How Direct Injection Engines Work

Components of a Direct Injection Fuel System

You'll find a couple of items in every direct injection engine: fuel injectors (at least one per cylinder); and a combustion chamber -- the gaseous hothouse that comprises the upper portion of every cylinder.

Additionally, depending on what type of direct injection system it belongs to, the engine may or may not feature several other components affiliated with the following systems:


  • Common Rail System -- A long metal cylinder called a fuel rail distributes fuel to the injectors under extremely high pressure.
  • Distributor and Inline Pump System -- Either a rotary wheel distributor or plunger-style pump is used to push pressurized fuel to the injectors.
  • Unit Direct System -- In this setup, the injector and a fuel pump just for that injector are integrated into a single unit and positioned over each cylinder [source: Bosch].

One more distinction between direct injection and regular engines: With a direct injection engine, the portion of the car's computer responsible for fuel management has to think a lot more quickly. That's because the fuel management system must pulse fuel into the cylinders at much shorter intervals. And in general, the precise rationing of fuel and manipulation of air-fuel ratios is more crucial on a direct injection engine in order to optimize performance, emissions and fuel efficiency [source: Sawyer].

Read on to learn some of the possible advantages of driving a car that packs a direct injection engine -- along with some reasons they took so long to catch on.