Recently Updated Mechanical Engineering Interview Questions Part – 23

What is the difference between the centrifugal pump and positive displacement pump ?

Ans : usually all the pumps are classified into this two categories. Actually in centrifugal pump flow rate varies with the change of pressure/pressure head. But in positive displacement pump the flow rate is always the same whether there is a pressure difference or not.

Differentiate between scavenging and supercharging / turbocharging ?

Ans: In Scavenging the burnt gases from the engine cylinder is pushed out by the fresh air that before the exhaust stroke ends. Turbocharging/Supercharging is the process of adding extra air to the engine for a better ignition.

Give the names of different Thermodynamic Processes .

Ans :

Isothermal Process :

Constant Temperature process

Isochoric Process :

Constant Volume Process

Isobaric Process :

Constant Pressure Process

Throttling Process :

Constant Enthalpy Process

Isentropic or Adiabatic Process :

Constant Entropy Process

Why more lubricating oil is needed in two-stroke engines than four stroke engines ?

Ans : In two stroke engine the lubricant is mixed with the fuel. As a result some of the lub oil is blown out with the process of scavenging and getting fresh charge. This phenomenon is not seen in four stroke engines.

What are Internal Combustion (IC) Engines ?

Ans : These are engines in which combustion of the fuel takes place inside the engine cylinder.

What are the usual sequence of operation in IC engines ?

Ans : The sequence involve : Suction Stroke, Compression stroke, Combustion, Expansion or Working Stoke and the exhaust .

What is the main difference between petrol engine and diesel engine ?

Ans: In petrol engine the ignition is initiated by the spark plug but in diesel engine the fuel and air mixture auto-ignites after reaching a certain temperature.

Describe different types of scavenging process or Define Crossflow Scavenging, Back flow or loop scavenging and Uniflow scavenging .

Ans :

Crossflow Scavenging:

In Crossflow scavenging the inlet port and the outlet port is situated in the opposite sides in the engine cylinder. This type of scavenging is used in 2 stroke engines.

Back flow or loop Scavenging: In this type of scavenging the inlet and outlet port are on the same side.

Uniflow Scavenging:

In this method the fresh charge can enter through one or two inlets . The exhaust port is situated on the top of the cylinder.