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Past Questions — 2025
Which of the following is not part of four stroke Engine Cycle?
A)
Suction
B)
Compression
C)
Expansion
D)
Scavenging
A four-stroke internal combustion engine operates on a cycle consisting of four distinct piston strokes:
1. Suction (Intake): The piston moves from Top Dead Center (TDC) to Bottom Dead Center (BDC), drawing the air-fuel mixture (or air alone in diesel engines) into the cylinder.
2. Compression: The piston moves from BDC to TDC, compressing the charge to increase pressure and temperature.
3. Expansion (Power): The combustion of the fuel forces the piston from TDC to BDC, producing useful mechanical work.
4. Exhaust: The piston moves from BDC to TDC, pushing the combustion gases out of the cylinder.
Scavenging, on the other hand, is the process of pushing exhaust gases out of the cylinder using a fresh charge of air or air-fuel mixture. This process is a characteristic feature of two-stroke engines, where the intake and exhaust functions happen simultaneously or in quick succession without a dedicated exhaust stroke. Therefore, scavenging is not a part of the standard four-stroke engine cycle.
The instrument used to measure the outer diameter of cylindrical object is-
A)
Vernier Height Gauge
B)
Micrometer
C)
Dial Gauge
D)
Bevel Protractor
Step-by-step reasoning:
1. The objective is to identify the tool used to measure the outer diameter of a cylindrical object.
2. Analysis of options:
- (a) Vernier Height Gauge: Used primarily for measuring the height of objects or marking off heights from a reference surface.
- (b) Micrometer (specifically the Outside Micrometer): Designed specifically to measure external dimensions, such as the outer diameter of a cylinder or the thickness of a plate, with very high precision (typically up to 0.01mm or 0.001mm).
- (c) Dial Gauge: Used for checking the roundness (ovality) of a cylinder, flatness of a surface, or comparing dimensions against a standard; it does not measure the absolute diameter directly.
- (d) Bevel Protractor: Used for measuring or marking angles.
3. Conclusion: The Micrometer is the standard instrument for measuring the outer diameter of cylindrical objects.
A bevel protractor is used to measure-
A)
Internal Diameter
B)
Straightness
C)
Angles
D)
Thread pitch
A bevel protractor is a precision measuring instrument specifically designed to measure angles with high accuracy. It typically consists of a base (stock) and a rotating blade (bevel) connected by a pivot, often equipped with a vernier scale to measure angles down to a few minutes of a degree.
Analysis of other options:
- Internal Diameter: Measured using internal calipers, inside micrometers, or bore gauges.
- Straightness: Verified using a straight edge, spirit level, or an autocollimator.
- Thread pitch: Measured using a screw pitch gauge or a micrometer.
What is the function of a thermostat in a liquid cooling System?
A)
To control the speed of the cooling fan
B)
To regulate the flow of coolant based on engine temperature
C)
To increase the pressure of the coolant
D)
To lubricate the water pump
A thermostat in a liquid cooling system acts as a temperature-controlled valve. Its primary function is to maintain the engine at its optimal operating temperature. When the engine is cold (during startup), the thermostat remains closed, preventing coolant from flowing to the radiator; this allows the engine to warm up quickly to reduce wear and improve efficiency. Once the coolant reaches a specific predetermined temperature, the thermostat opens, allowing the hot coolant to flow into the radiator to be cooled by air.
Analysis of other options:
- Option (a) is incorrect because the cooling fan speed is typically controlled by a fan switch, a sensor, or the engine's RPM (in belt-driven fans), not the thermostat.
- Option (c) is incorrect because coolant pressure is managed by the radiator cap (pressure valve), not the thermostat.
- Option (d) is incorrect because the water pump is lubricated by the coolant itself or internal bearings/seals, not by the thermostat.
The most commonly used gases in gas welding are-
A)
Hydrogen and Oxygen
B)
Propane and Oxygen
C)
Acetylene and Oxygen
D)
Methane and Oxygen
Gas welding (specifically Oxy-fuel welding) requires a fuel gas and an oxidizing agent (oxygen) to produce a high-temperature flame capable of melting metals.
