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What Is Electronic Direct Fuel Injection?

Updated on June 25, 2012
Porsche's Direct Fuel Injection System
Porsche's Direct Fuel Injection System

Electronic fuel injection systems have now widely replaced carburetors in automotive combustion engines. When this technology was new, however, it was a revolution in engine efficiency. The introduction of direct fuel injection systems over the standard multi-point system is a similar type of technological revolution.

The Difference: Multi-point VS. Direct Injection

In a direct fuel injection system gasoline is highly pressurized and injected, as the name would imply, directly into the combustion chamber. This differs from multi-point fuel injection systems in which fuel is injected into the intake, before the combustion chamber. This means that fuel is mixed with air before the intake valve opens to allow this mixture into the combustion chamber. The main advantage of direct injection is that it provides engineers and tuners more control over how the fuel burns. These systems also allow the ECU to quickly adjust air-fuel ratios. With direct injection you can safely run a car leaner because there is more accurate atomization and distribution of the fuel. This prevents certain areas of the combustion chamber from becoming hot spots and prevents predetonation and engine knock. All of these things mean that fuel and ignition maps can be less conservative than otherwise possible but still be as equally safe. Because of this, direct fuel injection can yield higher efficiency, both in power and fuel economy. Direct injection systems can also run a car super lean for short periods of time, greatly decreasing their emission levels. The disadvantage of the high pressure direct injection system, however, is that it is more difficult to design and manufacture. Direct fuel injection also requires a more advanced ECU. This is because the system requires more memory than a multi-point system and must process more information in the same time. As a result, these systems are more expensive to implement, raising the cost of the vehicle. The high pressure of the fuel also makes maintenance of the fuel lines and entire fuel system more difficult.


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