2610072
Descripción
Test por echowhiskey, actualizado hace más de 1 año
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Creado por echowhiskey
hace alrededor de 9 años
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Pregunta 1
Pregunta
A large We number indicates that the deforming aerodynamic forces are much larger than the reforming surface tension forces.
Respuesta
- True
- False
Pregunta 2
Pregunta
What do the terms dng and sg represent in the log-normal distribution?
Respuesta
-
dng is the number geometric mean dropsize and sg is the geometric standard deviation.
-
dng is the mean diameter of a droplet and sg is the standard deviation.
-
The terms have the same significance as the mean and standard deviation of a normal distribution function.
-
dng is the mean number of droplets in a sample and sg is the standard deviation.
Pregunta 3
Pregunta
What is the acronym SMD stand for?
Respuesta
-
Sauter Mean Diameter
-
Specimen Mean Diameter
-
Sample Mean Diameter
Pregunta 4
Pregunta
SMD describes the "average" diameter of an ensemble of droplets by weighting the average by both the surface area and the volume.
Respuesta
- True
- False
Pregunta 5
Pregunta
Why is SMD used to characterize droplet size?
Respuesta
-
Evaporation is a surface behavior.
-
The local AFR is volume dependent.
-
It explains the tendency of a spray to evaporate and form a particular AFR.
-
Reflects the spread of fuel through mass weighting.
-
It helps describe what happens to the droplets in theory.
-
It helps describes what happens to the droplets in reality.
Pregunta 6
Pregunta
What is the We number?
Respuesta
-
It is a dimensionless number describing the ratio of deforming aerodynamic forces to the reforming surface tension forces.
-
It is a dimensionless number describing the ratio of activation energy to thermal energy.
-
It is a dimensionless number describing the ratio of inertial fluid forces to viscous fluid forces.
Pregunta 7
Pregunta
The log normal distribution for droplet size is given by this equation.
Respuesta
- True
- False
Pregunta 8
Pregunta
What is one key advantage of the log-normal distribution?
Respuesta
-
It can be written such that there is a simple relationship between the surface and volume distributions.
-
It can be written such that there is a simple relationship between the weight and area distributions.
-
It can be written such that there is a simple relationship between the volume and diameter distributions.
Pregunta 9
Pregunta
What are some dropsizing techniques?
Respuesta
-
Malvern Particle Sizer (MPS)
-
Phase Doppler Velocimetry
-
Laser Sheet Dropsizing
-
Dynamic Light Scattering
-
Dilute Solution Viscometry
Pregunta 10
Pregunta
The log normal distribution is used because it has been found experimentally to be a good fit for sprays.
Respuesta
- True
- False
Pregunta 11
Pregunta
What are some of the disadvantages of using PDV as a dropsizing technique?
Respuesta
-
Line of sight
-
Point specific
-
Very expensive
-
Low spatial resolution
-
Requires a specific off axis forward scatter geometry
Pregunta 12
Pregunta
I want to measure a dense spray. Which drop-sizing technique should I use?
Respuesta
-
LSD
-
PDV
-
MPS
Pregunta 13
Pregunta
A "hollow core" or "air core" is formed by the swirl of the liquid.The tangential velocity of the outgoing liquid is given by two equations, relating the mass of liquid, the port area, and the chamber radius. At a radial position of r=0, the tangential velocity is equal to infinity. As this is impossible, a low pressure or vapor core is observed.
Respuesta
- True
- False
Pregunta 14
Pregunta
The process that govern CO formation are .....
Respuesta
-
.....controlled by the mass of fuel burnt.
-
......kinetically controlled.
-
..... controlled through AFR.
Pregunta 15
Pregunta
In the premixed flame, the CO concentration.....
Respuesta
-
...increases rapidly in the flame zone to a super equilibrium maximum.
-
....decreases slowly in the flame zone to a near zero state.
Pregunta 16
Pregunta
The Zeldovich mechanism is the mechanism that describes the formation of NO by breaking down O2 to O atoms and N2 to N atoms. The subsequent reactions produce NO.
Respuesta
- True
- False
Pregunta 17
Pregunta
What are some mechanisms of HC formation?
Respuesta
-
Incomplete combustion or a misfire in a fraction of the engine cycles.
-
Lean AFR resulting in knocking.
-
Trapping of unburnt mixture in crevices formed by the pistons and ring packs.
-
Burning a nitrogen rich fuel.
-
Flame quenching at the combustion wall.
Pregunta 18
Pregunta
Combustion behavior is substantially controlled by the AFR. What is this?
Respuesta
-
It is the mass ratio of air to fuel present in a combustion process.
-
It is the ratio of actual air to the theoretical air required for the complete combustion of fuel.
-
It is the ratio of the number of moles of fuel and air to the number of moles of fuel and air in a stoichiometric mixture.
Pregunta 19
Pregunta
How is No emissions mainly formed?
Respuesta
-
It is formed by the reaction of nitrogen and oxygen present in the combustion air.
-
It is formed by the reaction of nitrogen and fuel present during the combustion.
Pregunta 20
Pregunta
What are the pollutant emissions produced by a conventional gasoline engine?
Respuesta
-
Carbon Dioxide (CO2)
-
Carbon Monoxide (CO)
-
Hydrocarbons (HC)
-
Nitrogen Oxide (NOx)
-
Sulphur Dioxide (SO2)
Pregunta 21
Pregunta
The reactions to produce NO are very sensitive to temperature because the production of O atoms is essentially exponential with temperature.
