Parametric study of a diesel engine fueled with directly injected methanol and pilot diesel

•Effects of four parameters on a diesel/methanol dual fuel engine are investigated.•There is an optimal match of methanol nozzle diameter and injection pressure.•The interval angles α = 2° and β = 15° can achieve better fuel economy and lower emissions. A three-dimensional simulation model is established to investigate a diesel engine fueled with directly injected methanol and pilot diesel. Four parameters (methanol nozzle diameter, methanol injection pressure, and two diesel/methanol spray interval angles: α in the XZ plane and β in the XY plane) are selected to study their effects on combustion characteristics, engine performance, and emissions. The results indicate that methanol nozzle diameter and injection pressure have a great effect on the engine. When the methanol injection duration is kept constant, a larger nozzle diameter paired with a lower injection pressure lead to a lower Pmax, peak HRR, and NOx emissions, but higher soot, THC, and CO emissions. Furthermore, as nozzle diameter increases and injection pressure decreases, fuel economy first improves and then deteriorates. A nozzle diameter of 0.36 mm paired with an injection pressure of 27.4 MPa yield optimal results for both fuel economy and allowable combustion noise. When the direction of methanol spray injected towards the flame is tuned (when α is 2° and β is 15°), better fuel economy and lower pollutant emissions are achieved.