Combustion characteristics of F24 compared to Jet A in a Common Rail Direct Injection Research Compression Ignition Engine

Abstract

Abstract Research was conducted to determine combustion characteristics such as: ignition delay (ID), combustion delay (CD), combustion phasing (CA 50), combustion duration, derived cetane number (DCN) and ringing intensity (RI) of F24, for its compatibility in Common Rail Direct Injection (CRDI) compression ignition (CI) engine. The first part of this study is investigating the performance of Jet-A, F24, and ultra-low sulfur diesel #2 (ULSD) using a constant volume combustion chamber (CVCC) followed by experiments in a fired CRDI research engine. Investigations of the spray atomization and droplet size distribution of the neat fuels were conducted with a Malvern Mie scattering He-Ne laser. It was found that the average Sauter Mean Diameter (SMD) for Jet-A and F24 are similar, with both fuels SMD droplet range between 25–29 micrometers. Meanwhile, ULSD was found to have a larger SMD particle size in the range of 34–40 micrometers. It was observed during the study, utilizing the CVCC, that the ID and CD for neat ULSD and Jet-A are nearly identical while the combustion of F24 is delayed. F24 was found to have longer durations of both ID and CD by approx. 0.5 ms. This results in a lower DCN for the fuel of 43.5, whereas ULSD and Jet-A have DCNs of 45 and 47 respectively. The peak AHRR for ULSD and Jet-A are nearly identical, whereas F24 has a peak magnitude of approx. 20% lower than ULSD and Jet-A. It was found that both aviation fuels had significantly fewer ringing events occurring after peak high temperature heat release (HTHR), a trend also observed in the CRDI research engine. Neat F24, Jet-A and ULSD were researched in the experimental engine at the same thermodynamic parameters: 5 bar indicated mean effective pressure (IMEP), 50°C (supercharged and EGR) inlet air temperature, 1500 RPM, start of injection (SOI) 16°BTDC, and 800 bar of fuel rail injection pressure as the baseline parameters in order to observe their ignition behavior, low temperature heat release, combustion phasing, and combustion duration. It was found that the ignition delay of F24 and Jet-A was greater than ULSD, approx. 5% for both aviation fuels. This ignition delay also affected the combustion phasing, or CA 50, of the aviation fuels. The CA 50 of the aviation fuels was delayed by approx. 2% compared to ULSD. Jet-A had a nearly identical combustion duration compared to ULSD, however F24 had an extended combustion duration which was approx. 3% longer than that of ULSD and Jet-A. It was discovered with the accumulations of these delays in ID, CD, CA50, that the RI of the aviation fuels were reduced. F24 was discovered to have more delays, and the RI correlates with these results having a 70% reduction in RI compared to ULSD.