What is GDI Fuel Injection

GDI Injector

Not too long ago, gasoline direct injection (GDI) was reserved for a few luxury and sports cars. However, over time this technology has become more affordable. Matter of fact, according to the US Department of Energy (DOE), Gasoline Direct Injection was the most widely adopted emerging technology in the car industry during 2018. Nowadays, that trend shows no signs of slowing down.

Why is that? What makes GDI so special?

In this article, we will explore what is behind car makers’ excitement surrounding gasoline direct injection.

What is gasoline direct injection (GDI)?

As its name implies, DI engines’ injectors deliver fuel straight into the combustion chamber. This is a huge change from Multiport Injection (MPI) where fuel injectors spray gasoline into the intake manifold.

Changing fuel injectors’ location may seem not very important, but the truth is that it makes a world of difference. As you will learn, GDI technology brings many benefits ranging from better fuel economy to smaller engine designs.

GDI Injector

How do GDI injectors work?

The logic behind GDI injectors is the same as any other Electronic Fuel Injection (EFI) system. The Electronic Control Unit (ECU) gathers information from all powertrain sensors, calculates the optimal air-fuel ratio based on the vehicle’s driving conditions and activate DI injectors to deliver the required amount of fuel.

From a mechanical perspective, most GDI injectors use special “needle valve” solenoids since they require faster response times than MPI injectors. DI injectors are also sturdier than conventional injectors since they have to withstand higher fuel pressure and the extreme combustion chamber temperature.

GDI Injector

The electric operation of Gasoline Direct Injectors is somewhat a combination of Low impedance (peak and hold) injectors and High impedance (saturated signal) injectors.

  • DI injectors valve is normally closed when the engine is not running thanks to its internal spring mechanism.
  • Once the engine starts, the ECU keeps injectors closed by supplying a 5-volt signal to both terminals of their circuit.
  • To open any GDI injector, the ECU simultaneously supplies a “peak” signal of around 40 volts to the positive terminal and a ground signal to the negative terminal. At this point, you can expect a high current of about 6 amperes to beat the inertia against pressurized fuel.
  • Once the internal valve is fully opened, the “peak” voltage is replaced by a square-shaped signal that keeps the positive terminal fed with a lower voltage. During this stage the current drops to approximately 2.5-3.0 amperes.
  • Finally, the ECU finishes the cycle closing the injector by simultaneously supplying a 5-volt signal to both ends of its circuit.

Last but not least, GDI injectors’ distinctive characteristic is their ultra-high operating pressure. Opposed to conventional 45-80 psi fuel pressure managed by MPI injectors, a typical DI injector can handle over 4500 psi.

What are the benefits of GDI over Multiport injection?

Knowing how GDI injectors work is interesting but you may wonder, how can this technology benefit me? Does it bring any tangible improvement over Multiport injection? In short, is it worth choosing a direct-injected vehicle over an MPI-based one?

Below is a list describing the main benefits of GDI over Multiport injection.

  • Gasoline Direct Injection systems offer the utmost fuel economy. In a world where fuel economy is so important, DI injection offers an excellent solution. According to Bosch, one of the top GDI parts suppliers, gasoline direct injection systems alone can reduce fuel consumption by over 15%.
  • Gasoline Direct Injection systems offer the highest horsepower per liter. Aside from enhancing fuel economy, direct-injection systems also increase combustion efficiency. Thanks to GDI injectors the ECU can now deliver fuel with increased precision, resulting in an optimized air-fuel mixture. The higher combustion efficiency allows dramatic performance boosts. Depending on the engine design you can expect over 50% increase on low-end torque and over 20% power gains.
  • Gasoline Direct Injection systems pairs wonderfully with other technologies. A major advantage of DI systems is their great flexibility. You can add computer-controlled camshaft timing systems, supercharged (or turbocharged) induction, dual spark plug ignition systems, and so on without any issue. This flexibility allows automakers to increase ever further horsepower per liter ratios.
  • Gasoline Direct Injection systems allow designing smaller engines. The incredible efficiency and power-ratio of direct-injection systems allow car manufacturers designing smaller and thus lighter engines. Not too long ago a compact car required at least a 1.4-liter engine to achieve 100+ hp. Nowadays, thanks to DI, the same car only needs a 1.0-liter engine. Lighter engines help tremendously overall vehicle statistics. By reducing car weight, braking distances, fuel economy figures, drivability, acceleration, and stability are improved. Smaller engines also enable engineers to increase interior dimensions and thus roomier and more comfortable cabins.
  • Gasoline Direct Injection systems have ultra-low emissions. Yet another benefit from GDI systems is the ability to reduce emissions. Higher combustion efficiency combined with smaller engines helps DI vehicles to comply with current emissions. Even better, this technology is one step ahead of next-gen regulations. Direct-injected engines produce 25% fewer contaminants than conventional MPI systems, a huge win for the environment.
  • Gasoline Direct Injection systems bring better drivability. Better low-end torque and power figures enable engineers to use next-gen automatic transmissions with up to 8 gears. As a result, newer powertrains handle any driving condition with ease which translates is enhanced drivability.

As you can see, gasoline direct injection systems are worth all the hype surrounding them. However, that doesn’t mean they are perfect.

Keeping your GDI injectors clean with our Ethanol Defense.

What are the disadvantages of DI over Multiport injection?

Hopefully, by now you have a clear idea of what are the pros of GDI over MPI injection. But what about direct injection disadvantages? This article would not be complete without an overview of its weaknesses.

  • Carbon buildup on intake valves. Arguably the most widespread issue on direct-injected engines is the carbon buildup. As a result of the location of the injector inside the combustion chamber, intake valves are now prone to get clogged by carbon deposits. This can become a huge issue over time since carbon buildup reduces engine efficiency. Fortunately, car makers have taken several steps to prevent potential problems in the long-run. For one, DI car owners are advised to avoid using gasoline containing ethanol additives since using special fuel cleaners is preferred. Also, newer models use updated ECU software that sprays small amounts of fuel directly at intake valves to help keep them clean.
  • Higher price tag. Due to the complexity of GDI injectors, and associated direct injection components, you can expect these vehicles to have a higher price than their MPI counterparts. However, thanks to its multiple benefits, DI cars offer similar fuel economy and much better performance than current hybrid vehicles.
  • Cutting-edge technology. You can expect direct injection components to be more expensive than conventional MPI parts. This is a direct consequence of its cutting-edge nature.

Wrapping Up

Gasoline direct injection is here to stay. The benefits of DI systems clearly outweigh its drawbacks. DI advantages over former MPI systems are too many to ignore. Newer vehicles fitted with direct injection are more efficient in every aspect. As time passes you can expect direct-injection costs to decrease and issues like carbon buildup solved.

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