Surrogate Model Development for Fuels for Advanced Combustion Engines

Abstract

The fuels used in internal-combustion engines are complex mixtures of a multitude of different types of hydrocarbon species. Attempting numerical simulations of combustion of real fuels with all of the hydrocarbon species included is highly unrealistic. Thus, a surrogate model approach is generally adopted, which involves choosing a few representative hydrocarbon species whose overall behavior mimics the characteristics of the target fuel. The present study proposes surrogate models for the nine fuels for advanced combustion engines (FACE) that have been developed for studying low-emission, high-efficiency advanced diesel engine concepts. The surrogate compositions for the fuels are arrived at by simulating their distillation profiles to within a maximum absolute error of ∼4% using a discrete multi-component (DMC) fuel model that has been incorporated in the multi-dimensional computational fluid dynamics (CFD) code, KIVA-ERC-CHEMKIN. The simulated surrogate compositions cover the range and measured concentrations of the various hydrocarbon classes present in the fuels. The fidelity of the surrogate fuel models is judged on the basis of matching their specific gravity, lower heating value, hydrogen/carbon (H/C) ratio, cetane number, and cetane index with the measured data for all nine FACE fuels.

Modeling of Heating and Evaporation of FACE I Gasoline Fuel and its Surrogates

“…The model accounts for finite thermal and mass diffusivities inside the droplet and recirculation inside droplet [17]. The heat conduction equation inside spherically-symmetric droplet can be presented as [19]: (1) where is the thermal diffusivity, k l , c l and ρ l are the thermal conductivity, specific heat capacity and density of the liquid, respectively, t is time and R is the distance from the center of the droplet. In the case of moving droplets, the liquid thermal conductivity is replaced by the effective thermal conductivity k eff = χ T k l , where χ T = 1.86 + 0.86tanh[2.225log 10 (Pe d(l) /30)] increases from 1 to 2.72 when the liquid Peclet number.…”

“…The fuels for advanced combustion engines (FACE) have been formulated by the US Department of Energy and Coordinating Research Council (CRC) to eliminate the effect of variation in fuel composition on the combustion characteristics and to study low emissions, high efficiency compression ignition engines [1]. FACE fuels are complex mixture of hydrocarbons [2].…”

“…These processes include spray break-up, droplet heating, evaporation and collision. The large number of components in real fuels leads to high computational cost and considering all fuel components is not feasible in the near future [1]. Hence, reducing number of fuel components is essential.…”

A combustion model for multi-component fuels using a physical surrogate group chemistry representation (PSGCR)

“…Following the methodology of Anand et al [21] and Su et al [25], surrogate components and their composition are chosen to match measured distillation profiles and properties of the target fuel such as density, vapor pressure, surface tension, latent heat of vaporization, liquid and vapor phase specific heat capacity, viscosity and thermal conductivity, lower heating value, hydrogen to carbon (H/C) ratio, cetane number, etc.…”

“…A significant advance in the methodology of the modeling of realistic fuels was introduced recently by Anand et al [21,22] who represented the fuel's physical and chemical properties with two different sets of surrogates. The methodology was applied to study the nine FACE fuels (Fuels for Advanced Combustion Engines) that were developed in a joint project between the US Department of Energy and the Co-ordinating Research Council (CRC) for studying low-emissions, high-efficiency advanced diesel engine concepts.…”