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 the compression ratio to be changed for various working conditions, and obtain the required compression ratio for the required load conditions.

1. Seminar On
Variable Compression-Ratio
Engine
Presented by:
Gokul Krishna G
1DA14ME038
Department of Mechanical Engineering
Dr. Ambedkar Institute of Technology

2. 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 the compression
ratio to be changed for various working conditions,
and obtain the required compression ratio for the
required load conditions.

3. Compression Ratio
• It is ratio by which the fuel/air mixture is compressed before it is
ignited.
• It is also defined as the difference between the total volume of
the cylinder to the swept volume of the piston.
• It determines how efficiently the engine can utilize the energy in
the fuel.
• A higher compression ratio is able to achieve greater efficiency
and improved fuel consumption.
• Lower compression ratios offer greater power and torque,
particularly in turbocharged engines, but are known for reduced
fuel efficiency.
• In a typical engine the compression ratio is fixed to
14:1(Gasoline Engine) on all load conditions.

4. Need for Variable Compression-Ratio(VCR)
• A problem called ‘knocking’, a process of inefficiency which can occur
in higher compression ratio engines when the air-fuel mixture
combusts prematurely in the cylinder, potentially resulting in damage
to the engine.
• The compression ratio should be reduced in order to reduce knock.
• For low load condition(cruising, idling) which demands great
efficiency, the compression ratio should be high as 14:1.
• For high load condition which demands more performance, the
compression ratio should be as low as 8:1.
• 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.
• But CR should be sufficiently high for good starting and part load
operation.
• VCR concept is beneficial in low load, for better multi-fuel capacity.

5. How can it be achieved?
A: Articulated Cylinder Head
B: Hydraulic Pistons
C: Eccentrics On Bearings
D: Multilink Rod Crank Mechanisms
E: Additional Piston In Cylinder Head
F: Multi-Link Mechanisms

6. Articulated Cylinder Head
• Introduced by Saab, called as Saab Tilting
Monohead Design
• 2-part engine block allows the cylinder head to
be lowered closer to the crankshaft to
dynamically alter Vc
• CR varied by adjusting the slope of the mono-
head in relation to the engine block
• Unfortunately, Saab shelved this project due
to high cost.
Actuactor
Upper
engine block
(monohead)
Lower
Engine Block
Pivot Point
Increased
Volume

7. VCR-Saab Tilting Monohead Design
1. 2. 3.

8. Eccentric on Bearings
• Gomecsys (in English: GoEngine) is a
Dutch Engineering company that has
developed its own variable compression
ratio technology based on a 6mm eccentric
on the crankshaft pin.
• It has achieved compression ratio change
from 8:1 to 18:1
• 30% reduced fuel consumption and CO2
output without sacrificing full load p Eccentric
Internal Ring Gear

9. Gen4 VC
One of the big advantages of this system is the simplicity. The complete VCR
system is integrated on the crankshaft and every 4-stroke engine can be
upgraded by replacing a normal crankshaft with a Gomecsys VCR crankshaft.

10. Multi-Link Mechanisms
• This mechanism is developed by INFINITI, and is the
worlds first Variable compression Turbo-Charged
Engine
• 4 major steps to change the compression ratio
1. An harmonic drive like an electric motor drives the
actuator arm
2. The actuator arm rotates the control shaft, similar in
principle to camshaft which forces the lower linkage to
move up or down based on the orientation of the cam
lobe.
3. The lower link changes the angle of multilink, which is
connected by an upper link to piston
4. Upper link moves from the multilink rotation which
causes the piston move up or down changing the
compression ratio of the engine

11. Infiniti KR-20 VCR
• Compression ratio are varied from 8.0:1 to
14.0:1
• Compression ratio varied in 1.2 from 8 to 14 in
1.2 sec.
• The compression ratio is varied by varying the
TDC to upto 6mm

12. Additional Benefits in Infiniti VC turbo engine
• In typical engines, the piston during the expansion stroke,
generates lot of side forces on to the cylinder walls.
• This is because the connecting rod is at a significant angle w.r.t
cylinder
• In this engine the connecting rod is kept nearly vertical position,
thus almost eliminating the side-forces on to the walls of the
cylinder.
• This helps in reduced friction, thus improved efficiency and life
of the cylinder

13. Variable Compression Ratio
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
Dis-advantages
• New technology results in high research and
development and manufacturing costs.
• Complex design, hence reliability is not proven.
• Consumer reactions are unknown and
unpredictable.
• Repairs and maintenance initially may be
difficult and costly.

14. Conclusion
• 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.
• 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.