Gasoline direct injection (GDI) is a fuel injection system; that sprays gasoline, directly into the combustion chamber.
As a result, gasoline direct injection (GDI); has a separate fuel injector, for each of the engine’s cylinders.
Because of this, the cylinder head is the new home for the fuel injectors. Consequently, allowing for direct access to the combustion chamber.
So, with no fuel, the only thing going through the intake manifold and the intake valves is air.
Furthermore, with gasoline direct injection (GDI), the fuel enters each cylinder as a high pressure mist. (GDI), uses computer-controlled electric injectors, to spray fuel into the cylinders.
Consequently, the computer controls all aspects of the (GDI) system. So, with all the different running conditions; the computer will decide, when to inject the fuel.
Advantages Of Gasoline Direct Injection (GDI)
So, some advantages of direct injection are:
- Better fuel economy
- Less overall emissions
- Better performance
Also, the engine makes more power using less fuel as a result of:
- Spraying fuel directly into the combustion chamber, as compression is building.
- As well as, during and after initial combustion.
Also, engines with (GDI) can tolerate, extremely lean fuel mixtures (up to 40:1). Even under light load and cruise conditions. The net result, is typically 15 to 20 percent, better fuel economy.
(GDI) closely controls the fuel mixture, at just the right moment. Consequently, (GDI) engines can handle higher compression ratios. As a result, (GDI) engines usually produce more horsepower.
Disadvantages Of Gasoline Direct Injection (GDI)
The big disadvantage of (GDI) is, carbon buildup, on the backside of the intake valves.
This can throw a computer code, and result with an engine misfire or a ignition failure.
Also, the actual cost of this system tends to be higher. And, the fuel pump must be capable of very high pressures.
All this has led to the engine needing to drive the fuel pump. The main reason we are seeing vehicles on the market with direct injection, is tighter fuel economy standards.
Why Higher Operating Pressures
Direct injection requires extremely high operating pressures (up to 2200 PSI).
Direct injection requires more delivery pressure, to overcome compression pressure inside the cylinder. And, to deliver a higher volume of fuel in a shorter period of time.
The higher injection pressure also helps, to atomize the fuel into small droplets. So, it will mix better with air for more complete combustion.
How (GDI) Creates New Problems
Along with many automotive innovations comes a new set of problems:
Firstly, higher cylinder temperatures and pressures, released into the crankcase accelerate oil vaporization. Eventually this causes oil droplets to coat the intake valves. Also, with (GDI) systems fresh fuel is not sprayed onto intake valves.
So, the valves are no longer cleaned or cooled.
Secondly, it can cause piston rings to become stuck into their lands. Also, If the engine uses low-tension rings, the sludge can prevent them from properly sealing. It can also cause sludge and fuel deposits, to bake onto the top of the piston.
Since inception, (GDI) engines have had known problems with, build-up of cooked fuel deposits that foul injectors. As the deposits accrue over time and mileage; the engine’s timing can be altered. Carbon builds up on the backside of the valves, can alter ignition timing and the engine’s firing order.
The carbon also acts as an insulator, so the valves can heat up and fail. Over time, the carbon can fall off the valves and make its way to the bottom end of the engine. Finally, causing wear on the moving parts.
Carbon deposits may flake off and pass through, the combustion chamber and into the exhaust. Furthermore, if the engine is equipped with a turbocharger; there is a chance the carbon could, damage the turbine fins in the turbocharger.
The problem tends to be worse in (GDI) engines, that are used mostly for short trips. The intake valves never get hot enough, to burn off the deposits.
Cleaning The (GDI) System
The fix for dirty intake valves is:
- Use a chemical cleaner sprayed into the throttle body; or intake manifold directly into the intake ports.
- Remove the intake manifold and spray solvent; directly into the intake ports in the cylinder head.
- For extremely heavy carbon deposits; it may be necessary to remove the cylinder head to clean the valves.
Port injection, although much better than the old carburetors; throttle body systems, just can’t match the power and economy produced by (GDI). As fuel costs increase; the difference in manufacturing cost between port, and direct injection systems will diminish.
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