MECHANICAL THEORY

IC Engines-Cooling Systems,Types, Performance Parameters, Lubrication of IC Engines

IC Engines-Cooling Systems, Types, Performance Parameters, Lubrication of IC Engines: Already, I had discussed Classification of IC Engines-Types of Heat Engines, Basic Engine Components & IC Engine Nomenclature in a detailed way. Apart from that, if you want to know about SI Engine, CI Engine, Otto Cycle, Diesel Cycle, Carnot cycle, you can click on the links provided. Here, in this article, I want to discuss Cooling Systems, Types of Cooling systems, Air cooling, Fluid cooling systems, Performance Parameters of IC Engines and Lubrication of IC Engines.

IC Engines
IC Engines

IC Engines-Cooling Systems, Types, Performance Parameters, Lubrication of IC Engines:

The first Topic in this article is about Cooling systems. So, let’s discuss.

Cooling Systems:

If the engine is allowed to run without external cooling, then the cylinder walls, cylinder, and Piston will tend to assume the average temperature of the gases to which they are exposed, which may be of the order of 1000 to 1500 degree centigrade.

At that temperature, the metal will lose their characteristics and Piston will expand and seize the liner.

Thus the cooling system is provided in an engine for the following reasons.

  • The even expansion of piston in the cylinder may result in seizure of piston.
  • High temperatures reduce the strength of piston and cylinder liner.
  • The overheated cylinder may lead to pre-ignition of the charge in case of SI engine.
  • Physical and chemical changes may occur in lubricating oil which may cause stocking of piston rings and excessive wear of cylinder.

There are mainly two methods of cooling in IC engines.

1.Air Cooling or Direct Cooling

2.Liquid Cooling or Indirect Cooling

COOLING SYSTEMS-IC ENGINES
COOLING SYSTEMS-IC ENGINES

1.Air Cooling System:

  • In this method, heat is carried away by air flowing over and around the engine cylinder.
  • It is used in scooters, motorcycles, etc.
  • Here, fins are cast on the cylinder head which provides an additional conductive and radiating surface.
  • The fins are arranged in such a way that they are at right angles to the cylinder axis.

Advantages of Air Cooling:

  • Absence of cooling pipes, radiator etc.makes the cooling system simpler.
  • No danger of coolant leakage etc.
  • The engine is not subjected to freezing troubles etc.that are usually encountered in case of water cooling.
  • Installation of air-cooled engines is easier.
  • It requires no external components. Example: tank, radiator, etc.

Disadvantages of Air Cooling:

  • Their movement is noisy.
  • Non-uniform cooling.
  • The output of an air-cooled engine is less than that of a liquid-cooled engine.
  • Maintenance is not easy.

2.Liquid Cooling System:

  • In this method of cooling engines, the cylinder walls and heads are provided with jackets through which the cooling liquid can circulate.
  • The heat is transferred from cylinder walls to the liquid by conduction and convection.
  • The liquid is heated in its passage through the jackets and is itself cooled by means of air cooling radiator system. The heat from a liquid, in turn, is transferred to the air.

Advantages of Liquid Cooling:

In the case of a water-cooled engine, installation is not necessary at the front of mobile vehicles, aircraft, etc. As the cooling system can be conveniently located wherever required. This is not possible in case of air-cooled engines.

Dis-Advantages of Liquid Cooling:

  • This is a dependent system in which the supply of water for circulation in the jacket must be required.
  • In the event of failure of the cooling system, serious damage may be caused to the engine.
  • Cost of the system is considerably high.
  • The system requires considerable attention to the maintenance of various parts of the system.

Performance Parameters of IC Engines:

Indicated Power

Brake Power

Frictional Power

Indicated Thermal Efficiency

Brake Thermal Efficiency

Mechanical Efficiency

Volumetric Efficiency

Relative Efficiency/ Efficiency Ratio

The calorific value of the Fuel

Mean Effective Pressure

Specific Power Output

Fuel-Air or Air-Fuel Ratio

I.P.

