← Junior Engineer
Past Questions
Power transmitted through a pipe is maximum when the loss of head due to friction is -
A)
One-half of the total head supplied
B)
One-third of the total head supplied
C)
One-fourth of the total head supplied
D)
Equal to the total head supplied
For maximum power transmission through a pipe, the useful head available at the outlet must be maximized while accounting for friction loss. If the total head supplied is H and the friction loss is hf, then the discharge and hence power depend on the balance between available head and loss. Differentiating the power expression with respect to flow shows that maximum power occurs when hf = H/2, i.e., the loss of head due to friction is one-half of the total head supplied. Therefore, option (a) is correct.
Why the others are incorrect:
- (b) One-third of the total head supplied: this does not satisfy the maximum power condition for pipe flow.
- (c) One-fourth of the total head supplied: too small a friction loss; power is not maximized at this ratio.
- (d) Equal to the total head supplied: if all head were lost in friction, no useful head would remain, so transmitted power would be zero, not maximum.
The two important forces for a floating body are -
A)
Buoyancy, gravity
B)
Buoyancy, pressure
C)
Buoyancy, initial
D)
Inertial, gravity
Floating body equilibrium governed by buoyancy and gravity (weight).
The operating pressure for refrigerating units using R-12 asa refrigerant is -
A)
2 bar
B)
8 bar
C)
15 bar
D)
30 bar
R-12 is low-pressure refrigerant with condensing pressure around 8 bar in typical units.
The efficiency of a centrifugal pump is maximum when its blades are -
A)
Straight
B)
Bent forward
C)
Bent backward
D)
Bent forward first and then backward
Backward curved blades give highest efficiency due to lower losses and better flow guidance.
Refrigeration in aeroplane usually employs the following refrigerant -
A)
CO2
B)
Freon- 11
C)
Freon —22
D)
Air
Aircraft refrigeration uses air cycle, air itself is refrigerant due to light weight and availability.
Pneumatic and other power systems can support three kinds of motion; they are -
A)
Linear, reciprocating, and random motion
B)
Linear, flowing, and rotary motion
C)
Linear, zigzag, and spiral motion
D)
Linear, reciprocating, and rotary motion
Pneumatic/hydraulic systems can produce linear, reciprocating (linear back-forth), and rotary motion.
Compression ratio of I.C. engines is -
A)
The ratio of volumes of air in cylinder before compression stroke and after compression stroke
B)
Volume displaced by piston per stroke and clearance volume in cylinder
C)
Ratio of pressure after compression and before compression
D)
Swept volume/ cylinder volume
Compression ratio is ratio of maximum to minimum cylinder volume before and after compression.
Reaction turbines are used for -
A)
Low head
B)
High head
C)
High head and low discharge
D)
Low head and high discharge
Reaction turbines like Francis and Kaplan operate best with low head and high discharge.
If P is the gauge pressure within a spherical droplet, then gauge pressure within a bubble of the same fluid and of same size will be -
A)
P/4
B)
P/2
C)
P
D)
2P
Droplet: ΔP=4T/d (one surface). Bubble: ΔP=8T/d (two surfaces), so bubble pressure =2× droplet =2P.
Which of the following provides passages for the flow of cooling water?
A)
Crankcase
B)
Cylinder block
C)
Piston
D)
Cylinder head
The cylinder block provides passages (water jackets) for the flow of cooling water around the cylinders to remove heat from the engine. The piston does not carry cooling-water passages, and the crankcase mainly houses the crankshaft and related components. The cylinder head may also contain water passages in many engines, but the standard component identified as providing the main cooling-water passages is the cylinder block.
Which of the following is a classification of IC Engine?
A)
Four-stroke engines
B)
S.1Engines
C)
Otto cycle engine
D)
Carnot cycle engine
Four-stroke engines are a standard classification of internal combustion (IC) engines based on the number of strokes completed in one cycle. Option a is therefore correct. Option b, "S.1Engines," is not a recognized IC engine classification as written. Option c, "Otto cycle engine," refers to an ideal thermodynamic cycle used to describe spark-ignition engines, not a general classification category. Option d, "Carnot cycle engine," is an ideal theoretical engine cycle and is not used as a practical classification of IC engines.
