1 ERT 353 ENERGY POWER Internal combustion engines

1 ERT 353: ENERGY & POWER Internal combustion engines

2 INTRODUCTION Spark-Ignition Engines • Two strokes engine • Four strokes engine • Otto cycle • Bore, Stroke, Compression ratio, knocks • Rotary engine Compression-Ignition Engines • Diesel engine

3 ENGINE’S COMPONENTS PISTON • A movable part fitted into a cylinder, which can transmit power. • Through connecting rod, forces the crank shaft to rotate.

4 ENGINE’S COMPONENTS • Connecting rod attaches piston (wrist-pin) to the crank shaft (connecting rod caps).

5 ENGINE’S COMPONENTS • Valves: Minimum two valves per cylinder • Exhaust Valve lets the exhaust gases escape the combustion chamber. (Diameter is smaller then Intake valve) • Intake Valve lets the air or air fuel mixture to enter the combustion chamber.

6 ENGINE’S COMPONENTS • Car ignitions use spark plugs to bridge electricity across a gap, kind of like a lightning bolt. The voltage at a spark plug is normally somewhere in the range of 40, 000 to 100, 000 volts. • The cars that have high-performance engines, they generate more heat which better off with colder plugs. If the spark plug were to get too hot, it would ignite the fuel before the spark even fired

7 ENGINE’S COMPONENTS • Cylinder head that covers and encloses the cylinders. • Engine block is a foundation of the engine and contains pistons, crank shaft, cylinders, timing sprockets and others. Cylinder head Engine block

8 ENGINE’S COMPONENTS • Crank shaft converts up and down motion into circular motion and transmits the power to transmission.

9 TWO-STROKE ENGINE • A two-stroke engine is a type of internal combustion engine which completes a power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. • In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.

10 TWO STROKE ENGINE

11 FOUR-STROKE ENGINE Stroke-1: Intake of gas-air mixture from the carburetor • Engine pulls piston out of cylinder • Low pressure in cylinder • Atmospheric pressure pushes fuel air mixture into cylinder • Engine does work on gases during this stroke

12 FOUR-STROKE ENGINE Stroke-2: Compression of the air-gas mixture • Engine pushes piston into cylinder • High pressure and temperature in cylinder • Engine does work on gases during this stroke

13 FOUR-STROKE ENGINE Stroke-3: Ignition and Expansion of the air-gas mixture • Mixture burns to form hot gases • Gases push piston out of cylinder • As gas expands, pressure and temperature is lowered

14 FOUR-STROKE ENGINE Stroke-4: Exhaust of waste gas • Engine pushes piston back into cylinder • Pressure inside pushes burnt gas out of cylinder • As gas expands, pressure and temperature is lowered • Engine does work on gas during this stroke

15 FOUR-STROKE ENGINE Spark plug for SI engine Fuel injector for CI engine Valve Clearance volume Top Dead Center (TDC) Stroke TDC 0 o Bottom Dead Center (BDC) q 270 o 90 o 180 o BDC Crank shaft Valve Cylinder wall Piston

16 FOUR-STROKE ENGINE IVO - intake valve opens, IVC – intake valve closes, EVO – exhaust valve opens, EVC – exhaust valve opens, Xb – burned gas mole fraction

17 PISTONS ARRANGEMENTS Inline Engine V-shape engine Flat engine Ever heard of; V 6 engine, SOHC, DOHC, 24 -valves, VTEC, VVT, and others ?

18 FOUR STROKE ENGINE

ADVANTAGES & DISADVANTAGES OF 2 -STROKE OVER 4 -STROKE ENGINES 19 • Advantages • A two stroke cycle engine has twice the number of power strokes than the four stroke cycle engine at the same engine speed. • For the same power developed, a two stroke cycle engine is lighter, less bulky and occupies less floor area. • The initial cost of a two stroke cycle engine is considerably less than a four stroke cycle engine • The weight of the two stroke engine is less than four stroke cycle engine because of the lighter flywheel due to more uniform torque on the crankshaft. • Since there are only two strokes in a cycle, the work required to overcome the friction and the exhaust strokes is saved. • Since there are no mechanical valves and the valve gears, the construction of two stroke engine is simple which reduces its initial cost. • A two stroke engine occupies less space. • A lighter foundation will be sufficient for two stroke engine. • A two stroke engine has less maintenance cost since it requires only few parts

ADVANTAGES & DISADVANTAGES OF 2 -STROKE OVER 4 -STROKE ENGINES • Disadvantages • Thermal efficiency of a two stroke cycle engine is less than that a four stroke cycle engine • Overall efficiency of a two stroke cycle engine is also less than that of four stroke cycle engine. • The consumption of lubricating oil is large in a two stroke cycle engine because of high operating temperature 20

21 DIESEL ENGINE Obvious differences between diesel engine and a four-stroke gasoline engine are: • No sparkplug on Diesel engine. • Has a higher compression ratio. (14: 1 to 25: 1) • Better fuel consumption.

22 DIESEL ENGINE Intake Stroke: • Piston moves from TDC to BDC creating vacuum in the cylinder • Intake valve opens allowing only air to enter the cylinder and exhaust valve remains closed

23 DIESEL ENGINE Compression Stroke • Both valves stay closed • Piston moves from BDC to TDC, compressing air to 22: 1 • Compressing the air to this extent increases the temperature inside the cylinder to above 1000 degree F.

24 DIESEL ENGINE Power Stroke • Both valves stay closed • When the piston is at the end of compression stroke(TDC) the injector sprays a mist of diesel fuel into the cylinder. • When hot air mixes with diesel fuel an explosion takes place in the cylinder. • Expanding gases push the piston from TDC to BDC

25 DIESEL ENGINE Exhaust Stroke • Piston moves from BDC to TDC • Exhaust valve opens and the exhaust gases escape • Intake valve remains closed

OTHER DIFFERENCES BETWEEN SPARK IGNITION (SI) & COMPRESSION IGNITION (CI) ENGINES 26

ROTARY ENGINE 27

28 TUTORIAL #1

29 TUTORIAL #1

30 TUTORIAL #1

31 TUTORIAL #1

32 FIND ASSIGNMENT 1 IN PORTAL • Submission • • • Individual Hard Copy After class finish - next week (18/9/2019) Internet Plagiarism 0 Marks Buddy Plagiarism 0 Marks.