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

•PODE spray and combustion was studied based on the 2nd law of thermodynamics.•Inherent optimal fuel economy of PODE and n-dodecane is basically same.•Reasons affecting the inherent optimal fuel economy of PODE was analyzed.•Fundamental characteristics of chemical exergy destruction were revealed.•Emission characteristics of PODE per unit of exergy were evaluated 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 (NOx) and soot are reduced for the blended fuel compared with n-dodecane. Notably, the trade-off relationships of NOx-chemical exergy destruction as well as NOx-soot, can be improved by blending PODE3 into n-dodecane. [Display omitted]