This paper presents an experimental and numerical study of the combustion of isolated n -butyl acetate droplets in the standard atmosphere. Numerical simulations are reported using a model that incorporates unsteady gas and liquid transport, variable properties, and radiation. Three skeletal mechanisms of n -butyl acetate, derived from a large detailed mechanism comprised of 819 species and 52,698 reactions, were used in the numerical simulations to evaluate the influence of the kinetic mechanism on burning. The reduced mechanisms comprised 212 species and 5413 reactions, 157 species and 3089 reactions, and 105 species and 1035 reactions. The numerical model did not include soot formation, though qualitatively mild sooting was noted only for droplets larger than 0.7 mm. The numerical predictions were in good agreement with experi-mental measurements of droplet and flame diameters. Flame extinction was numerically predicted which was attributed to a decrease of the characteristic diffusion time relative to the chemical time as droplet burned. Effects of initial droplet diameter on the evolution of maximum gas temperature (Tmax) and peak mole frac-tions of CO2 and CO are also examined numerically.& COPY; 2022 Published by Elsevier Inc. on behalf of The Combustion Institute.

An experimental and numerical study of combustion of a gasoline certification fuel ('indolene'), and four (S4) and fiv e (S5) component surrogates for it, is reported for the configurations of an isolated droplet burning with near spherical symmetry in the standard atmosphere, and a single cylinder engine designed for advanced compression ignition of pre-vaporized fuel. The intent was to compare performance of the surrogate for these different combustion configurations and to assess the broader applicability of the kinetic mechanism and property database for the simulations. A kinetic mechanism comprised of 297 species and 16,797 reactions was used in the simulations that included soot formation and evolution, and accounted for unsteady transport, liquid diffusion inside the droplet, radiative heat transfer, and variable properties. The droplet data showed a clear preference for the S5 surrogate in terms of burning rate. The simulations showed generally very good agreement with measured droplet, flame, and soot shell diameters. Measurements of combustion timing, in-cylinder pressure, and mass-averaged gas temperature were also well predicted with a slight preference for the S5 surrogate. Preferential vaporization was not evidenced from the evolution of droplet diameter but was clearly revealed in simulations of the evolution of mixture fractions inside the droplets. The influence of initial droplet diameter (D o ) on droplet burning was strong, with S5 burning rates decreasing with increasing D o due to increasing radiation losses from the flame. Flame extinction was predicted for D o = 3.0 mm as a radiative loss mechanism but not predicted for smaller D o for the conditions of the simulations.& COPY; 2022 Published by Elsevier Inc. on behalf of The Combustion Institute.

Combustion of a seven-component surrogate for a research grade 87 octane gasoline mixed with 10% ethanol is investigated experimentally and numerically from the perspective of an isolated droplet burning under conditions that promote one-dimensional gas transport. The numerical analysis included a kinetic mechanism comprised of 398 species and 24,814 reactions and a soot model that accounted for nucleation, surface growth, coalescence/aggregation of soot particles, and luminous flame radiation. Measurements of droplet and flame diameters were made for an initial droplet diameter (D-o) of approximately 0.63 mm. The simulations agreed well with the measurements including the location of the soot shell. Preferential vaporization was revealed by simulations of the liquid concentrations in the droplet. Predicted peak soot volume fractions coincided with temperatures between 1300 K and 1400 K as a soot inception temperature. Simulations were also carried out for D-o between 0.25 mm and 5 mm to explore the effect of radiation and D-o on burning. Below 0.25 mm radiation was negligible and burning rates and flame temperatures converged to a single value. Increasing D-o up to 1.8 mm lowered the burning rate with luminous radiation having a strong effect. When radiation was entirely removed from the model the burning rate was nearly constant. Above D-o = 2 mm droplets extinguished almost immediately after ignition. The flame temperature decreased with increasing D-o while it increased when radiation was omitted. The simulations show that soot precursors including polyammatic hydrocarbons were concentrated around the soot shell.

This paper reports a study of the combustion dynamics of n-butyl acetate (BA) using the configuration of a burning droplet. Two grades of BA were examined: one (SBA) synthesized by a new process described in the paper that uses a metabolically engineered solventogenic Clostridium strain through an extractive fermentation process using n-hexadecane as the extractant; and one commercially available as a high-purity (99.9%) 'neat' BA grade produced by conventional Fischer esterification (NBA). The initial droplet diameter was primarily 0.6 mm with some limited experiments carried out for 0.4 mm droplets to show the influence of convection. Experiments were performed in the standard atmosphere and ignition was by spark discharge. The results showed the presence of impurities in the SBA at mass concentrations totaling about 6% which included n-butanol, n-hexadecane, iso-propyl alcohol and ethyl acetate. Droplet burning rates and flame structures were not influenced by these impurities at this concentration level. In the presence of convection created by buoyancy, droplets burned faster with stretched flames and a luminosity revealing the presence of soot by incandescence at the flame tips. Reducing the initial droplet diameter to 0.4 mm eliminated the convective effect and resulted in near spherical flames. The results presented show that the new synthesis process is a sustainable alternative for BA production with burning characteristics identical to NBA in both convective and stagnant gas transport fields.

Experimental data and detailed numerical modelling are presented on the burning characteristics of a model gasoline/biofuel mixture consisting of n-heptane and iso-butanol. A droplet burning in an environment that minimises the influence of buoyant and forced convective flows in the standard atmosphere is used to promote one-dimensional gas transport to facilitate numerical modelling of the droplet burning process. The numerical model includes a detailed combustion kinetic mechanism, unsteady gas and liquid transport, multicomponent diffusion inside the droplet, variable properties, and non-luminous radiative heat transfer from the flame. The numerical simulation was validated by experimental measurements in the standard atmosphere which showed good agreement with the evolutions of droplet and flame diameters. The iso-butanol concentration had a strong effect on formation of particulates. Above ~20% (volume) iso-butanol, flame luminosity was significantly diminished anddecreased with increasing iso-butanol concentration, while CO2 emissions as a representative greenhouse gas were not strongly influenced by the iso-butanol loading. The soot shell was located near a 1350 K isotherm for concentrations up to 20% (volume) iso-butanol, suggesting this value as a possible soot inception temperature for the mixture droplet. The combustion rate decreased with increasing iso-butanol concentration which was attributed to iso-butanol's higher liquid density. No evidence of a low temperature burning regime, or of extinction, was found (in experiments and simulations) for the small droplet sizes investigated.