The Key Role of Advanced, Flexible Fuel Injection Systems to Match the Future CO₂ Targets in an Ultra-Light Mid-Size Diesel Engine

The article describes the results achieved in developing a new diesel combustion system for passenger car application that, while capable of high power density, delivers excellent fuel economy through a combination of mechanical and thermodynamic efficiencies improvement. The project stemmed from the idea that, by leveraging the high fuel injection pressure of last generation common rail systems, it is possible to reduce the engine peak firing pressure (pfp) with great benefits on reciprocating and rotating components’ light-weighting and friction for high-speed light-duty engines, while keeping the power density at competitive levels. To this aim, an advanced injection system concept capable of injection pressure greater than 2500 bar was coupled to a prototype engine featuring newly developed combustion system. Then, the matching among these features has been thoroughly experimentally examined. The results confirmed the benefits of the employment of high fuel injection pressures as a way to reduce the pfp, combining competitive performance and excellent fuel efficiency with emissions and noise, vibration, and harshness (NVH) requirements of last generation diesel engines for passenger car applications. In particular, the article discusses the engine power and efficiency sensitivities to the boundary conditions of the charging/exhaust systems, the fuel injection pressure, and the mechanical base engine design (with particular reference to the pfp). Eventually, a balanced set of targets for the entire system based on such results is carried out.