Formulating a quaternary gasoline surrogate (MTRF-87) using laminar burning velocity measurements

Abstract

This work reports the formulating of a new quaternary gasoline surrogate (MTRF-87) model utilizing the measured burning velocities of methylcyclohexane (MCH), toluene (TL), n-heptane (nC7) and iso-octane (iC8) in a mixing rule (energy-fraction based). The laminar burning velocity (LBV) measurements are performed using an externally heated diverging channel (EHDC) method. The LBV measurements are reported for an equivalence ratio range, ϕ = 0.7–1.4 for different mixture temperatures (≤600 K) at atmospheric pressure to develop this model. The final MTRF-87 composition is governed by the octane number comparison with commercial gasolines, and constitutes 0.2, 0.2, 0.1 and 0.5 mol fractions of MCH, TL, nC7 and iC8 respectively. The MTRF-87 predictions exhibit excellent consistency with a Ranzi model (2014) and other commercially available gasolines at all mixture conditions, whereas a significant over-prediction (up to 16 %) by KAUST correlation is observed for ϕ > 1 at elevated temperatures. Experimental measurements of the formulated surrogate, MTRF-87atϕ = 1 showed that the LBV variation with the temperature ratioagrees well with the measured burning velocities of gasoline,as well asthe predictions ofvariousmodels. From sensitivity analysis, the reaction, H2 + OH = H + H2O tends to increase the LBV of lean-to stoichiometric conditions and decrease for ultra-rich mixtures (ϕ = 1.4). The temperature exponent (α) variation at different mixture conditions of toluene + air and gasoline + air mixtures follow a downward parabolic trend with minimal value at ϕ = 1.1, and shows parity with the predictions of distinct detailed kinetic model predictions.