2. Gasoline Engines Operation

3. Energy and Power Energy is used to produce power. Chemical energy is converted to heat energy by burning fuel at a controlled rate.  This is called Combustion If engine combustion occurs within the power chamber (combustion chamber) it is an internal combustion engine.

4. The chemical to heat energy conversion within the combustion chamber causes a pressure increase within the combustion chamber. This pressure is applied to the head of the piston to produce mechanical force. This mechanical force is converted into mechanical power. Energy and Power

5. Four-Stroke Cycle Engines All modern automotive engines utilize a four stroke design. The four strokes are:  Intake  Compression  Power  Exhaust

6. Four-Stroke Cycle Engines Intake stroke - the intake valve opens as the piston inside the cylinder travels downward.  This draws the air/fuel mixture into the cylinder

7. Compression stroke – the intake valve closes and the piston travels upward in the cylinder  this compresses the air/fuel mixture. Four-Stroke Cycle Engines

8. Power stroke – as the piston travels toward the top of the cylinder (top dead center) a spark plug ignites the compressed A/F mixture.  This forces the piston downward

9. Exhaust stroke – as the piston travels up tow  This expels the spent exhaust gasses Four-Stroke Cycle Engines

11. Crankshaft Mounted at the “center- line” of the engine The pistons are mounted to the crank via connecting rods As the crank rotates the pistons move up and down in the engine bore http://quadhub.com/wiki /images/a/ac/Cshaft.gif http://quadhub.com/wiki /images/a/ac/Cshaft.gif

12. 720 Degree Cycle Each cycle of a four stroke engine requires two complete revolutions of the crankshaft. The greater the number of cylinders, the more frequently power strokes occur.  This is why an eight cylinder engine runs smoother than a four cylinder.

13. Engine Classification Number of cylinders. Number of strokes. Cylinder arrangement  Inline engine  V-type engine  Horizontal (opposed) boxer or pancake design

15. Engine Classification (cont.) Longitudinal – the engine is mounted parallel with the length of the vehicle. Transverse – the engine is mounted crosswise to the length of the vehicle.

18. Valves and Camshafts A traditional style of engine uses one intake and one exhaust valve per cylinder. Newer designs use two intake and two exhaust valves per cylinder.

19. Valves and Camshafts Valve opening and closing is performed by the camshaft.

20. Valves and Camshafts If the camshaft is located in the engine block, valve operation will also utilize lifters, pushrods, and rocker arms.  This arrangement is called a pushrod engine.

21. Valves and Camshafts If the camshaft is located over the valves, in the cylinder head, it is considered an overhead cam engine.  Single overhead cam (SOHC) engines utilize a common cam to operate the intake and exhaust valves per cylinder head.

22. Valves and Camshafts  Double overhead cam (DOHC) engines utilize a separate camshaft for the intake and exhaust valves per cylinder head.  Note: a v-type DOHC engine will have four camshafts per engine!  Cam Operation Cam Operation

23. Bore & Stroke The diameter of the cylinder is the bore. The distance that the piston travels within the bore between TDC and bottom dead center (BTC) is the stroke.  The longer the stroke, the greater the amount of air- fuel mixture that can be drawn into the cylinder. The greater the A/F mixture, the greater the force when the mixture is ignited.

25. Engine Displacement Displacement is generally referred to in terms of cubic inches (cu. in.) cubic centimeters (cc) or liters (l). Displacement = the volume of the cylinder x the number of cylinders. Displacement = B x B x S x 0.7854 x # cyls.

26. Engine Displacement An over-square displacement engine has a larger bore than stroke. Transversely, an under-square engine has a larger stroke than bore. Over-square displacement

27. Engine Displacement

28. If an engine is said to be ‘bored” or “bored- out” the stock engine bore has been increased. If an engine is said to be “stroked” the stock engine stroke has been increased.  This is achieved at the crankshaft Either event effectively increases the stock displacement of the engine.

30. Engine Displacement If an engine is bored larger diameter pistons must be installed. If an engine is stroked the height of the piston must be compensated for and the engine may need to be “clearanced”.  This is generally done by decreasing the length of the connecting rod …  And/or raising the wrist pin bore in the piston.

32. Compression Ratio = PV+DV+GV+CV DV+GV+CV  PV = piston volume  DV = deck clearance volume  GV = head gasket volume  CV = combustion chamber volume (pg.298)

34. The Four Stroke Cycle Video

35. Torque Torque = twisting force Torque = the amount of force multiplied by the length of the lever through which it acts. Torque is measured in foot pound (ft. lbs.) or Newton-meters (N-m).

37. Work & Power Work = the applied force x distance of movement Power = the rate of doing work  If a 550 lb. object is moved one foot in 10 seconds or 10 minutes the same amount of work is performed.  More power is exerted to move the object in ten seconds.

38. Horsepower Horsepower = the power required to move 550lbs. one foot in one second. Or 33,000lbs. one foot in one minute. Horsepower = torque x RPM / 5,252 SAE gross H.P vs. SAE net H.P. pg.58.

40. H.P. vs. Torque

41. Engine Power Video

42. Engine Aspiration If the air-fuel mixture is introduced into the cylinder solely through vacuum it is considered to be a naturally aspirated engine. Turbocharged – an exhaust driven turbine forces the A/F mixture into the engine. Supercharged – an engine driven air-pump.  Roots-type  centrifugal

43. Engine Aspiration Turbocharged – an exhaust driven turbine forces the A/F mixture into the engine. Exhaust driven

44. Engine Aspiration Supercharged – an engine driven air- pump.  Crankshaft driven