Variable compression ratio and heat balance sheet
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The document discusses variable compression ratio (VCR) engines, which adjust their compression ratio during operation to optimize fuel efficiency under varying loads. It details the advantages and disadvantages of VCR technology, including improved fuel efficiency and reduced emissions, as well as challenges such as high development costs and reliability concerns. The text also explains the heat balance sheet related to engine performance, detailing how heat generated by fuel is utilized and lost in various ways.
Variable compression ratio and heat balance sheet
- 1. Variable Compression-Ratio Engine Submitted By:- DISHANT K. PATIWALA
- 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. 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. 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.
- 7. 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.
- 9. VCR-Saab Tilting Monohead Design
- 10. 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
- 12. 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.
- 13. Gen4 VC
- 14. 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
- 15. 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
- 16. 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.
- 17. Heat balance sheet 1. It is the account of heat supplied and heat utilized in various ways in the system. 2. It gives the information of the performance of the engine. 3. It is done of second/ minute/ hour basis 4. To draw heat balance sheet complete test on the engine is carried out at constant speed.
- 18. Calculation of heat Balance Sheet I ) Heat supplied by fuel : 1) For petrol / oil engine : Heat supplied = mf x C.V. KJ/Min Where , mf = Mass flow rate of fuel in Kg.min Cv = Calorific value of fuel in KJ/Kg 2) For gas engine : Heat supplied = V X C.V. Where, V = volume of gas supplied per minute.
- 19. Calculation of heat Balance Sheet II ) Heat expenditure / Heat utilized : Heat energy of the fuel is partly converted into useful work equivalent to B.P. Remaining heat is carried away by a) cooling water b) Exhaust gases c) Radiation, incomplete combustion , lubricating oil. A) Heat equivalent to B.P. = B.P. x 60 in KJ /min B) Heat rejected to cooling water : Qw = Mw x Cpw x ( t2-t1) • Where Cpw= 4.187 KJ/KgK
- 20. Calculation of heat Balance Sheet C) Heat carried away by exhaust gas : Qeg = Meg x Cpeg x ( tf – tr) Where , Meg = Mf + Mg tf= temperature of flue gas tr = temperature of engine. Cpeg = Specific heat of exhaust gas.
- 21. Heat Balance Sheet Heat Supplied KJ/min % Heat Expenditure KJ/min % Heat supplied by combustion of fuel Qs 100 Heat equivalent to Brake Power Qb Qb/Qs x 100 Heat lost to cooling water Qw Qw/Qs x 100 Heat lost by exhaust gas Qeg Qeg/Qs x 100 Heat lost by radiation Qu Qu/Qs x 100 Total Qs 100 Equal to Qs 100
- 22. thank you