Exceeding 100 kW/l Milestone: The Next Step towards Defining High Performance Diesel Engines

The paper describes the challenges and results achieved in developing a new Diesel combustion system for passenger car application capable of very high power density, thus exceeding the imaginative threshold of 100 kW/l. The three project partners have contributed their specialties for providing the high-quality state-of-art components, system integration and combustion development techniques needed to achieve this result on a 0.5 l single-cylinder research diesel engine set-up at Istituto Motori of CNR. Following extensive benchmark and analysis activities in order to identify the key design parameters to optimize, advanced piezo injection system concept by Continental capable of 3000 bar maximum injection pressure was selected, coupled to a robust base engine featuring GM-developed advanced combustion bowl and intake ports. The matching among the low compression ratio wide bowl, the high-density charge motion and the highly efficient injector nozzle have been thoroughly examined and experimentally parametrized, and the final injector nozzle specifications reflect the balance chosen between the somewhat conflicting requirements for rated power on one side and CO2 and pollutant emissions on the other side. The tests confirmed the benefits of the employment of very high fuel injection pressures as a way to solve the above-mentioned trade-off, combining high performance and fun-to-drive with excellent emissions, NVH and fuel economy typical of last generation diesels for passenger car. Finally, the paper discusses the system sensitivity to the boundary conditions of the charging and exhaust systems, and develops a balanced set of targets for the entire system (including the base engine reciprocating components) based on thermo-structural, fluid-dynamics and efficiency considerations. This would represent, in the authors' view, the 'recipe' for the next generation of high-performance diesel engine for passenger cars application.