Experimental analysis of functional requirements to exceed the 100 kW/l in high-speed light-duty diesel engines

The paper describes the results achieved in an experimental study aimed at identify the operating parameters, in terms of fuel injection characteristics, intake/exhaust conditions and thermomechanical stress of engine and turbocharger, required to exceed the high threshold of 100 kW/l for light-duty high speed diesel engines. In order to increase the power/weight-volume ratio, such target is currently one of the milestones for diesel engine development engineers. To achieve the specific power target a high-performance prototype 0.5 l single-cylinder engine demonstrator was developed employing some special very robust components and high-quality parts from the state-of-art automotive diesel technology. A prototype advanced piezo injection system, capable of 3000 bar maximum injection pressure, was employed. Geometrical features of the combustion system and injector nozzle were carefully preconfigured based on the characteristics of the most recent diesel engines developed for premium high-performance cars, as well as on the best knowledge of the authors. The operating parameters in terms of intake - exhaust conditions and injection strategy were properly parametrized in order to find the boundary conditions suitable for the desired specific power target. 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 complete system based on thermo-structural, fluid-dynamic and efficiency considerations. The tests confirmed the benefits of the employment of very high fuel injection pressures as a way to face with the trade-off of combining high performance and fuel economy for light-duty high-speed diesel engines.