Variable Compression Ratio of Engine

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 5 th 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, V c , 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

12. VCR Piston Arrangement

13. VCR Engine Block Gear Wheel Pistons Crankshaft Control jack Control Rack

14. 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

15. 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.

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