Experimental investigation of performance, emission, and combustion characteristics of a CI engine operating on blends of waste cooking oil biodiesel/diesel under variable compression ratios condition

With rising global energy demand and diminishing fossil fuel reserves, the pursuit of sustainable alternatives has become imperative. Biodiesel derived from waste cooking oil (WCO) is a renewable, low-emission fuel that also addresses environmental concerns associated with waste disposal. This study investigates the influence of compression ratio (CR) on the performance, combustion, and emission characteristics of a compression ignition (CI) engine fueled with WCO biodiesel–diesel blends. Blends of 10%, 20%, and 30% biodiesel with diesel, designated B10, B20, and B30, were tested at CRs of 16, 17, and 18. The fuel blends exhibited physical and chemical properties similar to diesel, allowing use without engine modifications. Experimental results revealed that brake thermal efficiency (BTE) decreased slightly with increasing biodiesel content, with B10, B20, and B30 showing reductions of 0.42%, 1.43%, and 2.12%, respectively, compared to diesel. Specific fuel consumption increased by 2%–4%. While NOx emissions rose by 2%–5% at higher CRs, HC and CO emissions declined significantly. CO emissions declined by 6%, 8%, and 4% at CRs 16, 17, and 18, respectively. Higher CRs also led to shorter ignition delay and an increase in peak cylinder pressure by 9.5%. However, the maximum heat release rate declined with increasing CR, with values of 40.4, 35.8, and 28.33 J/°CA at CRs 16, 17, and 18, respectively. Overall, WCO biodiesel/diesel blends demonstrate promising potential as a clean, sustainable alternative to diesel, offering acceptable performance with reduced emissions in CI engines.