To satisfy the Tier-4 requirements EMD as well as other large engine manufacturers are investigating the emission reduction potentials of different technologies whether they are application ready or in concept stage. One of the recent trends is to use dedicated cylinders as EGR gas suppliers. In this study the NOx reduction potential of dedicated cylinders for the two-cycle EMD 16-710 engine is evaluated analytically.
The performance of the well known and documented 16-710 T-2 engine is chosen as the base case. An analytical model is developed to simulate the engine operation by using the commercially available GT-Power code. Model parameters are adjusted to fit predictions to test data.
The base model is then modified for a high pressure cooled EGR system. The system parameters are changed to optimize the system for selected criteria. Predicted performance of the system is compared against the base case.
The system model with EGR is further modified to accommodate the use of dedicated cylinders as the gas supplier to the EGR loop. The following dedicated cylinder variables are changed to optimize the system performance for NOx reductions; (a). Number of dedicated cylinders, (b). Location of dedicated cylinders, (c). Dedicated cylinder’s flow rate (EGR rate), (d). Compression ratio, (e). Injection timing, (f). Valve timing, (g). Valve lift profile, (h). Valve opening and closing times. Predicted results are compared against cases with and without EGR.
The study demonstrates that a 3-cylinder dedicated system, supplying the EGR gases, has the potential to reduce the tailpipe BSNOx below Tier-4 emissions level at Notch 8 operation condition of the engine. The study also suggests that designing the dedicated cylinders as if they are a different engine, for BHP while designing the normal cylinders to reduce BSNOx can be a successful strategy.
During this study the basic mechanisms of EGR in reducing the engine NOx is classified into three groups. It is shown that the Flow Diversion Effect of EGR can be above 40% of total BSNOx reduction.