A threshold soot index-based fuel surrogate formulation methodology to mimic sooting tendency of real fuels in 3D-CFD simulations

Effect of Lagrangian-phase Modelling on Charge Stratification and Spatial Distribution of Threshold Soot Index for Toluene Reference Fuel Surrogates

“…In this study, the target properties are RON, MON, and αₛₜ, which describe the main flame propagation and ignition quality of the mixture, then the sooting tendency is also accounted for. In this study, TSI [23] is chosen as the representative index for the soot formation propensity quantification. The surrogate components are: 2,2,4 trimethyl-pentane (C₈H₁₈) as representative of the iso-paraffins, n-heptane (C₇H₁₆) for n-paraffins, and toluene (C₆H₅CH₃) for aromatics.…”

“…Cell-wise TSI values are calculated via user coding as the surrogate TSI (Table 1) times the fuel mole fraction in the cell for the lumped-single component, whereas for the multicomponent approach a linear-by-mole mixing rule ∑ 𝑥𝑥 i ⋅ TSI i i is applied using the cellwise mole fractions of each component 𝑥𝑥 i and the corresponding TSI value retrieved form [23].The cell-wise value occurrence frequency in the domain is show in Figure 7: the histograms obtained by the multicomponent and by the lumped approach are superimposed to better spot the differences, which expectedly are very limited for the PRF, while tend to increase for the TRF30 and TRF60 blends. To quantify the TSI spatial distribution, the fluid domain is split in coaxial cylindrical sectors by varying the radius from 0 mm to 40 mm with a 10 mm stepping.…”

“…Numerous examples of PRFs/TRFs can be found for soot formation and combustion investigation, both experimentally [19] and numerically [20][21] [22]. TRF surrogates are widely adopted to match the combustion-relevant properties of a fuel, such as the Research Octane Number (RON), Motor Octane Number (MON), the stoichiometric airfuel ratio αₛₜ, and the sooting tendency [23] whenever the oxygenate content is almost negligible [24]. The sooting tendency of a fuel can be expressed by proper indices such as: the Smoke Point (SP) [25], the Threshold Soot Index (TSI) [23], the Yield Sooting Index (YSI) [26], or the Oxygen Extended Sooting Index (OESI) [27].…”

“…TRF surrogates are widely adopted to match the combustion-relevant properties of a fuel, such as the Research Octane Number (RON), Motor Octane Number (MON), the stoichiometric airfuel ratio αₛₜ, and the sooting tendency [23] whenever the oxygenate content is almost negligible [24]. The sooting tendency of a fuel can be expressed by proper indices such as: the Smoke Point (SP) [25], the Threshold Soot Index (TSI) [23], the Yield Sooting Index (YSI) [26], or the Oxygen Extended Sooting Index (OESI) [27]. Once the surrogate is formulated, two approaches can be adopted for both spray and combustion modelling: one is the multicomponent approach, where each surrogate component is injected with its own properties, and the other is the lumped-single component approach, in which the surrogate is modelled as a single liquid with averaged properties, depending on the composition.…”

Quantitative investigation on the impact of injection timing on soot formation in a GDI engine with a customized sectional method

“…Such library is generated using chemical kinetics simulations of a surrogate fuel representative of a European Gasoline with 5%vol of ethanol. 23 The customized Sectional Method is then applied to multicycle analyses of a 3D-CFD model of an optically accessible research engine 24 operated with three different injection timings. Numerical results of particulate matter, particle numbers and particle size distribution functions are consistently compared to the experimental dataset provided in Irimescu et al 24 The impact on soot formation of both charge stratification and liquid film pools on the combustion chamber walls is also analyzed.…”