Combustion analysis of CI engine fuelled with calophyllum inophyllum methyl ester biodiesel and CeO₂ nanoparticle additives

This study investigates the effect of cerium oxide (CeO₂​) nanoparticle (NP) size on the combustion characteristics of a single-cylinder compression ignition (CI) or diesel engine fueled with a base blend (BD) composed of 20% Calophyllum Inophyllum Methyl Ester biodiesel (CIMEBD), and 80% diesel (by volume). The CIMEBD used in this study was synthesized via a two-stage transesterification process from crude Calophyllum Inophyllum oil. The challenges related to biodiesel properties such as viscosity and oxidation stability can limit the use of biodiesel blends to less than 20% biodiesel. As a result, 20%-biodiesel, 80%-diesel is a common and widely approved blend for use in modern diesel engines without modification, as per regulatory standards, such as the ASTM D7467 standard. NPs can be used with biodiesels in order to counteract their inherent higher viscosity, and thereby allowing the application of higher biodiesel percentages. CeO₂​ NP of four different average sizes (20, 40, 60, and 80 nm) were dispersed in the base biodiesel blend, BD at a fixed concentration of 90 ppm. The engine was operated at a constant speed of 1500 RPM under various loads. Key combustion parameters, including in-cylinder pressure, heat release rate (HRR), ignition delay (ID), cetane number (CN), and the coefficient of variation of indicated mean effective pressure (COVIMEP) were analyzed. Results show that the addition of NPs improves combustion stability and performance. The fuel blend with 40 nm NPs (BD40) exhibited the most favorable characteristics, demonstrating the lowest cyclic variability (COVIMEP​ of 1.9% at 30% load, compared to 3.1% for diesel) and the shortest ID, in crank angle degrees (CAD), that is, 3.14 CAD at 30% load for base biodiesel, vs. 4.5 CAD for diesel. This was attributed to the BD40 blend having the highest measured CN (55.4). A strong inverse correlation was established between CN, ID, and COVIMEP​. The findings indicate that an optimal NP size of 40 nm exists to maximize the catalytic benefits for biodiesel combustion, with agglomeration effects potentially diminishing the performance of larger NPs, thus establishing a clear, size-dependent relationship for combustion stability.