schiker
Well-Known Member
FYI
So I have been reading several threads on cams, compression ratio, and turbos etc and wanted to post something that may help some people.
I think I have been misinterpretting the term scavanging as it relates to air flow through the cylinder. And it may have different context to some.
I was thinking scavanging was more a flushing or blow through of the cylinder where intake and exhaust opening overlaps. BUT it doesn't necessairly have to blow through or flush through to be considered scavanging.
It can just be the continued movement of air from momentum of air mass independant of piston stroke like this definition taken from wikipedia. This was written from a gasoline context but it clarified "a" definition of scavanging for me. Yes on a naturally aspirated engine this is critical but SOME of the theory applies to turbo diesel as well.
Wikipedia....
" A running engine does not stop taking air & fuel into the cylinder when the piston reaches BDC; The mixture that is rushing into the cylinder during the downstroke develops momentum and continues briefly after the vacuum ceases (in the same respect that rapidly opening a door will create a draft that continues after movement of the door ceases). This is called scavenging. Intake tuning, cylinder head design, valve timing and exhaust tuning determine how effectively an engine scavenges. "
From that standpoint the ATT could very well improve "scavenging" as lower backpressure of the exhaust allows more gasses to exit thus it improves-increases the velocity of the intake air charge by lowering left over gasses in the cylinder on intake stroke. Increased velocity increases momentum of intake air mass thus more momentum more "scavanging".
Hopefully this helps more understanding of the ramifications of more scavanging/momentum and thus swirl/turbulence and how it can take on different contexts and directions of conservations for good cylinder air mix (left over exhaust and intake air) and fuel mix/burn.
So I have been reading several threads on cams, compression ratio, and turbos etc and wanted to post something that may help some people.
I think I have been misinterpretting the term scavanging as it relates to air flow through the cylinder. And it may have different context to some.
I was thinking scavanging was more a flushing or blow through of the cylinder where intake and exhaust opening overlaps. BUT it doesn't necessairly have to blow through or flush through to be considered scavanging.
It can just be the continued movement of air from momentum of air mass independant of piston stroke like this definition taken from wikipedia. This was written from a gasoline context but it clarified "a" definition of scavanging for me. Yes on a naturally aspirated engine this is critical but SOME of the theory applies to turbo diesel as well.
Wikipedia....
" A running engine does not stop taking air & fuel into the cylinder when the piston reaches BDC; The mixture that is rushing into the cylinder during the downstroke develops momentum and continues briefly after the vacuum ceases (in the same respect that rapidly opening a door will create a draft that continues after movement of the door ceases). This is called scavenging. Intake tuning, cylinder head design, valve timing and exhaust tuning determine how effectively an engine scavenges. "
From that standpoint the ATT could very well improve "scavenging" as lower backpressure of the exhaust allows more gasses to exit thus it improves-increases the velocity of the intake air charge by lowering left over gasses in the cylinder on intake stroke. Increased velocity increases momentum of intake air mass thus more momentum more "scavanging".
Hopefully this helps more understanding of the ramifications of more scavanging/momentum and thus swirl/turbulence and how it can take on different contexts and directions of conservations for good cylinder air mix (left over exhaust and intake air) and fuel mix/burn.