Experimental and 3D-CFD Analysis of Synthetic Fuel Properties on Combustion and Exhaust Gas Emission Characteristics in Heavy-Duty Diesel Engines 2023-24-0052

Synthetic fuels can significantly improve the combustion and emission characteristics of heavy-duty diesel engines toward decarbonizing heavy-duty propulsion systems. This work analyzes the effects of engine operating conditions and synthetic fuel properties on spray, combustion, and emissions (soot, NOx) using a supercharging single-cylinder engine experiment and KIVA-4 code combined with CHEMKIN-II and in-house phenomenological soot model. The blended fuel ratio is fixed at 80% diesel and 20% n-paraffin by volume (hereafter DP). Diesel, DP1 (diesel with n-pentane C5H12), DP2 (diesel with n-hexane C6H14), and DP3 (diesel with n-heptane C7H16) are used in engine-like-condition constant volume chamber (CVC) and engine experiments.

Boosted engine experiments (1080 rpm, common-rail injection pressure 160 MPa, multi-pulse injection) are performed using the same DP fuel groups under various main injection timings, pulse-injection intervals, and EGR = 0-40%. Once the 3D-CFD model is validated with the CVC and experimental engine data, in-cylinder combustion and emissions are analyzed. The CVC experiments show that DP2 and DP3 liquid penetrations are shorter than diesel oil. In engine tests, NOx did not change much for all DP fuels for the same engine operating condition. However, shorter-penetrated DP2 and DP3 reduce soot emissions by more than 60% and CO without worsening brake-specific fuel consumption compared to diesel oil. The 3D-CFD results show that n-hexane shifts the penetration of the high-carbon number to the low-carbon fuel. Vapor penetrations are found to be shortened by blending low-volatility fuels with diesel oil. Visualizations of the in-cylinder confirmed a decrease in the amount of soot formation near the wall for DP2 and DP3 fuels. In addition, equivalence ratio – temperature (phi-T) maps of these fuels indicate that at 40% EGR, soot emissions are reduced at lower equivalence ratios than diesel oil.