-: Scavenging Process :-
The process of clearing the cylinder after the expansion stroke is called scavenging process .
In a two stroke engine because of non - availability of an expression stroke , its combustion chamber is left full of combustion product so for this , scavenging process used in a two stroke engine .
In other words , Scavenging process is the replacement of combustion products in the cylinder from previous power stroke with fresh air charge to be burned in the next cycle . This process must be completed in a very short duration available between the end of the expansion stroke and start of the process of charging .
-: Scavenging Process in Two stroke Engine :-
Scavenging process can be divided into the following four parts -
1- Pre blowdown
2- Blow-down
3- Scavenging
4- Additional Charging
1- Pre-Blowdown :-
In this stage , On the opening of inlet port , the gases expending in the main cylinder tend to escape from it and to be pre discharge into the scavenge air manifold . This pre blowdown process ends with the opening of exhaust port .
2- Blow-down :-
In this stage with the opening of exhaust ports , the gases existing in the cylinder at the end of expansion stroke discharge simultaneously into exhaust manifold , consequently the pressure of main cylinder drops to a valve lower than existing in scavenge air manifold. This blowdown process terminates at the moment the gas pressure inside the cylinder attains a value slightly less than air pressure inside scavenge manifold .
3- Scavenging :-
This phase of the scavenging process starts at the moment when the spontaneous exhaust of gases from cylinder terminates and ends at the moment the exhaust ports are closed .
The scavenge air sweeps out all residual gases remaining in the main cylinder . At the end of spontaneous exhaust and replaces them as completely as possible with fresh charge .
4- Additional Charging :-
After the completion of scavenging phase , the fresh charge continues to flow till the scavenge ports are open and pressure in the cylinder rises . This last phase result in better filling of the cylinder .
The process of clearing the cylinder after the expansion stroke is called scavenging process .
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In a two stroke engine because of non - availability of an expression stroke , its combustion chamber is left full of combustion product so for this , scavenging process used in a two stroke engine .
In other words , Scavenging process is the replacement of combustion products in the cylinder from previous power stroke with fresh air charge to be burned in the next cycle . This process must be completed in a very short duration available between the end of the expansion stroke and start of the process of charging .
-: Scavenging Process in Two stroke Engine :-
Scavenging process can be divided into the following four parts -
1- Pre blowdown
2- Blow-down
3- Scavenging
4- Additional Charging
1- Pre-Blowdown :-
In this stage , On the opening of inlet port , the gases expending in the main cylinder tend to escape from it and to be pre discharge into the scavenge air manifold . This pre blowdown process ends with the opening of exhaust port .
2- Blow-down :-
In this stage with the opening of exhaust ports , the gases existing in the cylinder at the end of expansion stroke discharge simultaneously into exhaust manifold , consequently the pressure of main cylinder drops to a valve lower than existing in scavenge air manifold. This blowdown process terminates at the moment the gas pressure inside the cylinder attains a value slightly less than air pressure inside scavenge manifold .
3- Scavenging :-
This phase of the scavenging process starts at the moment when the spontaneous exhaust of gases from cylinder terminates and ends at the moment the exhaust ports are closed .
The scavenge air sweeps out all residual gases remaining in the main cylinder . At the end of spontaneous exhaust and replaces them as completely as possible with fresh charge .
4- Additional Charging :-
After the completion of scavenging phase , the fresh charge continues to flow till the scavenge ports are open and pressure in the cylinder rises . This last phase result in better filling of the cylinder .
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