Effect of compression ratio in an engine and controlling of CR. VCR Engine.

1. WELCOME
Internal Combustion Engine
VARIABLE CMPRESSION RATIO ENGINE
PRESENTATION BY:-
Atish Kumar Sahoo
5th Sem., Mechanical

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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

8. 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.

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

10. 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.

11.  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

13. VCR PISTON ARRANGEMENT

14. VCR ENGINE BLOCK
Gear
Wheel
Pistons
Control jack
Control
Rack
Crankshaft

15. 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

16. 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.