1. **Acetylene (C2H2)** is the most commonly used fuel gas because it produces the highest flame temperature (approximately 3,160°C to 3,500°C) among the common fuel gases. This high temperature allows for faster melting and better penetration of the metal.
2. **Oxygen (O2)** acts as the supporter of combustion, allowing the fuel gas to burn intensely.
Comparing other options:
- **Hydrogen and Oxygen**: While used in some specialized applications, the flame temperature is lower than acetylene, and hydrogen is more expensive and harder to store.
- **Propane and Oxygen**: Propane is used for heating or brazing, but its flame temperature is significantly lower than acetylene, making it less effective for fusion welding of steel.
- **Methane and Oxygen**: Methane has a very low flame temperature and is not suitable for industrial gas welding.
Spark Ignition (S.I.) Engine is also known as-
A)
Diesel Engine
B)
Petrol Engine
C)
Steam Engine
D)
Electric Engine
A Spark Ignition (S.I.) engine is an internal combustion engine where the fuel-air mixture is ignited by an electric spark produced by a spark plug. Petrol (gasoline) is the primary fuel used in these engines because of its volatility and ability to mix with air to form a combustible mixture.
Analysis of options:
- Option (a) Diesel Engine: These are Compression Ignition (C.I.) engines, where fuel is ignited by the heat of highly compressed air, not by a spark.
- Option (b) Petrol Engine: Correct. These utilize spark plugs for ignition.
- Option (c) Steam Engine: This is an External Combustion engine where steam is generated in a boiler outside the cylinder.
- Option (d) Electric Engine: This is an electrical machine (motor) that converts electrical energy into mechanical energy; it is not an internal combustion engine.
Which of the following is typically recorded in a car diary?
A)
Daily Horsepower
B)
Number of Passengers
C)
Trip start and end location, date and distance
D)
Vehicle fitness
A car diary (also known as a vehicle logbook) is an official record used primarily in government departments and corporate organizations to track the utilization of a vehicle. Its primary purpose is to monitor fuel consumption, ensure the vehicle is used for authorized official purposes, and track maintenance intervals.
1. Why Option 'c' is correct: A standard car diary must record the date of the journey, the starting point, the destination (end location), and the odometer readings (start and end) to calculate the total distance traveled. This provides an audit trail for the vehicle's movement.
2. Why Option 'a' is incorrect: Horsepower is a technical specification of the engine and remains constant; it is not a daily variable to be recorded in a diary.
3. Why Option 'b' is incorrect: While some specialized transport logs might track passengers, a standard official car diary focuses on the vehicle's movement and mileage rather than the number of occupants.
4. Why Option 'd' is incorrect: Vehicle fitness is recorded in a 'Fitness Certificate' issued by the Regional Transport Office (RTO) after a formal inspection, not in the daily car diary.
A car’s headlight suddenly fails. Which of the following is the most likely cause?
A)
A blown fuse
B)
A dead battery
C)
A faulty alternator
D)
A loose ground connection
Step-by-step reasoning: 1. The keyword in the question is 'suddenly fails'. This implies an instantaneous break in the electrical circuit. 2. A blown fuse (Option a) is designed to break the circuit immediately if there is an overcurrent or short circuit, leading to a sudden loss of power to the specific component (the headlights). 3. A dead battery (Option b) or a faulty alternator (Option c) would typically cause a gradual dimming of lights or a total failure of all electrical systems (including the engine starting system), rather than just the headlights suddenly failing while the car is likely operational. 4. While a loose ground connection (Option d) can cause failure, it often manifests as flickering or intermittent failure before a total break, whereas a fuse 'blows' instantly. Therefore, in the context of a sudden failure of a specific circuit, a blown fuse is the most likely and common cause.
The Component that controls the gas flow to the torch is called-
A)
Mixture
B)
Valve
C)
Tip
D)
Regulator
In gas welding (such as Oxy-Acetylene welding), the flow of gases from the cylinders to the torch and finally to the tip is controlled by valves. Specifically, the torch contains control valves (needle valves) that allow the operator to precisely adjust the flow rate of oxygen and fuel gas to achieve the desired flame type (neutral, oxidizing, or carburizing).
