Ultra-High Speed Imaging and OH-LIF Study of DMF and MF, Combustion in a DISI Optical Engine

The furan series of chemicals such as 2,5-dimethylfuran (DMF) and 2-methylfuran (MF) are promising alternative fuel candidates for internal combustion engines due to their advantages compared to gasoline. However, no research has been published on the optical diagnostics of their combustion process in the engine cylinder. In this paper, the planar laser-induced fluorescence (PLIF) technique has been used to investigate the OH distribution in the flames of DMF and MF in a direct injection spark ignition (DISI) optical engine. The images of OH-LIF in the combustion process combined with the high-speed imaging and heat release data at two different engine load conditions (4.5 bar and 5.5 bar IMEP) for DMF and MF were studied and compared with isooctane, the reference fuel representing gasoline. Interesting correlations were found between the heat release rate, flame speed, flame area and PLIF of OH for the tested fuels at the two loads and the proposed correlations have also been confirmed by using the data in previous studies. MF is shown to combust significantly faster than DMF and isooctane. It is found that at 4.5 bar IMEP, the pressure trace, flame speed and flame area growth rate of DMF are very close to those of isooctane, but lower than those of MF. The combustion phase of MF is earlier and the duration is shorter than DMF and isooctane. Normalized LIF signals show that MF always has the maximum values and the higher IMEP will advance the time of the OH peak. The rate of heat release (ROHR) matches the trend of OH development well before the flame goes beyond the visible area. Finally, a correlation between the results of MFB and OH-LIF reveals that the three fuels follow a similar trend, indicating that the OH generation matches the MFB data well, irrespective of the fuel. The correlations between the flame area and OH-LIF signal are also discussed.