Diploma Thermal Engineering 1 Important Questions Unit 4

Diploma Thermal Engineering 1 Important Questions

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Dept: Mechanical Engineering                                                     Scheme: N  

Subject: Thermal Engineering 1              

Unit – 4 Fuels and Combustion of Fuels & Performance of I.C. Engines

Chapter – 4 (A) Fuels and Combustion of Fuels

  1. What is Fuel?

Fuel is a substance which burns with oxygen in air and releases large amount of heat. The main elements of all fuels are carbon and hydrogen

  1. What are the classifications of Fuels?

Fuels are classified into three types

  1. Solid fuel example: Wood, Lignite and Coal
  2. Liquid fuel Example: Crude oil, petrol, diesel
  • Gaseous Fuels Example: Natural gas, Coal gas, LPG, Bio gas
  1. What are the requirements of good fuels?
  • Fuels should have higher calorific value
  • Fuels should have low ignition temperature
  • Fuels should burn freely with high efficiency
  • Fuels should not produce harmful gases, ash, smoke and soot
  • Fuels should be easy to store and handle
  1. What is Excess air?

During Combustion a portion of fuel may be unburnt. To avoid this, excess air is supplied. By supplying the excess air complete combustion is possible. The amount of excess air supplied generally depends on the type of fuel and furnace firing conditions. Generally, 25% to 50% Excess air is used

  1. Mention the effect of Excess air?

Excess air exerts a cooling effect on combustion process. To avoid this, the supplied excess air is preheated.

Total air supplied = Minimum air + Excess air

  1. Define Calorific value of a fuel

Calorific value of a fuel is defined as the amount of heat released (in kJ) by the complete combustion of 1 kg of fuel.

  1. What is higher or Gross Calorific Value?

Higher Calorific includes the energy obtained by condensing the water vapour

Higher calorific value is also called as Gross Calorific Value

Higher Calorific Value, H.C.V = 9270S +33800C + 144000 [ H2 – O2/8] kJ/kg

Diploma Thermal Engineering 1 Important Questions
Diploma Thermal Engineering 1 Important Questions
  1. Write the Dulong’s formula

Higher Calorific Value, H.C.V = 9270S +33800C + 144000 [ H2 – O2/8] kJ/kg

  1. What is the purpose of Bomb Calorimeter?

The purpose of Bomb calorimeter is to determine the calorific value of solid and liquid fuels.

  1. What is Lower Calorific Value?

Lower Calorific value does not include the energy obtained by condensing the water vapour.

Lower calorific value is also called as Net calorific value

L.C.V = H.C.V – (9H2 x x2465) kJ/kg

 

  1. What is Junker’s Gas Calorimeter?

Junkers calorimeter is used to determine the calorific value of gaseous fuels. It consists of a gas burner in which the gaseous fuel is burnt.

 

  1. What is Orsat apparatus?

Orsat apparatus is used to determine the volume percentages of Carbon di oxide (CO2), Carbon Mon oxide (CO), and oxygen (O2) in dry exhaust gas. Orsat apparatus consists of three flasks A, B and C.

Flask A Contains Caustic Soda (NaOH)/ This absorbs Carbon di oxide (CO2)

Flask B contains Pyrogallic acid solution. This absorbs oxygen(O2)

Flask C contains solution of cuprous chloride and hydrochloric acid. This absorbs Carbon Mon oxide (CO)

 

Chapter 4(b)– Performance of I.C. Engines

 

  1. Define Indicated mean effective pressure

Indicated mean effective pressure is the average pressure acting on the face of the piston for one complete cycle.

  1. What is Indicated power?

The power developed inside the engine cylinder is called indicated power

Indicated power (I.P) = pmi Lank

Where, Pmi – indicated mean effective pressure kN/m2

L – Stroke length, m

A – Area of the Piston, m2

n – Number of Power strokes (or) explosions per second

K – Number of Engine Cylinders

  1. Define Brake power.

Brake power is defined as the power available at the engine shaft. Brake power is less than Indicated power

Brake power = 2πNT

Where, N – Engine speed (RPS)

T – Engine Torque – N-m

  1. List the devices used to measure Brake power.

The devices used to measure brake power are

  1. Prony Brake dynamometer
  2. Rope Brake dynamometer

 

  1. Define Friction Power.

The difference between the indicated power and brake power is called Friction power

Friction power = Indicated poer – Brake power

F.P = I.P – B.P

  1. Define Mechanical Efficiency

Mechanical efficiency of an I.C. Engine is defined as the ratio of Brake power to Indicated power.

Mechanical Efficeincy = (B.P / I.P) X 100

  1. What is Specific fuel consumption (SFC)?

Specific fuel consumption is the most important term used in comparison of engines. Specific Fuel Consumption is the mass of fuel consumed per kW power developed per hour.

  1. Define Indicated thermal efficiency.

Indicated thermal efficiency is defined as the ratio of the actual power to the heat energy supplied to the engine

Indicated thermal efficiency = Indicated power / Heat supplied

  1. Define Brake thermal efficiency

Brake thermal efficiency is defined as the ratio of heat converted into useful work (BP) to the heat energy supplied to the engine

Brake thermal efficiency = Brake power / Heat energy supplied

  1. Define Volumetric Efficiency.

Volumetric Efficiency is defined ratio of the actual volume of the charge admitted into the engine cylinder during the suction stroke to the stroke volume of the piston

Volumetric efficiency = (Volume of the charge admitted during suction / Stroke volume of the piston) x 100

  1. What is Morse test?

Morse test is one of the method of finding indicated power of one cylinder in a multi cylinder I.C. Engines. This test is conducted for determining Indicated power of a multicylinder I.C Engines

  1. What is unaccounted heat loss?

The heat losses which cannot be determined accurately are known as unaccounted heat losses

Unaccounted heat loss may be determined by subtracting the accounted heat loss and heat converted into useful work from the heat supplied to the engine.

Check N Scheme Mechanical Department Study Materials
Strength of Materials Click here
Manufacturing Technology – 1  Click here
Thermal Engineering – 1  Click here
Metrology & Measurements Click here

 

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