Marine Engineering Flashcards
Continuous crankshaft diagram 4 stroke
Crankshaft diagram of 4 stroke
2 stroke scavenging
2 stroke:
Combustion air must be supplied under pressure
2 stroke crankshaft diagram
crosshead vs trunk piston
dry vs wet cylinder liner
Piston: parts
crankshaft to connecting rod to piston
crankcase
cylinder head
in-/outlet valves
(cross section / parts)
valve controls
valve control with pushrod
cam profile: overlap
cam profile plotted horizontally
valve clearance
too small: thermal overload
too big: mechanical overload
different ways to drive camshaft
Mechanical injector:
buildup
Injector includes nozzle, which houses the needle
Fuel pressure (150-200 bar) exerted on needle in the high pressure chamber lifts the needle against the spring load
Nozzle types
- Pintle type nozzle (mostly for indirect injection)
- Multi hole nozzle (mostly direct injection)
a very small amount of fuel leaks along the pressure pin (2) to lubricate it.
Different ways of injecting
Fuel pumps:
Types
Regulation of pressure, amount, timing :
- Mechanically
1.1 Jerk / Reciprocating plunger pump
1.2 Rotary plunger pump - Electrically
Jerk type fuel pump
Amount of fuel is determined by radial position of plunger (helix); the stroke is always constant
If vertical groove is in front of spill port then no pressure buildup
Injection
Principles, delays, etc
Movement of plunger from lowest position to beginning the delivery stroke is called press delay
Injection timing is determined by position of pump camshaft vs crankshaft. Injection amount is controlled through radial position of the plunger
=> the longer the plunger stroke before the helix opens the spill port, the more fuel is pumped
Although incompressible, it takes the pressure increase (a microsecond) to open the fuel injector: injection delay
The delivery valve in the fuel pump causes the pressure in the fuel line and injector to fall abruptly at the end of each delivery stroke
Fuel system
Schematic
Lubrication:
Functions
- Lubrication: separating parts to not come into contact for e.g. metal/metal contact. (vgl: Aquaplaning)
- Removal of combustion residues
- Heat dissipation
Bearing types
- Ball bearing
- Roller bearings, 1+x l/d (higher radial load bearing - but worse wit axial axial load bearing and capacity deteriorating if inner/outer races misaligned)
including- spherical roller bearing (stronger axial forces)
- needle bearings (4x)
Good lubrication:
prerequisites
- sufficient volume of luboil
- of correct quality and viscosity
- sufficient shaft rotational speed to form the wedge (aquaplaning)
Types of water cooling systems
- Open / Direct cooling water system
-
Closed cooling water systems
2.1 Keel or skin cooling
2.2 Indirect cooling
Open / Direct cooling systems:
Disadvantages
- Cooling water temperature not adjustable
- Overboard cooling water not clean
- Sediments in the water
- Oxygen in cooling water leads to corrosion
Closed cooling water systems:
Principles
- Require expansion / header tank
- more expensive (extra cooling pump, heat exchanger, etc)
- requires thermostatic valve
Ignition delays engine
- press delay
- injection delay
- combustion delay
What is a governor
RPM maintainer, based on centrifugal equilibrium
Drive train
Flexible coupling
Purpose
Absorb small movements, vibrations, and misalignments of the engine relative to the propeller shaft
Gearbox
Function
To couple/uncouple the propeller shaft to/from the engine, reverse the direction of rotation of the propeller shaft, and possibly reduce RPM
Thrust bearing
Function
Purpose: transfer the propeller thrust to the hull of the ship
Trust bearings of smaller vessels: spherical = tapered bearings
Propeller shaft seals:
Purpose and types
Purpose: prevent outboard water from entering the ship along the propeller shaft
Types:
1. Stern tube seal (= lip seal)
2. Shaft seal (=mechanical seal)
3. Stuffing box
Sterntube seal
= lip ring seal
Shaft seal
= mechanical seal
Stuffing box seal
packing Glen; Glencore; … under a lantern 😬
Pumps:
Categories
- Impulse Pumps : in-/output openly connected, some kind of circular movement in the pump (high volume; low pressure; no overpressure)
- Positive Displacement Pumps: increasing /decreasing the size of a chamber in the pump move the medium (small flows/volumes; high pressure)
Pumps:
Types and symbols
Centrifugal pump
Buildup
Discharge pressure limited
Not self priming
Pumps
Axial-flow; Side Channel
Piston Pump
Diaphragm pump
Flexible impeller pump
Cooling water pump
Not an impulse pp because flexible impellers change chamber size
Flexible impeller pump
Operation
Eccentric worm-driven pump
For OWS
Valves
Symbols
Valves
Photos
OWS
With eccentric worm driven pump
Rudder forces
Rudder force K made up of
Steering force S
Breaking force R
Battery safety
During chargin/(excessive) discharging: Oxyhydrogen
Regulations:
* no other wiring allowed in battery compartment
* good ventilation
* not excessively hot/cold
* batteries placed on cabinets
* smoking/open fire prohibited
* compartment not in crew accomodation
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