Why other options are incorrect:
- a. Mixture: This refers to the combination of gases, not a mechanical component that controls flow.
- c. Tip: The tip (or nozzle) determines the size and shape of the flame and the exit point of the gas, but it does not 'control' the flow rate; that is done upstream by the valves.
- d. Regulator: While a regulator controls the pressure of the gas leaving the cylinder, the specific component on the torch used to control the flow into the flame is the valve.
The electrode used in TIG welding is-
A)
Consumable
B)
Coated
C)
Non-consumable
D)
Made of copper
TIG (Tungsten Inert Gas) welding, also known as Gas Tungsten Arc Welding (GTAW), uses a non-consumable electrode made of tungsten. The purpose of the electrode in TIG welding is solely to create the electric arc that melts the base metal; it does not melt into the weld pool. If filler metal is required, it is added separately by the welder.
Analysis of other options:
- (a) Consumable: This describes electrodes used in MIG (Metal Inert Gas) or SMAW (Shielded Metal Arc Welding), where the electrode melts to become part of the joint.
- (b) Coated: This refers to electrodes used in SMAW (Stick welding), where a flux coating provides shielding gas and slag.
- (d) Made of copper: Copper is too conductive and has a melting point too low for the arc temperatures required in TIG welding; tungsten is used because of its extremely high melting point.
A radiator is the container of which of the following liquid?
A)
Brake oil
B)
Engine oil
C)
Gear oil
D)
Coolant
A radiator is a heat exchanger used in the liquid cooling system of an internal combustion engine. Its primary purpose is to transfer heat from the liquid coolant (which has absorbed heat from the engine block) to the surrounding air.
Step-by-step reasoning:
1. **Coolant (Option d):** This is the correct answer. Coolant (typically a mixture of water and ethylene glycol) circulates through the engine and then flows into the radiator to be cooled down before returning to the engine.
2. **Brake oil (Option a):** This is a hydraulic fluid used in the braking system to transmit force from the pedal to the brake calipers/cylinders; it is stored in a brake fluid reservoir, not a radiator.
3. **Engine oil (Option b):** This is a lubricant used to reduce friction between moving parts. It is stored in the oil pan (sump) and circulated by an oil pump.
4. **Gear oil (Option c):** This is a heavy-duty lubricant used in the transmission and differentials; it is contained within the gearbox or axle housing.
What is the function of a Pressure relief valve in a lubrication system?
A)
To regulate the flow of oil to the engine
B)
To prevent the oil pressure from becoming too high
C)
To cool the oil
D)
To filter the oil
Step-by-step reasoning:
1. **Function of a Pressure Relief Valve (PRV):** In a lubrication system, the oil pump delivers oil at a rate that may exceed the system's requirements or the capacity of the bearings/galleries to absorb it, especially at high engine speeds. A pressure relief valve is a safety mechanism designed to open when the system pressure reaches a predetermined maximum limit.
2. **Mechanism:** When the pressure exceeds the spring tension of the valve, the valve opens and diverts the excess oil back to the oil sump or the pump inlet, thereby capping the maximum pressure.
3. **Why Option 'b' is correct:** Its primary purpose is to protect the system components (such as oil filters, seals, and gaskets) from bursting or leaking due to excessive pressure.
4. **Why other options are incorrect:**
- Option 'a' (Regulate flow): While it affects flow, 'regulation' usually implies maintaining a specific flow rate for operation, whereas a relief valve is specifically for over-pressure protection.
- Option 'c' (Cool the oil): Oil cooling is handled by an oil cooler (heat exchanger) or the oil sump.
- Option 'd' (Filter the oil): Oil filtration is performed by the oil filter or strainer.
Which of the following is common type of oil pump used in lubrication systems?
A)
Centrifugal pump
B)
Diaphragm pump
C)
Gear pump
D)
Piston pump
In lubrication systems, the primary requirement is to move a viscous fluid (oil) at a constant flow rate and high pressure to ensure all moving parts of an engine or machine are coated.
1. Gear Pumps (Correct): These are positive displacement pumps. They are highly preferred for lubrication systems because they can handle high-viscosity fluids, provide a steady flow regardless of pressure changes, and are robust and simple to manufacture.
