This document summarizes the key features and advantages of a direct gasoline injection (GDI) system compared to port fuel injection and carburetor systems. The GDI system injects fuel directly into the engine cylinder, allowing for more precise control of the air-fuel ratio and enabling stratified and homogeneous combustion modes to improve fuel efficiency and power. The GDI system uses high-pressure fuel injection, a curved-top piston to control combustion, and upright intake ports to efficiently direct airflow for optimal fuel injection and mixing. This allows the GDI engine to achieve lower fuel consumption than diesel engines as well as higher output than port fuel injection systems.

1. ABSTRACT:
Fuel supply system in Spark Ignition Internal Combustion Engines plays an important role in the
output power of an engine as well as its performance in terms of fuel consumption. For many
years, carburetor systems are used for the spark ignition engines. Fuel injection method has
proved to be a good alternative in terms of lower emissions and better fuel consumption
compared to the carburetor systems. Earlier (before 1990) due to high initial cost, fuel injection
system was used only in aircraft engines and racing cars only. But now, due to pressure to
control air pollution and because of advantages of better power fuel economy, gasoline Injection
is being offered in large number of Spark Ignition Engines. In this paper an attempt is made to
compare the different types of fuel supply systems for Spark Ignition Engines with special focus
given on fuel injection systems (MPFI & GDI).A computer controlled direct gasoline fuel
injection(DGI) system has been modeled, programmed and constructed for a four-stroke SI
engine. Locally available materials have been used for this experimental model. All the old
model vehicle were equipped with carburetor for air fuel mixing and later on electronic fuel
injection system has been introduced for maintaining better air fuel ratio and mixing in many late
model vehicles. Later on Japan introduced direct gasoline fuel injection system in their SI engine
but it is not yet commercialized in many under developed countries. Direct gasoline fuel
injection (DGI) system has the advantage of fulfilling proper air fuel ratio in various operating
conditions and loads providing minimum air pollution. In four stroke engine, fuel needs to be
supplied once in every two revolution. A logic control and program is necessary to control and
supply fuel supply once in the cylinder at every two revolution. A program has been made to
control the system. Fuel injection period was maintained by opto-isolator sensor in this model.
But fuel injection period need to be varied depending on operating condition and loads. Further
research is necessary to develop this model and program depending upon engine loads. The
designed DGI system is found to work properly with the designed constant speed of 3000 rpm.
The development of this model with variable speed and load is necessary for improvement of
vehicle performances and emission control.

2. INTRODUCTION
In recent years, legislative and market requirements have driven the need to reduce fuel
consumption while meeting increasingly stringent exhaust emissions. This trend has dictated
increasing complexity in automotive engines and new approaches to engine design. A key
research objective for the automotive engineering community has been the potential
combination of gasoline-engine specific power with diesel-like engine efficiency in a cost-
competitive, production-feasible power train. One promising engine development route for
achieving these goals is the potential application of lean burn direct injection (DI) for gasoline
engines. In carburetors the fuel is sucked due to the pressure difference caused by the
incoming air. This will affect the functioning of the carburetor when density changes in air are
appreciable. There was a brief period of electronically controlled carburetor, but it was
abandoned due to its complex nature. On the other hand in fuel injection the fuel is injected
into the air. 2Nearly thirty percent of the population in USA is involved with automotive
business. Internal combustion engines are widely used in the field of transportation, irrigation,
power generation etc. Cylinder is the heart of energy generation of IC engine where energy is
generated from combustion of air-fuel mixture. The fuel system mixes gasoline or similar fuel
with air to make a mixture which is burned in the engine cylinder. Early model automobiles
used carburetor for supplying the air fuel mixture. The construction of the carburetor is
relatively simple and it has been used almost exclusively on gasoline engines in the past.
However, the recent demands for cleaner exhaust emissions, more economical fuel
consumption and improved drivability etc, the carburetor now must be equipped with various
compensating devices, making it a more complex system. In place of carburetor, therefore, EFI
system was used, assuring the proper air-fuel ratio by injecting fuel in the intake manifold
depending upon various driving conditions. EFI (Electronic Fuel Injection) system was
comparatively successful to maintain correct ratio fuel air mixture to the cylinders in various
speed and loads. In EFI system air- fuel mixing is done in the intake manifold or intake port
outside cylinder. An electronic control unit or computer controls one or more injectors.2
HISTORY
An early use of indirect gasoline injection dates back to 1902, when French aviation engineer
Leon Levasseur pioneered it on his Antoinette 8V aircraft power plant .Another early use of
gasoline direct injection (i.e. injection of gasoline, also known as petrol) was on the Hessel man
engine invented by Swedish engineer Jonas Hesselman in 1925. Hesselman engines use the ultra
lean burn principle; fuel is injected toward the end of the compression stroke, then ignited with a
spark plug.Direct fuel injection was used in notable World War II airplane engines such as the
Junkers Jumo 210, the Daimler-Benz DB 601, the BMW 801, the Shvetsov ASh-82FN (M-
82FN). German direct injection petrol engines used injection systems developed by Bosch from
their diesel injection systems. In the 1940s, hot rodder Stuart Hilborn offered mechanical
injection for racers, salt cars, and midgets.911 production range and until 1975 on the Carrera 3.0
in Europe. Porsche continued using this system on its racing cars into the late seventies and early

