Engines - Fundamentals Flashcards
What must be done to make a gas starting motor safe on an engine?
lock and tag the valves
True or false:
The gas used for pneumatic start motors or air injection start systems can be either compressed air or natural gas.
true
How should the battery be made safe when working on an engine?
remove the negative lead (first) to prevent arcing
What should be done to prevent rotation in engines that have had the flywheel removed or that have no provisions for locking?
block the engine under the throws of the crankshaft
Why is it a good idea to inspect all gaskets that come out of an engine that is being worked on?
they can provide clues to issues
What should be located on a scaffolding system before any personnel can use it?
an inspection tag;
this indicates that the scaffolding has been inspected and is ready for service
Why should one never point compressed air towards themselves?
injection injury;
compressed air can penetrate skin, causing death
What steps must be completed before any work on an engine can start?
disconnect electrical, close, lock, tag and purge all gas sources used for starting and operation
How should natural gas engines be shut down to prevent restarting?
the gas supply should be shut off, and the engine allowed to run out of gas
What special precautions must be taken when working on engines with magneto ignition systems?
they create their own spark without the need of a battery;
can cause a fire if the fuel system is not properly isolated vented
*usually seen with natural gas engines
Why type of engines have porting on the cylinders?
two-stroke engines
In an engine, the camshaft turns at _________ the speed of the crank.
1/2
This engine component seals and confines the expanding gas, along with housing the combustion chamber, valves, valve ports, valve guides, valve springs and rocker arms.
the cylinder head
This engine component is the main structure of the engine that supports all the working parts to keep them aligned.
the block or frame
This engine component is a hollow tube in which the piston slides up and down to harness the expansion of burning gases.
the cylinders
In an engine, the _______________ can be removable, non-removable or cast into the block or bolted to the block.
cylinders
This engine component forms the movable end of the combustion chamber, and transmits the power from the expansion of the burning gas into linear motion.
the pistons and rings
This engine component helps to seal the burning gases to harness as much energy as possible, while also controlling oil consumption and transfer heat from the pistons to the engine block.
the piston rings
This engine component is the link between the piston pin and the crankshaft.
the con-rod
What is the wrist pin of an engine also known as?
the piston pin
True or false:
The con-rod in an engine must be strong enough to absorb the force of the piston without flexing.
true
This engine component changes the linear motion of the piston to continuous usable rotary motion.
the crankshaft
This engine component connects the flywheel and balancer to form one rotating mass.
the crankshaft
This engine component opens and closes the intake and exhaust valves.
the camshaft
The lobes of the camshaft push on the ______________, which push on the pushrods and rocker arms.
lifters / cam followers / tappets
In an engine cylinder, the ___________ ____________ (2 words) change the direction of motion in order to open the valves.
rocker arms
This engine component stores energy and smooths the power pulses from the pistons.
the flywheel
In an engine, the ________________ (lighter/heavier) the flywheel, the smoother the engine runs.
heavier;
the greater the mass, the greater the pulsation dampening effect it has
This engine component is an easily replaceable part the reduces the possibility of damage to more expensive parts, such as the crankshaft and camshafts.
bearings
This engine component is used to reduce crankshaft torsional vibration.
the balancer
When referring to engine components, harmonic balancers, vibration dampeners, or torsional vibration dampeners are all referring to which component?
the balancer
The purpose of this engine component is to link the crankshaft, balance shafts, ignition system, and other accessories so that all the events in the engine occur at the correct time.
timing gears
When it comes to engines, what does the abbreviation BTDC stand for?
before top dead centre
When it comes to engines, what does the abbreviation ATDC stand for?
after top dead centre
With an engine, when the piston is at TDC, what position would the corresponding crankshaft throw be in?
also TDC;
they will be in the same positions (TDC = TDC, BDC = BDC, etc.)
