Time resolved in-situ biodiesel combustion visualization using engine endoscopy

• Combustion endoscopy for diesel, B20 and B50.
• Spatial soot distribution inside the combustion chamber.
• Higher soot concentrations during premixed combustion.
• Larger area of luminous flames with larger biodiesel blends.
• Lower spatial flame temperatures for higher biodiesel blends.

Optical visualization technique such as engine endoscopy is a very important tool for time resolved spatial combustion visualization and characterization. It provides valuable information about combustion in a production grade engine, which cannot be obtained by using any conventional techniques. In this study, engine endoscopy was done in a single-cylinder; constant speed compression ignition (CI) engine fuelled with diesel and biodiesel blends. A dedicated control circuit was developed to synchronize the camera with in-cylinder combustion events. Combustion images were captured at different engine loads to determine start of combustion (SoC), spatial soot distribution and spatial flame radiation temperatures. With increasing biodiesel content in the fuel, larger area of luminous flames in the combustion images was obtained for lower biodiesel blends (up to B20) however it became smaller for higher biodiesel blends (for B50 and higher). It was also found that the area of soot distribution decreased in later stages of combustion for all test fuels which indicates better oxidation of soot particles. Combustion images showed earlier SoC for biodiesel blends with increasing engine load, which was another important finding of these experiments. Rate of heat release (RoHR) was lower for biodiesel blends compared to mineral diesel. Higher blends of biodiesel showed lower flame radiation temperatures due to soot particles emission that caused lower soot particles volume fraction and higher oxygen content in fuel hence more NOx emission from biodiesel combustion.