Rheological and stability studies of date seed based-biochar diesel–hydrogen peroxide slurry fuels: Optimized dispersant strategies, coagulation analysis, and temperature performance

This study presents a comprehensive stability analysis of biochar-based diesel–hydrogen peroxide slurry fuels as a sustainable alternative for combustion applications. Biochar derived from date seeds was produced via controlled pyrolysis and incorporated into a diesel–H₂O₂ blend with 5 wt% biochar loading. To ensure stability, dispersants—Sodium Lignosulfonate (NaLS), Carboxymethylcellulose (CMC), and Sodium Polynaphthalene Sulphonic Acid (SPNS)—were applied at varying concentrations. Characterization through scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and particle size distribution confirmed the biochar’s enhanced porosity, high volatile matter (48.7 %), fixed carbon (45.5 %), and low ash (1.1 %). Stability was assessed by monitoring phase separation. The optimum formulation with 3 wt% NaLS delayed separation for up to 10 days, while CMC (1 wt%) and SPNS (2 wt%) achieved stability for 7 days. Rheological evaluations revealed shear-thinning behavior, with viscosity increasing from 4.78 to 8.72 mPa·s at 100 s⁻¹ as dispersant concentration rose, and decreasing from 8.72 mPa·s at 20 °C to 2.72 mPa·s at 60 °C, enhancing flow at elevated temperatures. Excessive dispersant dosages, particularly CMC and SPNS, induced coagulation and reduced stability. These results highlight that optimized dispersant levels minimize sedimentation and coagulation while improving pumpability and combustion performance. Future work should validate engine performance to establish these fuels as viable energy alternatives.