A comparative study for the n-butanol/n-octanol and n-butanol/ di-n-butylether fueled dual-fuel engines with different injection timings

In this study, numerical simulations were performed to compare the combustion and emission characteristics of n-butanol/n-octanol (B/O) and n-butanol/di-n-butylether (B/D) dual-fuel engines at the different start of injection (SOI) timings. The three-dimensional dual-fuel engine simulation was implemented by coupling KIVA-CHEMKIN with a multi-component chemical reaction mechanism containing n-butanol, n-octanol, and di-n-butylether (DnBE). The reliability of the numerical models was verified by comparing the simulated and experimental in-cylinder pressure, heat release rate (HRR), and emissions. Then B/O and B/D dual-fuel engines with different premixed n-butanol ratios (B0, B10, B20, B30, and B40) were simulated at 1500 rpm with normal SOI timing (7 deg BTDC) and advanced SOI timing (20 deg BTDC), respectively. It has been found that an increased ratio of premixed fuel would increase the peak cylinder pressure due to the higher oxygen content of n-butanol. The change of SOI timing has a significant effect on the B/O engine and a minor influence on the B/D engine. When the SOI timing is advanced from 7 deg BTDC to 20 deg BTDC, the B/O engine changes from premixed to premixed-diffusion combustion phase. In addition, the B/O engine exhibits a more significant reactivity-controlled combustion mode under advanced SOI timing. In terms of emissions, the B/O engine emits more CO than the B/D engine, which is due to the fact that n-octanol is less volatile, resulting in more local high equivalence ratio areas in the cylinder. Since the in-cylinder combustion temperature and combustion duration of the B/O engine are less than those of the B/D engine, the NOx emissions of the B/O engine are lower. With advanced SOI timing, the addition of premixed n-butanol can reduce both CO and NOx, but the emission values are still high and further optimization is needed.