Experimental study of droplet combustion and diesel engine characteristics for Azolla biodiesel

This study pertains to studying the feasibility of the third-generation biodiesel obtained from one of the algae species known as Azolla microphylla by exploring their fundamental droplet combustion behavior and diesel engine characteristics. Firstly, the droplet evolution and burn rate are investigated for diesel, Azolla100, and Azolla50 (50% biodiesel +50% diesel) based on the experimental study of suspended droplet combustion. The diesel droplet showed steady combustion with linear regression for the decrease in droplet surface with time throughout its lifetime, while the Azolla100 and Azolla50 droplets showed a linear trend initially, and after a certain point, they resulted in a non-linear trend as a result of disruptive burning. The evaporation and burn rate was found to be higher for Azolla100 and Azolla50 than diesel during the steady burning period and thereafter it decreased with increasing Azolla concentration. The time evolution of droplet combustion images indicated that with increasing biodiesel concentration, the combustion duration was decreased due to secondary droplet ejections and microexplosion, and the residue burning duration was increased. The microexplosion increased the rate of combustion, however, droplet ejection resulted in incomplete combustion. Secondly, the engine experiments were performed for Azolla50 at different fuel injection pressures. The results showed that in-cylinder pressure and Brake thermal efficiency (BTE) for Azolla50 at 300 bar injection pressure were lower than diesel due to limitations with the physical properties of biodiesel. In order to improve the engine characteristics of Azolla50, this study increased the fuel injection pressure to 900 bar. As a result, the BTE for Azolla50 at 900 bar injection pressure is improved by 9.2% and 10.2% at low and full load conditions, respectively, compared to Azolla50 at 300 bar injection pressure. Overall, the spray-driven combustion for Azolla50 is limited by the physical properties of the biodiesel, which affects the mixture formation. On the other hand, the microexplosion and droplet ejection observed with the biodiesel during the combustion study would favor the combustion by improving the atomization and mixing process.