Spray characteristics of biodiesel-polyoxymethylene dimethyl ethers (PODE) blends in a constant volume chamber

Biodiesel and polyoxymethylene dimethyl ethers (PODE) are both potential alternative fuels. Adding PODE to biodiesel can make up for the shortcomings of high viscosity and low volatility of biodiesel. The objective of this study is to reveal the effects of PODE addition to biodiesel in different ratios (0%, 10%, 20% and 30% in volume) on the spray and mixing characteristics under various injection and ambient pressures in a constant volume combustion chamber. The results show that the spray tip penetration increases when PODE is added to biodiesel, but when the PODE ratio is more than 20%, the spray tip penetration begins to decrease. Under all experimental conditions, the spray cone angle and spray projected area of the blends increase with the increase of PODE ratio, especially at low injection pressures. The spray tip penetration was further discussed by using models, and the value of the model empirical constant was obtained. Combined with the model and experimental data, the fuel equivalence ratio distribution was obtained. The results show the equivalence ratio of PODE blends are obviously smaller than that of pure biodiesel. These prove that the addition of PODE can effectively improve the spray and air-fuel mixing quality of biodiesel. Moreover, the experimental data of this paper fill the gap in the research on the spray characteristics of biodiesel-PODE blends, and provide the basis for the high-fidelity numerical simulation of the spray model.