MIDTERM REVIEW Flashcards
What is velocity?
The distance traveled by a moving point in a unit of time.
Velocity = distance/time
What is acceleration?
Change in the velocity of a moving body within a unit of time
Acceleration = change in velocity/time taken
What is pressure?
Force acting on a unit of area
Pressure = force/area
What is specific gravity?
The ratio of:
the weight of a certain volume of a liquid
to the weight of an equal volume of water
What is work?
Work is done when a force is moving a body through a certain distance
Work = force X distance
What is power?
The rate at which work is performed
Power = work/time
What is horsepower?
The rate at which work is done
1 hp equals 33,000 foot – pounds of work per minute
Hp = (force x velocity) / 33,000
What is brake horsepower?
The maximum power generated by an engine at a given RPM, as determined by the engine manufacturer
What is shaft horsepower?
The power delivered along the shaft to the propeller at a given rpm
What is effective horsepower?
The power required to overcome a vessels total resistance at a given speed, not including the power required to turn the propeller or operate any machinery
(This is close to the power required to tow a vessel)
What is indicated horsepower?
Horse power of reciprocating engines, particularly in the larger sizes
It is determined from the pressure in the cylinders and is the power required to drive a ship at a given speed, including the power required to turn the propeller and to overcome any additional friction inherent in the system
What is gauge pressure?
PSIG
Pressures that are measured in respect to the pressure of atmospheric air
What is absolute pressure?
PSIA
The actual pressure exerted on the gas, obtained by adding of the barometric pressure to the gauge pressure
Absolute pressure = gauge pressure + barometric pressure
Is barometric pressure constant? What is standard barometric pressure at sea level?
Barometric pressure is not constant because it changes with altitude and weather
Standard barometric pressure at sea level is 29.92 inches of mercury, or 14.7 psia
What is kinetic energy?
The energy of movement
Some examples include: thermal energy, mechanical energy, electrical energy, and magnetic energy
What is potential energy?
Stored energy
Some examples include: chemical energy, elastic energy, nuclear energy, and gravitational energy
What is internal energy?
Energy stored within a body
It can be a gas, liquid, or solid
What is chemical energy?
Energy that is released when bonds formed in a chemical reaction, often producing heat as a byproduct
Examples include: batteries petroleum natural gas and coal are stored chemical energy
What is a British thermal unit (BTU)?
A measure of the heat content of fuels or other energy sources
The quantity of heat required to raise the temperature of 1 pound of liquid water by 1°F
1 pound of water = 1.0 BTU
1 gallon of water = 8.33 BTU
1 gallon of diesel = 137,452 BTU
What is conduction?
The transfer of energy by actual contact from one body to another
What is radiation?
Energy that is transferred through space
What is convection?
A process in which a body and the energy in it are moved from one position to another without change of state
Think of a tea kettle
What is specific heat?
The amount of heat it takes to raise 1 g of a substance by 1°C
What is a Diesel engine?
Reciprocating, compression ignition engines in which the fuel is ignited upon injection by the hot compressed charged air in the cylinder
What is the Otto cycle?
Spark ignition
Gasoline engines use spark plugs to ignite the fuel/air mixture
What kind of ignition will you find in a diesel cycle?
Compression ignition
Diesel engines use the heat of compressed air to ignite the fuel
What is an in-line diesel engine?
The in-line diesel engine is the simplest arrangement with all cylinders parallel and in line
What is a V type diesel engine?
The V-type engine, with two connecting rods attached to each crank pin, permits the entire length to be reduced by 1/2, thereby making it much more rigid
What do you call the rows of cylinders in a V type of engine?
Each row of cylinders is called a bank
A bank, B bank, etc.
What is an opposed piston engine?
two pistons and one combustion space in each cylinder.
The Pistons are arranged in opposed positions, crown to crown with the combustion space in between
What constitutes a slow speed engine?
100 to 150 RPM
propeller can be directly connected without need for reduction gear
What constitutes a medium speed engine?
300 to 1000 RPM
What constitutes a high-speed engine?
Greater than 1000 RPM
What is a four stroke engine?
Internal combustion engine that utilizes four distinct piston strokes to complete one operating cycle
What are the four strokes of a four stroke engine?
Intake
Compression
Power
Exhaust
The operating cycle of a four stroke engine requires how many revolutions of the crankshaft?
Two revolutions, or 720°
When does fuel injection start in a four stroke diesel engine?
Fuel injection starts just before the piston reaches top dead center
What is a two-stroke engine?
And internal combustion engine that utilizes two distinct piston strokes to complete one operating cycle
What are the two strokes of a two-stroke engine?
Compression and power
How many revolutions of the crankshaft are needed to complete one operating cycle of a two-stroke engine?
One revolution, or 360°
In a two-stroke engine, what events occur during the first stroke?
