INTERNAL COMBUSTION ENGINES
Again, the study reference is CHAPMAN’S and the
AUXILIARY study guide.
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”
1. Uses SPARK IGNITION SYSTEM”
2. Called a “SPARK IGNITION ENGINE”.
3. Fuel and air mixed in a carburetor – ( Injection chamber if fuel
4. Fuel drawn into cylinders.
5. Fuel/air mixture ignited by electric spark from sparkplug(s).
1. Engine takes atmospheric air and compresses it in cylinder
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
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.
FOUR 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
1. Intake valve open.
2. Exhaust valve closed.
3. PISTON: Moving DOWN.
4. FUEL/AIR MIXTURE: Drawn IN through intake valve.
1. Both INTAKE and EXHAUST valves CLOSED.
2. PISTON moving UP.
3. Fuel/air mixture is COMPRESSED.
4. Ignition Spark and Compression heating ignites
1. INTAKE and EXHAUST valves are CLOSED
2. PISTON moving DOWN
3. CRANKSHAFT TURNS.
4. POWER stroke only time power is translated to
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.
1. DIESEL ENGINES ARE MOSTLY TWO STROKE
2. GASOLINE ENGINES MOSTLY LIMITED TO
3. HAS ONE COMPRESSION AND ONE POWER
TWO 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 SYSTEMS
UNIT 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
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
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
Includes the CYLINDERS, PISTONS, CONNECTING
RODS AND CRANKSHAFT
CYLINDERS – 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.
VALVE 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
1. 4-STROKE (Cycle): Air enters INTAKE VALVE.
2. 2-Stroke (Cycle): Air enters PORTS in cylinder wall.
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
WATER 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.
1. GENERATOR/ALTERNATOR: Produces the electrical current
to operate the vessel’s system and charge the battery.
2. VOLTAGE REGULATOR: Controls the voltage from the
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
5. Battery: Diesels require TWICE the power of gas engines.
6. Wiring harness: Carries the electrical current.
1. Ignition COIL
2. Mechanical Breaker
5. Spark Plug(s)
IGNITION SYSTEM COMPONENTS
1. IGNITION COIL: The generated power source (FOR THE SPARK IN
THE SPARK PLUG)
2. MECHANICAL BREAKER(POINTS): Break the current at
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
2. Ignition switch
3. Ignition coil (Low side)
4. Breaker points ( in distributor)
SECONDARY IGNITION CIRCUIT
1. DISTRIBUTOR (ROTOR)
2. IGNITION COIL (HIGH SIDE)
3. SPARK PLUGS
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
d. the number of valves used for exhaust determine the
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. 3
3. 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
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 _________
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
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
c. breaker points
d. ignition coil
END CHAPTER 3