Original Investigation of Non-Equilibrium Thermodynamics of Combustion in Biofuel-Diesel Hybrid Systems for Nigerian Power Generation

The thermodynamic analysis of combustion in multi-component biofuel-diesel blends under real engine conditions involves non-equilibrium transport processes that are inadequately described by classical equilibrium thermodynamics, particularly during the early stages of ignition and during soot formation in fuel-rich zones. This research conducts an original investigation of non-equilibrium thermodynamic behavior in the combustion of palm oil biodiesel-diesel blends at ratios of 0 to 100 percent biodiesel, with particular focus on entropy production rates, exergy destruction, and non-equilibrium kinetic coupling between species transport and chemical reaction. A theoretical framework based on extended irreversible thermodynamics is formulated for the multicomponent combustion system, incorporating Soret and Dufour cross-diffusion effects and explicit entropy production rate terms associated with chemical affinity-driven reactions. The non-equilibrium thermodynamic framework is implemented as extensions to the OpenFOAM reactive flow solver and validated against pressure-time traces and heat release rate measurements from a single-cylinder diesel engine operated on biodiesel blends at the Energy Laboratory of Covenant University, Ogun State. Original analytical expressions for the non-equilibrium contribution to second-law efficiency as a function of biodiesel blend fraction are derived, predicting a monotonic efficiency decrease with increasing biodiesel content primarily attributable to higher Soret diffusion entropy production from the broader fatty acid molecular weight distribution. The exergetic efficiency of palm oil biodiesel combustion at B50 is 3.1 percent lower than neat diesel, with implications for generator fuel consumption optimization in the Nigerian off-grid power sector. Keywords: non-equilibrium thermodynamics, biofuel combustion, exergy, entropy production, diesel engine