A conventional fuel-injected engine supplies all cylinders with a mist-like mixture of air and fuel that is flushed into the cylinders during the intake stroke and ignited by the spark plug. The throttle valve determines how much of the air/fuel mixture enters each cylinder.
In a direct-injection engine, the injection nozzle location is inside the combustion chamber, and each solenoid-controlled injector’s tiny outlet holes generates a finer mist, creating a well-atomized air/fuel mixture.
Each bank of cylinders has a high-pressure fuel rail that feeds the individual injectors and a high-pressure pump with a fuel rail pressure sensor on each rail that helps the vehicle powertrain control module precisely control the fuel pressure.
Indirect injectors positioned to the side of each cylinder aim the fuel directly into the cylinder, adjacent to the spark plug and alongside the intake and exhaust valves. These injectors spray fuel into the cylinders at pressures of up to 2,150 psi. That's about 35 times more intense than port fuel injection.
Surrounding the spark plug is the relatively small, precisely shaped volume of ignitable air/fuel mixture that results when the injector sprays fuel toward the spark plug just before ignition. When the injector sprays fuel into the cylinder, the shaped piston crown guides the air/fuel mix to the spark plug.
The precise metering of fuel and control of combustion chamber temperatures enables compression ratios of nearly 12:1 without the need for premium fuel, because direct injection reduces the tendency of engine knock. The higher compression ratio alone increases efficiency by about two percent.
Automakers realize major reductions in fuel consumption when direct injection is combined with technologies such as turbocharging. Mixing existing and proven technologies in a synergistic manner can offer double digit fuel economy benefits with a much lower cost than hybrid technologies.When servicing a direct injection system, keep the following tips in mind:
Whether your vehicle is fuel-injected or carbureted, be informed with ChiltonDIY’s comprehensive online repair procedures, inspections, specifications, diagnostics, and technical service bulletins for your next repair.
A muscle car enthusiast and drag racer, Jim Marotta is a freelance automotive writer with more than 25 years experience in the automotive industry.