Direct injection engine


Pollutant emissions of hydrocarbons, nitrogen oxides and carbon monoxide are reduced up to 99% with the mediation of a three-way catalyst.
Meanwhile, carbon dioxide (CO2) produced as a result of combustion, being the cause of the "greenhouse effect", can only be reduced based on lower fuel consumption.
Considering these factors, we see that the injection systems with external mixture formation (injection into the intake manifold MPi) are not used to meet these goals, hence the need to develop a system able to meet these commitments. This system is the engine with fuel injection.
Engines with direct fuel injection two main objectives are valid for today and for the future are achieved, these goals are to reduce fuel consumption and this also polluting exhaust emissions.
The different car brands increasingly are choosing to equip their models with gasoline direct injection engines. First it was the Japanese Mitsubishi GDi engine with, now followed with IDE Renault engines the PSA Group with HPi engine, and Volkswagen with FSi engines.

If we compare the fuel injection system on the manifolds (also called indirect injection MPI) with direct fuel injection, we understand why the latter is higher than the first. Injectors gasoline engine (MPI) are often located in the intake manifold, which explains the name of these systems. The fuel is injected in front of a closed or open up the valve and is almost completely mixed with the intake air in each of the nozzles of valve manifold. But this mixture of air and injected fuel mist does not allow perfect explosion in the cylinder if it is not prepared in accordance with a precise stoichiometric ratio comprised within very specific limits

 
In systems of direct fuel injection, fuel is injected directly into the combustion chamber and not in the manifold or intake port, which offers advantages in story to engine efficiency.
The fuel injection systems of gasoline were developed several decades ago by a bomb he was carrying fuel to an injector placed in the combustion chamber, however the problems presented by the high cost and emissions.
Other important features of this system, and the position of the injector in the combustion chamber are:
Precision injection time: In indirect injection engines, is not as important a time when fuel injection is performed, however, direct injection injection should be done at the stage of admission and / or compression.
High pressure injection: The fuel must be injected at high pressure to facilitate spraying and proper mixture with air. 

Piston head: The piston head has forms that allow the formation of turbulence within the combustion chamber to improve air-fuel mixture and / or direct the mixture at a specific space as close to the spark plug, to improve combustion. 

On some engines, direct injection stratified charge that fuel is injected at two times, the first time, in the intake phase and the second compression is used when the air is located near the spark plug, which causes the mixture turns which is close to the plug, leaving the rest of the lean cylinder with light, only expands, this combined mixture is used when the engine was not require too much power, as may be the case city ​​or when traveling at constant speed on level ground. Moreover, the combustion takes place near the spark plug and the rest of the mixture to swell only produces a lower temperature in the cylinder wall to improve engine performance.