An investigation on laminar burning speed and flame structure of anisole-air mixture

Abstract

In search for a feasible replacement for fossil fuels, there has been extensive research into biofuels in the past few decades. Oxygenated compounds, such as anisole, in particular have shown some promising characteristics. Anisole is an oxygenated biofuel widely adopted as a solvent and seems to be an apt fuel for the combustion application. Although being a potential biofuel, only a few investigations have been conducted for anisole; therefore, a lack of supplementary experiments in high temperatures and engine-relevant conditions is obvious. The experimental results are also highly demanded as a source of verification and update for the available chemical kinetic mechanisms. In this research, performance characteristics of anisole are studied; specifically, the Laminar Burning Speed (LBS), flame structure, and flame stability have been experimentally and theoretically discussed. The calculations have been produced using a constant volume combustion chamber (CVCC) and a z-type schlieren optical technique accompanying a differential-based multi-shell thermodynamic model. The data has been reported in a wide range of temperatures (T = 460–550 K), pressures (p = 0.5–5.5 atm), and equivalence ratios (ϕ = 0.8–1.4). In order to provide a convenient way for other researchers to access LBS for anisole in a wider range, a power-law correlation has been presented for LBS as a function of p, T and ϕ. Regarding the flame structure, the hydrodynamic sources have been shown to be the main influential root to spherical flame instabilities which is directly related with ϕ and reversely to pressure. The experiments demonstrated that anisole has a relatively high laminar burning speed, with a maximum at ϕ = 1.1 for different p and T conditions. As expected, the LBS increases by increasing the temperature and reducing the pressure. The two available chemical mechanisms for anisole combustion have been compared with the experimental results and a need for modification in the mechanisms are observed. A sensitivity analysis is performed to investigate the sources of discrepancies.