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MET 426 Final Exam Prep

Terms in this set (113)

engine induction system requirements are:
-to intake the [blank] possible amount of correct fuel/air [blank]
-evenly distributed to all [blank]
-across the entire engine [blank] range
(separate answers with a comma)
maximum, mixture, cylinders, speed
The [blank] efficiency of an engine indicates how effective the induction system is at intaking the highest possible amount of air or air-fuel mixture
volumetric
Sizing intake runners involves specifying a [blank] that is large enough to prevent load large flow losses yet small enough to maintain velocity and carry droplets in the flow
diameter
Sufficiently high runner velocity enhances the carrying of fuel droplets, [blank] of the fuel and air-fuel mixing
evaporation
For a carbureted or throttle body injection intake system, fuel in the intake manifold can occur as [blank], [blank], or a thin fuel [blank] on the manifold walls
(separate answers with a comma)
vapor, droplets, film
Volumetric efficiency is _________________ around the intake systems design point
highest
Volumetric efficiency is improved by the ram affect at higher RPMs but decreased at low RPM by_________________ caused by intake valve remaining open too long
backflow
The RPM of highest volumetric efficiency is also usually the RPM of _________________ torque
peak
The shape of the camshaft lobe determines _________________ lift as well as valve opening and valve closing times.
valve
The valve _____________ _________________ indicates how much flow can pass through the valve compared to a theoretical maximum
discharge coefficient
Valve choking occurs when the _________________ number in the valve minimum flow area exceeds 1.0
mach
_________________ valve timing allows high volumetric efficiency through a wider RPM range
variable
Driven by demands for improved fuel economy and reduced emissions the ___________ _________ fuel injection system has become the prevalent system for compression ignition engines across a wide displacement range
common rail
The fundamental principle of operation of the carburetor is the ______________ effect in which a low pressure region is created by reduction of the flow area and the resulting increase in velocity in that region
venturi
In a carbureted engine, when the throttle is only partly open the manifold pressure is______________________ and pumping loop area on the pV diagram is ___________
(separate answers with a comma
lower, increased
Multipoint port fuel ___________ eliminates the majority of the problems that arise from the fuel air mixture flowing through the intake manifold and runners
injection
Direct fuel injection in spark ignition engines allows higher ___________ ratios which yield increased fuel efficiency
compression
_______________ charge engines can operate at air-fuel mixtures as high as 40 or 50:1, leading to high efficiencies
stratified
A modern medium speed diesel engine the piston ___________shape, geometry, fuel spray ___________ and injection timing are designed together to create what is called a "___________" for optimal combustion efficiency and low exhaust emissions
(separate answers with a comma)
bowl, pattern, recipe
The ___________ charge for a 2-stroke engine must be pressurized
intake
The combined processes of intake and exhaust in a two stroke engine are referred to as ___________
scavenging
Test data discussed in class shows that ______________________ two stroke scavenging efficiency almost triples BMEP
doubling
The use of turbo chargers in automotive engines has become more widespread in response to government requirements for increased vehicle fuel ___________
economy
______________________ exhibit much faster throttle response than turbochargers but are a direct parasitic load on engine ___________
(separate answers with a comma)
superchargers, output
Turbo chargers ___________at low flow rates and ___________ at very high flow rates and cannot operate in either of these regions
(separate answers with a comma)
surge, stall
The turbo charger compressor map consists of an X-axis for mass ___________, a Y-axis for ___________ratio, and multiple lines of constant ___________and constant ___________ in the map region
(separate answers with a comma)
flow, pressure, speed, efficiency
A turbocharger that is well matched to the engine operates in the high ______________________ region of the compressor map
efficiency
The simplest model of _______________ in an engine cylinder is a sphere of flame expanding away from the spark plug in a uniform fashion
combustion
Sir Harry Ricardo was one of the early researchers who observed that because of ______________thermodynamic events in internal combustion engines occur about 10 times faster than they would without it
turbulence
Turbulent flow is characterized by wide ________________ of velocity, including flow actually traveling in the opposite direction of the average velocity of the flow
fluctuations
Turbulent flow exhibits _______________ flow that occur across a wide range of scales
counter
_______ ________ refers to the amount of swirl in a given flow
swirl ratio
Still mixture (or "quiescent") flame front ______________ is a function of fuel-to-air ratio and the chemistry of the fuel itself
speed
Turbulence dramatically increases the area of the flame front, and thus increases the amount of fuel mixture being ________________ at any time during combustion
burned
For a wide range of engine designs, turbulence intensity increases with an average ______________speed
piston
Swirl is the bulk rotation of the charge around the ______________ axis of the cylinder
longitudinal
________________ is the bulk rotation of the charge around a transverse axis of the cylinder
tumble
Both swirl and tumble are most directly affected by the design of the ________________ ports
intake
__________________ is the result of intake charge being squeezed out of the clearance volume as the piston approaches top dead center.
