If V₁ is the jet velocity and V₀ is the vehicle velocity, then propulsive efficiency of a turbojet engine is
V₁/(V₀ + V₁)
V₀/(V₀ + V₁)
2V₀/(V₀ + V₁)
2V₁/(V₀ + V₁)
Correct Answer :
C. 2V₀/(V₀ + V₁)
Related Questions
Supercharging is the process of
Supplying the intake of an engine with air at a density greater than the density of the surrounding atmosphere
Providing forced cooling air
Injecting excess fuel for raising more loads
Supplying compressed air to remove combustion products fully
Iso-octane (C8H18) has octane number of
0
50
100
120
In diesel engine, the compression ratio in comparison to expansion ratio is
Same
Less
More
Variable
The delay period in compression ignition engines depends upon
Temperature and pressure in the cylinder at the time of injection
Nature of the fuel mixture strength
Relative velocity between the fuel injection and air turbulence pressure of residual gases
All of the above
The cetane number of diesel oil, generally available, is
20 to 25
25 to 30
30 to 40
40 to 55
The magneto in an automobile is basically
Transformer
D.C. generator
Capacitor
Magnetic circuit
In a four stroke cycle petrol engine, the pressure inside the engine cylinder during the suction stroke is __________ the atmospheric pressure.
Equal to
Below
Above
None of these
The thermal efficiency of petrol and gas engines is about
15 %
30 %
50 %
70 %
The fuel in diesel engine is normally injected at pressure of
5-10 kg/cm²
20-25 kg/cm²
60-80 kg/cm²
90-130 kg/cm²
A supercharged engine as compared to an ordinary engine
Requires smaller foundation
Is lighter
Consumes less lubricating oil
All of these
Pick up the wrong statement
2-stroke engine can run in any direction
In 4-stroke engine, a power stroke is obtained in 4-strokes
Thermal efficiency of 4-stroke engine is more due to positive scavenging
Petrol engines occupy more space than diesel engines for same power output
The temperature of interior surface of cylinder wall in normal operation is not allowed to exceed
80°C
120°C
180°C
240°C
Which of the following medium is compressed in a Diesel engine cylinder?
Air alone
Air and fuel
Air and lub oil
Fuel alone
A gas engine has a swept volume of 300 cm3 and clearance volume of 25 cm3. Its volumetric efficiency is 0.88 and mechanical efficiency is 0.90. The volume of the mixture taken in per stroke is
248 cm3
252 cm3
264 cm3
286 cm3
The term scavenging is generally associated with
2-stroke cycle engines
4-stroke cycle engines
Aeroplane engines
High efficiency engines
The ignition quality of diesel oil is expressed by
Cetane number
Octane number
Calorific value
None of these
Combustion in compression ignition engines is
Homogeneous
Heterogeneous
Both (A) and (B)
Laminar
The theoretically correct air fuel ratio for petrol engine is of the order of
6 : 1
9 : 1
12 : 1
15 : 1
In compression ignition engines, swirl denotes a
Haphazard motion of the gases in the chamber
Rotary motion of the gases in the chamber
Radial motion of the gases in the chamber
None of the above
The increase of efficiency of a compression ignition engine, as the load decreases, is due to
Higher maximum temperature
Qualitative governing
Quantitative governing
Hit and miss governing
The theoretically correct mixture of air and petrol is
10 : 1
15 : 1
20 : 1
25 : 1
A diesel engine is _________ as compared to petrol engine, both running at rated load.
Equally efficient
Less efficient
More efficient
None of these
The reference fuels for knock rating of spark ignition engines would include
Iso-octane and alpha-methyl naphthalene
Normal octane and aniline
Isooctane and normal hexane
Normal heptane and isooctane
In order to mix air and petrol in the required proportion and to supply it to the engine during suction stroke, then _________ is employed.
Fuel pump
Injector
Carburettor
None of these
In a diesel engine, the fuel is ignited by
Spark
Injected fuel
Heat resulting from compressing air that is supplied for combustion
Ignition
If the compression ratio of an engine working on Otto cycle is increased from 5 to 7, the percentage increase in efficiency will be
2 %
4 %
8 %
14 %
The maximum propulsive efficiency of a turbojet engine is at a speed of
1000 km/h
2000 km/h
2400 km/h
3000 km/h
The calorific value of gaseous fuels is expressed in terms of
kcal
kcal/kg
kcal/m²
kcal/m3
Detonation is harmful due to
Increase in the rate of heat transfer, there is a reduction in the power output and efficiency of the engine
Excessive turbulence which removes most of the insulating gas boundary layer from the cylinder walls
High intensity of knock causes crankshaft vibration and the engine runs rough
None of the above
The knocking tendency in compression ignition engines for a given fuel will be
Enhanced by decreasing compression ratio
Enhanced by increasing compression ratio
Dependent on other factors
None of the above