Large eddy simulation of emulsified canola oil combustion in swirl-promoted combustion chamber

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Abstract
Recent studies have revealed that large eddy simulation (LES) as CFD technique is capable of capturing the unstable features of two-phase swirling flows during the combustion of straight vegetable oil (SVO) emulsions. In this study, blends of canola oil and methanol have been selected as emulsified SVO fuels for simulation purposes. To fully understand the effects of swirl number and equivalence ratio on combustion characteristics of emulsified canola oil, a numerical approach based on the discrete phase model (DPM), stochastic model and Taylor Analogy Breakup (TAB) model have been adopted to simulate SVO blend droplets in a swirl-promoted environment. Moreover, simulation results of fuel droplets distribution are compared directly with experimental results. Furthermore, a two-step chemical reaction mechanism and the Eddy-Dissipation model have been used to understand the effects of swirl number and equivalence ratio on the combustion characteristics of SVO. A robust and stable numerical algorithm has been selected and validated, which is capable of simulating turbulent combustion of emulsified canola oil using LES by considering two swirl numbers and equivalence ratios. Results reveal that turbulent flow and combustion characteristics are affected by the swirl number significantly. The simulation emission data show the same trends as the experimental results even though the simulations depict higher combustion temperatures in absence of heat losses. Nevertheless, the comprehensive numerical approach has been validated using experimental LDA droplet size distribution data. In summary, the numerical approach can be applied as a first order approximation to determine the effects of biofuel blend and swirl number on emission levels.

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