squish
Design for increased squish area is normally part of the design process to create a _____________combustion chamber
no clue, didn't get this one correct. lol
A divided _____________ engine is often also a stratified charge engine
chamber
While crevice volume is only a few percent of the total combustion chamber volume, as much as____________ of the fuel-air mixture can be trapped in the crevices at peak pressures
20%
While combustion is complicated and still not completely understood, simplified models have been developed that allow useful _____________-- to parameters like pressure, temperature, fuel type, knock, RPM, etc
correlations
The term _______________ refers to the period in the engine cycle when both the intake and the exhaust valves are open
overlap
Most of combustion Spark ignition engine history has consisted burning a mixture around the_________________ air-fuel ratio, but modern engines might also be lean-burn or stratified charge engine
stoichiometric
A lean-burn engine has a generally ___________ air to fuel ratio with special design features to allow for ignition
high
A stratified charge engine is designed to have a gradient of fuel to air ratio across the combustion chamber, with part of it ___________ enough to be ignited by the ignition spark
rich
Combustion in SI engines is divided into three regions - ignition and flame development, flame_______________, and flame termination
propagation
__________ to __________ % of the charge is consumed in the flame propagation stage, which produces most of the useful work for the stroke
10, 90
The ignition spark occurs anywhere from 10 to 30° _____________ top dead center, and flame can usually be to a detected at about 6° of crank ______________ after the spark
before, rotation
Spark voltage is generally between 25,000 to 40,000, with a maximum _______ of 200A that lasts about 10 ns (recall that a nanosecond (ns) is 10-9).
current
Peak temperature in the spark is around 60,000°____________, with an average temperature of around __________° kelvin
6000
While a hydrocarbon fuel mixture can require up to 3 mJ to establish self-sustaining flame and the ignition spark delivers between 30 and 50 mJ of energy, much of the spark energy is lost to _________ ____________, both to the relatively cold spark plug itself and the surrounding unburned mixture
heat transfer
Spark plug _______________ is anywhere from .7 to 1.7 (0.027 to .070 inches)
gap
Flame travel is fastest in a slightly _____________ mixture
rich
According to data presented, peak cylinder pressure can vary within a _____________% band during engine operation at a single operating point
30
A modern computer controlled engine has a number of ____________ and actuators that work in conjunction with the engine control module to set control variables such as spark timing as well as fuel injection amount and injection timing.
sensors
In the 1970s Honda Motor Company developed a unique, divided-chamber, combustion system that allow them to implement a stratified-charge combustion scheme that eliminated the need for a_____________ _______________, which at the time were expensive and short-lived.
catalytic converter
At cruise conditions, heat transfer increases and energy is lost for _______________ generation because there is more time for it to occur
combustion
At high power and RPM, pumping loop losses are very low, spark is retarded, and mixture is some what ___________ rich
fuel
A modern fast burn combustion chamber is very _________________ with most of the chamber volume close to the spark plug.
compact
In a compression-ignition engine, __________ output is determined by the amount of fuel injected
power
Before combustion can occur, injected fuel must ______________, then vaporize, and finally mix with air in the cylinder before it can self-ignite and burn
atomize
Ignition ____________ is longer in fuels with low cetane number
delay
There is a wide range of air-to-fuel ratio across the combusting spray _______________ in a direct fuel injected engine, from very lean at the outer edges to pre-atomized fuel in the middle
pattern
The homogeneous charge compression ignition engine offers both low ______________ and high fuel efficiency
emissions
The most challenging aspect of the homogeneous charge compression ignition engine is achieving reliable ignition at the proper _________________
timing
The bulk of exhaust gases exit the cylinder during the process called ________________
blowdown
The exhaust valve generally opens ________________ the piston reaches bottom dead center.
before
Exhaust valve opening too early results in lost ________________ on the power stroke
work
In order to recover the maximum amount of kinetic energy in the exhaust gases the turbo-charger should be ________________-________________ to the exhaust manifold.
close coupled
The largest pressure loss in the exhaust system occurs across the ____________ ___________ itself
exhaust valve
The period during which both the inlet and exhaust valves are open is called valve -________________.
overlap
The term ________________ refers to exhaust gases flowing into the intake system during the period of valve overlap.
