2. 1 [Translation: In the name of Allah, the Most Merciful, the Most Kind.]

3. 2 REG NO: BME: 01083004 SECTION: B DEPARTMENT: MECHANICAL THE UNIVERSITY OF LAHORE

4. 3 The Sparking Ignition engine. The term spark-ignition engine is normally used to refer to internal combustion engines where the fuel-air mixture is ignited with a spark. The term contrasts with

5. 4 compression-ignition engines, where the heat from compression alone ignites the mixture. Spark-ignition engines can be either two-stroke or four-stroke, and are commonly referred to as "gasoline engines" in America and "petrol engines" in Britain. However, these terms are not preferred, since spark-ignition engines can (and increasingly are) run on fuels other than gasoline, such as auto gas (LPG), methanol, ethanol, compressed natural gas (CNG), hydrogen, and (in drag racing) nitromethane. A four-stroke spark-ignition engine is an Otto cycle engine.

6. 5 Until recently, a major distinction between spark ignition and compression-ignition engines has been where the fuel is mixed - spark-ignition engines mix fuel outside the cylinders and compression-ignition engines mix fuel inside the cylinders. However, both two- stroke and four-stroke spark-ignition engines are increasingly being designed with gasoline direct injection (GDi), eliminating this distinction between the two systems.

7. 6 Pressure - Volume Diagrams Graph of pressure as a function of cylinder volume above the piston Bottom Dead Center - volume is maximum Top Dead Center - volume is minimum

8. 7 Cylinder Volume Change in volume as piston goes up and down Volume going TDC Volume going

9. 8 Change in Volume Volume BDCTDCBDC

10. 9 P-V Diagram - Gas Engine Bottom Dead Center Start of compression stroke - volume above piston filled with fuel/air mixture BDCTDC Volume Pressure

11. 10 P-V Diagram - Gas Engine Piston travels up, fuel/air compressed and pressure rises BDCTDC Volume Pressure

12. 11 P-V Diagram - Gas Engine Top Dead Center End of compression stroke - volume in cylinder at a minimum BDCTDC Volume Pressure

13. 12 P-V Diagram - Gas Engine Then have an instantaneous introduction of heat, which increases pressure again COMBUSTION BDCTDC Volume Pressure

14. 13 P-V Diagram - Gas Engine BDCTDC Volume Pressure Pressure forces piston down, creating torque on crank shaft

15. 14 P-V Diagram - Gas Engine BDCTDC Volume Pressure Piston reaches bottom dead center again, exhaust valve opens, burned fuel/air expelled

16. 15 Gas Engine Efficiency Remember, efficiency is work out divided by heat in P-V diagram tells us both things Heat in: temperature change from burning fuel BDCTDC Volume Pressure Work out: area between curves And, make a few assumptions, can calculate efficiency

17. 16 Gas Engine Efficiency Define compression ratio as: Then efficiency can be shown to be: Higher efficiency means higher compression ratio. BDCTDC Volume Pressure

18. 17 (sparking ignition engine) Advantages for Spark Ignition Engines: - Increase efficiency at part load operating conditions by operating at a higher effective compression ratio - Successfully avoid spark knock at full load conditions, even during rapid transients

19. 18

20. 19 Following is the explanation of the Four-Stroke and Two-Stroke SI Engines and their P-V Diagrams..

21. Four Stroke SI Engine Stroke 1: Fuel-air mixture introduced into cylinder through intake valve Stroke 2: Fuel-air mixture compressed Stroke 3: Combustion (~constant volume) occurs and product gases expand doing work Stroke 4: Product gases pushed out of the cylinder through the exhaust valve Compression Stroke Power Stroke Exhaust Stroke A I R Combustion Products Ignition Intake Stroke FUEL Fuel/Air Mixture

22. Crank shaft 90 o 180 o BC TC 0 o 270 o  Spark plug for SI engine Fuel injector for CI engine Top Center (TC) Bottom Center (BC) Valves Clearance volume Cylinder wall Piston Stroke Cylinder Components

