Direct Injection

Direct injection is a type of fuel-delivery injection technology used in internal combustion engines. The technology is a fairly recent development and has not been widely adapted to automobiles in the mass market. With direct injection technology, gasoline engines have the ability to burn fuel more efficiently, produce more power, and discharge less and cleaner emissions.^[1]

Direct injection differs in that air and gasoline are not pre-mixed. Instead, air intake occurs through an intake manifold as opposed to being drawn into the cylinder along with the gas. While the air comes in through an intake manifold, the gas is directly injected separately from the air inside the cylinder.^[2]

Diesel engines use a system of direct injection, though the process used to combust fuel greatly differs from that of gasoline engines. The design and operation of direct injection systems for both gasoline engines and diesel engines are therefore also very different.

[edit] How it Works

When gasoline engines were first developed, they used a carburetor to disperse a mixture of air and fuel into the combustion chamber. Eventually, carburetion fuel injection systems were replaced in conventional gasoline engines with electronic fuel injection systems.

For example, multi-point injection (MPI) systems inject fuel through intake ports. This is one of the most widely utilized fuel injection systems. The multi-point injection system provides a vast improvement in both response and combustion quality. However, the air and fuel are still premixed prior to entering the cylinder.^[3]

With a direct injection system, the gas and air are not premixed. Both enter the engine’s cylinder separately, resulting in a more even air and fuel mixture that ultimately yields a higher compression ratio.^[4] As a result, engines with direct injection are able to produce more power and get better fuel economy.

The technology is also combined with computer management systems that provide for more accurate monitoring and control of fuel metering (the amount of fuel injected) and injection timing (the moment when the fuel is first introduced into the cylinder). The injector is also position in such a way as to permit an optimal spray pattern that breaks apart gas into smaller-sized droplets.^[5]

There are two drawbacks to direct injection—complexity and cost. Components in direct injection systems are expensive to make because they have to be able to withstand a great degree of heat and pressure associated with combustion.^[6]

Though direct injection technology has been around since the mid-19th century, it was not widely utilized initially. However, resurgence in the technology has been renewed largely due to rising fuel costs and more stringent fuel economy and emissions legislation. Automakers are beginning to develop direct injection systems and it is anticipated that most gasoline engines will feature direct injection systems within the next several years.^[7]

[edit] References

1. ↑ Direct Injection. About.com. 2008-09-29.
2. ↑ Direct Injection. About.com. 2008-09-29.
3. ↑ Direct Injection. Freescale. 2008-09-29.
4. ↑ Direct Injection Gives Your Next Car More Power and Better Economy. 2008-09-29.
5. ↑ Direct Injection. About.com. 2008-09-29.
6. ↑ Direct Injection. About.com. 2008-09-29.
7. ↑ Direct Injection Gives Your Next Car More Power and Better Economy. 2008-09-29.