Effect of Intake Air Preheating on Performance and Emissions of a Diesel Engine Using Diesel–Biodiesel–Ethanol Blends

With growing concerns over fossil fuel depletion, environmental pollution, and the need for sustainable energy solutions, alternative renewable fuels have gained significant attention in the transportation sector. Biodiesel and ethanol are promising biofuels that can reduce dependence on conventional diesel and lower harmful emissions. However, challenges such as fuel compatibility and combustion inefficiencies limit their widespread adoption in compression ignition engines. This study investigates the combined effects of intake air preheating and diesel-biodiesel-ethanol ternary fuel blends on the performance and emission characteristics of a single-cylinder compression ignition engine. Cottonseed biodiesel, an underutilized nonedible feedstock abundant in regions like Ethiopia, was blended with ethanol and conventional diesel in three ratios: B20E10, B30E10, and B40E10. Experiments were conducted under ambient (25 °C) and preheated (51 °C) intake air conditions to evaluate brake thermal efficiency (BTE), brake-specific fuel consumption (BSFC), and gaseous emissions (CO, HC, NO _<i>x</i> , and CO₂). Results showed that intake air preheating enhanced combustion efficiency and reduced BSFC by up to 11.11% while increasing BTE by as much as 4.28%. CO and HC emissions were significantly reduced across all blends, though NO _<i>x</i> emissions increased due to higher in-cylinder temperatures. Among the tested blends, B20E10 exhibited the best balance between performance, efficiency, and emissions, delivering brake power comparable to that of diesel with the lowest BSFC and substantially cleaner exhaust. While particulate matter was not directly measured, existing literature supports the expectation of reduced PM due to the oxygenated nature of the fuels. The study highlights intake air preheating as a cost-effective strategy to enhance the viability of renewable fuel use in existing diesel engines. These findings offer a practical pathway toward cleaner combustion and energy diversification, particularly in low-resource settings, where local biofuel adoption is critical for energy security and environmental sustainability.