Experimental investigation of quaternary blends of diesel/hybrid biodiesel/vegetable oil/heptanol as a potential feedstock on performance, combustion, and emission characteristics in a CI engine

Hybrid oils ensure multifaceted technological (self-lubricating and favorable fatty acid properties), and sustainable (environmental, economic, and societal) benefits towards biodiesel conversions. The hybrid oils (Hydnocarpus wightiana oil and waste cooking oils [40:60 v/v]) were synthesized to methyl ester with alkaline catalyst sodium hydroxide through the base-transesterification process. The resulting hybrid oil methyl ester (HOME) is 96.68%. The crude oil (CO) and its HOME underwent characterization using gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy, and hydrogen-1 nuclear magnetic resonance spectroscopy. The physicochemical properties of crude oils and hybrid biodiesel were analyzed and compared to pure diesel. Different blends of biodiesel–diesel, including binary (20% HOME + 80% diesel [D]), ternary (60% D + 20% HOME + 20% heptanol [H]), and quaternary (20% HOME + 20% H + 10% CO + 50% D) blends, were tested in a single-cylinder compression ignition (CI) engine under various load conditions to assess their performance, emissions, and combustion properties. Experimental findings indicate that the addition of heptanol to diesel or hybrid biodiesel (ternary blend) enhances brake thermal efficiency, reduces brake-specific fuel consumption, and leads to longer ignition delays, resulting in higher internal combustion pressure and thermal energy release rates compared to the quaternary blend. Additionally, compared to pure diesel, the ternary blend exhibits decreased emissions of carbon monoxide (CO) and hydrocarbon (HC), with a slight increase in nitrous oxide (NO_x) and carbon dioxide (CO₂). Notably, the ternary blend emerges as a distinct alternative biodiesel blend suitable for direct use in CI engines without requiring any engine modifications.