Gasoline Engines

1. Gasoline Engines Operation

2. 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.

3. Energy and Power • 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.

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

5. 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

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

7. Four-Stroke Cycle Engines • 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

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

10. 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

11. 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.

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

14. 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.

17. 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.

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

19. 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.

20. 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.

21. 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

22. 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.

24. 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.

25. 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

26. Engine Displacement

27. Engine Displacement • 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.

29. 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.

31. 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)

33. The Four Stroke Cycle Video

34. 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).

36. 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.

37. 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.

39. H.P. vs. Torque

40. Engine Power Video

41. 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

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

43. Engine Aspiration • Supercharged – an engine driven air-pump. • Crankshaft driven