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I.C. Engine Testing and Pollution Control


IC Engine Testing:

a) Introduction of IC Engine Testing:

  • To obtain the information about the engine this cannot be determine by calculation.
  • To confirm data used in design, the validity of which is in doubt.

1) Indicated Power (I.P.) :-

  • The power developed inside the engine is called as indicated power.
  • It is denoted by I.P.

2) Brake Power :-

  • The brake power of an engine is the useful power available at the crank shaft it is called as brake power.
  • The brake power is less than indicated power.
  • It is denoted by B.P

Efficiency of Engine Testing :-

1)  Mechanical efficiency :-

It is the ratio of useful power available at crankshaft to power developed inside the engine.

2) Thermal efficiency :-

It is defined as the ratio of heat equivalent of power developed by the engine to the heat supplied by combustion of fuel in the engine.

3) Volumetric efficiency :-

It is defined as the ratio of actual volume of charge admitted during suction stroke at N.T.P. condition to the swept volume of the piston.

BSFC:

It is the mass of fuel required to develop 1kW brake power for a period of one hour is inversely proportional to break thermal efficiency.

Morse test on IC Engine :-

  • It is simple method, to determine the accurate indicated power of multi cylinder engine.
  •  This method is used only multi-cylinder IC engine only.
  • The Morse test consists of obtaining indicated power of the engine without any equipment.
  • The test making, in turn, each cylinder of the engine inoperative and nothing the reduction in brake power developed.
  • In a petrol engine each cylinder is inoperative by shorting the spark plug of the cylinder to be made inoperative.
  • In Diesel engine, a particular cylinder is made inoperative by cutting of the supply of the fuel.
  • It is assumed that pumping and friction are the same when the cylinder is inoperative as well as during firing.
  • In this test, the engine is run at required speed and brake power is measured.
  • One cylinder is cut off by short circuiting the spark plug if it is a petrol engine or cutting of fuel supply in diesel engine.
  • Since one of the cylinder is cut off the producing the power, the speed of engine will change.
  • The engine speed is brought to its original value by reducing the load of engine.
  • This will ensure that the frictional power is same.

Motoring test on IC Engine :-

  • In this test, the engine run at required speed and found friction power immediately.
  • Engine temperature is stable by oil, water etc.
  • The power of the engine during the period is absorbed by electric dynamometer.
  • Then fuel supply of the system is cut off by electric devices, the dynamometer is converted to run as a motor to drive for motor the engine at the same speed at which it was previously running the power supply to the motor is measure the friction power of the engine.

Pollution control in IC engines :-

1) Pollutants in exhaust gases of petrol and diesel engines :-

Pollution is produced by the incomplete burning of air and fuel mixture in combustion chamber.

a) Carbon monoxide (CO) :-

  • It is colorless gas of about the same density as air.
  • It is poisonous gas which, when inhaled, replace the oxygen in the blood stream so that the body metabolism cannot function correctly.
  • Small amount of CO concentrations, when breathed in slow down physical and mental activity, while large concentration will kill.
  • CO is intermediate produce of combustion remains in exhaust if the oxidation of CO to CO2 is not complete.
  • CO is generally formed when mixture is rich in fuel. The amount of CO formed increase the mixture becomes more and more rich in fuel.
  • Small amount of CO will come out of the exhaust even when the mixture is slightly lean in fuel.
  • This is due to the fact that equilibrium is not established when the product passes to exhaust.
  • As the product cool down to exhaust temperature, major part of CO react with oxygen from CO2 However, a relatively  small amount of CO will remain in exhaust, its concentration creasing with the rich mixture.

b) Hydrocarbon in S.I. engine :-

  • The emission amount of HC is closely related to design variable, operating variable and engine condition.
  • The surface to volume ratio greatly affects the HC emission.
  • Higher the surface volume ratio, higher the HC emission.
  • Even if air and fuel mixture enter in stochiometric condition perfect combustion does not occur because of improper mixing and engine condition.
  • In improper mixing the air and fuel mixture is not homogeneous.
  • In compression stroke the air and fuel compressed into crevice volume of the combustion chamber.
  • Up to 80% of all HC emission comes from this source.
  • An engine gets old the gap between piston rings and cylinder wall become greater, and the thick film of lubricating oil is leak on the wall.

