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inside the transient

As the next generation of turbocharged GDI engines moves towards production, the optimisation of transient behaviour is a high priority. The objective is to produce strong and predictable behaviour whilst supporting the use of higher gearing to maximise CO2 benefits.

Transient performance of these units depends not only on the hardware but also on the control system with strong effects resulting from the variable cam phasing control strategy in particular.

Whilst work is on-going to develop pure simulation techniques covering this regime, complex models are currently required to capture important details of gasflow, turbine interaction and gas exchange processes. Running and correlating these models is time consuming and it is difficult to depend on this approach to deliver practical solutions in typical project timescales.

IP has developed an alternative process to capture all of the key mechanisms and enable hardware and control strategies to be readily compared with confidence. The method combines simulation with a specially designed dynamometer based characterisation exercise and offers major advantages in terms of fidelity, model size and stability when compared with conventional simulation approaches.

The process starts with a 2 week dynamometer based characterisation which mimics the system behaviour across a range of transient events and control system settings. Information is gathered including volumetric efficiency, scavenging flow, combustion characteristics and turbocharger instantaneous efficiency. This information is then used to populate a specially developed quasi-dynamic engine sub-model within our Simulink vehicle and control system simulation.

By using test data in this way, correlation is automatically achieved and model run time is low. This enables in-depth analysis and optimisation of the transient behaviour including turbocharger specification, valve timing, system layout and control system strategy effects.