backflow
Exhaust valve area is normally in the range of ______ or _______ times that of intake valve area.(answer is two different numbers
0.8, 0.9
Much of the exhaust process occurs under the conditions of ________________ flow
choked
Exhaust gas temperature ________________ with higher engine speed and/or higher engine load
increases
Three and four intake/exhaust valve systems offer the advantage of ________________ spark plug location
centralized
Production exhaust manifolds are usually made out of ______________ __________________
cast iron
Locating the intake and exhaust manifolds in close proximity to each other generally improves fuel -________________
vaporization or heating
Close coupling the catalytic converter to the exhaust manifold allows it to ___________ __________faster and thus reduce exhaust emissions
heat up
Exhaust tuning takes advantage of both exhaust charge ________________ and ________________pulse reflection and inversion.
momentum, pressure
The Carnot cycle efficiency tells us that even the theoretically most ___________ heat engine needs heat removal
efficient
Anywhere from 20 to 45% of total energy in the _________exits the engine in the exhaust flow
fuel
The hottest locations in an engine are the area around spark plug, the region of the exhaust valve and port and the top surface of the _____________
piston
Variations in the rate of thermal expansion give rise to thermal _____________.
stress
In-cylinder heat transfer modes include conduction, _____________ , and radiation
convection
Heat transfer between cylinder contents and the cylinder wall can occur in both______________ at different points in the engine cycle
directions
Heat transfer correlations in engine calculations are highly _____________.
empirical
All else being held equal, as engine size increases engine ___________ increases as well
efficiency
Engine temperatures rise with both engine speed and engine ______________
load
Engine specific power has increased to the point where ________ cooling is no longer a viable cooling method in modern commercial automobiles.
air
Cooling systems need to transfer heat effectively over a wide range of __________
temperatures
In unlubricated surface contact between surfaces in relative motion the ___________ of each surface rub against each other and create a force opposite the direction of movement called __________
asperities, friction
________ is added to reduce friction
lubricant
the effect of the relative motion of two surfaces, lubricant __________, and lubricant __________ is to float one surface relative to the other
shearing, viscosity
a plain bearing with a sommerfeld number of _______ would have boundary lubrication, typical of pistons at TDC and BDC while pistons at mid-stroke would have a sommerfeld number number of _____________
0.001, 1
engine lubricants must adhere to the bearing solid surfaces, but must not require excessive _______ to shear adjacent layers
force
most energy is lost to ______ ends up heating engine oil and coolant
friciton
engine friction and determination of component contriubtions to frictions losses is best determined by testing on a motoring engine _________
dynamometer
the major thrust load on the piston occurs on the ________ stroke while the minor thrust load occurs on the _______ stroke
power, compression
the ________ number of diesel fuel is best determined by comparison of two standard reference fuels, with higher values indicating shorter ignition delay, which is the inverse of the performance indicated by octane number
cetane
design for increased squish area is normally part of the design process to create a _________ combustion chamber
compact
the rpm of highest volumetric efficiency is also usually the rpm of ________ torque
peak
exhaust valve opening too _________ results in lost work on the power stroke
early
increased intake air temperature reduces ________ efficiency and also increases the risk of potentially destructive knock
volumetric
the single most important factor that will increase engine NOx emissions in combustion _______
byproduct
CO emissions are reduced with the fuel-air mixture slightly __________
lean
HC emissions are reduced with the fuel-air mixture is slightly _____
lean
air-standard otto cycle analysis tells us that increased ______ __________ increases engine efficiency
compression ratio
flame travel is fastest in a slightly _______ mixture
rich
Is Bridgeman a good teacher?
If your answer is anything other than no then you're full of shit
Is Bridgeman disorganized?
Does a fat kid like cake?
Verified questions
physics
A guitar string with a mass of $10.0 \mathrm{~g}$ is $1.00 \mathrm{~m}$ long and attached to the guitar at two points separated by $65.0 \mathrm{~cm}$. b) If the guitar string is replaced by a heavier one that has a mass of $16.0 \mathrm{~g}$ and is $1.00 \mathrm{~m}$ long, what is the frequency of the replacement string's first harmonic?
Verified answer
chemistry
How many electrons are present in each of the following ions? $$ \mathrm{Br}^{-} $$
Verified answer
biology
Describe how microorganisms are prevented from entering the respiratory system.
Verified answer
physics
Ordinary eyeglasses. Ordinary glasses are worn in front of the eye and usually $2.0 \mathrm{~cm}$ in front of the eyeball. Suppose that a nearsighted person with a far point of $100 \mathrm{~cm}$ uses ordinary glasses to correct her vision of faraway objects. What eyeglass power will give her a sharp image of objects at infinity? (Do not ignore the distance between the eye and the glasses.)
Verified answer