Experimental Study on Combustion Characteristics and Regulated and Unregulated Emissions of a Common-Rail Diesel Engine Fueled with Waste Cooking Oil Biodiesel

The demand for fossil fuels can be reduced and environmental harm can be minimized by producing biodiesel from used cooking oil. This article was focused on investigating the combustion characteristics and regulated and unregulated emissions of a common-rail diesel engine fueled with different mixed concentrations of biodiesel and diesel fuel, including pure diesel fuel (B0), B10 (diesel containing 10%vol of biodiesel), B20, and B30. Experiments were conducted with three engine loads, corresponding to brake mean effective pressures (BMEP) of 0.289 MPa, 0.578 MPa, and 0.867 MPa at a constant speed of 1540 rpm. At medium and high loads, the waste cooking oil biodiesel (WCOB) increased in-cylinder pressure, advanced both the peak heat release rate and heat release center (CA50), shrunk the ignition delay (ID), and extended combustion duration (CD). The high viscosity of B30 blends under low load worsened the spray and led to poor combustion. Under high-load conditions, carbon dioxide (CO₂) and nitrogen oxides (NO_x) emissions increased by 14.3% and 3.1%, while carbon monoxide (CO), soot, and total hydrocarbon (THC) emissions decreased by 13.3%, 31.4%, and 30.37%, respectively, for the B30 blend compared to diesel. The emission trends for nitrogen dioxide (NO₂), formaldehyde (HCHO), methane (CH₄), ammonia (NH₃), ethylene (C₂H₄)_, and formic acid (HCOOH) were consistent with increasing volume ratios of WCOB under the three loads. And they had the lowest emissions at 75% load for B30, with reductions of 70.5%, 66.7%, 18.4%, 78.8%, 13.2%, and 84.6%, respectively, compared to diesel. Acetaldehyde (MECHO) emissions increased with increasing WCOB blending volume ratio at 25% load condition and were highest at the B30 blend. The above results show that the B30 blend is the most effective in reducing unregulated emissions under all three load conditions, especially at medium and high loads.