CFD Analysis of the Effect of the Injection Pressure on a Small 2S LPDI Engine

The paper investigates the influence of the fuel injection pressure on a small two-stroke engine with low pressure direct injection (LPDI). The authors in previous studies showed the benefits of the LPDI system in reducing the fuel short circuit, both from an experimental and numerical point of view. As a direct consequence, both the specific fuel consumption and the pollutant emissions were notably reduced, reaching the typical performance of a standard four-stroke engine of comparable size.The main drawback of the system is the limited time at disposal for delivering the fuel with difficulties in achieving a satisfactory air-fuel mixing and homogenization as well as fuel vaporization.In order to overcome the aforementioned issues, a detailed numerical analysis is carried out by performing a wide set of CFD simulations to properly investigate and understand the many complex phenomena occurring during the interaction between the injected fuel and the fresh scavenging air. Starting from the reference configuration working with a fuel delivery pressure of 5 bar, lower and higher injection pressures are considered. The higher pressure (10 bar) is investigated to evaluate the effects of shortening the injection duration and increasing the fuel atomization. The lower pressure (3 bar) is investigated to evaluate the effects of distributing the total amount of delivered fuel along a wider crank angle range and of increasing the interaction with the fresh air. Different engine operating conditions are analyzed by varying the engine speed and load.