Mechanical Engineering Interview Questions

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  • What is the purpose of scrapper ring

Scrap the excess lube oil from the cylinder walls. There by preventing oil from entering combustion zone.

  • How catalyst converter works?

In Fuel Cell, a catalyst is a substance that causes or accelerates a chemical reaction without itself being affected. Catalysts participate in the reactions, but are neither reactants nor products of the reaction they catalyze.

  • WHAT WILL HAPPEN IF RELIEF VALVE IN HYDRAULIC SYSTEM FAILS?

The main function of pressure relief valve is to maintain the pressure inhydraulic system. It is one mounting which is used for safety. When pressure increases then safety valve comes into action & if the valve get fail the system get damage due toexcessive pressure.

  • What does CC Stand for?

CC is the abbreviated form of cubic centimeter. It is the unit by which the capacity of an engine is designated. It is the volume between TDC and BDC. It represents the quantity of fuel-air mix or exhaust gas that is pumped out in a single piston stroke. Alternatively it can represent the volume of the cylinder itself.

  • We have read that when the piston goes up and down then the engine works i.e. the suction,compression etc etc. then what happens in the case of big vehicles, which start at stable condition, i.e. how does their piston moves when they are at rest. how suction,compression etc

Smaller vehicles like bikes, cars are started with the help of motors. initially, motors turn the crank shaft tillsufficient suction pressure is reached. when sufficient suction pressure is reached, the engine starts to suck the fuel in and then the cycle begins when the fuel is taken in and ignited. similarly, for huge engines, instead of motors, we use starting air. air at a pressure of 10-30 bar is fed to the engine which is at rest. this air rotates the engine till it attains sufficient suction pressure. once the pressure is reached, the cycle starts and it starts firing.

  • What is the name of the device used to transfer heat from a subsystem at lower temperature to the surroundings at higher temperature
    1. Heat engine
    2. Refrigerator
    3. Carnot’s engine
    4. Turbines

Answer:

Refrigerator

  • What is the difference between S.S to EN8

SS- Stainless steel

En- Medium carbon steel

SS is Non Magnetic material & EN8 is Magnetic material

SS is Corrosion resistant & EN8 is Magnetic material

  • The Compression ratio of Petrol engine is always less than Compression Ratio of Diesel engine why?

Petrol is not self igniting , it needs spark to flame up in chamber. Where as diesel is self igniting in dieselengine , to attain that state it requires high temp &pressure. This temperature & pressure is more than what’s required in Petrol Engines by property of that fluid .

  • What is the temperature of space ?

The short answer is that the temperature in space is approximately 2.725 Kelvin. That means the universe is generally just shy of three degrees above absolute zero – the temperature at which molecules themselves stop moving. That’s almost -270 degrees Celsius, or -455 Fahrenheit.

  • How to calculate the speed of conveyer in Meter Per Minute

Measure the diameter of the rollers around which the conveyor belt is wrapped. Multiply the diameter of the roller by pi (3.14159). This calculation will yield the circumference of the rollers. Every time the roller spins one revolution, the conveyor will be moved a linear distance equivalent to the circumference of the roller. Pi is a dimensionless factor, meaning it does not matter whether inches, centimeters or any other units of measurement are used. Measure the revolutions per minute (RPM) of the rollers. Count how many full revolutions (rotations) are made by the roller in one minute. Multiply the RPM by the circumference of the roller. This calculation will give the linear distance traversed by a point on the conveyor belt in one minute.

  • Inter-cooling in gas turbines
    1. Decreases net output but increases thermal efficiency
    2. Increases net output but decreases thermal efficiency
    3. Decreases both net output and thermal efficiency
    4. Increases both net output and thermal efficiency

Answer:

Increases both net output and thermal efficiency

Reason:

The gas turbine worked on the principle of Brayton cycle. Here the intercooler cool the Air/ Gas between L.P and H.P. stages of compression, allowing you to burn more fuel and generate more power.

New Battery Technology | Complete Recharge Within One Minute | Fast Recharge Batteries | 3D Batteries | 3D Film Technology

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Of all the criticisms of electric vehicles, probably the most commonly-heard is that their batteries take too long to recharge – after all, limited range wouldn’t be such a big deal if the cars could be juiced up while out and about, in just a few minutes. Well, while no one is promising anything, new batteries developed at the University of Illinois, Urbana-Champaign do indeed look like they might be a step very much in the right direction. They are said to offer all the advantages of capacitors and batteries, in one unit.

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"This system that we have gives you capacitor-like power with battery-like energy," said    U Illinois’ Paul Braun, a professor of materials science and engineering. "Most capacitors store very little energy. They can release it very fast, but they can’t hold much. Most batteries store a reasonably large amount of energy, but they can’t provide or receive energy rapidly. This does both."

The speed at which conventional batteries are able to charge or discharge can be dramatically increased by changing the form of their active material into a thin film, but such films have typically lacked the volume to be able to store a significant amount of energy. In the case of Braun’s batteries, however, that thin film has been formed into a three-dimensional structure, thus increasing its storage capacity.

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Batteries equipped with the 3D film have been demonstrated to work normally in electrical devices, while being able to charge and discharge 10 to 100 times faster than their conventional counterparts.

To make the three-dimensional thin film, the researchers coated a surface with nano scale spheres, which self-assembled into a lattice-like arrangement. The spaces between and around the spheres were then coated with metal, after which the spheres were melted or dissolved away, leaving the metal as a framework of empty pores. Electro polishing was then used to enlarge the pores and open up the framework, after which it was coated with a layer of the active material – both lithium-ion and nickel metal hydride batteries were created.

The system utilizes processes already used on a large scale, so it would reportedly be easy to scale up. It could also be used with any type of battery, not just Li-ion and NiMH.

The implications for electric vehicles are particularly exciting. "If you had the ability to charge rapidly, instead of taking hours to charge the vehicle you could potentially have vehicles that would charge in similar times as needed to refuel a car with gasoline," Braun said. "If you had five-minute charge capability, you would think of this the same way you do an internal combustion engine. You would just pull up to a charging station and fill up."

Braun and his team believe that the technology could be used not only for making electric cars more viable, but also for allowing phones or laptops to be able to recharge in seconds or minutes. It could also result in high-power lasers or defibrillators that don’t need to warm up before or between pulses.