When it comes to engines, what does the abbreviation ABDC stand for?
after bottom dead centre
When it comes to engines, what does the abbreviation BBDC stand for?
before bottom dead centre
When it comes to engines, what does the abbreviation CR stand for?
compression ratio
When it comes to engines, what does the abbreviation CI stand for?
compression ignition (diesel)
When it comes to engines, what does the abbreviation SI stand for?
spark ignition (gas)
When it comes to engines, what does the abbreviation A/F ratio stand for?
air to fuel ratio
When it comes to engines, what does the abbreviation OHV stand for?
overhead valves
When it comes to engines, what does the abbreviation OHC stand for?
overhead cam
When it comes to engines, what does the abbreviation EGR stand for?
exhaust gas recirculation
When it comes to engines, what does the abbreviation ft-lb stand for?
foot-pound
*this is a unit of work done, not torque (lb-ft)
What is the difference between ft-lb and lb-ft?
lb-ft (pound feet) → torque
ft-lb (foot pound) → work done
When it comes to engines, what does the abbreviation NOx stand for?
oxides of nitrogen
A(n) ______________ is a mechanical device that converts the chemical energy stored in a fuel to heat and then to mechanical energy.
engine
A(n) ______________ is a mechanical device that converts fluid or electrical energy into mechanical energy.
motor
______________ is the action of one body on another, tending to change the state of motion of the body acted upon.
force
1 kgf = __________ lbf = ________ N
1 kgf = 2.2 lbf = 9.8N
_________________ is an applied force causing the movement of an object.
work
What formula can be used to calculate work, if force and distance are known?
work = force x distance
1 J = _______ Nm = _________ ft-lb
1 J = 1 Nm = 0.7376 ft-lb
True or false:
Work must have a distance component.
true
______________ is twisting force acting at a radius that produces a turning moment.
torque
What formula can be used to calculate torque if force and distance are known?
T = F x D
T = torque (Nm, in-lb, ft-lb)
F = force (N, lb)
D = distance/radius (cm, m, in, ft)
The torque produced by an engine is dependant on the break mean effective pressure (BMEP). What is this?
the average pressure acting on the piston crown during the power stroke
What two things dictate the torque produced by an engine?
- BMEP
- engine displacement
What three things dictate the displacement of an engine?
- bore
- stroke
- number of cylinders
When it comes to engines, what does the abbreviation BMEP stand for?
break mean effective pressure
*this is the average pressure acting on the piston crown during he power stroke of the engine
_________________ is the rate at which work is being done.
power
What are the four different types of horsepower used when working on engines?
- horsepower
- friction horsepower
- indicated horsepower
- brake horsepower
1 hp = _______________ ft-lb/min
1 hp = 33,000 ft-lb/min
1 hp = ________________ ft-lb/sec
1 hp = 550 ft-lb/sec
1 W = ________ J/s = _________ Nm/s
1 W = 1 J/s = 1 Nm/s
hp = kW x ___________
hp = kW x 1.341
What is the friction horsepower (FHP) of an engine?
the power required to overcome engine frictional and pumping losses
Where do the friction losses occur in an engine?
at any location where two parts slide against each other;
bearings, cylinders, etc.
What is the indicated horsepower (IHP) of an engine?
the theoretical power of an engine
True or false:
Indicated horsepower (IHP) ratings of engines take into account friction and pumping losses when being calculated.
false;
they do not take these into account; IHP = theoretical hp
What is the brake horsepower (BHP) of an engine?
the actual hp measured at the end of the crankshaft
What formula can be used to calculate FHP if IHP and BHP are known?
FHP = IHP - BHP
FHP = friction hp
IHP = indicated hp
BHP = brake hp
What formula can be used to calculate BHP if IHP and FHP are known?
BHP = IHP - FHP
BHP = brake hp
IHP = indicated hp
FHP = friction hp
______________ is the resistance to motion between two surfaces.
friction
What are the three kinds of friction seen in mechanical components?
- sliding friction
- rolling friction
- fluid friction
______________ friction exists on engine bearings and cylinder walls when there is metal to metal contact.
sliding
_______________ friction is found in anti-friction bearings.
rolling
True or false:
Sliding friction changes to fluid friction when the surfaces become separated by a film of oil.
true
_____________ is the tendency of an object in motion to stay in motion, or the tendency of an object at rest to stay at rest.
inertia
True or false:
An object’s mass determines the amount of inertia an object has.
true
True or false:
The inertia of a flywheel and crankshaft causes them to continue rotating in between firing strokes.
true
__________________ is the application of a force per unit area.
pressure
__________________ refers to pressure that is below atmospheric pressure.
vacuum
A vacuum gauge measures zero at atmospheric pressure and __________ in. of mercury at absolute zero pressure.
