The Effect of EGR on HCCI Engines Using Ethanol as Fuel

HCCI engines have great potentials in high efficiency with ultra-low NO and particulates emissions and high flexibility in using various fuels. Although these advantages make HCCI engines as an alternative for present normal SI and CI engines, Control of combustion phenomenon and ignition timing are the main issues of these engines and the exhaust gas recirculation (EGR) method is one of the attempts in order to control the combustion process. This strategy involves displacing some of the oxygen inducted into the engine as part of its fresh charge air with inert gases and it has been shown that EGR is a very effective way for NOx reduction. In this research, a mechanism containing ethanol reactions is employed and the effects of EGR on operation parameters such as ignition timing, burn duration, temperature, pressure and NOx emission are studied in which a homogeneous mixture is assumed. The results show that the increase of EGR delays the ignition timing, slows down the combustion reaction rate, reduces the temperature and pressure in cylinder, and decreases the NOx emission. Heat transfer from cylinder contents to surrounding surfaces is calculated using Woschni's heat transfer correlation. The result obtained from the model is compared with the experimental data published in the literature and the comparison showed a reasonable compatibility.