3. eighties.The first commercial electronic fuel injection (EFI) system was the ELECTROJECTOR
developed by Bendix Corporation in 1957. Chrysler offered Electrojector on the 1958 Chrysler
DeSoto Adventurer, Dodge D-500 and Plymouth Fury, arguably the first series-production cars
equipped with an EFI system. It was jointly engineered by Chrysler and Bendix. Bosch
developed an electronic fuel injection system, called D- Jetronic (D for Druck, German for
“pressure“), which was first used on the VW 1600TL/E in 1967. Bosch superseded the D-
Jetronic system with the K-Jetronic and L-Jetronic systems for 1974, though some cars (such as
the Volvo 164) continued using D-Jetronic for the following several years.The Cadillac Seville
was introduced in 1975 with an EFI system made by Bendix and modelled very closely on
Bosch“s D-Jetronic .In Japan, the Toyota Celica used electronic, multi-port fuel injection in the
optional 18R-E engine in January 1974.The limited production Chevrolet Cos worth Vega was
introduced in March 1975 using a Bendix EFI system with pulse-time manifold injection, four
injector valves, an electronic control unit (ECU), five independent sensors and two fuel pump3
OPERATION
The different possible fuel supply systems for SI Engines are described as follows:
CARBURETOR SYSTEM:
In this method air and fuel are mixed in the required quantities in a device called carburetor
before supplying to the engine cylinder. Many complex subsystems are required for the effective
working of the engine as the engine is subjected to various operating conditions in practice. Even
by using a modern carburetor, which has many features, it still has some drawbacks as explained
below:
In multi-cylinder engines the mixture supplied to various cylinders varies in quality and quantity
since the induction passages are of unequal lengths and offer different resistances to mixture
flow. The mixture proportion is also affected due to fuel condensation in induction manifold.
Carburetors, with their choke tubes, jets, throttle valves, inlet pipe bends, etc., do not give a free
flow passage for the mixture. Thus there is loss of volumetric efficiency on this account.
The carburetor has many wearing part. After wear it operates less efficiently. Freezing may take
place at low temperatures, unless special means are provided to obviate this. Surging of the fuel
takes place when the carburetor is tilted or during acrobatics in aircraft, unless special means are
adopted to avoid this. Vapor lock in the fuel systems may result in hot weather. There is
possibility of back fire in intake manifold and popping in the carburetor in cold weather unless
the flame traps or fitted. it involves and additional complications which tend to reduce the
volumetric efficiencies. All the above points lead to lower fuel consumption and improper
utilization of engine capacity
Fuel injection:
The three different types of fuel injection methods are:

