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- Technology never stands still in the automotive world, and one of the technologies that's starting to become more common in the aftermarket tuning industry is direct injection.
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Now, this isn't exactly a new technology and it's been used in production vehicles for many years now but the complexity of controlling direct injection and the fact that it wasn't initially embraced by performance vehicles has meant that there has been some lag in support being offered.
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To understand direct injection we must start by understanding traditional fuel injection, which we refer to as port injection.
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Here, the fuel injector injects into the intake port.
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| 00:44 |
In a port injection engine, the injector is injecting against the pressure in the intake manifold.
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| 00:51 |
In order to get the fuel to flow through the injector we need to have a higher pressure in the fuel rail than what we have in the intake manifold.
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| 01:02 |
In a port injected engine, we may see fuel pressure sitting somewhere between three and four bar, or 43.5 to 58 psi, which we would consider a relatively low pressure.
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| 01:15 |
Due to the location of the fuel injectors in a port injection engine, it's possible to inject fuel continuously throughout the entire engine cycle.
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| 01:26 |
Obviously the fuel will only be drawn into the cylinder when the intake valves are open, but during the rest of the engine cycle the injected fuel will sit behind the closed intake valves until the next intake stroke when the fuel will be drawn into the cylinder.
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| 01:43 |
Direct injection on the other hand locates the fuel injector inside the combustion chamber, hence the term direct injection.
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| 01:51 |
Locating the injector here offers many advantages.
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| 01:55 |
In particular, it allows for much more control over the formation of the fuel air mixture and due to the fact that the fuel is being directly injected into the combustion chamber, it provides a greater cooling effect on the combustion charge as the fuel goes through a phase change from liquid to vapour.
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| 02:15 |
Cooling the combustion charge makes the engine less prone to suffering from knock, and in turn, this means that the manufacturer can achieve better performance by way of a higher compression ratio, more ignition timing, more boost, or perhaps a combination of all of the above.
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| 02:35 |
In economy applications, a leaner air fuel ratio can also be used to improve fuel efficiency.
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| 02:42 |
One of the downsides of direct injection is that the available window for the injection to occur is much smaller than in a port injection engine.
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| 02:52 |
Generally, the injection will start somewhere around the beginning of the intake stroke, and it must be completed sometime before the spark event occurs near the top of the compression stroke.
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| 03:03 |
At best, this means that the direct injector has a little less than 50% of the engine cycle available to get the fuel into the engine.
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| 03:13 |
To help deliver the fuel into the engine during the short window available, as well as injecting into the relatively high pressure we can expect to see in the cylinder during the compression stroke, the fuel pressure of a direct injection engine is much higher than in a port injection engine.
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| 03:30 |
Usually in the range of 10 to 20 megapascals, or 1450 to 2900 psi.
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| 03:38 |
As manufacturers strive for increasing performance and reduced fuel consumption, direct injection is seeing wider use.
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| 03:47 |
There are already several stand alone ECU manufacturers providing support for direct injection engines, and this is likely to increase as time goes by.
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