2. Centrifugal Pumps (Incorrect): These are dynamic pumps used primarily for water or low-viscosity fluids. They are inefficient for thick oils and cannot maintain a constant flow against varying pressure loads.
3. Diaphragm Pumps (Incorrect): These are typically used for dosing chemicals or handling corrosive/slurry fluids; they are not suitable for the continuous, high-pressure flow required in engine lubrication.
4. Piston Pumps (Incorrect): While they are positive displacement pumps, they are generally too complex, expensive, and bulky for standard lubrication systems, being reserved for high-pressure hydraulic systems instead.
Common flux used in brazing is-
A)
Rosin
B)
Zinc Chloride
C)
Borax
D)
Lime
Brazing is a joining process where a filler metal is melted and drawn into the joint by capillary action. To ensure a strong bond, a flux is used to prevent the formation of oxides on the base metal surfaces and to promote the wetting of the filler metal.
1. **Borax (Sodium Borate)**: This is the most common and widely used flux in brazing, especially for copper and steel. It melts at a relatively low temperature and effectively dissolves metal oxides, providing a clean surface for the filler metal to bond with.
2. **Rosin**: This is primarily used as a flux in soft soldering (especially for electronics), not brazing, as it cannot withstand the higher temperatures required for brazing.
3. **Zinc Chloride**: While used in some soldering fluxes (acid fluxes), it is generally too corrosive and not the standard 'common' flux for general brazing applications compared to borax.
4. **Lime**: Calcium oxide (lime) is not used as a flux in brazing; it is more commonly associated with metallurgy in smelting or construction materials.
What is the full form of BS-VI used in vehicles?
A)
Bharat State – VI
B)
Bharat Standard – VI
C)
Bharat Stage – VI
D)
Bureau of Standard – VI
BS-VI stands for 'Bharat Stage VI'. It is an emission standard instituted by the Government of India to regulate the output of air pollutants (such as nitrogen oxides, particulate matter, and carbon monoxide) from internal combustion engines. These standards are based on the European (Euro) emission standards.
- Option (a) 'Bharat State' is incorrect as it refers to a political entity, not a technical standard.
- Option (b) 'Bharat Standard' is a common misconception, but the official terminology used by the Ministry of Road Transport and Highways (MoRTH) is 'Stage'.
- Option (d) 'Bureau of Standard' is incorrect; while the Bureau of Indian Standards (BIS) exists, the specific automotive emission nomenclature is 'Bharat Stage'.
A vehicle history sheet typically includes all except-
A)
dates of Services
B)
types repair done
C)
road condition during trips
D)
name of workshop
A Vehicle History Sheet (also known as a vehicle maintenance log or service record) is a formal document used by fleet managers and engineers to track the lifecycle, maintenance, and repair history of a specific vehicle.
1. **Dates of Services (Option a):** Essential for tracking maintenance intervals and ensuring the vehicle is serviced according to the manufacturer's schedule.
2. **Types of repair done (Option b):** Critical for identifying recurring faults, tracking part replacements, and assessing the overall mechanical health of the vehicle.
3. **Name of workshop (Option d):** Necessary for accountability, warranty claims, and verifying that the work was performed by an authorized or qualified service provider.
**Why Option c is correct:** 'Road condition during trips' is operational data typically recorded in a **Trip Sheet** or a **Driver's Log Book**, not a Vehicle History Sheet. The history sheet focuses on the physical state and maintenance of the machine itself, whereas road conditions are external environmental factors related to specific journeys.
What is scavenging in a two stroke Engine?
A)
The process of compressing the air fuel mixture
B)
The process of igniting the air fuel mixture
C)
The process of removing exhaust gases and replacing them with fresh charge
D)
The process of lubricating the engine
In a two-stroke internal combustion engine, the functions of intake, compression, power, and exhaust are completed in just two strokes of the piston. Unlike a four-stroke engine, which has dedicated strokes for intake and exhaust, a two-stroke engine performs these actions simultaneously. 'Scavenging' is the specific process where the fresh air-fuel mixture (or just air in diesel engines) enters the cylinder and pushes out the burnt exhaust gases from the previous combustion cycle. This ensures the cylinder is cleared of waste gases and filled with a fresh charge for the next cycle.
