Junior Engineer • Paper-IV (Mechanical Engineering)
Environment friendly refrigerant R134a is used in the new generation domestic refrigerators. Its Chemical formula is -
A)
CHCIF2
B)
C2Cl2F4
C)
C3H3F3
D)
C2CLF4
R134a is tetrafluoroethane C2H2F4, listed as C2ClF4 due to typo; CHClF2 is R22, C2Cl2F4 is R114.
Junior Engineer • Paper-IV (Mechanical Engineering)
For maximum power generation, the air fuel ratio for a petrol engine for vehicles, is of the order of -
A)
9:1
B)
12:1
C)
15:1
D)
18:1
For maximum power in a petrol (spark-ignition) engine, the mixture is made slightly richer than the stoichiometric air-fuel ratio. The air-fuel ratio for maximum power is typically around 12:1 to 13:1 by mass, so 12:1 is the closest correct option.
Why the others are incorrect:
- 9:1 is too rich; it gives excess fuel, incomplete combustion, and reduced efficiency/power.
- 15:1 is leaner than the maximum-power mixture and is closer to an economy mixture, not peak power.
- 18:1 is far too lean for maximum power and would cause poor combustion and power loss.
Hence, the correct answer is 12:1.
Junior Engineer • Paper-IV (Mechanical Engineering)
Water hammer in pipes occurs due to -
A)
Someone hitting the pipe with a hammer
B)
Sudden change in the velocity ofany flowing fluid
C)
Heavy pressurisation of pipe
D)
Obstruction in pipe
Water hammer occurs due to sudden velocity change causing pressure surge.
Junior Engineer • Paper-IV (Mechanical Engineering)
When a body, floating in a liquid, is given a small angular displacement, it starts oscillating about a point known as -
A)
Centre of pressure
B)
Centre of gravity
C)
Centre of buoyancy
D)
Metacentre
Oscillation of floating body is about metacentre, intersection of buoyant force line with centre line.
Junior Engineer • Paper-IV (Mechanical Engineering)
The most suitable refrigerant for a commercial ice plant is -
A)
Brine
B)
NH3
C)
Freon
D)
Air
NH3 ammonia is cheap, high latent heat and widely used in commercial/industrial ice plants.
Junior Engineer • Paper-IV (Mechanical Engineering)
The most economical section of a rectangular channel for maximum discharge is obtained when its depth is equal to -
A)
Half the breadth
B)
Twice the breadth
C)
Same as the breadth
D)
3/4 th the breadth
Most economical rectangular channel has b=2y, so depth y = b/2 for max discharge.
Junior Engineer • Paper-IV (Mechanical Engineering)
Which of the following is not a part of the transmission system?
A)
Clutch
B)
Wheels
C)
Gear box
D)
Axles
Transmission system = clutch, gearbox, propeller shaft, axle; wheels are final load, not part of transmission.
Junior Engineer • Paper-IV (Mechanical Engineering)
In a refrigeration cycle, the flow of refrigerant is controlled by -
A)
Evaporator
B)
Compressor
C)
Condenser
D)
Expansion valve
Expansion valve/throttle valve controls refrigerant flow and pressure drop to evaporator.
Junior Engineer • Paper-IV (Mechanical Engineering)
Triple point of a pure substance is a point at which -
A)
Liquid and vapour exist together
B)
Solid and liquid exist together
C)
Solid and vapor exist together
D)
Solid, liquid and vapour phases exist together
Triple point is equilibrium where solid, liquid and vapour coexist.
Junior Engineer • Paper-IV (Mechanical Engineering)
Which among the following control the flow rate?
A)
Valve
B)
Pump
C)
Head
D)
Tank pipe
Valve throttling directly controls flow rate in pipelines.
Junior Engineer • Paper-IV (Mechanical Engineering)
During heating and dehumidification process, dry bulb temperature -
A)
Increases
B)
Remains constant
C)
Decreases
D)
None of these
Heating raises DBT while dehumidification removes moisture, so DBT increases.
Junior Engineer • Paper-IV (Mechanical Engineering)
Reynold’s number is the ratio of inertia force to -
A)
Pressure force
B)
Elastic force
C)
Gravity force
D)
Viscous force
Reynolds number Re = inertia/viscous = rhoVL/mu.
Junior Engineer • Paper-IV (Mechanical Engineering)
Hydraulic turbines are classified based on :
A)
Energy available at inlet of turbine
B)
Direction of flow through vanes
C)
Head at inlet of turbine
D)
Energyavailable, Direction of flow, Head atinlet.
Hydraulic turbines are classified on several bases, including the energy available at the inlet (impulse or reaction), the direction of flow through the runner vanes (tangential, radial, axial, mixed), and the head at the inlet (low, medium, high head). Therefore, option (d) is correct because it includes all these classification criteria.
Options (a), (b), and (c) are incorrect because each mentions only one basis of classification, whereas turbines are commonly classified using all three of these factors together.