Respuesta
- True
- False
Pregunta 22
Pregunta
How can the production of NOx be controlled or reduced?
Respuesta
-
Catalytic Abatement
-
Lean burn operation for AFR 22:1
-
Excess air and exhaust gas recirculation
-
Increasing or decreasing temperature of combustion
Pregunta 23
Pregunta
What are some of the requirements for using catalytic abatement to reduce NOx?
Respuesta
-
It needs an AFR of 14.5:1.
-
It needs a specially designed engine.
-
It needs a high temperature to function.
Pregunta 24
Pregunta
In order to reduce the production of NO, a lean burn operation is used. This requires a specifically designed engine where a port fuel injector is made through an open inlet valve.
Respuesta
- True
- False
Pregunta 25
Pregunta
Increasing the AFR can significantly reduce the formation of CO and HC.
Respuesta
- True
- False
Pregunta 26
Pregunta
Ignition delay period (or time) is the delay time between the start of injection and the start of combustion in a Diesel engine. What determines the delay time?
Respuesta
-
Cetane number
-
AFR
-
Pressure
-
Temperature
-
Fuel air mixing
-
Swept Volume
-
Calorific value of fuel (ie how much energy the fuel gives off when it burns)
Pregunta 27
Pregunta
What happens when there is a long ignition delay period?
Respuesta
-
It risks a large amount of mixture since the in-cylinder temperature will be low
-
The larger part of premixed combustion may take place
-
It leads to an increase in compression work (and thus reduces engine power output)
-
It leads to an increase of soot formation because a proportion of fuel may remain unburnt
-
It results in high engine temperatures and "knocking"
Pregunta 28
Pregunta
The three distinct phases of combustion for a diesel engine are premixed combustion, mixing controlled combustion, and end-phase combustion.
Respuesta
- True
- False
Pregunta 29
Pregunta
Which phase of the combustion process in a diesel engine produces the most NO?
Respuesta
-
Pre-mixed combustion
-
Mixing-controlled combustion
-
End phase combustion
Pregunta 30
Pregunta
During which phase of combustion in a diesel engine is most of the soot formed?
Respuesta
-
Pre-mixed combustion
-
Mixing-controlled combustion
-
End-phase combustion
Pregunta 31
Pregunta
What is the break up time of spray?
Respuesta
-
Defined from the experimental results, it is the rate at which the spray tip penetration changes.
-
Defined from the theory of sprays, it is the rate at which the spray tip penetration changes.
-
It is the rate at which a jet spray changes to a fully atomized spray.
Pregunta 32
Pregunta
Advanced diesel combustion combines split injection strategies with catalytic abatement.
Respuesta
- True
- False
Pregunta 33
Pregunta
What is the prime parameter in determining the quantities of NOx formed in a traditional gasoline engine?
Respuesta
-
Mass of fuel burnt
-
AFR
-
Incomplete combustion or misfires.
-
Temperature.
Pregunta 34
Pregunta
A "split injection" system allows the rich zone of the fuel to be significantly reduced whilst maintaining flexibility with engine load (eg the amount of fuel injected) .
Respuesta
- True
- False
Pregunta 35
Pregunta
How does a split injection system (single pulse) help reduce smoke production?
Respuesta
-
It minimizes rich and hot zones of combustion
-
It reduces the combustion efficiency and lowers the amount of soot and smoke produced
-
It maximizes the rich and hot zones of combustion
-
It increases the combustion efficiency and lowers the amount of soot and smoke produced
Pregunta 36
Pregunta
How does using EGR help with diesel combustion?
Respuesta
-
It increases the heat capacity which reduces NOx
-
It dilutes the combustion which reduces NOx
-
It increases the overall efficiency
-
It reduces the amount of smoke production
Pregunta 37
Pregunta
What are some benefits of using high pressure injection in a DI Diesel Engine?
Respuesta
-
Higher pressures improve fuel customization and enhance fuel-air mixing
-
A smaller SMD (Resulting from high pressure) enhances the formation of fuel-air mixture in diffusion combustion phase
-
It reduces both soot and NOx production.
Pregunta 38
Pregunta
A DIG achieves a lean burn by manipulating a rich region to the spark plug by controlling the timing and form of injection in conjunction with the in-cylinder air flow.
Respuesta
- True
- False
Pregunta 39
Pregunta
How does lean burn increase bfsc?
Respuesta
-
It decreases pumping losses
-
It allows for more air to be drawn into the cylinder for a given amount of fuel
-
There is less throttling
-
It improves the overall efficiency
-
It restricts the amount of air drawn into the cylinder for a given amount of fuel
-
There is more throttling
Pregunta 40
Pregunta
The cone angle is defined as the angle between two straight lines originating from the orifice exit of the nozzle and being tangent to the spray outline. This angle
usually ranges from 5 to 30 degrees.
Respuesta
- True
- False
Pregunta 41
Pregunta
Fuel spray tip penetration is defined as the maximal distance measured from the injector to the spray tip. It represents the maximum penetration length
achieved by the droplets in the center of the spray.
Respuesta
- True
- False
Pregunta 42
Pregunta
How is the cone angle mainly affected?
Respuesta
-
Geometric characteristics of the nozzle
-
The fuel and air density
-
Reynolds number of the fuel
-
Velocity and Pressure of the fluid
-
Change of crank angle
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