**4. Background**

Smoke and NOx emissions in diesel engines have an inherent exchange off connection among them and in this way endeavors to limit one of them would normally bring about expanding the other. To add to this hopelessness, endeavors to decrease outflows would regularly result in misfortune in execution of the engine. This is because efficient combustion often results in high cylinder temperatures and reduces smoke but promotes NOx formation. On the other hand, lowering the combustion temperature results in incomplete combustion and favors NOx emissions but increases smoke formation and reduce engine performance. Adding oxygenated biofuels like bioalcohols to diesel reduces smoke emissions by the way of providing additional oxygen during combustion in fuel-rich zones via fuel-bound oxygen content. However this often results in higher NOx emissions. Exhaust gas recirculation (EGR) is a NOx reduction technology which involves bypassing a percentage of the combusted gases back to engine cylinder along with the intake charge that reduces peak combustion temperatures responsible for NOx formation by the way of its thermal, chemical and dilution effects. However, EGR causes a drop in engine performance as it disturbs the normal combustion process. Modifying the injection timing also affects the emission and performance characteristics. Delaying the injection up to the TDC causes low combustion temperatures and reduces NOx emissions and engine performance. Early injection improves air-fuel mixing and promotes complete combustion. This increases peak combustion temperatures and reduce NOx emissions. Hence it could be inferred that optimization of parameters like oxygenate composition in diesel, EGR and injection timing could achieve low emission and high performance in a diesel engine.
