An investigation on pyrolysis characteristics of low-sulfur heavy fuel oil spray under diesel engine-like conditions

The pyrolysis characteristics of low-sulfur heavy oil fuel (HFO) spray under diesel engine-like conditions were investigated for the first time using both experimental and numerical methods. The high speed diffused back-imaging method was adopted to measure the macroscopic features of the low-sulfur HFO spray, and its products were sampled and analyzed by the gas chromatography with mass spectrometry. The low-sulfur HFO spray behaves as a quasi-evaporating spray under high temperature conditions, integrating the characteristics of evaporating and non-evaporating sprays. The increase of temperature shows little effect on its penetration characteristics, but a great effect on the vapor distribution. The low-sulfur HFO spray can pyrolyze at the temperature below 650 K due to the high heating-up rate and ambient pressure, and the aromatics contained in it are easy to pyrolyze, producing some oxygenate and amide components. Based on the experimental results, an integral pyrolysis model with multi-component evaporation and pyrolysis was established and implemented into the Eulerian-Lagrangian framework to simulate the low-sulfur HFO spray, and its predictions agree very well with the experimental results. The pyrolysis shows a large effect on the HFO spray evolutions. Ignoring the pyrolysis process would underestimate the droplet temperature and distribution number at the HFO spray tip and overestimate the vapor concentration of heavy-end hydrocarbons, because most of them are trapped inside the droplet enclosed by the pyrolytic residues.