29.92 in. of mercury
________________ is the potential to do work.
energy
________________ energy is the energy possessed by a substance because of its position, condition, or chemical composition.
potential
What is the potential energy of an engine system?
the fuel (gasoline, diesel, etc.)
_________________ energy is the energy of an object has because of its motion.
kinetic
What type of fuel has the most potential energy of all they types of fuels used in an engine.
diesel fuel
_________________ is the movement of the piston from TDC to BDC or vis versa.
stroke
This type of engine has the same dimensions for bore diameter and stroke length.
square engine
This type of engine has a larger bore diameter than stroke length.
oversquare engine
Oversquare engines have _______________ (lower/higher) piston speeds than undersquare engines of the same piston displacement when running at the same rpm.
lower
*this is due to the stroke being shorter for the same displacement, meaning that the piston doesn’t have to travel as quickly to complete the stroke
This type of engine has a longer stroke length than the bore diameter.
undersquare
Undersquare engines have _______________ (lower/higher) pistons speeds than square or over square engines of the same piston displacement when running at the same rpm.
higher
*this is due to the piston being “skinnier”, resulting in it having a longer stroke for the same displacement at the same rpm
What two effects does an over square piston have on the engine?
- better breathing = larger bore = larger valves
- higher max rpm;
the shorter stroke = less G forces on the piston when changing direction, which allows it to move faster
What is the piston displacement of an engine?
the swept volume of the piston when making one complete stroke
What formula can be used to calculate the piston displacement of an engine?
piston displacement = bore area x stroke length
What is the displacement of an engine?
the volume swept by all of the pistons in the engine
What formula can be used to calculate the displacement of an engine?
displacement = bore area x stroke length x # of cylinders
What is the clearance volume (CV) of an engine?
the volume remaining above the piston at TDC
True or false:
If an engine cylinder is not flat topped, then any reliefs in the piston and the head are not considered part of the clearance volume.
false;
they are considered part of the clearance volume
In an engine, what is squish?
the clearance volume (CV)
What formula can be used to calculate the CR of an engine?
CR = (displacement + CV) ÷ CV
CR = clearance ratio
CV = clearance volume
displacement + CV is at TDC
CV is at BDC
In an engine, the __________________ ______________ (2 words) is the total volume of the cylinder (displacement) and the combustion chamber (clearance volume) when the piston is at BDC to the clearance volume when the piston is at TDC.
compression ratio (CR)
True or false:
The displacement of an engine cylinder is the same as the swept volume.
true
What is the main limiting factor of CR in spark engines?
the type and quality of the fuel
True or false:
In engines, the more compression = the more power produced.
true
- What is the CR of a typical gas engine?
- What is the CR of a typical diesel engine?
- 9:1
- 18:1
In engines, the ratio (expressed as a percentage) of the volume of atmospheric air drawn into the cylinder on the intake stroke to the cylinder displacement is the:
volumetric ratio
intake air : displacement
What type of engine do volumetric efficiency (VE) ratios apply to?
four-stroke engines
*two-stroke engines are mechanically aspirated, which results in a 100% VE
What type of things reduce the VE of an engine?
Things that restrict the flow of air into the cylinder;
restrictions in the intake manifold, air cleaner, valves, valve timing, and engine design
True or false:
The high point on an engine torque curve indicates the approximate rpm for maximum VE.
true
- In most engines, a ______% VE is good.
- What type of engines can achieve higher VE’s?
- 95%
- two-valve pushrod engines
_________________ efficiency shows how well an engine converts the energy in fuel into mechanical energy.
Thermal
What is the thermal efficiency of most engines?
30% to 40% thermally efficient
In an engine, what is blowby?
the leakage of burned and unburned gases past the compression rings into the crankcase
On what two strokes of a four-stroke engine does blowby happen?
- compression
- power stroke
*any stroke where pressures are high
What effect does blowby have on an engine’s power?
it reduces it
True or false:
There is always some blowby in an engine.
true
What effect does blowby have on engine oil?
it contaminates it
What three things are required to make fuel combust inside of an engine?
- fuel
- air
- ignition (spark)
What needs to happen to the fuel before it can burn inside of an engine?
it needs to be atomized;
the better the fuel atomizes = faster it burns
What effect does the compression of the piston have on the ignition of an engine?
it heats the air;
this aids in vapourization
What are the four strokes of one cycle of a four-stroke engine?
