Preparation of TiO2 submicroparticles via ultrasonication and their application in diesel–biodiesel blends for improving performance and emissions of diesel engine

TiO2 nanoparticles have been used as fuel additives due to high surface area–to–volume (S/V) ratio, high reactive surfaces, and heat transfer enhancer properties of the particles. However, smaller commercial–grade nanoparticles were significantly more expensive due to the methods used for synthesis, such as the sol–gel method, involving various chemicals and solutions. The main objective in this study was to produce ultrasonically size–reduced TiO2 particles (STP) from cheap commercial–grade TiO2 microparticles (TMP) and use them as diesel–biodiesel fuel blend additives. The size reduction of TMP was carried out under pulsed ultrasonic conditions, with an ultrasound on–time of 60 s and off–time of 60 s (60 s ON/60 s OFF). The size reduction process was designed using an inscribed central composite design (CCI) with 5–level variables and optimized by response surface methodology (RSM) and analysis of variance (ANOVA). The results showed that STP with an average size of 360.4 nm was achieved under the conditions of 540 s sonication time and 0.15 wt% TMP in diesel medium. Diesel–biodiesel–STP fuel blends (D90B10Ti, D70B30Ti, D50B50Ti, D30B70Ti, and D10B90Ti) were prepared and tested on a diesel engine rig to study engine performance (Pb, BSFC, BTE), and emissions (O2, CO, CO2, NOx, EGT, smoke opacity) at various engine speeds (1100–2300 rpm), and loads (0–75 %). At 2300 rpm maximum speed, and maximum load of 75 %, the D90B10Ti blend showed a slightly lower Pb than diesel by 0.64 %, and a slightly higher BSFC by 0.87 %. A 0.62 % decrease in BTE for the D90B10Ti blend was observed under the same conditions compared to diesel. For emissions, the D90B10Ti blend showed increases in O2 and EGT levels by 5.88 %, and 4.32 %, respectively. CO, CO2, and NOx emissions were found to be 7.13 %, 5.22 %, and 5.50 % lower than diesel, respectively. Moreover, the smoke opacity result of D90B10Ti blend was decreased by 11.39 %. The results indicated that improved combustion efficiency can be achieved by using biodiesel and STP as fuel additives. When compared to D100B0E0Ti fuel blend with TiO2 nanoparticles (TNP), it was found that D90B10Ti has comparable engine performance parameters but slightly higher emissions. Moreover, the production cost of D90B10Ti fuel blend with STP was significantly lower than that of D100B0E0Ti blends with commercial–grade TiO2 nanoparticles (TNP) by approximately seven times.