Energy and exergy analysis of low-temperature combustion in a light-duty diesel/CNG and biodiesel/CNG fueled engine

• First cycle-resolved exergo-economic evaluation directly comparing diesel/CNG and biodiesel/CNG RCCI-LTC operation on a single-cylinder Faryamann 18 W engine. • Performance assessed via six unified metrics: exergy efficiency, exergy destruction rate, exhaust emissions, specific investment cost (SIC), specific fuel cost (SFC), and exergo-economic factor (f k ). • Optimal LTC found for Bio5 at rp = 80 % and SOI = −62 °CA BTDC, boosting exergy efficiency by 5.2 pp (36.0 → 41.2 %) and lowering irreversibility. • Bio20 at rp = 60 % and SOI = −61 °CA BTDC cuts NO x by 61 %, while pure diesel (Bio0) delivers the lowest SFC (0.186 USD/kWh) and highest f k (95.6 %). • Tornado-style sensitivity: SIC swings −19.9 %/+20.2 % under ±20 % engine-price changes; SFC shifts ±20.0 % with ±20 % fuel-price variation, pinpointing key economic drivers. • Design and policy guidance: adopt ≥5 % biodiesel blending with optimized methane premix and SOI timing to balance efficiency, emissions, and cost. The growing demand for sustainable energy solutions has intensified research into low temperature combustion (LTC) technologies for internal combustion engines. This study uniquely integrates single-cylinder RCCI-LTC experiments with a cycle-resolved MATLAB® energy–exergy model and an exergo-economic evaluation the first to compare diesel/CNG and biodiesel/CNG blends under controlled injection timing. Through the use of alternative fuels and optimized LTC strategies, we aim to enhance thermal efficiency while mitigating environmental impacts. We tested a modified Faryamann 18 W engine at 1800 rpm using B0, B5, and B20 blends at r p = 60–80 % and injection angles of 36–62 °CA BTDC. Key performance metrics including thermal and exergy efficiencies, combustion characteristics, and emission profiles were analyzed. Exergy efficiency improved by 5.2 % for Bio5 at r p = 80 %, while NO x dropped by 61 % for Bio20 at r p = 60 %. Diesel/CNG at 62 °CA BTDC yielded the lowest specific fuel cost (0.186 USD/kWh) and specific investment cost (293.5 USD/kW). These findings guide cost-effective LTC integration in next-generation engines.