Performance Analysis and Modeling of the Combustion Characteristics of Carbonized Rice Husk Briquettes: Effects of Clay-Binder Ratio and Compaction Level

Abstract

This study investigates the combined effects of clay binder ratio and compaction level on the combustion performance of carbonized rice husk briquettes, focusing on ignition time, burning rate, flame duration, peak temperature, and thermal efficiency. Experimental results revealed that moderate clay contents (5–15%) and compaction levels (6–18 mm) significantly enhanced ignition stability, peak combustion temperature (up to ~970 ºC), and burn duration (up to 130 minutes). Moderate clay addition improved briquette strength but slightly reduced thermal efficiency, as the inert clay fraction diluted fuel energy. Low compaction (6 mm) increased porosity and airflow, resulting in rapid ignition and higher peak temperatures suited for quick, intense heating, whereas moderate compaction (12 mm) ensured balanced ignition, stable combustion, and prolonged flame duration. Excessive clay content (>15%) and high compaction (18 mm) reduced combustion efficiency due to increased ash formation and restricted airflow, leading to lower peak temperatures and incomplete combustion. Water boiling tests confirmed that briquettes with 5–10% clay and moderate compaction achieved optimal heat output for household cooking. A third-order polynomial regression model incorporating interaction terms accurately predicted ignition time, peak temperature, and burn duration (R2 = 0.900–0.997), effectively capturing nonlinear combustion behavior. The findings provide practical insights for tailoring briquette formulations to diverse cooking requirements—from quick, high-heat applications to long-duration simmering—thereby supporting the development of efficient, sustainable biomass fuels for rural and low-income communities.