Comprehensive Investigation of Combustion Characteristics, Emissions, and Tribological Properties of Synthetic Kerosene (S8) in a CVCC and CRDI Research Engine

There is a need to reduce both the greenhouse gas emissions of internal combustion engines, and the reliance on traditional fossil fuels like Ultra Low Sulphur Diesel (ULSD). In this research, a synthetic aviation fuel created from natural gas feedstocks using the Fischer-Tropsch process was investigated to determine its autoignition and combustion characteristics, emissions, and tribological properties. This fuel, S8, has a Derived Cetane Number (DCN) of 62, which reflects a short Ignition Delay (ID) and Combustion Delay (CD) compared to ULSD, which has a DCN of 48. However, due to the chemical properties of S8, it lacks sufficient lubrication qualities in comparison to ULSD, so addition of 3% methyl oleate by mass was used to improve lubricity. The shorter ignition delay of S8, initially observed in a Constant Volume Combustion Chamber (CVCC), was also observed in the instrumented Common Rail Direct Injection (CRDI) engine. Investigations with an He-Ne laser apparatus with Mie scattering revealed the superior atomization of S8, which resulted in a Sauter Mean Diameter (SMD) of 19.2 µm, 8% smaller than ULSD. The combined effect of the superior atomization and shorter ID of S8 resulted in a reduction of the premixed combustion event for S8, with smoother engine operation due to the greater proportion of mixing controlled combustion. This characteristic was also reflected in the comparison of the Low Temperature Heat Release (LTHR) region of S8 compared with ULSD. In LTHR, S8 released more energy during the low temperature cool flame formation region, and entered High Temperature Heat Release (HTHR) sooner than ULSD. Analysis of the emissions of the CRDI engine when operated with S8 was conducted with the engine under a sustained load at 5.4 bar Indicated Mean Effective Pressure (IMEP), and the results were compared with identical operating parameters using ULSD. A 6% reduction in NOx emissions and a 30% reduction in soot was achieved compared to ULSD.