- intake (suck)
- compression (squeeze)
- power (bang)
- exhaust (blow)
How many revolutions of the crankshaft are required to complete all four strokes in one cycle of a four-stroke engine?
2 full revolutions;
720°
In a four-stroke engine, this engine stroke takes place when the piston travels down from TDC, allowing air or a air-fuel mixture into the cylinder, and completing when the piston approaches BDC.
intake stroke
- What enters the cylinder on the intake stroke of a four-stroke CI engine?
- What enters the cylinder on the intake stroke of a four-stroke SI engine?
- air
- air-fuel mixture
In a four-stroke engine, during this engine stroke, both the intake and exhaust valves close and the piston travels towards BTDC, where ignition takes place.
compression stroke
- What happens at BTDC in a four-stroke CI engine during the compression stroke?
- What happens at BTDC in a four-stroke SI engine during the compression stroke?
- fuel is injected
- a spark ignites the air-fuel mixture
In a four-stroke engine, during this stroke, a rapid increase in pressure and temperature due to the fuel burning pushes the piston down, until it reaches BBDC at which time the exhaust valve opens.
power stroke
When does the intake stroke of a four-stroke engine end?
when the piston approaches BDC
When does the power stroke of a four-stroke engine end?
when the exhaust port opens at BBDC
During this stroke in a four-stroke engine, the exhaust valve is open as the piston travels from BDC to TDC, with the intake valve opening a few degrees BTDC and the exhaust valve closing a few degrees ATDC.
exhaust stroke
What is the valve overlap in a four-stroke engine?
the number of degrees the crankshaft travels when both the intake and exhaust valve are open at the same time
*when both valves are open, scavenging happens, which is where the exhaust gases are replaced with fresh intake gases
How many revolutions of the crankshaft are required to complete all two strokes in one cycle of a two-stroke engine?
one full revolution;
360°
In a two-stroke engine, during the intake and compression stroke, when the piston moves from BDC towards TDC, the 1.__________ ports are covered, followed by the 2.__________ ports.
- inlet
- exhaust
*the exhaust ports are always located closer to TDC than the inlet ports
What are the two strokes found in a two-stroke engine?
- intake and compression
- power and exhaust
True or false:
All two-stroke engines are artificially aspirated.
true;
this could be a blower, scavenger piston, etc. but something pushes air into the cylinder
What starts the power stroke on a two-stroke engine?
ignition
What ends the power stroke on a two-stroke engine?
as the piston travels past the exhaust port
On a two-stroke engine, what is blow down?
when the piston moves past the exhaust port, ending the power stroke
True or false:
A two-stroke engine does not have twice the power because the effective power stroke is shorter due to the ports in the cylinder.
true
How is rotation determined on an engine?
by the rotation of the engine when looking at the flywheel;
when looking at the flywheel:
right = CW rotation
left = CCW rotation
*as set by the SAE (Society of Automotive Engineers)
In engines manufacturers in North America, how are the cylinders numbered?
starting opposite the flywheel;
How are cylinders numbered on engines manufactured outside North America?
starting at the flywheel;
What two things determine the firing order of an engine?
- position of the crankshaft throws
- arrangement of the lobes on the camshaft
When setting a firing order on an engine, why should adjacent cylinders not fire in sequence?
this would cause excess main bearing loads
The _____________ ______________ (2 words) of an engine is used to ensure evenly divided power pulses throughout the complete rotation of the engine.
firing order
What information is needed in order to install the a distributor or magneto and set the engine valves correctly?
the cylinder numbering and firing order
How is the power pulse interval in degrees calculated on a four-stroke engine?
720º ÷ # of cylinders = power pulse interval in degrees
How is the power pulse interval in degrees calculated on a two-stroke engine?
360º ÷ # of cylinders = power pulse internal in degrees
In an engine, what is a running mate?
cylinders that have the pistons reaching TDC at the same time
In what stroke will running mate cylinders be in relation to each other?
they will be in the opposite stroke to each other
*one in compression, the other will be in overlap, but in the same location (TDC, BDC, ATDC, etc.)
