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Re: Direct Injection
In short direct injection means on average an extra 30-40 hp.
Currently most, if not all (except for the RSR Cup Car) motors that Porsche use, only have one throttle control valve for ALL 6 cylinders. It controls the amount of fuel sprayed into each cylinder depending on that particular cylinders cycle. The problem is that each cylinder is in a diffent position of their cycle at any one time and ONE throttle control valve does not take that into consideration - instead it averages the amount fo fuel required by each cylinder and sprays it in, some cylinders get more fuel than they need, and some get less. In efficient and power robbing.
What direct injection does is it controls each cylinder separatly and injects the exact amount of fuel that that specific cylinder requires depending on where it is on its cycle.
So basically a direct injection engine has 6 control valves ONE for each cylinder and non-direct injection only has ONE that controls all 6 cylinders.
Tuners have been selling mechanical direct injection-like systems for the 993 motor, which gives on average 35hp.
The RSR also uses a mechanical system which is responsible in part for the 485hp that engine makes.
Currently most, if not all (except for the RSR Cup Car) motors that Porsche use, only have one throttle control valve for ALL 6 cylinders. It controls the amount of fuel sprayed into each cylinder depending on that particular cylinders cycle. The problem is that each cylinder is in a diffent position of their cycle at any one time and ONE throttle control valve does not take that into consideration - instead it averages the amount fo fuel required by each cylinder and sprays it in, some cylinders get more fuel than they need, and some get less. In efficient and power robbing.
What direct injection does is it controls each cylinder separatly and injects the exact amount of fuel that that specific cylinder requires depending on where it is on its cycle.
So basically a direct injection engine has 6 control valves ONE for each cylinder and non-direct injection only has ONE that controls all 6 cylinders.
Tuners have been selling mechanical direct injection-like systems for the 993 motor, which gives on average 35hp.
The RSR also uses a mechanical system which is responsible in part for the 485hp that engine makes.
Jan 10, 2007 1:56:38 PM
- Silver Bullet
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- Reply to: RR4
Re: Direct Injection
Quote:
RR4 said:
In short direct injection means on average an extra 30-40 hp.
Currently most, if not all (except for the RSR Cup Car) motors that Porsche use, only have one throttle control valve for ALL 6 cylinders. It controls the amount of fuel sprayed into each cylinder depending on that particular cylinders cycle. The problem is that each cylinder is in a diffent position of their cycle at any one time and ONE throttle control valve does not take that into consideration - instead it averages the amount fo fuel required by each cylinder and sprays it in, some cylinders get more fuel than they need, and some get less. In efficient and power robbing.
What direct injection does is it controls each cylinder separatly and injects the exact amount of fuel that that specific cylinder requires depending on where it is on its cycle.
So basically a direct injection engine has 6 control valves ONE for each cylinder and non-direct injection only has ONE that controls all 6 cylinders.
Tuners have been selling mechanical direct injection-like systems for the 993 motor, which gives on average 35hp.
The RSR also uses a mechanical system which is responsible in part for the 485hp that engine makes.
I could not have said it better myself. We should now close this thread to preserve its perfection.
Jan 10, 2007 2:20:30 PM
- Leawood911
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Re: Direct Injection
Direct Injection is far better than the multipoint injection you mention the 993 getting! The two are easy to confuse.
It's all about the air-fuel ratios Direct Injection allows...
Wikipedia-
Gasoline direct injection or GDI is a variant of fuel injection employed in modern four stroke petrol engines. The gasoline or biobutanol is injected right into the combustion chamber of each cylinder (AT VERY HIGH PRESSURE), as opposed to conventional multi point fuel injection that happens in the intake manifold.
GDI enables stratified charge (ultra lean burn) combustion for improved fuel efficiency and emission levels at low load. Further improving efficiency and high-load output-power, the engine power is governed by modulating fuel injection, like a diesel engine; as opposed to restricting intake airflow, like a conventional gas internal combustion engine.
Theory of operation
The major advantages of a GDI engine are increased fuel efficiency and high power output. This is achieved by the precise control over amount of fuel and injection timings which are varied according to the load conditions. In addition, there are no throttling losses when compared to a conventional fuel injected or carburated engine, which greatly improves efficiency. Basically, the engine management system continuously chooses between three different modes of combustion: ultra lean burn combustion, stoichiometric combustion, and high power output mode.
Each mode is characterized by air-fuel ratio, the amount of fuel in the air-fuel mixture; the stoichiometric ratio for petrol is 14.7 to 1 by weight, but in ultra lean mode, it could be as high as 65 to 1. These leaner mixtures than those ever achieved in the conventional engines are desired because of reduced fuel consumption.
