If you flip through the list of features on just about any new car or truck, you’re likely to see the words “direct fuel injection,” or DI. The concept is straightforward enough — engineers have moved the fuel injector from the car’s intake port (“port fuel injection”) and placed it in directly into the combustion chamber; the fuel is injected at the exact moment combustion is needed rather than having to mix with incoming air and flow around an intake valve.
DI operates at far higher pressure than port fuel injection; that, combined with the precise control offered by modern microprocessors, has a huge effect on engine tuning, especially when that engine is turbocharged. The net result is better fuel economy and more power for a given engine size, along with lower emissions. Advances in direct injection are the reason efficient, small turbocharged gasoline engines have become so common, from economy cars to luxury sedans.
The adoption of DI hasn’t been completely seamless: Removing the fuel spray from the intake port also removes the cleaning effect gasoline has on intake valves; combined with increased blow-by from turbocharged engines, oil and carbon can collect on intake valves, reducing engine performance. Some manufacturers have resolved the problem by combining direct and port fuel injection. This means there are two sets of fuel injectors, but the system can switch between direct and indirect fuel delivery on demand –- keeping the problems with carbon build up at bay.
Since direct injection is the future of fuel delivery, it’s a safe bet these are merely technological growing pains; they’ll be less and less of an issue in the future. In the meantime, don’t fear DI — enjoy the blend of performance and fuel economy these gasoline marvels deliver.