Compression and injection
In a two-stroke engine, what events occur during the second stroke?
Ignition and expansion/exhaust
What is a cetane number?
The rating of a diesel fuel’s quality of ignition
Actually a measure of the fuels ignition delay, or the time period between the start of injection and the start of combustion (ignition)
In general, I hire cetane fuel will have a shorter ignition delay than a lower cetane fuel
Why is a higher cetane number better?
Shorter ignition delay
More complete combustion of fuel
Quicker starting
Quieter operation, less chatter
Improved fuel efficiency
A reduction of harmful emissions
Why is a higher compression ratio better?
Higher thermal efficiency
Better fuel economy
What is thermal efficiency?
The measure of an engine’s efficiency in converting heat energy contained within the liquid fuel into mechanical energy
Efficiency of: heat into mechanical energy
What is the cylinder block?
The part of the engine frame which supports the engine cylinder liners and heads
What is a crank case?
The part of the engine frame which houses the crankshaft
What is a bedplate?
The bedplate supports the engine and ensures alignment of the shaft
The crank case provides housing for the crankshaft. In large engines, the crankcase and bedplate come in one piece
What is the entablature?
A cylinder block which incorporates the scavenge airspace and the cooling water spaces
What are tie rods?
Long, strong rods that hold the three major engine components in compression and transmit the firing load to the bed plate
The three major components being the cylinder block or entablature, the A-frame, and the crank case
What are access covers?
They permit access to internal parts and spaces within the engine for inspection and maintenance
What is an explosion cover, or safety cover, on a crank case?
Explosion covers relieve excessive pressure
What is an anti-friction bearing?
Any bearing having the capability to reduce friction effectively
What are cylinder liners?
Bores in which pistons move back-and-forth
Forms part of the combustion space
Replaceable
Wet and dry types
What are dry type liners?
Coolant circulates within passages in the engine block and does NOT come in contact with the liner
Used on small engines
What are wet type liners?
A water jacket is formed by the liner and a separate jacket fitted with an engine block or frame
Used on medium and low speed engines
What is a cylinder head?
The space at the combustion chamber top is formed and sealed by a cylinder head
The cylinder head houses the intake and exhaust valves, the fuel injection valve, etc.
What is a camshaft?
The camshaft is a shaft with eccentric projections, called cams
Designed to control the operation of valves
Provide proper firing order of the cylinders
What are the functions of the cams on a camshaft?
The shape determines the point of opening and closing, the speed of opening and closing, and the amount of valve lift
The camshaft is driven by _______.
The crankshaft
It is connected to the crankshaft most commonly by gears or a chain and sprocket
How quickly must the camshaft rotate in a four stroke engine? In a two stroke?
Four stroke: 1/2 the crankshaft speed
Two-stroke: same speed as the crankshaft
What kind of valves are used on the intake and exhaust ports?
Poppet valves
What is characteristic of a poppet valve?
They have a beveled edges and seats, giving them a self centering action
Intake valves are made of what kind of metal?
Low alloy steel, as intake valves are not subjected to hot exhaust gases
Exhaust valves are usually made of what kind of metal?
Steel alloy to resist corrosion caused by high temperature gases
What is the function of a rocker arm?
Rocker arms are part of the valve actuating mechanism
They put it on a pivot pin or shaft secured to a bracket mounted on the cylinder head
One end of a rocker arm contacts the top of the valve stem on the other end is actuated by the camshaft
What is the function of a pushrod?
In installations wear the camshaft is located below the cylinder head, the rocker arms are actuated by pushrods
One rocker arm and a bridge maybe used to open two valves simultaneously
What is the function of a cam follower?
Cam followers change the rotary motion of the camshaft to reciprocating motion this action opens the valves
Cam followers a ride to the flat of the cam
They rise and lower as the cam rotates
What is the function of the lash adjuster?
Hydraulic valve lifters
Used on some engines to avoid the necessity of a clearance otherwise needed in the valve gear to allow for expansion resulting from temperature changes
What is a piston?
A piston is one of the principal parts in the power transmitting assembly
Piston serve as the unit which transmits the force of combustion to the connecting rod
Pistons conduct the heat of combustion to the cylinder wall
What are the three functions of piston rings?
Seal the cylinder
Distribute lubricating oil on the cylinder wall
Transfer heat from the piston to the cylinder wall
What are the two general types of piston rings? What do they do?
Compression rings seal the cylinder and combustion space, preventing gases from escaping
Oil rings distribute lubricating oil on the cylinder wall to prevent metal to metal contact
What is the function of the connecting rods?
The connecting rods transmit the firing force from the piston
Together with the crankshaft, connecting rods convert the reciprocating motion of the piston to a rotary motion on the crankshaft
What is the function of the crankshaft?
