Design of synthetic EGR and simulation study of the effect of simplified formulations on the ignition delay of isooctane and n-heptane

•A method to design synthetic EGR with a desired oxygen mass fraction is defined.•The validity of simplified synthetic EGR's was studied for isooctane and n-heptane.•Intervals of use (oxygen mass fraction) for each simplified EGR were established. A method to create synthetic mixtures that simulate the Exhaust Gas Recirculation (EGR) of an internal combustion engine, using O2, N2, CO2, H2O and Ar, has been designed. Different simplifications of this synthetic EGR have been validated in order to reproduce ignition delays. To do this, a parametric study has been carried out with CHEMKIN. The ignition delay of each simplified mixture and the ignition delay of the complete mixture have been simulated for different initial pressures, temperatures, equivalence ratios, oxygen mass fractions and for two different fuels, isooctane and n-heptane. The results obtained with each simplification have been compared with the results obtained with the complete EGR, and based on this comparison the errors in ignition delay have been calculated. The behavior of the errors in ignition delay with the variation of the different parameters of the simulations has been studied. In summary, it can be seen that the relative error increases with temperature and decreases with pressure, equivalence ratio and oxygen mass fraction. Finally, the limit oxygen mass fractions for the use of each simplification have been obtained. Based on these results, it can be concluded that the only gas that can be obviated to keep the error in ignition delay under 1% is Ar.