Experimental and numerical study of sooting tendency of IBE in a laminar diffusion flame
Type of DegreeMaster's Thesis
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Recent advancements in metabolic engineering have demonstrated that through cost-effective batch fermentation processes, isopropanol-butanol-ethanol (IBE) can be produced at sufficient quantities from switchgrass biomass. As such, IBE is seen as a promising third-generation biofuel candidate that can potentially address the inadequacies of its predecessor, acetone-butanol-ethanol (ABE), which was known to corrode engine parts. Previous studies have shown that when IBE is blended with diesel at proportions as high as 40% by volume, it can retain favorable spray and combustion characteristics while exhibiting lower sooting tendencies. However, there is not only a lack of experimental data demonstrating reduced sooting of IBE with diesel blends, but also a lack of understanding of how IBE kinetically contributes to lowering soot formation. In this study, the soot reduction potential of IBE when mixed with surrogate diesel (a binary mixture of 70% vol. of n-decane and 30% vol. 1-methylnaphthalene) is examined in an atmospheric co-flow diffusion flame burner. Furthermore, the individual effect of carbon and oxygen loading of IBE on its sooting tendency is studied by modifying its component ratio. Finally, the oxidizer stream of the burner is diluted with CO2, thus replicating exhaust gas recirculation (EGR) system in a compression ignition (CI) engine and enabling to study its effect on total soot yield in the flame. Experimental measurements of soot volume fractions are obtained by a soot emission-based color-ratio pyrometry technique and the sooting tendency of different IBE-surrogate diesel blends is reported in terms of Yield Sooting Index (YSI). To gain further insight into the reaction chemistry affecting soot formation, experimental results are corroborated with numerical modelling results. Simulations are performed with a CFD laminar co-flow flame modelling solver, laminarSMOKE++ and a C1-C16 high temperature kinetic mechanism including polycyclic aromatic hydrocarbons (PAH) and soot sub-modules. Through rate of production (ROP) analysis, dominant reaction pathways to soot formation are identified for different IBE-surrogate diesel blends at several CO2 concentrations in the oxidizer stream as well as for various IBE component ratios. The major objectives of this research work were to benchmark an existent kinetic mechanism for its reliability to perform soot studies of IBE and study the chemical effect of IBE and CO2 on traditional soot precursor formation pathways typically seen in diesel fuels.