The crankshaft converts the movement of the piston in and connecting rod into rotary motion
The rotary motion of the crankshaft drives reduction gears, the propeller shaft, generators and pumps
The crankshaft consists of a series of cranks or throws formed as offsets along a shaft
What is the function of a flywheel?
A flywheel stores of energy during the power events and releases it during the remaining events of the operating cycle
When the speed of the shaft tends to increase the flywheel absorbs energy
When the speed it tends to decrease the flywheel gives up energy to the shaft in an effort to keep shaft rotation uniform
It limits the increase or decrease in speed during sudden changes of load
It aids in forcing the piston through the compression event when an engine is running at low or idling speed
It also helps to bring the engine up to speed when it is been cranked
What is characteristic of a naturally aspirated engine?
The fuel/air mixture is forced into the cylinder by a vacuum
What is the Venturi effect?
Air being drawn through a narrow valve opening is accelerated.
As the passage begins to widen again vacuum occurs.
When comparing a naturally aspirated engine with a turbo charged or supercharged engine of the same displacement…
The naturally aspirated engine will generally give less power
How does a turbocharger work?
Air is forced into the combustion chamber under a greater pressure
Exhaust gases from the engine drive the supercharger, hence no power is taken from the engine’s output
Sometimes referred to as centrifugal blowers
How do superchargers work?
Air is forced into the combustion chamber under a greater pressure
Powered by the engine’s output
What are three types of superchargers?
Roots type blower
Screw type
Centripetal
What is a roots type blower?
A positive displacement air pump
The compression process is external to the blower
As the volume of air present in the intake manifold increases, the air pressure increases accordingly
What is a screw type supercharger?
Relies on internal compression
Operates by pulling air through a pair of meshing lobes that resemble a set of worm gears
Air is trapped in pockets created by the lobes. As air pockets decrease in size, air moves from the fill side to the discharge side. Air pockets shrink and the air is squeezed into a smaller space
What is a centrifugal type supercharger?
Similar in nature to a turbo charger, however, the centrifugal type supercharger is mechanically driven by the engine crankshaft rather than exhaust gases
What are three types of air intake systems?
Dry type
Viscous type
Oil bath type
What about silencers?
Silencers are generally constructed as part of the air cleaning components, preventing a high-pitched whistle
What are the characteristics of a dry type cleaner and silencer?
Intake air is drawn through a fine mesh or screen which filters the air
What are the characteristics of a viscous type cleaner and silencer?
Intake air is drawn through a fine mesh or screen which filters the air
The mesh is wet, usually with a medium weight oil
What are the characteristics of oil bath type air filters?
Incoming air is forced or vertically down toward oil reservoir
Once the air reaches the oil it changes direction rapidly and is then forced back up to the engines intake system
The sluggish dirt particles cannot change direction as quickly and end up being trapped in the oil reservoir
What is an intake manifold?
A passage through which air travels to reach the valves and combustion space of an engine
In two-stroke engines, the passages that conducts intake air to the cylinders are generally referred to as an _______.
Air box.
An airbox does what?
Surrounds the cylinders, is usually built into the block.
The passage that contacts intake air to the cylinders in two stroke engines
The scavenging air passages in a Fairbanks Morse opposed piston engine are referred to as the _____.
Air receiver
What is the single most common problem accelerating air system wear and failure?
Dust ingestion!
What are some of the results of dust ingestion in an air system?
Accelerated abrasive where of piston rings and liners
Often caused by inlet leaks around flexible joints
May also be caused by defective or damaged air filters
Poor maintenance practices
What are some other causes of air system wear and failure?
Plugged air filters
Turbo charger failures
Coolant to air leaks in the aftercooler
Hydraulic lock
How does temperature affect air density?
Excessive temperatures lead to reduce air density and higher combustion temperatures
This can negatively affect torque, power and emissions
What is the function of the heat exchanger?
To reduce the temperature of the charge air, cooling the air as it leaves the compressor
What are three names for a heat exchanger?
Charge air cooler
Intercooler
After cooler
What is the function of the exhaust system?
To carry away gases from the cylinders of an engine
muffle exhaustion noise
quench sparks
Remove solid material from exhaust gases
Furnish energy to a turbine driven supercharger
What is the function of an exhaust manifold?
When the gases of combustion air force from the cylinders, they enter the exhaust manifold
What is an open cooling system?
In an open system, the engine is cooled directly by seawater
Not used on most Marine Diesel engines
What is a closed cooling system?
A closed cooling system is a freshwater circuit system that is self-contained and used continuously for the cooling of the engine
The cooling of a diesel engine is accomplished by the use of either a heat exchanger, Keel cooler, or radiator and fan
What component is responsible for the cooling of an internal combustion engine? What are the four types?
Heat exchanger:
Keel coolers
Radiators and fans
Tube and shell type
Plate type
