Simulations and Measurements of a Two-Stage Turbocharged Heavy-Duty Diesel Engine Including EGR in Transient Operation

To meet future demands with respect to emissions for heavy-duty diesel engines high EGR rates together with an optimized injection system are most likely required. The increase in smoke production associated with EGR, especially during transient operation implies that high boost pressures are needed to at least maintain the air excess ratio. To reach required boost pressure without extending the response time a more advanced turbocharger system than the use of a single turbocharger might be needed. A possible solution is two-stage turbocharger systems.

Experiments and simulations with focus on transient performance were therefore made on a heavy-duty diesel engine with a two-stage turbocharger system and a high pressure loop for EGR. The turbocharger system consists of a twin-entry turbine used at the high pressure stage and a variable geometry turbine at the low pressure stage. The simulation results are verified with experimental data to show to which extent it is possible to predict the performance of the gas exchange system for transient operation with today's simulation tools.

The results show that the turbocharger model which is based on stationary measured performance data needs adjustment of up to 10% to give a good correlation to the measurements. The turbocharger system configuration used for the study shows good potential for the engine to run with high amounts of transient EGR.