A Skeletal Mechanism for MILD Combustion of n-Heptane/Air Mixtures

Abstract

Moderate, intense or low-oxygen dilution (MILD) Combustion has many attributes such as low emissions, noiseless combustion with high thermal efficiency which are attractive for greener combustion systems. Past studies investigated flow and chemical kinetics effects in establishing this combustion mode for methane-air mixtures. Many of the practical fuels are large hydrocarbons and hence this study aims to develop a skeletal mechanism suitable for turbulent MILD combustion simulations of n-heptane/air. Computer Assisted Reduction Mechanism approach is employed to develop a mechanism involving 36 species and 205 reactions, which is validated for wide range of conditions using measurements or results obtained from a comprehensive mechanism. This mechanism is found to be excellent for predicting both ignition delay times and flame speeds for MILD conditions. The OH* and CH* obtained using quasi-steady state assumptions agree well with those obtained using the comprehensive mechanism with these chemiluminescent species. The performance of the skeletal mechanism for turbulent MILD combustion simulation is tested using Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations with a finite-rate chemistry model. The computed statistics of temperature and OH number density agree quite well with measurements for highly diluted combustion cases.