EGR) pump and e-compressor to meet performance targets while maximizing efficiency. Engine and vehicle simulations predict greater than 14% fuel economy improvement on a long-haul representative duty cycle over a baseline diesel-only powertrain in a drag-reduced future class 8 tractor trailer.