What type of engine can have running mates?
four-stroke engines;
two-stroke engines cannot have running mates because they fire on all cylinders every revolution
This cylinder and crankshaft arrangement is the most common style, with each side of each cylinder having a main bearing.
an in-line arrangement
Which type of cylinder and crankshaft arrangement has a greater bearing area per cylinder than other arrangements?
in-line;
each crankshaft throw has a bearing on each side of the throw
*in-line 6 cylinder = 7 bearings vs. V8 engine = 5 bearings
This cylinder and crankshaft arrangement provides a more compact unit for the power delivered, and has results in a shorter crankshaft when compared to an in-line engine.
a V-type arrangement
What are two common angles for V-type cylinder arrangements?
60º and 90º
What is the main disadvantage of V-type cylinder arrangements?
more susceptible to torsional vibration, making them prone to fatigue problems
This cylinder and crankshaft arrangement has both an engine and compressor running off of a common crankshaft.
intergral arrangement
What is the main advantage of an integral cylinder arrangement?
no alignment;
as the compressor runs directly off of the master crankshaft, no alignment is required
*also, much smaller
This cylinder and crankshaft arrangement has two crankshafts, one above the block and one below.
opposed piston arrangement
*this is based off of a two-stroke design, with no valves, only ports
This cylinder and crankshaft arrangement has one crankshaft with cylinders located 180º from each other and has a high power-to-weight ratio.
horizontally opposed arrangement
What type of cylinder arrangement is often referred to as pancake engines?
horizontally opposed
This cylinder and crankshaft arrangement has the cylinders located around the circumference of the block, and are most often used in aircraft to save space and weight.
radial cylinder arrangements
What are three common valve arrangements in engines?
- overhead valve (I head)
- multi-valve
- flat head (L head)
This engine valve arrangement has the valves in the cylinder head on top of the piston, creating an I formation.
overhead valve (I head)
This type of engine valve arrangement is the most efficient because the combustion chamber has a minimum surface area for its volume, which results in less energy lost to the cooling system.
overhead valve
This type of engine has more than two valves per cylinder head.
Multi-valve
- What is the main advantage of a multi-valve engine?
- What is the main disadvantage?
- increases efficiency ⟶ two smaller valves flow better than one larger valve (also, less mass which is easier to control)
- expensive to manufacture
True or false:
With overhead valve engines, the intake is normally a larger diameter than the exhaust.
true
This type of engine valve arrangement has the valve located within the block, and is not very efficient due to the large surface area and limited valve lift.
flat head (L head)
What type of engine valve arrangement is known as an I-head?
overhead valve arrangment
What type of engine valve arrangement is known as a L-head?
flat head valve arrangement
What are the two camshaft positions found in engines and which one is more common?
- overhead cams (OHC)
- cam in the block (pushrod engine) ⟶ most common
What problem does an OHC arrangement solve when compared to a cam in the block arrangement?
excessive valve train mass
What is the main advantage of a DOHC arrangement?
increased efficiency;
the valves can be arranged more strategically for better efficiency
What are the two categories of engine cooling and which type is more common?
- air-cooled
- liquid-cooled ⟶ most common type
- Which type of engine is lighter: air-cooled or liquid-cooled?
- Why?
- air-cooled
- liquid-cooled engines have more components (cast-in water jackets, radiator and coolant, accessories such as water pumps, lines, hoses, etc.)
- Which type of engine has a larger lubrication supply: air-cooled or liquid-cooled?
- Why?
- air-cooled
- to aid in cooling
This type of engine induction method charges the cylinders with air using atmospheric pressure only.
naturally aspirated engine
True or false:
Naturally aspirated engines can achieve a VE of 100%.
false;
they cannot due to the restrictions the air must overcome as it enters the cylinder
True or false:
Two-stroke engines can be naturally aspirated.
false;
only four-stroke engines can be naturally aspirated
This type of engine induction method uses some mechanical means to fill the cylinders with air.
artificially aspirated
True or false:
Artificially aspirated engines can achieve a VE of 100%.
true;
they can pack in more air than it would normally displace
What are the three types of engine speed ratings and what are their associated rpm’s?
