Page 265 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Crankcase Emission: Crankcase emission occurs between the piston and the crankcase in the engine cylinder.
This is due to the difference in pressure generated. In this, fuel emissions constitute about 5-10% of the total
fuel emissions. In this type of emissions, various components (lubricants) present inside the engine along with
the gases released after fuel combustion start evaporating and being emitted due to the pressure present in the
engine’s cylinder.
The gases emitted are mainly hydrocarbons (HC) and carbon monoxide (CO). To avoid this emission, EGR
(Exhaust Gas Recirculation) valve is used.

Carburettor: Carburetor is a device which takes petrol in liquid form from the fuel pump, vaporizes it with air,
mixes it in appropriate quantity and sends it to the cylinder through intake stroke of the engine.
Exhaust system with egr or air injection system in to exhaust manifold with catalytic converter
• Exhaust system: The exhaust manifold is used to collect the exhaust gases from the different cylinders
and send them to the silencer. The exhaust manifold is generally made of cast iron. The exhaust manifold
may include a heat control valve or a heat riser which has a thermostatically operated butterfly valve fitted in
exhaust manifold. When the engine is cold, the valve is closed and hot gases are directed around the inlet
manifold. When the engine attains operating temperature the valve opens and the exhaust gases are directly
sent to the muffler. Now exhaust system comes with EGR (Exhaust Gas Recirculation).
• EGR Valve
• Purpose of exhaust gas recirculation (egr) system: Purpose of exhaust gas recirculation (EGR) system’s
purpose is to reduce NOx emissions that contribute to air pollution.
• Working principle of egr valve: Exhaust gas recirculation reduces the formation of NOX and engine knock
control. By re-circulating an allowing a small amount of exhaust gas into the intake air-fuel mixture on intake
manifold as shown in Fig.

EGR, valve, connected between the exhaust port, or manifold, and the intake system. If engine conditions are
likely to produce oxides of nitrogen, the EGR valve opens, letting some gases is (only about 6 to 10% of the total)
pass from the exhaust, into the intake system. During combustion, these exhaust gases absorb heat from the
burning air and fuel. This lowers peak combustion temperatures (below 1500 degrees c) to reduce the reaction
between the reaction between nitrogen and oxygen that forms NOx. Older EGR systems use a vacuum regulated
EGR valve while newer vehicles tend to have an electronic EGR valve to control exhaust gas recirculation. When
the engine is idling, the EGR valve is closed and there is no EGR flow into the manifold. The EGR valve remains
closed until the engine is warm and is operating under load. As the load increase and combustion temperatures
start to rise, the EGR valve opens and starts to leak exhaust back into intake manifold this has a quenching effect
that lowers combustion temperatures and reduces the formation of NOx.
The EGR valve opens and closed the passage between the exhaust manifold and intake manifold. Vacuum is
remove EGR valves. Inside the vacuum actuated EGR (Fig 3) valve is a valve, diaphragm and spring. When
vacuum is applied to diaphragm lifts the valve off its seat allowing exhaust gases into the intake air stream. When
vacuum is removed the spring forces the diaphragm and valve downward closing the exhaust passage.

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CITS : Automotive - Mechanic Diesel - Lesson 80 - 83