Describe three engine modifications to be done to reduce SI engine Emission.
Engine Modifications to be Done to reduce SI Engine Emission are:
1. Use of leaner air-fuel ratios:
The carburettor may be modified to provide relatively lean air fuel mixtures during idling and cruise operation. With this modification, idle speed needs to be increased to prevent stalling and rough idle. Fuel distribution is improved by better manifold design, Inlet air heating, raising of coolant temperature and use of electronic fuel injection system.
2. Retarding Ignition timing:
The controls are designed to retard the spark timing at idle and providing normal spark advance during acceleration and cruising. Retarding spark reduces NOX. Emission. It also reduces HC emission.
3. Modification of combustion chamber:
Modification in combustion chamber is attempted to avoid flame quenching zones, resulting in HC emission. This includes reducing surface to volume ratio, reduced squish area, reduced deal space around piston ring and reduced distance of the top piston ring from the top of the piston.
4. Lower compression ratio:
The lower compression ratio reduces the quenching effect by reducing quenching area reducing HC. It also reduces NOX. Emission. Reducing compression ratio results in some loss of power and fuel economy.
5. Reduced valve overlap:
Increased valve overlap allows some mixture to escape directly to increase emission level. This can be controlled by reducing valve overlap.
6. Alterations in induction system:
The supply of designed air fuel ratio to all cylinders under all operating conditions can be affected by alterations in induction. This includes inlet air heating, use of carburettor with closer tolerances and using special type of carburettors. This also includes fuel injection in manifold.