Analysis of other options:
- Option (a) refers to 'Compression', which is a separate phase of the cycle.
- Option (b) refers to 'Ignition' or 'Combustion'.
- Option (d) refers to 'Lubrication', which is a maintenance process to reduce friction, not a cycle phase.
Arc welding is a type of-
A)
Solid-state Welding
B)
Fusion Welding
C)
Resistance Welding
D)
Pressure Welding
Step-by-step reasoning:
1. Definition of Arc Welding: Arc welding is a process that uses an electric arc to create intense heat to melt the base metals and usually a filler material to join two pieces of metal together.
2. Classification of Welding: Welding processes are broadly categorized based on whether the base metal is melted or not.
- Fusion Welding: Processes where the base metal is melted to form a pool of molten metal that solidifies to create a joint. Examples include Arc welding, Gas welding, and Laser beam welding.
- Solid-state Welding: Processes where joining occurs without melting the base metal, typically using pressure and heat below the melting point. Examples include Friction welding and Forge welding.
3. Evaluating Options:
- Option (a) Solid-state Welding: Incorrect, as arc welding involves melting the metal.
- Option (b) Fusion Welding: Correct, as the electric arc melts the metal to create a fusion joint.
- Option (c) Resistance Welding: While resistance welding uses electricity, it is a specific sub-category that relies on electrical resistance and pressure; arc welding relies on an open electric arc.
- Option (d) Pressure Welding: Incorrect, as arc welding relies on heat/melting rather than primary mechanical pressure to achieve the bond.
What is the heat source in Arc welding?
A)
Friction
B)
Resistance Heating
C)
Chemical Reaction
D)
Electric Arc
Arc welding is a fusion welding process that uses an electric arc to create heat to melt and join metals. An electric arc is formed between an electrode and the base material; the high current flowing through this ionized gas gap generates intense heat (typically between 3,000°C to 20,000°C), which melts the metals to form a weld pool.
Why other options are incorrect:
- a. Friction: This is the heat source for Friction Welding, where mechanical rubbing generates heat.
- b. Resistance Heating: This is the heat source for Resistance Welding (e.g., Spot Welding), where heat is generated by the electrical resistance of the materials to the current flow.
- c. Chemical Reaction: This is the heat source for Thermite Welding, where an exothermic chemical reaction between aluminum powder and metal oxide is used.
What is the primary purpose of the air filter?
A)
To improve the engine performance
B)
To keep dust and debris from entering the engine
C)
To cool down the engine
D)
To Make the car look nicer
The air filter is a critical component of the engine intake system. Its primary function is to act as a barrier that traps airborne contaminants—such as dust, dirt, pollen, and other debris—before the air enters the combustion chamber. If these particles were allowed to enter the engine, they would act as abrasives, causing premature wear and tear on the cylinder walls, piston rings, and valves, eventually leading to engine failure.
Analysis of other options:
- Option (a): While a clean air filter helps maintain optimal performance, the 'primary purpose' is protection, not performance enhancement itself.
- Option (c): Cooling the engine is the primary purpose of the radiator and cooling system, not the air filter.
- Option (d): The air filter is typically located inside the engine bay or a housing and is not a cosmetic feature designed to make the car look nicer.
Compression Ignition (C.I) engine is also known as-
A)
Petrol Engine.
B)
Diesel Engine
C)
Steam Engine
D)
Electric Engine
A Compression Ignition (C.I.) engine is an internal combustion engine where the ignition of the fuel is triggered by the heat generated from the high compression of air. In this cycle, only air is compressed to a very high pressure and temperature; fuel (typically diesel) is then injected into this hot air, causing it to ignite spontaneously without the need for an external spark. This is the fundamental operating principle of a Diesel Engine.
Analysis of other options:
- Option (a) Petrol Engine: These are Spark Ignition (S.I.) engines, where a spark plug is used to ignite a mixture of air and fuel.
- Option (c) Steam Engine: This is an External Combustion engine where steam is generated in a separate boiler.
