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GMPT Europe, Engine Development & Simulation

Vincenzo Bevilacqua, Jany Krieg, Roland Maucher, Raymond Reinmann

Development of a Double Variable Cam Phasing Strategy for

Turbocharged SIDI Engines

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Contents

• Introduction

• Synergies between different engine technologies

• Cam Phasing Optimization

• Comparison between simulation and experiments

• Summary

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Contents

• Introduction

• Synergies between different engine technologies

• Cam Phasing Optimization

• Comparison between simulation and experiments

• Summary

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Introduction – Turbo Diesel Engines

Turbocharged diesel engines gained persistently increasing market shares in the European Market in the last decade.

This success can be explained with the

• high low-end torque

• output power comparable with the competitor SI engines

• low fuel consumption

Tough challenge for SI engines developers!

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Introduction – SI Engines

Compete against turbo diesel engines represents a tough challenge for SI engine developers and require a sophistication of the engine concept:

• Dual Variable Cam Phasing

• Direct Injection

• Turbocharger

optimizes the volumetric efficiency and improves fuel consumption at part load;

allows the downsizing of the engine and consequently improves fuel consumption;

Full factorial experimental approach is too time consuming to optimize the system

increases the specific torque and power, and, eventually, allows lean stratified operating condition at part load;

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Synergies between different engine technologies

• Introduction

• Synergies between different engine technologies

• Cam Phasing Optimization

• Comparison between simulation and experiments

• Summary

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Synergies between different engine technologies

By combining the proprieties of different technologies, synergies can be achieved:

LOW END TORQUE

A high degree of scavenging can be provided by the cam phasing. This increases the VE and the efficiency of the turbo. Thanks to DI no fuel is lost.

FUEL CONSUMPTION

Engine Speed [rpm]

Bra

ke T

orqu

e [N

m]

The variable cam phasercan be used to shift compression work from engine to thecompressorand improve system efficiency (versus waste-gate control)

MAXIMUM TORQUE PLATEAU

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Synergies between different engine technologies

FUEL CONSUMPTION

Making the engine work with lower volumetric efficiencyan higher boost pressure is required to fulfill the target.

The positive pumping work is then increased.

Engine Speed [rpm]

Bra

ke T

orqu

e [N

m]

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Contents

• Introduction

• Synergies between different engine technologies

• Cam Phasing Optimization

• Comparison between simulation and experiments

• Summary

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Cam Phasing Optimization

With the help of the cam maps, the cam position can be optimized for each operating point, to achieve:

• the maximum performance potential

• the minimum fuel consumption

In the diagram (as example) the point at 1800 rpm is shown.

Overlap positionOverlap Width

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Cam Phasing Optimization - PerformanceVOLU METRIC EFFICIENCY

The VE is maximized by maximum overlap

PMEP

Positive PMEP is increased advancing exhaust cam.

The trade off depends on engine speed:

• low rpm: high scavenging

• high rpm: low neg. PMEP

MANIFOLD PRESSURE

The manifold pressure (index of performance potential) shows a minimum in a intermediate region.

Low High

Maximum Performance Potential Cam Timing

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Cam Phasing Optimization - PerformanceVOLU METRIC EFFICIENCY

The VE is maximized by maximum overlap

PMEP

Positive PMEP is increased advancing exhaust cam.

The trade off depends on engine speed:

• low rpm: high scavenging

• high rpm: low neg. PMEP

MANIFOLD PRESSURE

The manifold pressure (index of performance potential) shows a minimum in a intermediate region.

Low High

Maximum Performance Potential Cam Timing

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Cam Phasing Optimization - Consumption

PERCENT BURNED MASS

The content of residual gas is an index of the COV of Torque and the knock intensity. A limit of 3% has been chosen.

BSFC

In the BSFC cam map the Minimal Consumption Cam Timing can be located.

Low High

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Contents

• Introduction

• Synergies between different engine technologies

• Cam Phasing Optimization

• Comparison between simulation and experiments

• Summary

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Comparison with experimentIn order to validate the outcome of the numerical optimization experimental test have been carried out.

Both maximum performance potential and minimal consumptiontimings have been tested.

Due to cam phaserauthority, cam phasing has been slightly modified (dotted lines).

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Comparison with experimentMANIFOLD PRESSURE

Maximum performance potential timings allows to reach the target torque with a significant lower boost pressure.

BSFC

Minimal consumption timings allows a reduction of BSFC up to 7.5%.

7.5%

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Contents

• Introduction

• Synergies between different engine technologies

• Cam Phasing Optimization

• Comparison between simulation and experiments

• Summary

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Summary

The cam phasing for a turbocharged GDI engine has been analyzed with 1-dimensional simulation.

The analysis provide a deep insight of the cam phasing effect and in particular permit to highlight two strategies:

• maximum performance potential

• minimal consumption

Increasing the compressor work, fuel consumption can be improved

Experiments confirmed the outcomes of the simulation work showing potential in fuel economy (cam phasing vs. waste gate)

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Thank you for the attention!

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