2. ARUN BABU
ARUN THANKACHAN
ASHIK SAHADEVAN
GUIDED BY
Dr. SUDHIR KUMAR . R

3. Variable Compression Engine
Theory
Our Work
Experiment & Result
Conclusion

4. What is it?
 Is the 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
Compression Ratio (CR)

5. CR – How is it determined?
volcylinder
volcylinder
CR
min
max
-or-
Where
b=cylinder bore
(diameter)
s = piston stroke length
Vc = Clearance volume

6. For an ideal Otto cycle the theoretical efficiency is given by,
 Where r is the compression ratio and γ is the ratio of specific heats.
For an SI-engine operating at stoichiometric mixture γ=1:3.
 Theoretically, increasing the compression ratio of an engine can
improve the thermal efficiency of the engine by producing more
power output.
 If the compression ratio is too high, the air/fuel mixture are
exposed to higher temperatures, the fuel will auto ignite, giving rise
to knocking, which could damage the engine.

7. Increased Efficiency and Pollution
Reduction with VCR:

8. 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

9. 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.

10.  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. Ways to Modify CR:
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

12. OUR WORK
VARIABLE COMPRESSION
RATIO ENGINE TEST RIG
SPECIFICATIONS
 FOUR STROKE,SINGLE
CYLINDER,VERTICALLY
MOUNTED PETROL ENGINE
 BRAKE POWER : 2.20 kW
 SPEED : 2000rpm
 STROKE : 66.7 mm
 BORE : 70 mm
 ORIFICE DIA : 20 mm

13. FAULT DETECTION
We find out the following components
were not in working condition
1. Spark Plug
2. Condenser
3. Contact Switch
4. Scale showing Compression Ratio
5. Cooling Water Pipe
6. Fuel pipe

14. CHANGING COMPRESSION RATIO

15. EXPERIMENT
 Note down the time taken for 10cc fuel consumption by varying CR(at
2000 rpm)
 At load we conduct the same experiment ,ie note down the time taken
for 10cc fuel consumption by varying CR( at 2000 rpm, 110 v and 3
Ampere)

16. CHARACTERISTICS

18.  Variable Compression Ratio engines have great
potential to increase engine power and fuel
economy.
 When coupled with technologies such as
turbocharging, 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.