Comparison of Combustion and Emissions Properties of Jet-A vs. ULSD in Both Indirect and Direct Compression Ignition Engines at Same IMEP

This study investigates combustion and emissions of Jet-A in an indirect injection (IDI) compression ignition engine and a direct injection (DI) compression ignition engine at 4.5 bar IMEP and 2000 RPM. The Jet-A was blended with ULSD that resulted in 75%Jet-A and 25% ULSD#2 by mass. Both engines were instrumented with Kistler pressure sensors in the main chamber and the IDI engine had a second pressure sensor in the pre-chamber. Combustion properties and emissions from both engines using the 75% jet-A blend (75Jet-A) were compared to a baseline test of Ultra Low Sulfur Diesel #2 (ULSD). The ignition delay was shorter when running on 75Jet-A compared to ULSD in the DI engine. For ULSD, the ignition delay was 1.8 ms and it reduced to 1.7 ms when operating on 75Jet-A (difference of 6%). In the IDI engine the ignition delay for both fuels was 2.3 ms based off the gross heat release in the Pre-Chamber. There were insignificant differences in 50% mass burned (CA50) for both fuels in both engines. In the DI engine, CA50 occurred at 368 crank angle degrees (CAD) for both ULSD and 75Jet-A. In the IDI engine, CA50 occurred in the Main Chamber at 374 CAD for ULSD and 75Jet-A. A Low Temperature Heat Release (LTHR) developed in the DI engine for both fuels tested in this investigation. The LTHR is a product of fuel undergoing isomerization processes when initially introduced to high temp environments. However these LTHRs did not develop in the IDI engine due to the fuel premixing more heavily with the air thus the fuel and oxygen started their combustion process sooner. AHRRs from the IDI engine showed that the premixed and diffusion burn stages were combined into one combustion stage for both fuels. In the DI engine, NOx emissions produced from ULSD were 14.8 g/kWh and they reduced to 13.4 g/kWh when using 75Jet-A (9% reduction). In the IDI engine, NOx emissions were 1.7 g/kWh for ULSD and 1.8 g/kWh for 75Jet-A (6% increase). 75Jet-A resulted in lower NOx emissions due to the fuel's higher vaporization rate compared to ULSD. It was discovered that the IDI engine's lower NOx emissions were due to the low lambda value that the prechamber created. In the DI engine, soot emissions from ULSD were 54.4 mg/kWh and they lowered to 50 mg/kWh when using 75Jet-A (8% reduction). In the IDI engine, soot emissions reduced from 6.7 mg/kWh when running on ULSD to 6 mg/kWh when running on 75Jet-A (9% reduction). 75Jet-A resulted in lower soot emissions compared to ULSD due to its smaller Sauter Mean Diameter of injection droplets. The Jet-A showed significant reductions in NOx and soot emissions when compared to ULSD in the DI engine while having very similar combustion characteristics with ULSD in both combustion systems. Jet-A also resulted in higher indicated thermal efficiencies than ULSD in both DI and IDI engines. The findings in this study provides supporting results for Jet-A to be a viable candidate for becoming the fuel for the "Single Fuel Forward Policy".