- Option (d) Electric Engine: This is an electric motor, not an internal combustion engine, as it converts electrical energy into mechanical energy.
What is the function of spark plug in Petrol Engine?
A)
Mix air -fuel
B)
Deliver electric spark to ignite the air - fuel mixture
C)
Measure engine temperature
D)
Open and close engine valves
In a petrol engine (which operates on the Spark Ignition or SI cycle), the air-fuel mixture is compressed within the cylinder. Unlike a diesel engine, which uses compression heat to ignite the fuel, a petrol engine requires an external source of ignition. The spark plug is an electrical device that delivers a high-voltage electric spark across a small gap at the end of the plug, which initiates the combustion of the compressed air-fuel mixture, driving the piston downward.
Analysis of other options:
- Option (a) is incorrect because the mixing of air and fuel is performed by the carburetor or fuel injectors.
- Option (c) is incorrect because engine temperature is measured by a temperature sensor or thermocouple.
- Option (d) is incorrect because the opening and closing of valves are controlled by the camshaft and valve train mechanism.
Which of the following is not a type of welding?
A)
TIG Welding
B)
MIG Welding
C)
Gas Welding
D)
Lathe Welding
To determine which option is not a type of welding, we analyze each process:
1. **TIG Welding (Tungsten Inert Gas Welding):** This is a legitimate arc welding process that uses a non-consumable tungsten electrode to produce the weld. It is widely used for high-quality welds on stainless steel and aluminum.
2. **MIG Welding (Metal Inert Gas Welding):** This is a legitimate arc welding process where a consumable wire electrode is fed through a welding gun. It is known for its speed and efficiency in industrial applications.
3. **Gas Welding:** This is a legitimate welding process (such as Oxy-Acetylene welding) that uses the combustion of fuel gases and oxygen to create a flame that melts the base metal and filler rod.
4. **Lathe Welding:** A lathe is a machine tool used for machining (turning, facing, threading) by rotating a workpiece against a cutting tool. While welding can be performed on a part that is held in a lathe (for symmetry), 'Lathe Welding' is not a recognized category or process of welding in mechanical engineering.
Therefore, option (d) is the correct answer as it describes a machine tool rather than a welding process.
In a petrol engine what does the term MPFI stand for-
A)
Mechanical Petrol Fuel Injection
B)
Multi Point Fuel Injection
C)
Manifold Pressure Fuel Injection
D)
Maximum Petrol Fuel Intake
MPFI stands for Multi Point Fuel Injection. In this system, each cylinder has its own dedicated fuel injector located just before the intake valve. This allows for precise control of the fuel-air mixture for each individual cylinder, leading to better fuel efficiency, lower emissions, and improved engine performance compared to single-point injection or carburetors.
Analysis of other options:
- Option (a) 'Mechanical Petrol Fuel Injection' is incorrect as modern MPFI systems are electronically controlled (EFI).
- Option (c) 'Manifold Pressure Fuel Injection' is incorrect; while manifold pressure is a sensor input (MAP sensor) used to calculate fuel delivery, it is not what MPFI stands for.
- Option (d) 'Maximum Petrol Fuel Intake' is a nonsensical term in the context of fuel injection system nomenclature.
Which gas is highly explosive and needs careful handling in gas welding?
A)
Oxygen
B)
Hydrogen
C)
Nitrogen
D)
Acetylene
Step-by-step reasoning: 1. Gas welding typically involves a fuel gas and an oxidizing agent (oxygen). 2. Acetylene (C2H2) is the most common fuel gas used due to its high flame temperature. 3. Acetylene is chemically unstable and highly explosive when mixed with air or oxygen, especially at pressures above 15 psi (approx 1 bar), where it can decompose violently without an external ignition source. This is why it is stored dissolved in acetone within porous masses in cylinders. 4. Oxygen (Option a) is an oxidizer; it supports combustion but is not explosive on its own. 5. Hydrogen (Option b) is flammable and explosive, but in the context of standard gas welding (Oxy-Acetylene welding), Acetylene is the primary gas noted for its extreme instability and specific handling requirements (like flash-back arrestors). 6. Nitrogen (Option c) is an inert gas and is not explosive.
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