4. i) Multi point fuel injection (MPFI) ii) Gasoline direct injection (GDI)
iii) Electronic fuel injection (EFI)
MULTI POINT FUEL INJECTION:
This MPFI system is to supply the proper ratio of gasoline and air to cylinders. These systems
function under two basic arrangements, namely
i) Port injection ii) Throttle body injection
In the port injection arrangement the injector is placed on the side of intake manifold near the
Intake port .The injector sprays gasoline into the air, inside intake manifold. In the throttle body
injection system an injector is placed slightly above the throat of the throttle body .The injector
sprays gasoline into the air in the intake manifold .The advantages of MPFI over the carburetor
system can be summarized as follows :Increased volumetric efficiency and hence increased
power and torque, due to the absence of any restriction such as ventures and other metering
elements in the air passage. Better distribution of mixture to each cylinder and hence lower
specific fuel consumption. Lower mixture temperatures in the engine cylinders, despite the
increase in power developed and hence possibility of employing higher compression ratios.

5. Engines fitted with gasoline injection system can be used in any tilt position, which will cause
surge trouble in carburetors. Even in MPFI Engines there are limits to fuel supply response and
the combustion control because the fuel mixes with air before entering the cylinder.
GASOLINE DIRECT INJECTION (GDI):
A GDI System
In conventional engines, fuel and air are mixed outside the cylinder. This ensures waste between
the mixing point and the cylinder, as well as imperfect injection timing. But in the GDI engine,
petrol is injected directly into the cylinder with precise timing, eliminating waste and
inefficiency. By operating in two modes, Ultra-Lean Combustion Mode and Superior Output
Mode, the GDI engine delivers both unsurpassed fuel efficiency and superior power and torque.
The GDI engine switches automatically between modes with no noticeable shift in performance.
All the driver notices is a powerful driving experience, and much lower fuel bills. It's the best
engine on the market. A Gasoline direct injection system consist various components as shown
in the figure below.

6. MAJOR OBJECTIVES OF THE GDI ENGINE:
Ultra- low fuel consumption, which betters that of diesel engines. Superior power to
THE DIFFERENCE BETWEEN NEW GDI AND CURRENT MPI
For fuel supply, conventional engines use a fuel injection system, which replaced the carburetion
system. MPI or Multi-Point Injection, where the fuel is injected to each intake port, is currently
the one of the most widely used systems. However, even in MPI engines there are limits to fuel
supply response and the combustion control because the fuel mixes with air before entering the
cylinder. Mitsubishi set out to push those limits by developing an engine where gasoline is
directly injected into the cylinder as in a diesel engine, and moreover, where injection timings
are precisely controlled to match load conditions. The GDI engine achieved the following
outstanding characteristics.
Extremely precise control of fuel supply to achieve fuel efficiency that exceeds that of diesel
engines by enabling combustion of an ultra-lean mixture supply.Very efficient intake and
relatively high compression ratio unique to the GDI engine deliver both high performance and
response that surpasses those of conventional MPI engines.
OUTLINE: Major Specifications (Comparison with MPFI)

7. TECHNICAL FEATURES
The GDI engines foundation technologies
TECHNICAL FEATURES :
The GDI engines foundation technologies
There are four technical features that make up the foundation technologies are described below.
The Upright Straight
Intake Port supplies
optimal airflow
into the cylinder.
Item GDI Conventional MPFI
Bore x Stroke (mm) 81.0 x 89.0 ß
Displacement 1834 ß
Number of Cylinders IL-4 ß
Number of Valves Intake: 2, Exaust: 2 ß
Compression Ratio 12.0 10.5
Combustion Chamber Curved Top Piston Flat top Piston
Intake Port Upright Straight Standard
Fuel System In-Cylinder Direct Injection Port Injection
Fuel Pressure (MPa) 50 3.3

