Modelling and Experimental Study of Internal EGR System for NOx Control on an Off-Road Diesel Engine

This study deals with the development of an internal EGR (Exhaust Gas Recirculation) system for NOx reduction on a six cylinder, turbocharged intercooled, off-road diesel engine based on a modified cam with secondary lift. One dimensional thermodynamic simulation model was developed using a commercially available code. MCC heat release model was refined in the present work by considering wall impingement of the fuel as given by Lakshminarayanan et al. The NOx prediction accuracy was improved to a level of 90% by a generic polynomial fit between air excess ratio and prediction constants. Simulation results of base model were correlating to more than 95% with experimental results for ISO 8178 C1 test cycle.

Parametric study of intake and exhaust valve events was conducted with 2IVO (Secondary Intake Valve Opening) and 2EVO (Secondary Exhaust Valve Opening) methods. Combinations of different opening angles and lifts were chosen in both 2IVO and 2EVO methods for the study. Residual gas content has been estimated for each combination along with performance parameters and NOx emission. Simulation results showed 2IVO with 12 - 13% of main lift closing at 60°CA prior to main lift was found to be meeting the target internal EGR rates. Experimental set up was developed with instrumentations for performance, emission and internal EGR residual measurement along with temperatures and pressures. Experimental results showed a NOx emission reduction upto 27% with secondary lift of 12% to the main lift which is producing 10% iEGR rate. Experimental results of modified cam correlated to simulation results to a higher degree.