Technologies like exhaust gas recirculation (EGR), soot traps and exhaust gas after treatment are essential to cater to the challenges posed by stringent environmental emission legislations. This book basically concentrated on the exhaust gas recirculation system for Mahua (Maduca indica) methyl ester application on CI engines, for reduction of NOx. This book is mainly targeted for the researchers in the field of bio-diesel applications and also gives the guidelines for bachelors and masters degree engineering students. In this book the chapter 1 deals with literature review regarding formation of NOx. The chapter2 mainly concentrated on bio-diesel preparation process i.e transesterification. Chapter 3 deals with the mathematical modeling for the computation of the net heat release rate during combustion. Chapter 4 deals with the experimental set up and experimentation on CI engine with Neat MME with EGR. Chapter 5 deals with the results analysis, conclusions and future scope of the experiment. The last chapter finished with references and future scope.