For a given set of operating pressure limits of a Rankine cycle, the highest efficiency occurs for -
A)
Saturated cycle
B)
Superheated cycle
C)
Reheat cycle
D)
Regenerative cycle
For a given set of operating pressure limits in a Rankine cycle, the highest thermal efficiency is obtained by the regenerative cycle. Regeneration extracts some steam from intermediate turbine stages to preheat the feedwater, which raises the average temperature of heat addition in the boiler and reduces irreversibility, thereby improving efficiency more than the basic cycle modifications listed.
Why the others are incorrect:
- Saturated cycle: Lowest among these because steam enters the turbine without superheat, leading to higher moisture content and lower average heat-addition temperature.
- Superheated cycle: Better than saturated cycle because superheating increases turbine work and reduces moisture, but it does not improve efficiency as much as regeneration for the same pressure limits.
- Reheat cycle: Also improves efficiency and reduces turbine moisture, but for the same pressure limits it generally gives less efficiency gain than regeneration.
Hence, the correct answer is regenerative cycle.
A refrigeration cycle operates between condenser temperature of +27°C and evaporator temperature of -23°C, The Carnot coefficient of performance of cycle will be -
A)
0.2
B)
1.2
C)
5
D)
6
COP_carnot = Te/(Tc-Te)=250/(300-250)=5 with Te=250K (-23C) and Tc=300K (27C).
The basic part of the engine, to which the other engine parts are attached or assembled is the -
A)
Cylinder head
B)
Crankshaft
C)
Cylinder block
D)
Oil pan
Cylinder block is the main body to which head, crankshaft, piston and other parts are assembled.
The most effective air cleaner in the case of diesel engines is -
A)
Whirl type
B)
Oil bath type
C)
Wet type
D)
Dry type
Oil bath type removes heavy dust effectively, preferred for diesel engines in dusty atmosphere.
The cetane (C,,H,,) which is a straight chain paraffin, is assigned a cetane number of -
A)
0
B)
50
C)
100
D)
120
Cetane n-hexadecane is straight chain paraffin assigned cetane number 100 for diesel knock rating.
An open cycle gas turbine works on -
A)
Otto cycle
B)
Carnot cycle
C)
Stirling cycle
D)
Joule’s cycle
Open cycle gas turbine operates on Joule or Brayton cycle of constant pressure heat addition.
The seat belt tensioners are built in the -
A)
Front seats
B)
Shoulder anchors
C)
Seat belt retractors
D)
Seat belt buckles
Seat belt tensioners/pyrotechnic pretensioners are built into the retractor mechanism.
Which of the following is not an internal combustion engine?
A)
2-stroke petrol engine
B)
4-stroke petro! engine
C)
Diesel engine
D)
Steam turbine
Steam turbine is external combustion; others are internal combustion engines.
Axial flow pump is started with its delivery valve -
A)
Kept fully closed
B)
Kept fully open
C)
Irrespective ofany position
D)
Kept 50% open
Axial flow pumps have low head at zero flow; starting with fully open delivery reduces starting torque and power.
A 150 cc engine has following parameter as 150 cc -
A)
Fuel tank capacity
B)
Swept volume
C)
Cylinder volume
D)
Clearance volume
150 cc denotes swept volume (piston displacement) of engine.
A steam nozzle converts -
A)
Kinetic energy into heat
B)
Heat energy into potential energy
C)
Potential energy into heat
D)
Heat energy into kinetic energy
Nozzle converts enthalpy (heat) into kinetic energy by expansion.
Air refrigeration cycle is used in aeroplanes because of -
A)
High heat transfer rate of air
B)
Higher Coefficient of Performance
Air cycle preferred in aircraft for low weight per ton refrigeration and using ambient air; original options truncated.
What is the function of the alternator?
A)
Voltage Regulator
B)
Recharging the battery
C)
Auto-ignition
D)
Mixture of air and fuel
Alternator generates electricity to recharge battery and power electrics.
Which of the following does not relate to a compression ignition engine?
A)
Fuel pump
B)
Fuel injector
C)
Governor
D)
Carburettor
CI engines use fuel injection, not carburettor which is for SI engines.