CHAPTER 3INTERNAL COMBUSTION ENGINES

Again, the study reference is CHAPMAN’S and the AUXILIARY study guide.

INTERNAL COMBUSTION ENGINES

DEFINITION: BOTH DIESEL AND GAS; CHANGE OR CONVERT HEAT ENERGY INTO WORK BY BURNING FUEL IN A CLOSED COMBUSTION CHAMBER. THE PISTONS USE AN UP-AND-DOWN MOTION. THUS, THEY ARE CLASSIFIED AS “RECIPROCATING” ENGINES.

IGNITION PRINCIPLESGASOLINE ENGINES

1. Uses SPARK IGNITION SYSTEM”

2. Called a “SPARK IGNITION ENGINE”.

3. Fuel and air mixed in a carburetor – ( Injection chamber if fuel injected).

4. Fuel drawn into cylinders.

5. Fuel/air mixture ignited by electric spark from sparkplug(s).

IGNITION PRINCIPLESDIESEL ENGINES

1. Engine takes atmospheric air and compresses it in cylinder head.

2. Injects fuel into combustion space ( cylinder head)

3. Fuel injectors. NO carburetors

4. Require extremely CLEAN fuel to properly ignite

5. Compression heating ignites fuel

6. NO SPARK PLUGS

OPERATING CYCLE

1. All reciprocating engines have definite operating cycle

2. Either 2-Stroke or 4-Stroke

3. STROKE: Up or Down movement of piston

4. Each PISTON completes 2 strokes for each revolution of the crankshaft.

OPERATING CYCLEFOUR STROKE (CYCLE)

1. Each piston goes through 4-strokes

2. Crankshaft has 2 revolutions / one cycle

3. One power stroke per 2 revolutions of crank shaft

THE OPERATING CYCLE 4-STROKES

1. INTAKE

2. COMPRESSION

3. POWER

4. EXHAUST

OPERATING CYCLEINTAKE STROKE

1. Intake valve open.

2. Exhaust valve closed.

3. PISTON: Moving DOWN.

4. FUEL/AIR MIXTURE: Drawn IN through intake valve.

OPERATING CYCLECOMPRESSION STROKE

1. Both INTAKE and EXHAUST valves CLOSED.

2. PISTON moving UP.

3. Fuel/air mixture is COMPRESSED.

4. Ignition Spark and Compression heating ignites mixture.

OPERATING CYCLEPOWER STROKE

1. INTAKE and EXHAUST valves are CLOSED

2. PISTON moving DOWN

3. CRANKSHAFT TURNS.

4. POWER stroke only time power is translated to crankshaft.

OPERATING CYCLEEXHAUST STROKE

1. EXHAUST valve OPEN

2. INTAKE valve CLOSED

3. PISTON moving UP

THIS ENDS THE 4-STROKE CYCLE

The piston immediately starts down again and the cycle process starts over.

OPERATING CYCLETWO STROKE

1. DIESEL ENGINES ARE MOSTLY TWO STROKE

2. GASOLINE ENGINES MOSTLY LIMITED TO OUTBOARDS

3. HAS ONE COMPRESSION AND ONE POWER STROKE

OPERATING CYCLETWO STROKE (DIESEL)

1. ONE power stroke for each revolution of the crankshaft

2. TWICE as many power strokes as in the four-stroke engine.

3. Cylinder has exhaust valve but NO INTAKE VALVE.

4. Air comes in through PORTS in cylinder wall

5. 2-STROKE DIESELS GIVE EXCELLENT SERVICE

FUEL INJECTION SYSTEMSUNIT INJECTOR and COMMON RAIL

1. UNIT INJECTOR: Cylinder and plunger in cylinder head, sprays or squirts fuel into combustion chamber, for ignition. Fuel is INDUCTED from fuel tank to fuel injectors under pressure from a pump.

2. COMMON RAIL: Most commonly used. One pump for all cylinders. Fuel under pressure from tank to cylinder.

DRAWBACKS: System must be purged of all air until only fuel comes out. Time consuming, awkward and messy.

CARBURETOR

1. A device used to send a fine spray of fuel into a moving stream of air through the intake valves into the combustion chamber in the cylinder head of the engine.

2. On gasoline engines, used to control the fuel/air mixture.

OPERATING CYCLECOMPRESSION RATIOS

1. With compression ratio in diesel of 14:1, cylinder head temperature ~ 1000ºF. This heat ignites the fuel mixture without the spark plug ignition.

2. Diesel compression ration are close to 14: 1 to 16: 1

3. Gas compression ratios are close to 4: 1` to 8: 1

POWER SYSTEMIncludes the CYLINDERS, PISTONS, CONNECTING

RODS AND CRANKSHAFT

POWER SYSTEMCYLINDERS – PISTONS - CRANKSHAFTS

1. PISTONS: Move up and down in the cylinder; attached to the crankshaft and transmits power to the crankshaft .

2. CYLINDERS: Cast in a single engine block with a hardened sleeve alloy sleeve to reduce wear.

3. CRANKSHAFT: Changes the reciprocating motion of the piston and rods into rotary motion of the crankshaft which turns the propeller.

POWER SYSTEMVALVE and CAMSHAFT

1. VALVES: Opened by a CAMSHAFT which is driven by a CRANKSHAFT.

2. Let fresh air in. Allow combustion gasses to vacate.

3. CAMSHAFT: Changes rotary to intermittent reciprocating motion.

POWER SYSTEMAIR

1. 4-STROKE (Cycle): Air enters INTAKE VALVE.

