Edible oil refinery waste biodiesel-diesel blends: Production, engine performance, exhaust emissions and economic analysis

The growing global energy demand and depletion of fossil fuel reserves have intensified the search for sustainable and renewable energy sources. Biodiesel has emerged as a promising alternative due to its renewability, biodegradability, and lower environmental impact compared to conventional diesel. This study focuses on the production, performance, emission, and economic analysis of biodiesel derived from edible oil refinery waste, referred to as Transesterified Acidic Oil (TAO). The TAO biodiesel was synthesized through citric acid–catalyzed transesterification, converting refinery waste triglycerides into fatty acid ethyl esters (FAEEs). The fuel exhibited suitable physicochemical properties with improved cetane number, viscosity, and flash point, ensuring compatibility with diesel engines. Four fuel blends D–TAO5, D–TAO10, D–TAO15, and D–TAO20 were tested on a single-cylinder, four-stroke, water-cooled CI engine under varying loads. Among all, D–TAO15 achieved the highest brake thermal efficiency (36.4%), a 3.4% improvement over diesel, along with an 11.11% reduction in CO emissions, and lower HC and smoke levels. A marginal increase in NOx was observed due to higher combustion temperatures. The production cost of TAO biodiesel was estimated at INR 65.62 per litre, while the D–TAO15 blend showed an energy cost of INR 22.24 per kWh, approximately 7.8% lower than diesel. These results confirm that biodiesel from refinery waste feedstock offers a sustainable, economical, and eco-friendly solution to meet future energy challenges while promoting waste valorisation and emission reduction.