Effect of Exhaust Gas Recirculation (EGR) Variation on Performance and Emissions of a Dual-Fuel Diesel Engine (Diesel + CNG): A Comparative Review

This study aims to systematically evaluate the effect of Exhaust Gas Recirculation (EGR) variation on engine performance and exhaust emissions in dual-fuel diesel–CNG compression ignition engines, in response to increasing emission regulations and the need for cleaner yet practical combustion technologies. The research employs a comparative review approach, synthesizing experimental findings from selected peer-reviewed studies to analyze the influence of different EGR rates on key performance indicators, including Brake Thermal Efficiency (BTE) and Brake Specific Fuel Consumption (BSFC), as well as major emission components such as NOx, HC, CO, and smoke. The findings indicate that increasing EGR rates effectively reduce NOx and smoke emissions due to lower combustion temperatures and oxygen dilution; however, excessive EGR leads to deteriorated combustion efficiency, reflected in reduced BTE and increased HC and CO emissions. An intermediate EGR level, particularly around 10%, is consistently identified as providing the most favorable balance between emission reduction and performance retention in dual-fuel diesel–CNG operation. These results imply that optimized EGR control is a critical parameter for improving the environmental performance of dual-fuel engines without significant efficiency penalties, supporting its application as a transitional technology toward cleaner transportation systems. The originality of this study lies in its integrated comparative synthesis of performance–emission trade-offs across multiple EGR levels and fuel substitution ratios, offering a clearer operational insight that is not explicitly addressed in individual experimental studies.