8. The Curved-top Piston controls combustion by helping shape the air-fuel mixture. The High
Pressure Fuel Pump supplies the high pressure needed for direct in-cylinder injection. The High
Pressure Swirl Injector controls the vaporization and dispersion of the fuel spray.
MAJOR CHARACTERISTICS OF THE GDI ENGINE
Lower fuel consumption and higher output: Using methods and technologies, 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 load conditions required of average urban driving, fuel is injected late in the compression
stroke as in a diesel engine. By doing so, an ultra-lean combustion is achieved due to an ideal
formation 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 of in
conventional MPI engines to deliver higher output. Two Combustion Modes: In response to
driving conditions, the GDI engine changes the timing of the fuel spray injection, alternating
between two distinctive combustion modes- stratified charge (Ultra-Lean combustion), and
homogenous charge (Superior Output combustion).Under normal driving conditions, when speed
is stable and there is no need for sudden acceleration, the GDI engine operates in Ultra-Lean
Mode. A spray of fuel is injected over the piston crown during the latter stages of the
compression stroke, resulting in an optimally stratified air-fuel mixture immediately beneath the
spark plug. This mode thus facilitates lean combustion and a level of fuel efficiency comparable
to that of a diesel engine.
The GDI engine switches automatically to Superior Output Mode when the driver accelerates,
indicating a need for greater power. Fuel is injected into the cylinder during the piston's intake
stroke, where it mixes with air to form a homogenous mixture. The homogenous mixture is
similar to that of a conventional MPI engine, but by utilising the unique features of the GDI, an
even higher level of power than conventional petrol engines can be achieved.

9. IN-CYLINDER AIRFLOW:
The GDI engine has upright straight intake ports rather than 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 airflow into a strongreverse tumble for optimal fuel
injection.
PRECISE CONTROL OVER THE AIR/FUEL MIXTURE:
The GDI engine's ability to precisely control the mixing of the air and fuel is due to a new
concept called wide spacing," whereby injection of the fuel spray occurs further away from the
spark plug than in a conventional petrol engine, creating a wide space that enables optimum
mixing of gaseous fuel and air.In stratified combustion (Ultra-Lean Mode), fuel is injected
towards the curved top of the piston crown rather than towards the spark plug, during the latter

10. stage of the compression stroke. The movement of the fuel spray, the piston head's deflection of
the spray and the flow of air within the cylinder cause the spray to vapourise and disperse. The
resulting mixture of gaseous fuel and air is then carried up to the spark plug for ignition. The
biggest advantage of this system is that it enables precise control over the air-to-fuel ratio at the
spark plug at the point of ignition.
The GDI engine's intake ports have been made straight and upright to create a strong
flow that facilitates mixing of the air and fuel. Air is drawn smoothly and directly down through
the intake ports toward the cylinder, where the piston head redirects it, forcing it into a reverse
vertical tumble flow, the most effective flow pattern for mixing the air and fuel and carrying the
mixture up to the spark plug. The GDI engine's pistons boast unique curved tops-forming a
rounded combustion chamber-the most effective shape for carrying the gaseous fuel up to the
spark plug.In addition to its ability to mix thoroughly with the surrounding air, the fuel spray
does not easily wet the cylinder wall or the piston head. In homogeneous combustion (Superior
Output Mode), fuel is injected during the intake stroke, when the piston is descending towards
the bottom of the cylinder, vapourising into the air flow and following the piston down. Again,
it's all in the timing. By selecting the optimum timing for the injection, the fuel spray follows the
movement of the piston, but cannot catch up. In this case, as the piston moves downward and the
inside of the cylinder become larger in volume, the fuel spray disperses widely, ensuring a
homogenous mixture.