23. IVO - intake valve open, IVC – intake valve close EVO – exhaust valve open, EVC – exhaust valve close X b – burned gas mole fraction Four-Stroke SI Engine Exhaust gas residual

24. 23 Two Stroke SI Engine The two-stroke engine is simpler mechanically than the four-stroke engine. The two-stroke engine delivers one power stroke every two strokes instead of one every four; thus it develops more power with the same displacement, or can be lighter and yet deliver the same power. For this reason it is used in lawn mowers, chain saws, small automobiles, motorcycles, and outboard marine engines.

25. 24

26. Two Stroke SI Engine Intake (“Scavenging”) Compression Ignition Exhaust Expansion Fuel-air-oil mixture Fuel-air-oil mixture compressed Crank shaft Check valve Exhaust port

27. EPO – exhaust port open EPC – exhaust port closed IPO – intake port open IPC – intake port closed Exhaust area Intake area Two-Stroke SI Engine scavenging

28. 27 Achievements: Three prototype pistons were manufactured: two pistons for a spark ignition engine and one piston for a compression ignition engine. All three were tested experimentally in single cylinder engines. Models of the piston operation were also developed to investigate the piston concept at different operating conditions. Spark Ignition Engine Test Result Summary The spark ignition PRP prototypes demonstrated the utility of the PRP concept when applied to a spark ignition engine. At low loads, the piston behaved like the elevated compression ratio, yielding a brake specific fuel consumption (BSFC) improvement of 3.5-10% during low load conditions. At high load conditions, the PRP limited the peak cylinder pressure to that of the baseline (lower compression ratio) piston.

29. Cylinder Arrangement Single-cylinder engine gives one power stroke per crank revolution (2 stroke) or two revolutions (4 stroke). The torque pulses are widely spaced, and engine vibration and smoothness are significant problems. Used in small engine applications where engine size is more important Multi-cylinder engines spread out the displacement volume amongst multiple smaller cylinders. Increased frequency of power strokes produces smoother torque characteristics. Engine balance (inertia forces associated with accelerating and decelerating piston) better than single cylinder. Most common cylinder arrangements: - In-line 4-cylinder - In-line 6-cylinder - V-6 and V-8

30. Power Regulation (Throttling) An IC engine is basically an air engine, the more air you get into the cylinder, the more fuel you can burn, the more power you get out. The initial pressure in the cylinder is roughly equal to the pressure in the intake manifold. Pressure in the intake manifold is varied by opening and closing the throttle plate to change the pressure drop. Maximum air flow (and power) achieved at wide-open-throttle (WOT). Minimum air flow at idle P atm P int < P atm Intake manifold Fuel WOT Idle

31. Basic Carburetor Design Venturi Throttle Air Flow Mixture to manifold Fuel

32. Fuel Injection System Throttle Fuel tank Air intake manifold During start-up the components are cold so fuel evaporation is very slow, as a result additional fuel is added through a second injecting valve

33. Superchargers and Turbochargers increase the power of an IC engine by raising the intake pressure and thus allowing more fuel to be burned per cycle. Knock or autoignition phenomenon limit precompression. Superchargers are compressors that are mechanically driven by the engine crankshaft and thus represent a parasitic load. Compressor P atm P int > P atm

34. Turbochargers couple a compressor with a turbine driven by the exhaust gas. The compressor pressure is proportional to the engine speed

35. The peak pressure in the exhaust system is only slightly greater than atmospheric – small  P across turbine. In order to produce enough power to run compressor the turbine speed must be very fast (100k-200k rev/min) – long term reliability an issue. It takes time for turbine to get up to speed so when the throttle is opened suddenly there is a delay in achieving peak power - Turbo lag. Waste gate valve controls the exhaust gas flow rate to the turbine. It is controlled by the intake manifold pressure INTAKE AIR EXHAUST FLOW