Chapter 6 - Application of exhaust gas recirculation of NOx reduction in SI engines

Abstract

One of the primary pollutants obtained from both petrol and diesel engines is NOx emissions. The exhaust gas recirculation (EGR) technique is a widely used methodology to mitigate NOx emissions from the engine. This technique was initially implemented in diesel engines while it is now implemented in spark-ignition engines along with various other methods. The EGR technique minimizes the need for fuel enrichment in spark-ignition engines to prevent knocking combustion inside the cylinder. The primary purpose of t his chapter is to review the various causes and effects of EGR and its effect on NOx emissions on spark-ignition engines. A comprehensive study comparing hot and cooled EGR and its effects on suppressing the knock intensity correlating to NOx emissions has been done. The extreme possible EGR rate is restricted by great cycle-by-cycle variations, reduction in efficiency, misfire, and the decrease in NOx emissions. These cases could be solved by the application of a stratified EGR system. From the detailed study, one could see that EGR can reduce NOx, improve knocking combustion and fuel consumption, and prevent the tendency of the engine to produce soot emissions. A study of the various advanced SI engine techniques such as gasoline direct injection engine, multipoint fuel injection engine, and lean burn combustion engine has been done. Also, the SI engine technique with the implementation of other alternatives such as natural gas and hydrogen along with the EGR suppressing the NOx emissions has been studied.