Problems related to GDI Engines

The evolution of the gasoline direct injection (here onwards referred to as GDI) engines dates back to the times of World War II, and this system of fuel injection has since developed continuously to become the GDI system we know of today. However it wasn't until the 1990s that they became widely adopted in modern cars. In the early days of internal combustion engines, fuel was typically delivered through a carburetor and mixed with air before entering the engine. This was later replaced by electronic fuel injection (EFI) systems, which allowed for more precise control over the amount of fuel delivered to the engine.

GDI systems take this a step further by delivering fuel directly into the combustion chamber, rather than through the intake manifold. This allows for even greater control over the combustion process, resulting in better fuel efficiency and lower emissions. The first GDI system was introduced by Mitsubishi in the 1990s, and was later adopted by other automakers. Since then, GDI systems have continued to evolve, with improvements in fuel efficiency, power output, and emissions reduction.

But like all things, every good system has its own cons to be dealt with, and this is no any difference to GDI systems. One major challenge with GDI systems is the buildup of carbon deposits on the intake valves, commonly known as valve gunk. GDI engines have their fuel injectors inside the combustion chambers and this means that the fuel never touches the intake valves, where valve gunk is likely to build up. All engines have the ingredients to make valve gunk, but in a regular engine (indirect injection engine) much of this valve gunk is blown away by the fuel sprayed from the fuel injectors whenever the engine is running. So the valve gunk builds up very slowly over time. However in a GDI engine, as the fuel does not touch the intake valves, there's no cleaning of gunk form the intake valve and this leads to the accumulation of valve gunk at a higher rate in direct injection engines when compared with other regular engines.?

Another problem related to GDI engines is the excessive timing chain wear. Generally, direct injection systems tend to form a much richer air-fuel mixture because the fuel has less time to mix with air when compared with indirect injection system. Though this has its perks of its own, especially during cold starts, the rich air-fuel mixture may result in incomplete combustion and therefore the formation of soot. The soot gets accumulated on the cylinder walls, and overtime this soot will blow by through the piston rings into the crank case and get mixed up with the oil. The dispersants in the oil will prevent this soot agglomerating into larger chunks. The idea of using dispersants is to keep this soot floating in the oil until the next oil change. This soot is rather not very problematic for many engine parts as there is enough clearance available for the oil film. However in timing chains, specifically in silent timing chains, the clearance in the pins connecting the links of the chain is very minuscule. Soot in the oil can enter into this clearances and cause abrasion. There are hundreds of such pins in a timing chain and this activity can cause wearing of the chain resulting in chain elongation/ loosening and thereby disrupting the valve timing. And we all know how improper valve timing can cause a "nightmare come true" to any vehicle owner. This effect can be minimized by using proper engine oil in your vehicle, specifically meeting requirements of ILSAC GF-6 or API SP.

Fuel dilution is also another major concern related with GDI engines. In a cold start, where the engine temperature is not within the recommended operating temperature, more fuel will be injected for a richer air-fuel mixture to allow better combustion. This means that in a direct injection system, excess fuel will touch the cylinder wall during a cold start. Some of this fuel can blow by and mix with the oil resulting in thinning of the engine oil. As a result the viscosity of the engine oil reduces, increasing the wear of engine. Now this can be minimized in a few ways. One way is to reduce the number of short trips the vehicle runs, thereby reducing the number of cold starts. The other way is to increase the number of long trips. This is because as the engine runs for a longer time and then oil heats up, the fuel in the oil vaporizes and the positive crankcase ventilation (PCV) valve will remove the gases and feed it back into the combustion chamber.

Lastly, another common issue is the limitation of producing peak power at higher engine rpm is limited since the time period available for injecting the amount of fuel needed for the power production is limited. In normal gasoline engines, fuel can be actually added to the intake valve at any time and the valve will open up according to the timing. However, in GDI engines, the fuel is only injected during the intake and combustion processes. This is a restriction in higher rpms as the duration of a combustion cycle is very limited. Some GDI engines have introduced a hybrid use of direct injection and manifold injection during higher rpm to minimize this issue.

Overall, GDI engines offer several benefits over traditional fuel injection systems, including improved fuel efficiency, increased power, reduced emissions, better cold start performance, and improved durability. There are many aspects about this system that are still open for improvement. That is what engineers are here for; to invent, to innovate and improve.