WELCOME

Internal Combustion Engine VARIABLE CMPRESSION RATIO ENGINE

PRESENTATION BY:-

Atish Kumar Sahoo

5th Sem., Mechanical

WHY VCR ?

Need of high specific power output accompanied by good reliability and longer engine life.

Use of high pressure turbo charging results induces high thermal load.

Turbocharger doesn’t have good adiabatic efficiency.

High peak pressure problem occurs at full load.

Can be minimized by reducing CR.

But CR should be sufficiently high for good starting and part load operation.

VCR concept is beneficial in low load, for better multifuel capacity.

INTRODUCTION

Variable compression ratio is a technology to adjust the compression ratio of an internal combustion engine while the engine is in operation.

This is done to increase fuel efficiency while under varying loads. Higher loads require lower ratios to be more efficient and vice versa.

Variable compression engines allow for the volume above the piston at Top dead centre to be changed. For automotive use this needs to be done dynamically in response to the load and driving demands.

COMPRESSION RATIO

It is ratio by which the fuel/air mixture is compressed before it is ignited.

Limited in conventional engines due to auto ignition.

Determines how efficiently the engine can utilize the energy in the fuel.

Variable Compression Ratio can be obtained by alternating:

The Clearance Volume

Both the Clearance volume and the Swept Volume.

CR - CHARACTERISTICS

CR of traditional engine is fixed and is a compromise across a wide range of operating conditions.

CR for passenger cars ranges between 8:1 and 10:1, while CR for diesel engines can be much higher.

VARIABLE COMPRESSION RATIO (VCR)

The combustion chamber volume, Vc, is altered to meet the power needs to the vehicle.

At low power levels, high CR captures fuel efficiency benefits.

At high power levels, low CR prevents knock.

VCR - ADVANTAGES

CR modified to meet power demand (CR’s range from 7:1 to 21:1)

Increased fuel efficiency Claims of up to 30% reduction in fuel consumption Adding variable valve actuation and turbo-charging

further improves fuel efficiency (7-10% additional reduction in fuel consumption)

Reduced combustion emissions

VCR - DISADVANTAGES

New technology results in high research and development and manufacturing costs.

Reliability is not proven.

Consumer reactions are unknown and unpredictable.

Repairs and maintenance initially may be difficult and costly.

A reduction in fuel consumption is achieved by increasing the work output and/or decreasing the frictional and pumping losses.

WAYS TO MODIFY CR

Moving the cylinder head.

Variation of combustion chamber volume.

Variation of piston deck height.

Modification of connecting rod geometry.

Moving the crankpin within the crankshaft (effectively varying the stroke).

Moving the crankshaft axis.

A: articulated cylinder head

B: hydraulic pistons

C: eccentrics on bearings

D: multilink rod-crank mechanisms

E: additional piston in cylinder head

F: gear-based mechanisms

VCR PISTON ARRANGEMENT

VCR ENGINE BLOCK

Gear Wheel

Pistons

Crankshaft

Control jack

Control Rack

FUEL CONSUMPTION REDUCTION STRATEGIES

Fuel Consumption Reduction Strategy

Sources of effectiveness Engine strategies

1 - Increased effective expansion ratio

Improved indicated efficiency •High Fixed Compression Ratio (FCR)•Variable Compression Ratio

2 - Downsizing •Pumping losses reduction•Internal heat transfer surface reduction•Flame travel distance reduction•Friction losses reduction

•High supercharging•Increased average BMEP•10:1 Compression Ratio (FCR)•From 8:1 to 16:1 Compression Ratio (VCR)

3 - Downspeeding •Pumping losses reduction•Friction losses reduction

•High supercharging•Increased average BMEP

4 - Unthrottled load control •Pumping losses reduction •Load control by air/fuel ratio•Load control by Late Intake Valve Closing

5 - Engine mechanical efficiency improvement

•Friction losses reduction •Reduction of all friction sources

CONCLUSIONS

Variable Compression Ratio engines have great potential to increase engine power and fuel economy.

When coupled with technologies such as turbo charging, variable valve actuation, and direct fuel injection, the effectiveness of the system is further increased.

Once established, this technology will likely become commonplace due to increasing energy and environmental concerns and the ease of integration.

Due to use of high compression ratio at low loads the VCR engines has a good starting and idling performance.

THANK YOU