Surrogate models of thermally cracked hydrocarbon fuels at typical pyrolysis temperatures

Abstract Construction of surrogate fuel model for thermally cracked fuel holds fundamental importance to its combustion characteristics. In the present study, series of thermal cracking experiments of hydrocarbon fuel were carried out at supercritical pressure. Thermally cracked fuels at three typical pyrolysis temperatures, which covered the low, middle, and high levels of thermal cracking, were selected and analyzed. A formulation method to construct surrogate models for thermally cracked fuels was developed, in which the pyrolysis gas and liquid were considered separately, and then combined by a key parameter of gas-production rate. Laminar burning velocities of the target fuels and their corresponding surrogate models were measured using a constant-volume bomb, and then compared to validate the fidelity of surrogate models. Results show that the pyrolysis gas can be well substituted by a mixture of hydrogen, methane, ethylene, ethane, and propylene. Surrogate models of pyrolysis liquids contain eight large hydrocarbons, taking into account the variations of hydrocarbon classes and carbon number distribution. By changing mole fractions of candidate species, the proposed surrogate models of pyrolysis liquids reasonably match all target properties, including the averaged molecular weight (MW), hydrogen-to-carbon ratio (H/C), lower heating value (LHV), derived cetane number (DCN) and density. Surrogate models of thermally cracked fuels combine those of both pyrolysis gases and liquids, and can accurately predict the laminar burning velocities. With thirteen candidate components and the formulating strategy, the current method is capable of constructing a surrogate model for thermally cracked fuel with a fuel-conversion rate up to 73%.