An Analytical Examination of the Effects of Exhaust Gas Recirculation on the Compression Ignition Process of Engines Fuelled with Gaseous Fuels

The action of exhaust gas recirculation (EGR) is examined numerically to find out whether EGR can be used to enhance the preignition reactions of a cylinder charge in a motoring, compression ignition engine fuelled with a homogeneous gaseous fuel - air mixture. The changes to the concentrations and properties of the contents of the cylinder and the associated changes in the preignition reaction rates are followed over a number of consecutive, calculated working cycles at a constant engine speed to establish whether autoignition will take place and the number of cycles required for its occurrence. It is shown that controlled EGR can enhance the autoignition processes in gas-fuelled compression ignition engines by suitably ‘seeding’ the intake charge of the current cycle with the chemical species found in the exhaust gases of the previous cycle. Some of these chemical species improve the ignition process by bringing about substantial changes to the reactivity of the charge that may make regular cyclic autoignition a practical possibility. However, these effects can also be moderated by the diluting effects of some of the products in EGR.