Evaluation of the performance and emissions of diesel engines powered by minimally refined palm oil produced using calcined limestone

• Novel low-energy palm oil refining using calcined limestone catalyst. • 1050-hour engine test shows MRPO performance matches standard biodiesel. • Production cost is ∼70% lower than conventional biodiesel methods. • MRPO meets national fuel standards with comparable emissions to B40. • Enables decentralized, affordable biofuel for off-grid electrification. Decarbonizing off-grid power generation in palm-oil-producing nations requires affordable biofuels. Conventional palm biodiesel production via transesterification or hydrotreating adds high processing costs (USD 4.77–12.53/kg) and energy burden (20–25 MJ/L). This study presents a novel minimally refined palm oil (MRPO) produced through a low-intensity route: dry fractionation of crude palm olein, treatment with a limestone-derived CaO/Ca(OH) 2 alkaline precursor (5 wt%, 80–95°C, 5 min), centrifugation, five-stage warm-water washing, and vacuum drying, bypassing transesterification entirely. The precursor, synthesized by calcination of natural limestone at 800°C and hydration–dehydration, exhibited strong basicity (H_= 15.0–18.4) and reduced acid value by 96%, phosphorus by 99%, and kinematic viscosity by 29% relative to crude palm oil. Total process energy was only 0.66 MJ/L. The resulting MRPO met Indonesian stationary biofuel specifications and was benchmarked against B40 (40% FAME/60% diesel) in a 1,050 h diesel-generator endurance test on a 37 kW engine. MRPO showed comparable torque (≤0.84% penalty), 5.74% lower power, and 7.93% higher specific fuel consumption, attributed to higher viscosity and lower heating value. Exhaust opacity was reduced by 3.8-fold (3.5% vs. 13.3%), while NOx and CO were similar. Used oil analyses (viscosity, TBN, TAN, wear metals) remained stable throughout the test, and post-test inspection revealed no critical wear or deposits. With estimated production cost of USD 1.4/kg and a 30-fold lower process energy than transesterification, MRPO offers a technically viable, low-emission, and economically accessible stationary fuel.