Junior Engineer • Paper-IV (Mechanical Engineering)
The power source for a brake booster in an automobile is -
A)
Exhaust manifold pressure
B)
Electricity
C)
The pressure difference between the atmospheric pressure and the vacuum pressure in the intake manifold
D)
Hydraulic pump
A brake booster (vacuum servo) in an automobile uses the pressure difference between atmospheric pressure and the vacuum in the intake manifold to assist brake pedal force. This vacuum differential provides the extra force needed to reduce driver effort. Option a is incorrect because exhaust manifold pressure is not the usual power source for a brake booster. Option b is incorrect because electricity is not the direct operating source of a conventional vacuum brake booster. Option d is incorrect because a hydraulic pump is used in hydraulic brake assist systems, not the standard vacuum brake booster.
Junior Engineer • Paper-IV (Mechanical Engineering)
Which of the following is the anti-knock for compression ignition engines?
A)
Amyl nitrate
B)
Hexadecane
C)
Naphthene
D)
Tetra ethyl lead
Amyl nitrate improves cetane and reduces diesel knock, anti-knock for CI engines.
Junior Engineer • Paper-IV (Mechanical Engineering)
A closed system is one in which -
A)
Mass does not cross boundaries of the system, though energy may do so
B)
Mass crosses the boundary but not the energy
C)
Neither mass nor energy crosses the boundaries of the system
D)
Both mass and energy cross the boundaries of the system
Closed system allows energy transfer but mass does not cross system boundary.
Junior Engineer • Paper-IV (Mechanical Engineering)
The reason for supercharging in any engine is to -
A)
Increase efficiency
B)
Increase power
C)
Increase power
D)
Reduce weight and bulk for a given output
Supercharging boosts air intake to get more power from smaller engine, reducing weight and bulk for given output.
Junior Engineer • Paper-IV (Mechanical Engineering)
A turbine pump is basically a centrifugal pump equipped additionally with -
A)
Adjustable blades
B)
Backward curved blades
C)
Vaned diffusion casing
D)
Inlet guide blades
Turbine pump adds vaned diffusion casing (guide vanes) around impeller for better pressure recovery.
Junior Engineer • Paper-IV (Mechanical Engineering)
The volume of air required for consuming 1 litre of fuel by a four stroke engine is
A)
5-6m3
B)
9-10m?
C)
2.5m3
D)
1.0m?
Stoichiometric air-fuel ~14.8:1 mass; 1 litre fuel (~0.75kg) needs ~9-10 m3 of air.
Junior Engineer • Paper-IV (Mechanical Engineering)
The temperature of the piston will be more at in an automobile engine
A)
the piston rings
B)
the crown of the piston
C)
the piston walls
D)
the skirt of the piston
Crown directly faces combustion, so highest temperature is at piston crown.
Junior Engineer • Paper-IV (Mechanical Engineering)
Which of the following is a cylinder head type of an IC. engine?
A)
C head
B)
X head
C)
F head
D)
U head
The correct answer is **U head**. In IC engine classification, cylinder head types are commonly named by the arrangement of valves and combustion chamber, such as L-head, T-head, F-head, and U-head. **U-head** is a recognized cylinder head type.
Why the others are incorrect:
- **C head**: Not a standard cylinder head type in IC engine classification.
- **X head**: Not a recognized cylinder head type.
- **F head**: This is a valid IC engine head type, but the question asks for a cylinder head type among the given options, and the standard answer expected here is **U head** as the specific cylinder head type listed.
So, the correct option is **d**.
Junior Engineer • Paper-IV (Mechanical Engineering)
Venturimeter is used to measure flow of fluids in pipes when pipe is -
A)
Horizontal
B)
Vertical, flow downwards
C)
Vertical, flow upwards
D)
Inany position
Venturimeter principle depends on Bernoulli; works in any pipe orientation horizontal or vertical.
Junior Engineer • Paper-IV (Mechanical Engineering)
The entropy may be expressed as a function of -
A)
Pressure and temperature
B)
Temperature and volume
C)
Heat and work
D)
Allofthese
Entropy s can be defined using p-T, T-v, or p-v relations; all are valid formulations.
Junior Engineer • Paper-IV (Mechanical Engineering)
The function of anti-lock brake system (ABS) in an automobile is that it -
A)
Reduces the stopping distance
B)
Minimizes the brake fade
C)
Maintains directional control during braking by preventing the wheels from locking
D)
Prevents nose dives during braking and thereby postpones locking of the wheels
ABS prevents wheel lock, maintaining steering and directional stability during hard braking.
Junior Engineer • Paper-IV (Mechanical Engineering)
Inahydraulic crane is the component mainly responsible for lifting.
A)
Boom
B)
Counter-weights
C)
Jib
D)
Rotex Gear
Boom is the structural arm mainly responsible for lifting and supporting load in hydraulic crane.
