Combustion Characterizations of Ethanol/Gasoline Blended Fuel in SI Engine Using Fractal Combustion Model 2017-26-0041
Worldwide IC engine fuels are increasingly blended with oxygenate fuels to reduce the dependency on the conventional petroleum reserves. Among these fuels, biomass-derived ethanol is very popular for SI engine operation as it is not only economical and renewable source of energy, but it also allows increasing the engine performance. High latent heat of vaporization of ethanol combined with its high octane number make the engine less sensitive to knock. However, the real potential of ethanol blended fuels still has to be explored and their impact on engine combustion characterization has to be investigated.
The objective of this study is to extend predictive fractal combustion model for ethanol/gasoline blends and assess the influence of ethanol addition to gasoline in a Port Fuel Injection (PFI) engine. Quasi dimensional simulation is carried out using AVL Boost under wide open throttle condition at 1500 and 3000 rpm. The developed AVL Boost engine model is validated for gasoline on an experimental data available in literature obtained for the same engine. PFI preblend have been applied to assess the extent of the improvements obtained through spark timing optimization. The combustion characteristic of different ethanol/gasoline blends have been evaluated in terms of cylinder pressure traces, Heat Release Rate (HRR), Mass Fraction Burned (MFB), position of CA50 and the effective Octane number (ONeff) .
The use of higher fractions of ethanol results in higher in-cylinder pressures. Advanced spark timing and higher flame velocity of ethanol lead to an earlier combustion phasing and higher peak cylinder pressures, and this causes an increase in performance. The ONeff values obtained from the simulations were close to the RON stated in literature. Both the ONeff and the RON shows that increasing the fraction of ethanol in the fuel increases the antiknock benefits, but the benefit diminishes once the fraction of ethanol exceeds 30%.