Engine Construction and Cycles Flashcards
(15 cards)
Describe the function of the Bedplate
- To support and give rigidity to the rest of the engine
- Also ensuring good alignment by connecting the engine to the ships hull.
Describe the function of Tie Rods
- Secures main components such as the cylinder block and bedplate with the use of compression.
- Which then distributes the stress and loads from the combustion ensuring proper alignment.
Describe the function of the Holding Down Bolts
- These bolts secure the engine to the bedplate which prevents any movement
- While also allowing for proper alignment.
Describe the function of the Crankshaft
- Converts the reciprocating movement of the pistons into rotational motion which drives the propeller.
Explain constructional differences between 2 stroke and 4 stroke?
(with respect to the connection between the piston and the crankshaft)
- 2 Stroke possess a crosshead and piston rod between piston and crankshaft, while a 4 stroke connects the connecting rod to the piston directly via a gudgeon pin.
- 2 stroke engines also have scavenge ports rather than exhaust valves which also ensures a 4 stroke doesn’t possess a scavenge space either.
- 4 stroke engine possess and intake and an exhaust valve which means the 4 stroke must have rocker arms as they operate both valves. this means that the 2 stroke does not have rocker arms as it only has 1 intake and no exhaust valve.
- 4 stroke engines do not posses either a stuffing box or diaphragm as the 4 stroke lacks necessary components to make them useful.
Describe the function of the Diaphragm
- Isolates the lower part of the cylinder and scavenge space from the crankcase.
- Prevents contamination by stopping oil from entering the scavenge space.
- The piston rod can pass through the diaphragm and is able to do so with the use of a stuffing box
Describe the function of the Stuffing Box
- The stuffing box creates a seal allowing the piston rod to pass through the diaphragm freely without contamination
- Prevents oil ingress into the scavenge space and air from leaking into the crankcase
State the purpose of the camshaft
- The camshaft is used to operate the timing of valves and fuel pumps which control the engines cycles.
- The profile and shape for each cam is designed to give the correct timing, speed and height of lift to its corresponding follower.
State 2 methods of driving a camshaft
- Chain Drive
- Gear Drive
State the speed of the Camshaft relative to the Crankshaft
4 Stroke = 2 to 1
2 Stroke = 1 to 1
State 2 differences between Trunk Type and a Crosshead Type engine
- Crosshead type possess crosshead and piston rod while the trunk type does not
- Crosshead type needs tie rods to hold the engine together as it is made of separate parts while the trunk type is an entablature
Describe with the aid of sketches, the operating principle of the 2 Stroke Cycle diesel engine
INCLUDES SKETCH
Compression Stroke - As the piston moves up, fuel is injected and ignited by the heat of the compression.
Power Stroke - After ignition, combustion forces the piston downward, the exhaust gases then exit as fresh air enters.
Describe with the aid of sketches, the combustion process of the two-stroke compression ignition engine
INCLUDES SKETCH
Compression Stroke - As the piston moves up, fuel is injected and ignited by the heat of the compression.
Power Stroke - After ignition, combustion forces the piston downward, the exhaust gases then exit as fresh air enters.
Describe with the aid of sketches, the operating principle of the 2 stroke cycle diesel engine
INCLUDES SKETCH
Compression Stroke - As the piston moves up, fuel is injected and ignited by the heat of the compression.
Power Stroke - After ignition, combustion forces the piston downward, the exhaust gases then exit as fresh air enters.
Describe with the aid of a sketch, the operation of a 4 stroke cycle diesel engine
INCLUDES SKETCH
- Intake Stroke - Piston moves downward which draws fresh air into the cylinder through the intake valve.
- Compression Stroke - Piston moves upward which compresses the air, increasing pressure and temperature.
- Power Stroke - Near TDC, fuel is injected into the compressed air which causes combustion. This combustion forces the piston downward towards the BDC.
- Exhaust Stroke - Piston then moves upward allowing combustion gases to exit the cylinder through the exhaust valve.
