Li, Qibo (2015-08). Numerical Fluid Dynamics and Combustion Study of Emulsified Canola Oil Droplets in a Swirl Promoted Combustion Chamber. Doctoral Dissertation.
Thesis
Recently, straight vegetable oils (SVO) have been considered as combustion fuels due to their relatively high heating value and negligible content of sulfur and nitrogen, which is beneficial from the combustion point of view. However, the high viscosity of SVO has hindered their ability and applicability in combustion systems. In order to reduce the effect of high viscosity of SVO, methanol has been used as an additive to reduce its apparent viscosity. Furthermore, a twin-fluid atomizer has been used to form and dispense a fine spray of SVO to ensure complete combustion. To enhance the combustion characteristics of SVO, a multiple vane swirler has been adapted and used inside a conventional combustion chamber to enhance the mixing between the emulsified SVO fuel blend and the surrounding flowing air. However, the effects of vortex generation and droplet distribution on combustion emissions for SVO biofuels in a combustion chamber still are not well understood. Recent studies have revealed that large eddy simulation (LES) as CFD technique is capable of capturing the unstable features of two-phase swirling flows. This technique provides an effective and economical approach to study the behavior of air and coupled with the other model to predict the fuel spray droplets and combustion characteristics in a conventional combustion chamber. In this study, blends of canola oil and methanol have been selected as emulsified fuels for simulation purposes. To fully understand the effects of swirl number and equivalence ratio on the distribution of emulsified canola oil droplets, the discrete phase model (DPM), stochastic model and TAB model have been adopted to simulate SVO blend droplets. Furthermore, the Eddy-Dissipation model has been used to understand the effects of swirl number and equivalence ratio on combustion characteristics of SVO. A robust and stable numerical algorithm has been selected and validated. The interaction between the swirling air flow and fuel droplets have been simulated using LES by considering two swirl numbers. The effects of swirl number and equivalence ratio on droplet size distribution and combustion characteristics in the combustion chamber have been considered and evaluated correspondingly. Results reveal that turbulent flow, fuel blend droplet distribution, and combustion characteristics are affected by the swirl number significantly. Moreover, the simulation results have the same trend as the experimental work, but the error of simulation depends on the intensity of turbulence.
