Advanced Ignition and Combustion Analysis of Second-Generation Biodiesels in Turbocharged Diesel Engines

Abstract

This study investigates the energy release characteristics of second-generation biodiesel blends derived from beef tallow and castor bean in a turbocharged compression ignition engine. The primary objective was to evaluate ignition delay, combustion phasing, and energy release rates at various engine loads using blends of B10 and B20 biodiesel concentrations. A comprehensive experimental setup, including a diesel engine and a detailed thermodynamic model, was employed for this analysis. Dynamometric testing was conducted to assess the performance of the biodiesel blends compared to mineral diesel and soybean biodiesel. Key parameters such as cetane number, viscosity, and fatty acid composition of the biodiesels were correlated with their combustion behavior. Energy release characteristics were measured under low (250 kPa), medium (500 kPa), and high (750 kPa) load conditions. The study revealed that beef tallow biodiesel advanced ignition timing, reducing premixed combustion phases across all loads. At low load, castor bean biodiesel showed significant ignition delays (around 3° crank angle longer than diesel), leading to higher peak energy release rates, notably at high loads where it surpassed mineral diesel. The B20 blend of castor bean biodiesel emitted 320 mg/kg of unburned hydrocarbons at low load, compared to 21 mg/kg for diesel, indicating challenges in achieving complete combustion. Beef tallow biodiesel exhibited favorable ignition characteristics, while castor bean biodiesel faced issues with delayed ignition and higher energy release rates due to its high viscosity and low cetane number. Optimizing the molecular composition of castor bean biodiesel and exploring advanced fuel injection strategies could enhance its combustion efficiency. Further research is recommended to investigate the long-term effects on engine wear and emissions, ensuring these biodiesels' viability as sustainable alternatives to conventional fuels.