B.P.

F.P.

ηith

ηbth

ηm

ηv

ηrel

CV (HCV/ LCV)

pm OR mep

Ps

F/A or A/F

 

The explanation of Performance parameters of IC engines is as follows.

1.Indicated power (I.P):

The total Power developed by the combustion of the fuel in the combustion chamber is called as Indicated power.

2.Break power (B.P):

The Power developed by an engine at the output shaft is called break power.

B.P=[2πNT/60]*1000 KW

3.Frictional power (F.P):

The difference between Indicated Power(I.P) and Brake Power(B.P) is called frictional power (F.P).

                           F.P=I.P-B.P

4.Indicated Thermal Efficiency (ηith):

It is defined as the ratio of energy in the indicated power, to the input fuel energy in appropriate units.

ηithI.P/(mass of fuel*Calorific value of fuel)

       = I.P/(mf*CV)

5.Brake Thermal Efficiency (ηbth):

It is defined as the ratio of energy in the brake power, to the input fuel energy in appropriate units. 

ηbth = B.P/(mass of fuel*Calorific value of fuel)

       = B.P/(mf*CV)

6.Mechanical Efficiency (ηm):

It is defined as the ratio of Brake Power (delivered power) to the Indicated Power (power provided to the piston).

ηm = B.P/I.P

Or

 It is also defined as the ratio of the brake thermal efficiency to the indicated thermal efficiency.

ηm = ηbth/ηith

7.Volumetric Efficiency (ηv):

It is defined as the ratio of the volume of air actually inducted at ambient conditions to the swept volume of the engine.

ηv = Vol.of air actually inducted/Swept Volume

8.Relative Efficiency or Efficiency ratio(ηrel):

It is defined as the ratio between actual thermal efficiency to the ideal efficiency (air standard efficiency) of the cycle employed.

ηrel = Actual thermal efficiency/ideal efficiency (air standard efficiency)

9.Calorific Value:

It is the thermal energy released per unit quantity of the fuel when the fuel is burned completely and the products of combustion are cooled back to the initial temperature at the combustion mixture.

10.Mean Effective Pressure:

It is defined as the average pressure inside the cylinders of an I.C engine based on the calculated or measured power output.

11.Specific Power Output:

It is defined as the broken output per unit of piston displacement.

Specific Power Output=B.P/(A*L)

12.Fuel-air Ratio:

It is defined as the ratio of the mass of the fuel to the mass of the air in the air-fuel mixture.

 This is the detailed explanation of Performance Parameters of IC Engines.


Lubrication of IC Engines:

Lubrication is the admittance of oil having relative motion between two surfaces.

The purpose of lubrication maybe one or more of the following.

  • Reduce wear and friction between the parts having relative motion.
  • Cool the surfaces by carrying away heat due to friction.
  • Seal a space adjoining the surfaces such as Piston rings and cylinder liner.
  • Absorb shock between bearings and other parts and consequently reduce noise.
  • Cleaning the surfaces by carrying away the carbon and metal particles caused by wear.

Properties of Lubricant:

  • Fire point

It is the lowest temp at which oil burns continuously.

  • Cloud point

When the oil is subjected to low temperature, the change in the state takes places from liquid to plastic or solid-state such that it appears to a cloud called Cloud Point.

  • Pour Point

It is the lowest temperature at which the lubricating oil will pour. It is an indication of its ability to move at low temperature.

  • Oiliness

Property which enables oil to spread over is called Oiliness.

  • Corrosion

Should not corrode the working parts

  • Physical and chemical stability

Physically and chemically stable between operating temperatures

  • Adhesiveness

Oil particles stick to the metal surface is called Adhesiveness.

  • Specific gravity

It is the measure of the density of oil.


Types of Lubrication Systems:

  1. Dry sump lubrication
  2. Mist lubrication
  3. Wet sump lubrication
  • Splash
  • Semi pressure system or Pressure Fed or Force Feed.
  • Full pressure system or Combination Pressure Fed and Splash.

 

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.