Superior Output Mode
When the GDI engine is operating with higher loads or at higher speeds, fuel injection takes place during the intake stroke. This optimizes combustion by ensuring a homogeneous, cooler air-fuel mixture which minimizes the possibility of engine knocking.
The GDI engine’s foundation technologies
There are four technical features that make up the foundation technology. The ‘upright straight intake port’ supplies optimal airflow into the cylinder. The ‘curved top piston’ controls combustion by helping to shape the air-fuel mixture.
The ‘high-pressure fuel pump’ supplies the high-pressure needed for direct in-cylinder injection. In addition, the ‘high pressure swirl injector’ controls the vaporization and dispersion of the fuel spray.
These fundamental technologies, combined with other unique fuel control technologies, enabled Mitsubishi to achieve both development objectives – fuel consumption lower than that of diesel engines and output higher than that of conventional MPI engines. The methods are shown below.
Lower fuel consumption and higher output
Using methods and technologies unique to Mitsubishi, the GDI engine provides both lower fuel consumption and higher output. This seemingly contradictory and difficult feat is achieved with the use of two combustion modes. Put another way, injection timings change to match engine load.
For the load conditions required in average urban driving, fuel is injected late in the compression stroke, as in a diesel engine. By doing so, ultra-lean combustion is achieved due to an ideal form of a stratified air-fuel mixture. During high-performance driving conditions, fuel is injected during the intake stroke. This enables a homogeneous air-fuel mixture, like that in conventional MPI engines, to deliver a higher output.
Ultra-lean combustion mode
Under most normal driving conditions, up to speeds of 120 km/h, the Mitsubishi GDI engine operates in ultra-lean combustion mode, resulting in less fuel consumption. In this mode, fuel injection occurs at the latter stage of the compression stroke and ignition occurs at an ultra-lean air-fuel ratio of 30: 40 (35: 55, including EGR).
In-cylinder airflow
The GDI engine has upright straight intake ports rather than the horizontal intake ports used in conventional engines. The upright straight intake ports efficiently direct the airflow down at the curved top piston, which redirects the a
Realization of lower fuel consumption
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 purposes has proved that an air-fuel mixture with the optimum density gathers around the spark plug in a stratified charge. This is also borne out by analyzing the behave our of the fuel spray immediately before ignition and analyzing the air-fuel mixture itself.
Last word
The curved-top piston controls the shape of the air-fuel mixture as well as the airflow inside the combustion chamber and has an important role in maintaining a compact air-fuel mixture. The mixture, which is injected late in the compression stroke, is carried towards the spark plug before it can disperse.
