Combustion Research in Wide DCN Range Synthetic Aviation Fuels in a High Compression Ratio Engine

Abstract

Abstract An investigation was conducted on the performance and emissions characteristics of two Fischer-Tropsch (F-T) synthetic kerosenes, Gas-to-Liquid (GTL) S8 and Coal-to-Liquid (CTL) Iso-Paraffinic Kerosene (IPK), in a high compression ratio research engine with separate combustion chamber and using neat ULSD as a baseline. A 50% and a 70% by mass blend S8 with ULSD and a 50% and a 70% by mass blend of IPK with ULSD were analyzed for performance and emissions at 5, 6, and 7 bar Indicated Mean Effective Pressure (IMEP) and 2400 rpm. Additionally, neat S8, neat IPK, and neat ULSD were investigated in the Constant Volume Combustion Chamber (CVCC) for Ignition Delay (ID), Combustion Delay (CD), and Derived Cetane Number (DCN). S8 was found to have the highest DCN at 62 with very short ID and CD while IPK was found to have the lowest DCN at 26 and with the longest ID and CD. ULSD has a DCN between the two F-T fuels at 48. As a result of its long ID and CD, IPK showed extended regions of Low Temperature Heat Release (LTHR) and Negative Temperature Coefficient Region (NTCR) in the CVCC. It was also found that neat IPK, 50ULSD50IPK, and 30ULSD70IPK exhibit little to no ringing events at peak pressure and after High Temperature Heat Release (HTHR). In the research engine, peak heat release for ULSD, 50ULSD50S8, and 50ULSD50IPK was found to be 24.2 J/CAD, 20.5 J/CAD, and 23.4 J/CAD respectively. Due to the increase of the DCN with the addition of S8 to the blend, the 50ULSD50S8 blend exhibited minimal difference between the pre-chamber and the main chamber as it ignites earlier in the cycle with the flame front traveling quickly to the main chamber. IPK, however, had a short physical ignition delay and a long chemical ignition delay, as indicated by its low DCN, takes longer to ignite and creates a more homogeneous mixture in the highly turbulent pre-chamber. This causes a spike in heat release in the pre-chamber before the flame front propagates to the main chamber. This resulted in 50ULSD50IPK having the highest Peak Pressure Rise Rate (PPRR) and 50ULSD50S8 having the lowest PPRR. While both fuel blends reduced the soot emissions due to their low aromatic content, 50ULSD50IPK showed a 25% reduction in soot when compared to ULSD while 50ULSD50S8 showed only a 6% reduction in soot when compared to neat ULSD. There was a increase in CO emissions with the addition of IPK and a reduction in CO at low load with the addition of S8. With both F-T fuels, CO2 and NOx were found to decrease.