2. 2-Stroke (Cycle): Air enters PORTS in cylinder wall.

POWER SYSTEMLUBRICATION

VITAL TO THE HEALTH OF THE ENGINE

1. Delivers oil to moving parts to assist in engine cooling and reducing friction.

2. Uses a PUMP and FILTER to cleanse and deliver

COOLING SYSTEMWATER and AIR

1. WATER: Holding tank, circulating pump and radiator to get rid of the heat in the water.

2. Both SEA and FRESH water are used.

3. FRESH water used with self-contained system.

4. SEA water straight from the environment.

ELECTRICAL SYSTEMS1. GENERATOR/ALTERNATOR: Produces the electrical current

to operate the vessel’s system and charge the battery.

2. VOLTAGE REGULATOR: Controls the voltage from the generator/alternator

3. CUT OUT: Keeps the battery from discharging through the alternator/generator at low speeds.

4. STARTER: An electric motor. Diesel may have separate starter motor.

5. Battery: Diesels require TWICE the power of gas engines.

6. Wiring harness: Carries the electrical current.

IGNITION SYSTEM(S)

1. Ignition COIL

2. Mechanical Breaker

3. Condenser

4. Distributor

5. Spark Plug(s)

6. Switch

7. Wiring

IGNITION SYSTEM COMPONENTS1. IGNITION COIL: The generated power source (FOR THE SPARK IN

THE SPARK PLUG)

2. MECHANICAL BREAKER(POINTS): Break the current at proper time

3. CONDENSER: Prevents “arcing” when the points are open.

4. DISTRIBUTOR: Serves as a “selector switch” to distribute the current to the individual spark plugs (gas engine only)

5. SPARK PLUG(S): ( Gasoline engines only)Provided the “fire” to ignite the fuel in the combustion chamber. (Spark comes from the COIL, NOT the battery)

PRIMARY IGNITION CIRCUIT(LOW VOLTAGE)

GASOLINE ENGINE

1. Battery

2. Ignition switch

3. Ignition coil (Low side)

4. Breaker points ( in distributor)

5. condenser

SECONDARY IGNITION CIRCUIT(HIGH VOLTAGE)

GASOLINE ENGINE

1. DISTRIBUTOR (ROTOR)

2. IGNITION COIL (HIGH SIDE)

3. SPARK PLUGS

TROUBLE SHOOTING

GAS ENGINES REQUIRE:

1. CORRECT FUEL-AIR MIXTURE

2. GOOD COMPRESSION

3. GOOD SPARK

DIESEL ENGINES REQUIRE:

1. CORRECT FUEL PRESSURE

2. HIGH COMPRESSION

3. NO AIR IN FUEL LINE(S)

REVIEW QUESTIONS NO.1

1. All reciprocating engines have a definite cycle of operation and __________________

a. operate on either a 2-stroke or 4-stroke cycle.

b. the number of cycles depends on the number of cylinders.

c. the 2-stroke cycle is used only in diesel engines since 4-stroke cycle is required for proper function of a gasoline engine.

d. the number of valves used for exhaust determine the operating cycle.

REVIEW QUESTIONS NO. 2

2. The cam shaft_____________________

a. drives the propeller.

b. carries cams that are usually square in shape.

c. is used to rotate the cams that open the valves.

d. changes reciprocating motion to rotary motion .

REVIEW QUESTIONS NO. 33. Diesel engines have high compression ratios, in the range of 16:1 to 20:1, in order to_________

a. easily exhaust heavy diesel fuel.

b. provide maximum power in the intake stroke.

c. compress air to generate heat for fuel ignition.

d. assist the entrance of fuel from the carburetor.

REVIEW QUESTIONS NO. 4

4. A 2-stroke engine______________

a. has a compression and a power stroke.

b. is only used in diesel engines

c. has twice the power in very large gasoline engines

d. is so designated because there is a cycle of 2-strokes between the opening and closing of the exhaust valves

of each cylinder.

REVIEW QUESTIONS NO. 5

5. In a diesel engine, fuel__________________

a. is injected directly into the cylinder or combustion chamber

b. is mixed with air, then injected into the cylinder

c. is also used for lubrication

d. consumption is constant at all speeds

REVIEW QUESTIONS NO. 6

6. In a gasoline engine the fuel-air mixture ratio is controlled by the _________

a. throttle

b. carburetor

c. intake valve

d. fuel pump

REVIEW QUESTIONS NO. 7

7. Lubricating oil in engines_______

a. is used for ignition and for friction reduction

b. is used only to lubricate the bearings and bushings

c. is always under constant pressure

d. is used to reduce friction and increase cooling.

REVIEW QUESTIONS NO. 8

8. Which of the following groups of items are common to both diesel and 4-cycle gasoline engines?

a. valves, carburetor and fuel pumps

b. valves, pistons and spark plugs

c. valves, cylinders and fuel pumps

d. valves, distributor and carburetor

REVIEW QUESTIONS NO. 9

9. The primary circuit of the ignition system for gasoline engines includes the ________

a. distributor and breaker points

b. battery and spark plugs

c. ignition coil and breaker points

d. ignition coil and distributor

REVIEW QUESTIONS NO. 10

10. The high voltage that produces the spark in the spark plug in a gasoline engine is produced in the _____________________

a. battery

b. condenser

c. breaker points

d. ignition coil

END CHAPTER 3