A Crank-angle model for the “real-time” simulation of Diesel engines in HiL/SiL applications.

It is well known that in automotive applications the design and testing of powertrain management systems play a key role in performance improvement and in reduction of fuel consumption and exhaust emissions. In this field theoretical models proved to be powerful tools to reduce development time and costs. Growing complexity of powertrains and related management systems, however, give rise to challenging issues in the development and applications of theoretical models. Improvements recently introduced in the original library developed by the authors for “real-time” simulation of automotive powertrains are described in the paper. Used in the last years to build up Mean Value Models (MVMs) of engines and powertrains and embedded in several HiL platforms, the tool has been recently enhanced to allow for a “crank-angle” resolution introducing models for intake and exhaust valves and for in-cylinder processes. Combustion effects have been described through a classic single-zone approach with a suitable Heat Release Rate (HRR). The hierarchical structure of the library respects causality and allows to couple blocks to model different components. Features of each sub-model have been defined taking account of the application, choosing whenever possible white/grey-box models and using black-box empirical approaches when needed. The simulation algorithm has been improved to allow for finer time steps in the solution of in-cylinder processes, still keeping a larger time step for the simulation of other events (e.g., intake/exhaust flows). These tools were used to model a four-cylinder turbocharged automotive Diesel with Exhaust Gas Recirculation. Starting from a Mean Value Model (MVM) of the engine, simulation of in-cylinder thermodynamic processes with a resolution of 1deg CA has been introduced obtaining a “crank-angle” model still running faster than real-time. Valves and cylinder sub-models have been developed and integrated in the existing library blocks and combustion process has been described following a classic single-zone approach based on a proper Heat Release Rate (HRR). After calibration and validation –with reference to an automotive Common Rail Diesel- comparing calculated results with experimental data in steady operating conditions, the proposed model has been embedded in an original PC-based Hardware-in-the-Loop (HiL) system previously developed by the authors fulfilling the expected requirements.