c) Hydrocarbon in C.I. engine :-

  • As CI engine operate with an overall fuel-lean equivalence ratio, CI engine have only one-fifth of HC emission of a CI engine.
  • In generally CI engine has 98% combustion efficiency, that means only 2% of HC fuel is emitted.
  • Homogeneous mixture of fuel occur pollution.
  •  In improper mixing the air and fuel mixture is not homogeneous.
  • In compression stroke the air and fuel compressed into crevice volume of the combustion chamber.
  • An engine gets old the gap between piston rings and cylinder wall become greater, and the thick film of lubricating oil is leak on the wall.

d) Oxides of nitrogen (NOx) :-

  • Oxides of N2 is generally occur mainly in the form of NO and NO2.
  • These are generally formed at high temperature.
  • Hence high temperature and availability of O2 are the main reason for the formation of NO and NO2.
  • Oxide of nitrogen and other obnoxious substances are produce in very small quantities and, in certain environments can cause pollution, while prolonged exposure is dangerous to health.

Catalytic converters :-

  • Catalytic converter shown in figure.
Catalytic converters

Catalytic converters

  • Catalytic converter is device used to reduce the toxicity of emission from an internal combustion engine.
  • Catalytic converters, fitted in series with the exhaust pipe of gasoline fueled vehicle, convert the over 90 percent of hydrocarbon(HC), carbon monoxide(CO) and  nitrogen oxide (NOx) from the engine into less harmful carbon dioxide (CO2), nitrogen and water vapor.
  • Catalytic converter is first fitted cars in 1974.
  •  The core or substrate. The core is often a ceramic honeycomb in modern catalytic Converters, but stainless steel foil honeycombs are used, too. The honey-comb surface
  • Increases the amount of surface area available to support the catalyst, and therefore is often called a “catalyst support”.
  • The wash coat A wash coat is used to make converters more efficient, often as a Mixture of silica and alumina.
  • The wash coat, when added to the core, forms a rough, irregular surface, which has a far greater surface area than the flat core surfaces do, which then gives the converter core a larger surface area, and therefore more places for active precious metal sites.
  • The catalyst is added to the wash coat (in suspension) before being applied to the core.
  • The catalyst itself is most often a precious metal. Platinum is the most active catalyst and is widely used. It is not suitable for all applications, however, because of unwanted additional reactions and/or cost.
  •  Palladium and rhodium are two other precious metals used.
  • Platinum and rhodium are used as a reduction catalyst, while platinum and palladium are used as an oxidization catalyst.

a) Two way :

  • The two way catalytic converter is used in light vehicle like scooter, moped motorcycle and cars etc.
  • A two way catalytic converter consists of cylindrical unit of small silencer and it installed in exhaust system.
  •  It is fitted in between exhaust manifold and silencer.
  • Inside the converter there is a honey comb structure of a ceramic which will be coated with alumina base material and thereafter a second coating of precious metals platinum of the same.
  • When the exhaust gases pass over the converter, the toxic gases like CO, HC, NOx are converted into harmless CO2, N2.

b) Three way:

  • Three way catalytic converter is used in large vehicle like cars, Heavy vehicle etc.
  • It is fitted exhaust line between manifold and muffler.
  • The converter has a mesh metal construction inside.
  • The catalytic is coated on mesh. It is commonly used in petrol engine.
  • The exhaust gas enters from one side, in first stage NOx reduces by rhodium into N2 and O2.
  • In second stage air form the air pump is supplied with the exhaust gas.
  • The oxygen from air mixed with HC and CO present in exhaust gas.

This converter is most efficient when the engine is operating with stochiometric air fuel ration and depends on catalyst used.


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