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Combustion Modeling of Internal combustion engines is still a complex matter, requiring further developments to better simulate the performance and emissions of different fuels. In order to study the influence of gasoline-ethanol blends on a Flex-Fuel engine, a computer model was designed to simulate the experimental conditions using Fractal combustion and Woschni based heat transfer models. The simulations were validated with engine dynamometer experimental tests. In-cylinder maximum pressure, IMEP and emissions data were calculated for different gasoline-hydrous ethanol blends at different engine conditions. The computer model presented a predictive behavior and a good agreement with experimental data for in-cylinder maximum pressure and IMEP. Regarding emissions, the simulations of some pollutants could not match precisely the experimental data, showing the need for additional combustion modeling improvements.

Nowadays computer simulation is an important tool to support new internal combustion engine projects, but still further studies are necessary for its use in fuel development. In order to study the influence of fuel properties on engine combustion and emission performance, a computer model was designed based on a Flex-Fuel engine geometric data. Model was validated with experimental tests done on an engine dynamometer. A simulation software was used to simulate the experimental conditions, by using Wiebe two zone combustion and Woschni heat transfer models. In-cylinder maximum pressure, IMEP and emission data were calculated for different gasoline-hydrous ethanol blends at 3875 rpm, 60 Nm and 105 Nm. Total hydrocarbons concentration was simulated comparing the experimental data of hydrocarbons added with unburned ethanol emission measured with a FTIR analyzer.

Brazil is known for its long experience on using alternative fuels, mainly ethanol for light duty vehicles. In 2002, it was released the Flexible fuel car that can run with gasohol (gasoline with 22% of ethanol), hydrated ethanol or any blend of these fuels. By the end of 2006, national production of these vehicles represented around 80% of the total. Brazil is also the second world fleet of Natural Gas Vehicles (NGV), with more than 1,4 million light duty converted vehicles. This paper describes the development of a computational thermodynamic model of compression, combustion and expansion processes of gasohol, ethanol and Natural Gas (NG) for the cylinder pressure curve prediction of a Flexible Fuel engine, working with a NG kit installed. The combustion process is modeled using a Wiebe function, which establishes the mass fraction of burned fuel. Convective heat transfer to cylinder walls is estimated with an empirical correlation for heat transfer coefficient determination.

This paper describes the development of a computational thermodynamic model of compression, combustion and expansion processes of gasohol, ethanol and Natural Gas (NG) for the cylinder pressure curve prediction of a Flexible Fuel engine, working with a NG kit installed. The combustion process is modeled using a Wiebe function. Equations for specific heat at constant pressure (Cp) were developed for each fuel for temperatures up to 4000 K. The model output generates the cylinder gas pressure and temperature, work output and heat release profiles as functions of crank angle, allowing studies of engine performance parameters in different working conditions for each fuel. The differences between the experimental and simulation results were lower than 4% for the maximum cylinder pressure value.