Synthesis and evaluation of third-generation Azolla pinnata methyl ester for combustion and emission characteristics of a direct injection CI engine with isopropanol as an additive

The increasing demand for sustainable transportation fuels has strengthened the interest in third-generation biodiesels and higher alcohol. This study investigates the effect of Azolla pinnata methyl ester (APME) a fast-growing aquatic biomass derived biodiesel blended with isopropanol as an oxygenated additive for improving compression ignition (CI) engine performance. Two binary blends (D80B20 and D70B30) and two ternary blends containing 20% isopropanol (D60B20P20 and D50B30P20) were synthesized and tested in a common-rail direct injection (CRDI) CI engine under loads ranging from 25 to 100% without engine modification. Results showed that D60B20P20 blend showed the favourable performance compare to other blends in the test. It shows a peak pressure of 66.69 bar and net heat release rate of 55.27 J/deg at 75% load, which is only 5–14% lower than diesel. The lower viscosity and oxygenated nature of isopropanol improved the atomization and premixed combustion, reducing HC and CO emissions by 3.44% and 16.66%, respectively, while NOₓ emissions decreased by 7.26% due to the cooling effect of isopropanol’s high latent heat of vaporization. In contrast, blends with 30% biodiesel (D50B30P20) exhibited prolonged combustion duration and a 28% reduction in brake thermal efficiency. It is concluded that less than 20% of APME content in the ternary blend offer a best optimize performance and emission trade-off, achieving 40% fossil fuel substitution without engine modifications. These findings shows that APME-isopropanol fuel can be a sustainable low carbon alternative biofuel for IC engine application.