11. Fuel Spray:
Newly developed high-pressure swirl injectors provide the ideal spray pattern to match each
engine operational modes. And at the same time by applying highly swirling motion to the entire
fuel spray, they enable sufficient fuel atomization that is mandatory for the GDI even with a
relatively low fuel pressure of 50kg/cm2
.
Optimized Configuration of the Combustion Chamber:
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 toward the spark plug
before it can disperse. Realization of lower fuel consumption 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 purpose has proved that the air-fuel mixture with the optimum
density gathers around the spark plug in a stratified charge. This is also borne out by analyzing
the behavior of the fuel spray immediately before ignition and the air-fuel mixture itself. As a
result, extremely stable combustion of ultra-lean mixture with an air-fuel ratio of 40 is achieved
as shown below.

12. COMBUSTION OF ULTRA-LEAN MIXTURE:
In conventional MPI engines, there were limits to the mixtures leanness due to large
changes in combustion characteristics. However, the stratified mixture of the GDI enabled
greatly decreasing the air-fuel ratio without leading to poorer combustion. For example, during
idling when combustion is most inactive and unstable, the GDI engine maintains a stable and fast
combustion even with an extremely lean mixture of 40 to 1 air-fuel ratio.
VEHICLE FUEL CONSUMPTION:
FUEL CONSUMPTION DURING IDLING:
The GDI engine maintains stable combustion even at low idle speeds. Moreover, it offers
greater flexibility in setting the idle speed.Compared to conventional engines, its fuel
consumption during idling is 40% less.
FUEL CONSUMPTION DURING
CRUISING DRIVE:

13. At 40km/h, for example, the GDI engine uses 35% less fuel than a comparably sized
conventional engine.
BETTER FUEL EFFICIENCY:
The concept of wide spacing makes it possible to achieve a stratified mixture, enabling the
GDI engine to offer stable, ultra-lean combustion, allowing a significant improvement in fuel
efficiency. In addition to ultra-lean combustion, the GDI engine achieves a higher compression
ratio because of its anti-knocking characteristic and precise control of injection timing. These
features contribute to drastically lower fuel consumption. The GDI engine improves fuel
economy by 33% in the Japanese 10-15 mode driving cycle which represents typical urban
driving conditions.
Emission Control:
Previous efforts to burn a lean air-fuel mixture have resulted in difficulty to control NOx
emission. However, in the case of GDI engine, 97% NOx reduction is 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 a use of a newly developed lean-NOx catalyst.

14. REALIZATION OF SUPERIOR OUTPUT:
To achieve power superior to conventional MPI engines, the GDI engine has a high
compression ratio and a highly efficient air intake system, which result in improved volumetric
efficiency. In high-load operation, a homogeneous mixture is formed. (When extra power is
needed, the GDI engine switches automatically to Superior Output Mode.) Because it burns a
homogenous mixture in this mode, the GDI engine functions like any other MPI engine.
However, by maximizing its technical features, the GDI engine achieves substantially higher
power than a conventional engine. One of the principal reasons for this is that a fine spray of fuel
is injected in a wide shower directly into the cylinder, where it vapourises instantly into the air
flow. This causes the air to cool and contract, allowing additional air to be drawn in and
improving volumetric efficiency. The cooling of the intake air prevents knocking, and results in
higher power output.Another reason for the GDI engine's ability to offer such superb power is
that it prevents knocks. With conventional MPI engines, strong knocking occurs during
acceleration. This is caused by petrol adhering to the intake ports. The low-octane elements of
the fuel are forced into the cylinder immediately after accelerating, where they mix with air and
ignite, causing knocking. With the GDI engine, fuel is injected directly into the cylinder and
burned completely, meaning that transient knocking is suppressed. This in turn, allows higher
output in the early stages of acceleration, when power is most needed. The most significant
feature of petrol direct-injection is the fact that engine technology has finally achieved precise
control over formation of the air/fuel mixture. We have capitalized on this achievement to
develop an innovative anti-knock technology called Two-Stage Mixing. In high load, when it is
necessary to supply large amounts of fuel, a homogenous air/fuel mix is used to prevent partially
dense mixtures that cause soot to form. In contrast, the new Two-Stage Mixing technology
prevents soot even during stratified mix, when a dense mixture forms. This is how knocking can
be prevented.In Two-Stage Mixing, about 1/4 of the total volume of fuel is injected during the
intake stroke. This forms an ultra-lean fuel mixture which is too lean to burn under normal
conditions. The remaining fuel is injected during the latter stages of the compression stroke. The
key is that the air/fuel mixture is divided into a very lean air/fuel mixture and a rich air/fuel
mixture. Knocking occurs most frequently in a stochiometric mixture, but is less likely to occur
when the mixture becomes leaner or richer. Because the rich mixture is formed immediately
before ignition, there is no time for the chemical reaction that causes knocking to take place. This

