Investigating the thermodynamic limits of dimethyl ether - dodecane blends for heavy-duty diesel engines: An RSM-based numerical modeling of adiabatic flame temperature and specific exergy

In this study, the effect of substituting up to 60 wt% Dimethyl Ether into dodecane (C12H26), representing conventional diesel fuel, on the theoretical thermodynamic limits of combustion was numerically investigated. To eliminate the masking effect of mechanical and thermal losses inherent in physical engine tests, a zero-dimensional (0D) thermodynamic equilibrium model based on the Gibbs Free Energy Minimization principle was established using DWSIM software. Adiabatic Flame Temperature and Specific Exergy data, obtained at various excess air ratios (0.8, 0.95, 1.10 and 1.4), were statistically analyzed via Response Surface Methodology (RSM). ANOVA results demonstrated that substituting up to 60 wt% DME into the blend did not lead to a statistically significant degradation in the maximum combustion temperature and the work potential (exergy) of the system (P > 0.05). The excess air ratio was identified as the sole parameter dominating both thermodynamic responses (P < 0.001). Consequently, new second-order empirical equations (surrogate models) with high predictive accuracy for AFT (R2 = 91.61%) and Specific Exergy (R2= 88.56%) were introduced to the literature, enabling engine designers to directly compute the potential of fuel blends without requiring computationally expensive thermodynamic simulations. These findings indicate that DME is a promising alternative fuel that preserves the theoretical thermodynamic limits and maximum work potential of the combustion products. However, realizing this potential in practical applications requires accounting for real-engine dynamics such as spray atomization, combustion kinetics, and heat transfer, which dictate the actual mechanical power output.