Gasoline direct injection engines work by injecting fuel at high pressure directly into the combustion chamber. This is far more precise than older fuel-injection systems or carburetors.
This direct injection results in a more complete combustion and cooler temperatures inside the cylinder. The cooler temperatures allow for a better compression ratio, meaning greater efficiency and power with the same amount of fuel.
This might all sound too good to be true. And in a way it is. While the efficiency gains are without a doubt real, GDI technology creates a whole new set of problems. The main advantage of Gasoline Direct Injection technology, its precision, is also its main drawback.
To accomplish those greater power and compression ratios, GDI engines operate by spraying fuel directly into the engine cylinder, providing a cooling effect. The cooling effect allows the engine to produce increased compression ratios and more torque, resulting in greater fuel efficiency. GDI engines can also incorporate turbocharger technology TGDI , which recovers energy that is otherwise lost through exhaust systems to further increase fuel efficiency.
Four cylinders produce less friction and maintain more energy than six cylinders, directly contributing to better fuel economy. While downsizing is a reliable path to reaching fuel economy goals, downsized engines run under more extreme conditions than traditional engines—and that requires heightened durability and protection from lubricants.
GDI and TGDI engines rely on increased cylinder pressure, slower operating speeds and hotter temperatures to generate the power that allows them to operate more efficiently than PFI engines. However, due to these more severe operating conditions, there is concern over the following:.
A higher shear stability means the lubricant can withstand GDI conditions without succumbing to oxidation, mixing and increased consumption. Realization of lower fuel consumption 1 Basic Concept In conventional gasoline engines, dispersion of an air-fuel mixture with the ideal density around the spark plug was very difficult.
However, this is possible in the GDI engine. Furthermore, extremely low fuel consumption is achieved because ideal stratification enables fuel injected late in the compression stroke to maintain an ultra-lean air-fuel mixture. An engine for analysis purpose has proved that the air-fuel mixture with the optimum density gathers around the spark plug in a stratified charge. This is also borne out by analyzing the behavior of the fuel spray immediately before ignition and the air-fuel mixture itself.
As a result, extremely stable combustion of ultra-lean mixture with an air-fuel ratio of 40 55 , EGR included is achieved as shown below. However, the stratified mixture of the GDI enabled greatly decreasing the air-fuel ratio without leading to poorer combustion. For example, during idling when combustion is most inactive and unstable, the GDI engine maintains a stable and fast combustion even with an extremely lean mixture of 40 to 1 air-fuel ratio 55 to 1, EGR included.
Moreover, it offers greater flexibility in setting the idle speed. Moreover, these results indicate that the GDI engine uses less fuel than even diesel engines. Emission Control Previous efforts to burn a lean air-fuel mixture have resulted in difficulty to control NOx emission. Realization of Superior Output 1 Basic concept To achieve power superior to conventional MPI engines, the GDI engine has a high compression ratio and a highly efficient air intake system, which result in improved volumetric efficiency.
The upright straight intake ports enable smoother air intake. And the vaporization of fuel, which occurs in the cylinder at a late stage of the compression stroke, cools the air for better volumetric efficiency. When oil thickens it flows less easily, so that when some oil gets behind the rings it tends to stick. Over time it hardens and restricts ring function, reducing the all-important compression, and allowing even more gases, soot and fuel into the oil.
The impact on compression is also a feature. BG Products tested a Ford 2. So, while GDI engines are known for efficiency, the constant struggle between low tension piston rings and high operating pressures will eventually erode fuel efficiency and diminish horsepower.
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