- low-speed ⟶ below 500 rpm
- medium speed ⟶ 500 rpm to 1000 rpm
- high speed ⟶ over 1000 rpm
This type of engine ignition system requires high compression ratios to heat the air enough to ignite the fuel, along with high-pressure injection systems to overcome and penetrate the highly compressed air.
compression ignition (CI) engines
This type of engine ignition system uses high-voltage electricity to arc across a gap at the spark to ignite the fuel, which is premixed with air before it compresses.
spark ignition (SI) engines
What kind of compression ratios would be expected in a spark ignition engine?
6:1 to 10:1
What kind of compression ratios would be expected in a compression ignition engine?
14:1 to 23:1
What kind of compression pressures would be expected in a spark ignition engine?
100 psi to 260 psi
What kind of compression pressures would be expected in a compression engine?
300 psi to 500 psi
What type of ignition system would most likely be found on an engine using gasoline, natural gas, or propane as fuel?
spark ignition (SI)
What type of ignition system would most likely be found on an engine using diesel or bunker fuel?
compression ignition (CI)
What are the two main type of engine loads and which is more common?
- integral engine loads
- independent engine loads ⟶ more common
This type of engine load is built with the load as part of the engine, with the load using the same crankshaft and engine block.
integral engine loads
What formula can be used to convert cubic inches into litres?
L = in³ ÷ 61.024
What formula can be used to covert litres into cubic inches?
in³ = L x 61.024
True or false:
A close-coupled engine load has its own mounting feet and relies on the rigid base to ensure correct alignment is maintained between the engine and load.
false;
this type of engine load is usually located on a single skid for portability
True or false:
Integral engine units are usually block mounted so that the that whole unit rests on the same foundation.
true;
for this reason, the engine block must fasten flatly to the foundation to ensure alignment is correct
When it comes to machine alignment, what is chock?
a polymeric grout shim
This type of engine load has the load attached to either end of the crankshaft.
independent load engines
What are the two types of independent engine load arrangements?
- close-coupled load
- remote mounted load
This type of engine with independent load arrangement is when the driven unit attaches directly to the engine flywheel and flywheel housing.
close-coupled load
This type of engine with independent load arrangement is when the load has independent bearing supports on each end of the shaft.
remote-mounted load
- Which type of independent engine load arrangement requires a more rigid set-up: close-coupled or independent?
- Why is this?
- independent
- the base must be able to withstand the reaction force of the load
True or false:
When working in areas of high concentrations of H₂S, you should always wear a personal alarm monitor.
true
*also known as a sniffer
The amount of air an engine can take into the cylinder compared with the volume if the cylinder is called:
the volumetric efficiency
In an engine, the cylinder volume plus the combustion chamber volume, divided by the combustion chamber volume indicates the:
compression ratio
combustion chamber volume = clearance volume
cylinder volume = swept volume
Which type of engine head design has valves in the block?
L-head engine
True or false:
An undersquare engine is an engine with a larger stroke than bore.
true
Where is the camshaft located on a pushrod engine?
In a pushrod v8 the crankshaft is below the camshaft like most modern v8 engines. The cam is beside and above the crank on inline pushrod engines
True or false:
The position of the crankshaft throws and the arrangement of the lobes on the camshaft determine the firing order of an engine.
true
What type of energy is released when fuel inside an engine made to react with oxygen?
chemical energy
Which abbreviation is used to describe an engine with one camshaft located in the head?
OHC
*overhead cam
When you are determining engine rotation using the SAE standard, you view the engine from:
the main power end of the engine;
often the flywheel end
The _______________ efficiency of an engine is the ability of an engine to change the energy in the fuel to usable heat energy and power.
thermal
True or false:
In an engine, fuel must be atomized and mixed with air to be burned.
True
True or false:
A two-stroke engine makes twice as much power as a four-stroke engine of the same capacity.
False;
*two-strokes have a shorter power stroke vs. a four-stroke
What is an example of an external combustion engine?
Steam engine
The thermal efficiency of an engine is best described as the ability of the engine to;
change the energy in the fuel to a useable energy and power
On a 16 cylinder, 64 valve, 4 stroke engine the crankshaft must make how many revolutions for all cylinders to fire?
2
A four-stroke engine completes all strokes in 720º.
Where on a running engine would one likely be able to read pressures of less than atmospheric pressure?
between the air filter and the intake manifold
In a two stroke engine, when the power stroke has ended, the cylinder is said to be in __________ _____________ (two words).
Blow down