Ultra lean combustion mode is effective under normal running conditions, when little acceleration is required. The fuel is not injected at the intake stroke but rather at the latter stages of the compression stroke, so that the small amount of air-fuel mixture is optimally placed just near the spark plug. This stratified charge is surrounded by mostly air which keeps the fuel away from the cylinder walls for lowest emissions. The combustion takes place in a toroidal cavity on the piston's surface. This technique enables the usage of ultra lean mixtures with very high air-fuel ratio, impossible with traditional carburetors or even intake port injection.
Stoichiometric combustion mode is activated for moderate load conditions. In this mode, fuel is injected during the intake stroke. The air-fuel mixture is homogeneous with the stoichiometric rates necessary for the catalytic converter to remove a maximum of the major pollutants CO and NOx from the exhaust gas.
In full power mode, the air-fuel mixture is homogeneous as well and contains the minimum mass of fuel over the amount required for stoichiometric that is possible to ignite without knocking out, as defined by the compression ratio of the engine and the mass of air in the combustion chamber. The fuel is injected during the intake stroke. This mode activates at high load conditions and provides maximum output and torque.
Direct injection can also be accompanied by traditional methods such as VVT and VLIM, which provide conventional control over airflow swirl patterns at stoichiometric and full power modes. Water injection or EGR can help reduce NOx emissions inevitable when burning ultra lean mixtures.
It's all about the air-fuel ratios Direct Injection allows...Wikipedia-
Gasoline direct injection or GDI is a variant of fuel injection employed in modern four stroke petrol engines. The gasoline or biobutanol is injected right into the combustion chamber of each cylinder (AT VERY HIGH PRESSURE), as opposed to conventional multi point fuel injection that happens in the intake manifold.
GDI enables stratified charge (ultra lean burn) combustion for improved fuel efficiency and emission levels at low load. Further improving efficiency and high-load output-power, the engine power is governed by modulating fuel injection, like a diesel engine; as opposed to restricting intake airflow, like a conventional gas internal combustion engine.
Theory of operation
The major advantages of a GDI engine are increased fuel efficiency and high power output. This is achieved by the precise control over amount of fuel and injection timings which are varied according to the load conditions. In addition, there are no throttling losses when compared to a conventional fuel injected or carburated engine, which greatly improves efficiency. Basically, the engine management system continuously chooses between three different modes of combustion: ultra lean burn combustion, stoichiometric combustion, and high power output mode.
Each mode is characterized by air-fuel ratio, the amount of fuel in the air-fuel mixture; the stoichiometric ratio for petrol is 14.7 to 1 by weight, but in ultra lean mode, it could be as high as 65 to 1. These leaner mixtures than those ever achieved in the conventional engines are desired because of reduced fuel consumption.
Ultra lean combustion mode is effective under normal running conditions, when little acceleration is required. The fuel is not injected at the intake stroke but rather at the latter stages of the compression stroke, so that the small amount of air-fuel mixture is optimally placed just near the spark plug. This stratified charge is surrounded by mostly air which keeps the fuel away from the cylinder walls for lowest emissions. The combustion takes place in a toroidal cavity on the piston's surface. This technique enables the usage of ultra lean mixtures with very high air-fuel ratio, impossible with traditional carburetors or even intake port injection.
Stoichiometric combustion mode is activated for moderate load conditions. In this mode, fuel is injected during the intake stroke. The air-fuel mixture is homogeneous with the stoichiometric rates necessary for the catalytic converter to remove a maximum of the major pollutants CO and NOx from the exhaust gas.
In full power mode, the air-fuel mixture is homogeneous as well and contains the minimum mass of fuel over the amount required for stoichiometric that is possible to ignite without knocking out, as defined by the compression ratio of the engine and the mass of air in the combustion chamber. The fuel is injected during the intake stroke. This mode activates at high load conditions and provides maximum output and torque.
Direct injection can also be accompanied by traditional methods such as VVT and VLIM, which provide conventional control over airflow swirl patterns at stoichiometric and full power modes. Water injection or EGR can help reduce NOx emissions inevitable when burning ultra lean mixtures.
Jan 10, 2007 2:32:55 PM
- Leawood911
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Re: Direct Injection
Having said all that - the 997 model will forever be divided by this (pre DI and post DI). Those who don't have it will want it more than PSE, X-51, PCCB. It's THE hot ticket. Better mileage, lower emissions, more power. Porsche has changed injection many times but this will be the biggest improvement by far. If I'm not mistaken fuel is pressurized to about 1400+ PSI and then sprayed directly into the combustion chamber (like a Diesel). Precise control of the mixture and combustion process can be achieved. Makes the current system look crude by comparison.
This has been used in many different engines so this is not first gen stuff. I have had an Aprilia 50cc DiTech scooter for years with this. It gets 130mpg and goes 50mph (on a level road). I'm certain Folks in Europe are familiar with the Aprilia DiTech engine.
The time to sell your 997 is now. The cosmetic facelift does not matter, it's the direct injection. Who cares about the PDK now?
