A Controlled EGR Cooling System for Heavy Duty Diesel Applications Using the Vehicle Engine Cooling System Simulation

In order to comply with 2002 EPA emissions regulations, cooled exhaust gas recirculation (EGR) will be used by heavy duty (HD) diesel engine manufacturers as the primary means to reduce emissions of nitrogen oxides (NO_x). A feedforward controlled EGR cooling system with a secondary electric water pump and proportional-integral-derivative (PID) feedback has been designed to cool the recirculated exhaust gas in order to better realize the benefits of EGR without overcooling the exhaust gas since overcooling leads to the fouling of the EGR cooler with acidic residues. A system without a variable controlled coolant flow rate is not able to achieve these goals because the exhaust temperature and the EGR schedule vary significantly, especially under transient and warm-up operating conditions. Simulation results presented in this paper have been determined using the Vehicle Engine Cooling System Simulation (VECSS) software, which has been developed and validated using actual engine data. Simulation results indicate that a controlled EGR cooling system can maintain the EGR cooler outlet exhaust temperature at 130±8°C, as compared to 110±60°C for an EGR cooling system without coolant flow control. A system with controlled EGR cooling combined with a controlled engine cooling system indicates decreased warmup times for fast warmup of aftertreatment devices, decreased power consumption, and better engine temperature control.

The previous version of VECSS did not include the capability to simulate EGR. Therefore, literature related to EGR is reviewed within the paper. Cooling system simulation results at high and low ambient temperature with EGR are also included along with the models created for the EGR cooler, EGR valve, and secondary electric water pump and controller. The engine cycle analysis subroutines were also modified to consider variable mixture compositions, as the thermal properties of the intake air vary significantly with the decreased oxygen concentration present with EGR.