Numerical study on the combustion characteristics of n-dodecane/PODE3 blend spray from the perspective of the second law of thermodynamics

Polyoxymethylene dimethyl ethers (PODE), as a potential e-fuel, can realize the carbon neutrality for internal combustion engines. Existing studies on PODE are primarily engine-based, leading to contradictory conclusions about fuel consumption and pollutant emissions due to the different engine specifications and operating conditions. This work applies the second law of thermodynamics under constant-volume conditions to analyze fuel economy and emissions characteristics without the influence of particular test conditions or engine types. The fundamental fuel economic and emission-related behaviors of pure n-dodecane and PODE₃/n-dodecane blended fuels were numerically studied. For the spray and combustion processes, compared with n-dodecane, the blended fuel exhibits the low-temperature heat release (LTHR) in the region with leaner fuel/air mixture and higher temperature. However, the high-temperature heat release (HTHR) of the blended fuel is closer to the stoichiometric combustion but with lower temperatures. Blending PODE₃ into n-dodecane increases the exergy destruction induced by chemical reactions but decreases the exergy destruction related to heat conduction and mass transfer, resulting in a basically unchanged overall potential maximum fuel economy. Heightened sensitivity of the exergy destruction from chemical reactions to temperature and equivalence ratio is found under low-temperature and high-equivalence ratio conditions. This sensitivity trend is nearly consistent for different PODE₃/n-dodecane blends. The exergy destruction arising from chemical reactions for the LTHR of PODE₃ is higher than that of n-dodecane. Less exergy destruction induced from chemical reactions can be achieved by controlling the combustion temperature higher than 1760 K and 1900 K respectively for n-dodecane and the blended fuel. Moreover, both nitrogen oxide (NO_x) and soot are reduced for the blended fuel compared with n-dodecane. Notably, the trade-off relationships of NO_x-chemical exergy destruction as well as NO_x-soot, can be improved by blending PODE₃ into n-dodecane.