15. is another of the factors that prevent knocking.More important to note, is that the emission of
soot is prevented, even when a dense air/fuel mixture is formed, and excess air is not sufficient.
If air were the only gas present in the combustion chamber-as is the case with an ordinary diesel
engine-the enriched charge would cool, causing soot to form. With Two-Stage Mixing, the
enriched charge, created in the part of the chamber where the dense air/fuel mixture exists, shifts
toward the other side of the chamber, where the mixture is leaner, as it burns. At this point, the
enriched charge causes the ultra-lean mixture, which is too lean to burn under ordinary
circumstances, to ignite. The combustion of the ultra-lean mixture, in turn, causes the enriched
charge to re-ignite. It is this process that suppresses the formation of soot. This is the first time in
the long history of petrol engines that direct control of combustion has been used to suppress
knocking, and it further underscores the importance of achieving precise control over the air/fuel
mixture.
Improved Volumetric Efficiency: Compared to conventional engines, the Mitsubishi GDI
engine provides better volumetric efficiency. The upright straight intake ports enable smoother
air intake. And the vaporization of fuel, which occurs in the cylinder at a late stage of the
compression stroke, cools the air for better volumetric efficiency.
Increased Compression Ratio:
The cooling of air inside the cylinder
by the vaporization of fuel has another
benefit, to minimize engine knocking. This allows a high compression ratio of 12, and thus
improved combustion efficiency.

16. ACHIEVEMENTS:
Engine performance: Compared to conventional MPI engines of a comparable size, the GDI
engine provides approximately 10% greater outputs 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 conventional MPI
engine.
ADVANTAGE :
1. Frequent operation in stratified mode.
2. Reduction of CO2 production by nearly 20 percent.
3. Provides improved torque.
4. Fulfils future emissions requirements.
5. 97% NOx reduction is achieved.
6. Improve the brake specific fuel consumption.
7. Smooth transition between operation modes
8. Consumer Benefit
9. Reduced fuel consumption 15-20%
10. Higher torque 5-10%
11. Up to 5% more power
12. Spontaneous response behavior
DISADVANTAGE:
1.Non uniform distribution of mixture in multi cylinder engines and hence loss of thermal
efficiency/ higher exhaust emissions.

17. 2.Loss of volumetric efficiency due to restrictions for the mixture flow and possibility of back
firing.
CONCLUSION
The gasoline direct injection engines can be widely used in modified cars which prefer
the power of the car and also to ordinary cars which prefer better fuel efficiency .In the era of
high petrol consumption and heavy air pollution the adaptation of gasoline direct injection can
play a vital role which gives a total answer to the scenario. The initial cost of the engine can be
affordable to the common man when the engine is used or produced in greater number .Another
is the compression ratio and also the fuel efficiency which is more than that of ordinary diesel
engines. Also is the less amount of pollution which is due to the fewer amounts of unburned
fuels due to the injection inside the manifold.
REFERENCES
http://www.howstuffworks.com
Internal Combustion Engines by H.N.Gupta
Internal Combustion Engines by M.L. Mathur & R.P.Sharma
DOMKUNDWAR, “A course in IC engines
www.slide share.com
Internal combustion engine by V. Ganesan