This has been used in many different engines so this is not first gen stuff. I have had an Aprilia 50cc DiTech scooter for years with this. It gets 130mpg and goes 50mph (on a level road). I'm certain Folks in Europe are familiar with the Aprilia DiTech engine.
The time to sell your 997 is now. The cosmetic facelift does not matter, it's the direct injection. Who cares about the PDK now?
Jan 10, 2007 2:44:20 PM
- mcdelaug
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- Reply to: Leawood911
Re: Direct Injection
Let me take a stab at it...as much of what is said above is correct, but not quite as succinct as it might be.
Here's the simple way to think about fuel delivery with gasoline engines.
Carburetion: one or more carburetors sits atop the intake manifold, constantly mixing fuel into the intake path's airstream at a rate controlled by how hard you're pressing the accelerator pedal.
Throttle body fuel injection: replace the carburetor(s) with a one or two large fuel injectors that sit on the intale manifold, providing more precise fuel delivery, but still not cylinder specific delivery.
Multi-point fuel injection: each cylinder has its own injector that sprays gasoline into the intake manifold just above the intake valve, not into the cylinder itself.
Direct Injection: each cylinder has its own fuel injector that sprays directly into the cylinder, (as opposed to the intake manifold just above the intake valve in MPFI) using the more sophisticated mulitple pulses of varying sizes and with a particular "spray" pattern alluded to above.
I hope this clarifies things a little.
mcdelaug
Here's the simple way to think about fuel delivery with gasoline engines.
Carburetion: one or more carburetors sits atop the intake manifold, constantly mixing fuel into the intake path's airstream at a rate controlled by how hard you're pressing the accelerator pedal.
Throttle body fuel injection: replace the carburetor(s) with a one or two large fuel injectors that sit on the intale manifold, providing more precise fuel delivery, but still not cylinder specific delivery.
Multi-point fuel injection: each cylinder has its own injector that sprays gasoline into the intake manifold just above the intake valve, not into the cylinder itself.
Direct Injection: each cylinder has its own fuel injector that sprays directly into the cylinder, (as opposed to the intake manifold just above the intake valve in MPFI) using the more sophisticated mulitple pulses of varying sizes and with a particular "spray" pattern alluded to above.
I hope this clarifies things a little.
mcdelaug
Jan 10, 2007 3:24:13 PM
- BMCG
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Reply to:
Ron (Houston)
Re: Direct Injection
Mitsubishi was the first company to introduce it on production cars (on the Carisma, which was infamous for its complete lack thereof 
).
So far DI has been used in pedestrian cars, not so much in high-performance cars. I think it accounts for about half the sales of gasoline cars in Europe today.
Manufacturers are mostly moving towards it because of future emission regulations, not because of fuel economy or performance. Actually, most fuel economy or performance claims of gasoline DI eventually proved to be exagerated.
).
So far DI has been used in pedestrian cars, not so much in high-performance cars. I think it accounts for about half the sales of gasoline cars in Europe today.
Manufacturers are mostly moving towards it because of future emission regulations, not because of fuel economy or performance. Actually, most fuel economy or performance claims of gasoline DI eventually proved to be exagerated.
Re: Direct Injection
Quote:
mcdelaug said:
Let me take a stab at it...as much of what is said above is correct, but not quite as succinct as it might be.
Here's the simple way to think about fuel delivery with gasoline engines.
Carburetion: one or more carburetors sits atop the intake manifold, constantly mixing fuel into the intake path's airstream at a rate controlled by how hard you're pressing the accelerator pedal.
Throttle body fuel injection: replace the carburetor(s) with a one or two large fuel injectors that sit on the intale manifold, providing more precise fuel delivery, but still not cylinder specific delivery.
Multi-point fuel injection: each cylinder has its own injector that sprays gasoline into the intake manifold just above the intake valve, not into the cylinder itself.
Direct Injection: each cylinder has its own fuel injector that sprays directly into the cylinder, (as opposed to the intake manifold just above the intake valve in MPFI) using the more sophisticated mulitple pulses of varying sizes and with a particular "spray" pattern alluded to above.
I hope this clarifies things a little.
mcdelaug
Perfect description. The big deal is straight into cumbustion chamber when its called for, better mix with the air right before spark.
There is a great video on both the lexus LS site where they have a hybrid version and audi has the best graphic.
A mazda vehicle also uses direct injection.
Jan 11, 2007 4:09:44 AM
- Leawood911
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Jan 11, 2007 4:32:05 AM
- bostonmini
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Re: Direct Injection
I still don't get it, in regular cars, that is non race cars, at least to date, the technology doesnt seem to have improved much, esp the 2.0/3.2 Audi engines. Perhaps later it will provide a performance benefit in the porsches, though I think the GT3 would be the one to get it first if it could...
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