Gas direct-injection engines


Discussions of direct fuel injection are almost entirely focused on diesel engines. Increasingly, however, direct injection is being utilized in gasoline engines ranging from the one in the family car to pickups and now to smaller engines. Yet, gas engine fuel injection is completely different from the diesel pump-line nozzle systems.


Ford was the first to bring true fuel injection to the pickup truck market in 1986. That innovation was the port fuel-injection system (PFI). With this design, there is a fuel injector for each cylinder that is mounted at the junction of the intake manifold to the cylinder head (located approximately 100 mm or less than 4 inches from the intake valve).


虽然通用电机TBI在低燃料压力(9至13psi)上操作,但福特系统在45 psi下运行。一旦行业转移到PFI,操作燃油压力范围就在45到60 psi之间。

The need to meet stricter emissions and fuel economy standards brought the introduction of gasoline direct injection (GDI).

这个设计,特别设计的喷嘴placed in the combustion chamber of the cylinder head similar to that of a fuel injector in a diesel. This device injects gas directly into the combustion chamber at pressures up to 2,200 psi.

与PFI相比,GDI的益处是,由于乳化混合物通过气缸盖的进气流液而在运输中没有燃料。主要优点在于气缸中的气体发生的相变。由于蒸发潜热,这为燃料 - 空气混合物提供了冷却效果,因为热量用于将液体汽油转化为稀土状态。



Yet, the evolution of these systems did not stand still. The latest trend is the combination PFI and GDI engine. With this design, the number of injectors is double the number of cylinders. There is a PFI injector at the cylinder head end of the intake manifold runner and an injector in the combustion chamber. The engine controller toggles back and forth between these two fuel injectors.


Problems with Valve Deposits

As many manufacturers do real-life testing before a design goes into production, they cannot duplicate every scenario that leads to GDI’s pitfalls. With GDI, there is no fuel wetting on the back side of the intake valve. Yet, during cam overlap, combustion gases are reverted there and turn into carbon deposits. These deposits tent-up on the intake valve and block airflow into the cylinder.



The series of events that can produce LSPI are too technical and in-depth to cover here. It has been determined that the engine oil is a huge contributor, though. It was found that engine oils with a high level of calcium are very prone to cause LSPI.



随着PFI / GDI系统的就业,可以通过PFI系统引起带LSPI的发动机运行状态,不再是一个问题。请记住,一旦发动机保修期满,就没有一家汽车公司将有义务尊重LSPI销毁的发动机的索赔。




If the engine is a PFI/GDI system, its care doesn’t require much more than using the specified engine oil and a good in-tank fuel system cleaner every 3,000 miles. The chemistry will keep the valves clean along with the PFI and GDI injector pintles and make the system carefree.



Tip of the Day


螺旋座覆盖2月21日 An old water tank lying around our place was useless for its original purpose because of a bad leak. But now, cut in half, part of more

Machinery Talk

Most Recent Poll

Will you plant more corn or soybeans this year?