Roller Cam
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- Stripped66
- Posts: 1904
- Joined: Tue Sep 18, 2001 12:01 am
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- raygreenwood
- Posts: 11895
- Joined: Wed Jan 22, 2003 12:01 am
A couple of notes on direct injection to provide some food for thought.
Direct injection is no more or less.....exactly what the name implys.
The fuel is injected directly into the cylinder....and not behind the valve. It has hurdles to overcome....and they have been:
(1) It must have a very high temperature injector.
(2) That injector must operate at a very high pressure...comparable to....or higher than....the original Bosch high presure injection.
This high pressure is for one reason alone. The amount of fuel necessary for teh proper "dosage"...must be delivered in approximately 60+% less time than on a standard port injection system.
This is because....with direct injection...fuel is ONLY delivered on the intake stroke. That means that instead of a possible injection cycle like many cars use....of well over 200* of duration....which works out to somewhere between 10 to 18 milliseconds....you get somewhere around 90* of effective injection time...wherin you must get all of the injection done between 1.2 to 1.8 milliseconds.
Pressure X time = volume with an injector.
The benefit is this. At extreme pressure you get extreme atomization.
This also is.....perfectly sequential injection.
Like I have been harping about for ages....this "perfect sequentialness" also means that the atomization....and teh fuel...does not end up wasting its microdroplet pattern by spraying against the back of a closed valve or a port wall. With normal port injection ...especially that which is not sequential....a lot of intake energy iswated trying to pull fuel off of port walls. So ...with regular port, non-sequential injection....the dose rate for each cylinder will never be perfect...and neither will atomization. There is too much ineterference for that nice spray pattern.
Thats where the HP...and the ability to use high compression comes from in direct injection. Perfect fuel doses....and superb atomization.
That also brings to light.....the many many things they can then do with pistons.
In the VW TDI...which is Turbo-diesel direct injection.....they get superb...never been done before on a diesel.....combustion...because the piston actually has a "pit" or hole...that the fuel is injected into. This is a combustion chamber inside of a combustion chamber. It allows an extended combustion cycle and teh ability to completely combust the diesel......at very high temperatures and pressures. This makes it more efficient and powerful....and cleaner....with less fuel.
Just putting direct injection on a type 4 should not be that hard. Very little has to change with anything else but the injection system itself.
It also...takes away a little of the design issues with the plenum and runners. You no longer need worry so much about turbulence issues at the port with refernce to injected fuel....only with reference to entry through the open valve.
This may also take away a few issues with reversion with refernce to disturbance of injected....but not yet ingested fuel. Its some cool stuff.
There are still some equipment dependability issues they are fighting with. Ray
Direct injection is no more or less.....exactly what the name implys.
The fuel is injected directly into the cylinder....and not behind the valve. It has hurdles to overcome....and they have been:
(1) It must have a very high temperature injector.
(2) That injector must operate at a very high pressure...comparable to....or higher than....the original Bosch high presure injection.
This high pressure is for one reason alone. The amount of fuel necessary for teh proper "dosage"...must be delivered in approximately 60+% less time than on a standard port injection system.
This is because....with direct injection...fuel is ONLY delivered on the intake stroke. That means that instead of a possible injection cycle like many cars use....of well over 200* of duration....which works out to somewhere between 10 to 18 milliseconds....you get somewhere around 90* of effective injection time...wherin you must get all of the injection done between 1.2 to 1.8 milliseconds.
Pressure X time = volume with an injector.
The benefit is this. At extreme pressure you get extreme atomization.
This also is.....perfectly sequential injection.
Like I have been harping about for ages....this "perfect sequentialness" also means that the atomization....and teh fuel...does not end up wasting its microdroplet pattern by spraying against the back of a closed valve or a port wall. With normal port injection ...especially that which is not sequential....a lot of intake energy iswated trying to pull fuel off of port walls. So ...with regular port, non-sequential injection....the dose rate for each cylinder will never be perfect...and neither will atomization. There is too much ineterference for that nice spray pattern.
Thats where the HP...and the ability to use high compression comes from in direct injection. Perfect fuel doses....and superb atomization.
That also brings to light.....the many many things they can then do with pistons.
In the VW TDI...which is Turbo-diesel direct injection.....they get superb...never been done before on a diesel.....combustion...because the piston actually has a "pit" or hole...that the fuel is injected into. This is a combustion chamber inside of a combustion chamber. It allows an extended combustion cycle and teh ability to completely combust the diesel......at very high temperatures and pressures. This makes it more efficient and powerful....and cleaner....with less fuel.
Just putting direct injection on a type 4 should not be that hard. Very little has to change with anything else but the injection system itself.
It also...takes away a little of the design issues with the plenum and runners. You no longer need worry so much about turbulence issues at the port with refernce to injected fuel....only with reference to entry through the open valve.
This may also take away a few issues with reversion with refernce to disturbance of injected....but not yet ingested fuel. Its some cool stuff.
There are still some equipment dependability issues they are fighting with. Ray
- Stripped66
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- Joined: Tue Sep 18, 2001 12:01 am