<![CDATA[This study experimentally compared the thermal response and direct fuel expenditure of coal supplemented with rubber wood biomass and waste oil in a small-scale crucible furnace for aluminum melting. The objective was to evaluate how renewable solid biomass and waste-derived liquid fuel supplementation influenced furnace temperature development, heating rate, melting duration, and direct fuel cost under comparable operating conditions. A fixed aluminum charge and coal input were used throughout the experiments, while rubber wood was added at a constant mass ratio and waste oil was tested at three increasing addition levels. Furnace configuration, airflow, measurement geometry, and operating procedures were maintained consistently across the experiments. Independent repeated runs were conducted for the coal-only and waste-oil conditions, whereas the coal–rubber wood condition was evaluated as a single-run screening comparison. Temperature was recorded at one-minute intervals as temporal observations, and the results were analyzed descriptively without inferential significance testing. Waste-oil supplementation generally resulted in higher sustained furnace temperatures and shorter aluminum-melting times than coal alone. Increasing waste-oil addition was associated with higher final temperatures, with the highest addition level producing the highest mean final temperature and shortest melting duration. The coal–rubber wood condition exhibited a different temperature-development pattern but did not produce the highest early-stage mean heating rate. Direct fuel expenditure increased only modestly across the waste-oil conditions, whereas the coal–rubber wood condition required higher direct fuel expenditure under the tested configuration. Overall, the results provide a comparative screening of solid-biomass and waste-oil supplementation for coal-fired small-scale aluminum melting, highlighting differences in thermal response, melting duration, and direct fuel expenditure. The findings are limited to the tested conditions and do not establish combustion efficiency, thermal efficiency, emissions performance, or overall economic viability.]]>
