Technology:Gasoline Direct Injection Engine (2024)

I. Introduction

Formany years, innovative engine technology has been a development priorityof Mitsubishi Motors. In particular, Mitsubishi has sought to improve engineefficiency in an endeavor to meet growing environmental demands, such asthose for energy conservation and the reduction of CO2 emission to limitthe negative impact of the green-house effect.

In Mitsubishis endeavorto design and build ever more efficient engines, it has devoted significantresources to developing a gasoline direct injection engine. For years,automotive engineers have believed this type of engine has the greatestpotential to optimize fuel supply and combustion, which in turn can deliverbetter performance and lower fuel consumption. Until now, however, no onehas successfully designed an in-cylinder direct injection engine for useon production vehicles. A result of Mitsubishis engine development capabilities,Mitsubishis advanced Gasoline Direct Injection GDI engine is the realizationof engineering dream.

II. Major Objectives of the GDI engine

• Ultra-low fuel consumption that betters that of evendiesel engines
• Superior power to conventional MPI engines

• Extremely precise control of fuel supply to achieve fuelefficiency that exceeds that of diesel engines by enabling combustion ofan ultra-lean mixture supply.
• Very efficient intake and relatively high compressionratio unique to the GDI engine deliver both high performance and responsethat surpasses those of conventional MPI engines.

For Mitsubishi, the technology realized for this GDI enginewill form the cornerstone of the next generation of high efficiency enginesand, in its view, the technology will continue to develop in this direction.

Transition of Fuel Supply System

2. Outline

(1) Major Specifications

(2) Engine Diagram

3. Technical features

• Upright straight intake ports for optimal airflow controlin the cylinder
• Curved-top pistons for better combustion
• High pressure fuel pump to feed pressurized fuel intothe injectors
• High-pressure swirl injectors for optimum air-fuel mixture

III. Major characteristics of the GDI engine1 . Lower fuel consumption and higher output

(1) Optimal fuel spray for two combustion mode
Using methods and technologies unique to Mitsubishi, the GDI engine providesboth lower fuel consumption and higher output. This seemingly contradictoryand difficult feat is achieved with the use of two combustion modes. Putanother way, injection timings change to match engine load.

For load conditions required of average urban driving, fuel is injectedlate in the compression stroke as in a diesel engine. By doing so, an ultra-leancombustion is achieved due to an ideal formation of a stratified air-fuelmixture. During high performance driving conditions, fuel is injected duringthe intake stroke. This enables a hom*ogeneous air-fuel mixture like thatof in conventional MPI engines to deliver higher output.

Ultra-lean Combustion Mode
Under most normal driving conditions, up to speeds of 120km/h, theMitsubishi GDI engine operates in ultra-lean combustion mode for less fuelconsumption. In this mode, fuel injection occurs at the latter stage ofthe compression stroke and ignition occurs at an ultra-lean air-fuel ratioof 30 to 40 (35 to 55, included EGR).
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 combustionby ensuring a hom*ogeneous, cooler air-fuel mixture that minimized the possibilityof engine knocking.

(2) The GDI engines 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 shape the air-fuelmixture. The High Pressure Fuel Pump supplies the high pressure neededfor direct in-cylinder injection. And the High Pressure Swirl Injectorcontrols the vaporization and dispersion of the fuel spray.

These fundamental technologies, combined with other unique fuel controltechnologies, enabled Mitsubishi to achieve both of the development objectives,which were fuel consumption lower than those of diesel engines and outputhigher than those of conventional MPI engines. The methods are shown below.

In-cylinder Airflow

The GDI engine has upright straight intake ports rather thanhorizontal intake ports used in conventional engines. The upright straightintake ports efficiently direct the airflow down at the curved-top piston,which redirects the airflow into a strong reverse tumble for optimal fuelinjection.

Fuel Spray

The curved-top piston controls the shape of the air-fuelmixture as well as the airflow inside the combustion chamber, and has animportant role in maintaining a compact air fuel mixture. The mixture,which is injected late in the compression stroke, is carried toward thespark plug before it can disperse.
Mitsubishis advanced in-cylinder observation techniques including laser-methodsare utilized to determine the optimum piston shape.

2 . Realization of lower fuel consumption

(1) Basic Concept
In conventional gasoline engines, dispersion of an air-fuel mixture withthe ideal density around the spark plug was very difficult. However, thisis possible in the GDI engine. Furthermore, extremely low fuel consumptionis achieved because ideal stratification enables fuel injected late inthe compression stroke to maintain an ultra-lean air-fuel mixture.

An engine for analysis purpose has proved that the air-fuel mixture withthe optimum density gathers around the spark plug in a stratified charge.This is also borne out by analyzing the behavior of the fuel spray immediatelybefore ignition and the air-fuel mixture itself.

As a result, extremely stable combustion of ultra-lean mixture with anair-fuel ratio of 40 (55 , EGR included) is achieved as shown below.

(2) Combustion of Ultra-lean Mixture
In conventional MPI engines, there were limits to the mixtures leannessdue to large changes in combustion characteristics. However, the stratifiedmixture of the GDI enabled greatly decreasing the air-fuel ratio withoutleading to poorer combustion. For example, during idling when combustionis most inactive and unstable, the GDI engine maintains a stable and fastcombustion even with an extremely lean mixture of 40 to 1 air-fuel ratio(55 to 1, EGR included)

(3) Vehicle Fuel Consumption
Fuel Consumption During Idling
The GDI engine maintains stable combustion evenat low idle speeds. Moreover, it offers greater flexibility in settingthe idle speed.
Compared to conventional engines, its fuel consumption during idling is40% less.

Fuel Consumption during Cruising Drive
At 40km/h, for example, the GDI engine uses 35% less fuel than a comparablysized conventional engine.

Fuel Consumption in City Driving
In Japanese 10E15 mode tests ( representative of typical japaneseurban driving ), the GDI engine used 35% less fuel than comparably sizedconventional gasoline engines. Moreover, these results indicate that theGDI engine uses less fuel than even diesel engines.

Emission Control
Previous efforts to burn a lean air-fuel mixture have resulted in difficultyto control NOx emission. However, in the case of GDI engine, 97% NOx reductionis achieved by utilizing high-rate EGR (Exhaust Gas Ratio) such as 30%that is allowed by the stable combustion unique to the GDI as well as ause of a newly developed lean-NOx catalyst.

Newly Developed Lean NOx Catalyst (HC selective deoxidizationtype)

3 . Realization of Superior Output (1) Basic concept
To achieve power superior to conventional MPI engines, the GDI engine hasa high compression ratio and a highly efficient air intake system, whichresult in improved volumetric efficiency.

Improved Volumetric Efficiency
Compared to conventional engines, the Mitsubishi GDI engine providesbetter volumetric efficiency. The upright straight intake ports enablesmoother air intake. And the vaporization of fuel, which occurs in thecylinder at a late stage of the compression stroke, cools the air for bettervolumetric efficiency.

Increased Compression Ratio
The cooling of air inside the cylinder by the vaporization of fuelhas another benefit, to minimize engine knocking. This allows a high compressionratio of 12, and thus improved combustion efficiency.

(2) Achievement
Engine performance
Compared to conventional MPI engines of a comparable size, the GDIengine provides approximately 10% greater output and torque at all speeds.

Vehicle Acceleration
In high-output mode, the GDI engine provides outstanding acceleration.
The following chart compares the performance of the GDI engine with a conventionalMPI engine.