Experimental Study on Biodiesel Injection Characteristics and Spray Development Tendency

The conversion of biodiesel’s chemical energy into mechanical work in diesel engines is strongly influenced by the formation and quality of the fuel–air mixture. The physical and chemical properties of biodiesel, together with the operating characteristics of the fuel injection system, play a crucial role in this process. This study presents experimental findings on the injection behavior of a mechanically controlled injection system using three fuel types: pure rapeseed biodiesel, a 50% biodiesel–diesel blend, and conventional diesel fuel. The analysis focused on injection pressure, injection timing, injection duration, and fuel delivery under various operating conditions. In the second part of the experimental investigation, spray visualization was carried out by injecting fuels into a transparent liquid-filled chamber. A dedicated imaging and processing system was applied to capture and analyze spray development. From the recorded sequences, macroscopic spray parameters—including spray penetration length, spray cone angle, and projected spray area—were determined across different injection regimes. This approach allows clear identification of spray development tendencies and supports systematic comparison between fuels, particularly in relation to differences in injection pressure, injection duration, and delivered fuel quantity arising from the mechanically governed injection system. Correlation analysis between spray penetration length and peak injection pressure further highlights pressure-driven contributions to spray evolution. The findings contribute to better understanding of biodiesel spray behavior under realistic mechanically controlled conditions, supporting optimization of fuel injection performance and aiding in the selection or formulation of biodiesel fuels with improved spray characteristics.