Tech:Direct Injection Engines & Carbon Build Up Part 1

Most of the latest petrol engines use direct injection (DI) technologies, meaning that the fuel is directly injected into the cylinder, bypassing the air inlet assembly and the intake valves.

Direct Injection System

Petrol engines feature an oil vapor return system, which is –for environmental reasons- fed into the intake plenum. This system retrieves the vapors that come from the crankshaft ventilation and is required for many reasons, such as the pressure normalization. Most of these engines also feature an EGR –stands for Exhaust Gas Recirculation – system which is a common way to increase efficiency during cold starts and reduce the nitrogen oxide (NOx) emissions. As simple as that, exhaust gas is fed into the inlet plenum and intake valves through the EGR valve (you can see a typical EGR valve above).

Both of these systems mean–without doubt- that deposits can build-up the intake valves which can lead to weak cylinder compression and massive engine misfires.

Clean intake valves

Intake valves with deposits

On the other hand, fuel is an excellent cleaning agent, which means that indirect injection petrol engines feature a self-cleaning system of any build-up that may occur because of the EGR or the crankshaft ventilation system and usually they only accumulate a hydrocarbon build up, slowly. In most cases of indirect injected engines with indication of build ups, chemical cleaning agents are used as additives to the fuel system, to resolve the problem. In DI engines though, the fuel bypasses the intake valves so these agents cannot be effective and deposits such as carbon build-up is a potential problem.