Assignment 7

INTRODUCTION:-

Fast Running Engine Models are dynamic, fully-physical engine models that are designed specifically to run fast. While high-fidelity engine models are commonplace in the engine performance department, they are often too slow running to incorporate into system level models where long transient events may be simulated, or where the simulation model must respond faster than real-time, such as for HiL (Hardware-in-the-loop) simulations. When simulation speed is of priority, high fidelity GT-POWER engine models can be simplified into FRMs using a standard conversion process. It is up to the user how far to simplify the model, depending on the accuracy-vs-runtime requirement. FRMs are able to achive such fast run times by two means:

1. Increasing the simulation time step size and
2. Decreasing the number of calculations per time step.

These two means are often accomplished at the same time by lumping various flow volumes together which will reduce the total number of subvolumes and also allow for a larger time step size by increasing the effective subvolume lungth (which is responsible for the time step size). In addition to simplifying and combining flow volumes, there are additional solver options that can reduce the number of calculations per time step and thus, further decrease the run time without changing the time step size.

This tutorial covers the process of creating a Real-Time capable Fast Running Engine Model from a detailed, high-fidelity engine model. While this tutorial shows a specific set of steps, note that each engine model is unique and so the steps required to convert a detailed model will depend on the complexity of the model, as well as on the goals of the end user. For certain applications, such as vehicle thermal management where engine coolant heat rejection must be maintained, the procedure may differ slightly in order to maintain certain key results. While this FRM process will focus on preserving general engine performance results, special considerations will be noted along the way.

Model:

The engine is a 4-cylinder, four-stroke, Turbocharged direct injection, 2L gasoline engine.Combustion is modelled by the’Si-Wiebe’. In-cylinder heat transfer is modelled using the ‘Woschni’ model. Turbine waste-gate is being controlled to achieve target BMEP. Fuel ratio is specified by FAR.

Fig: 4 cylinder Turbochargerd GDi Model

FRM Conversion:

Step 1: Exhaust manifold

In high fidelity Model, Exhaust manifold where High exhaust gas velocities occurs and hence take large time steps.

Step 2: Exhaust Pipes

For the second step of model simplification, the exhaust pipes downstream of the turbine will be simplified. Since the pipe at the outlet of the Turbine is rather short (70mm), this pipe will be combined with the Catalyst volumes into a single FlowSplit part using ’Combine Flow Volumes wizard’.

Step 3: Intake Manifold

For the third step of model simplification, the intake Manifold will be simplified.

Step 4: Compressor Outlet Pipes

For the Fourth step of model simplification, the compressor outlet pipes will be simplified.

Step 5: Intake Pipes

For the Fifth step of model simplification, the Inlet pipes will be simplified.

Step 6: Exhaust Port

For the Sixth step of model simplification, the Exhaust ports will be combined into single one using ’Combine Flow Volumes wizard’.

Step 7: Cylinder Slaving

‘Master’ indicates that the calculated cylinder pressure for this cylinder will be analyzed, and the resulting burn rate and heat transfer rate will be stored for use by other cylinder parts designated as "slave".

Step 8: Real-Time Solver

By adding Real Time Solver allows us to operate GT Suite with Hardware in Loop(HiL) with Real Time Response.To run with the real-time solver, the license type of the model must be changed.

Fig: simplified Engine Model with Real Time Solver

Thus, any High fidelity Engine model can be converted into Fast Running Model using FRM Converter.

The generated engine model is shown below:

25 cases were set up and five cases were run individually:

Case 1-5:

a. Case setup:

b. Results:

Averaged compressor and turbine speed maps:

Case 6-10:

a. Case setup

b. Results:

Averaged compressor and turbine speed maps:

Case 11-15:

Results:

Averaged compressor and turbine speed maps:

Case 16-20:

a. Case setup:

Results:

Averaged compressor and turbine speed maps:

Case 20-25:

a. Case setup

Results:

Averaged compressor and turbine speed maps:

Conclusions:

1. All cases were able to produce target BMEP.
2. High-speed cases(4000 RPM) have higher BSFC values compared to low-speed cases with a disadvantage of producing less power and torque.
3. compressors and turbines operate at critical speeds in full load condition, some cases produce operating points outside the compressor maps.
4. FRM models operated in real-time speeds.