A Report on

Gasoline Direct Injection Engine

Third Year

Mechanical Engineering

Semester V Term work

By

Sr.

No

Name Roll Number

1 Vishal B. Andhale 10

2 Nilesh B. Mulik 63

3 Sagar S. Thakare 72

Mechanical Engineering

Don Bosco Institute of Technology

Kurla (West), Mmbai-70

(2015)

Index

Sr. No

Title

Page no.

1

Abstract

03

2

Introduction

2.1 Objectives

2.2 Technical features

04

3

Discussion on Topic

3.1 Working principle

3.2 Combustion process

3.3 Major characteristics

06

4 Limitations

4.1 Advantages

4.2 Disadvantages

12

5 Conclusion

15

6

Future scope

16

7

References

17

Abstract

The general demand in the market today is for two wheelers with excellent fuel

economy, superb power performance and cleaner & greener emissions. But the actual situation is

somewhat contrary in the sense that the two wheeler generally bought by the public have

characteristics which include very high levels of pollution caused by scavenging losses,

uneconomical operation because of fresh charge losses, less scope for lean operation and no

control on the engine once the valves have closed. Therefore the goal of this paper is to design an

injection system to achieve optimum emission values and noise levels. In addition this paper

looks at improving fuel consumption and drivability independent of the operating point, which is

implemented by a mechanical variable injection timing system. For this, the effect of different

head designs on the exhaust gas emissions is analyzed initially. Also a light weight and compact

Aluminum housing is designed for the pump – follower junction. This is directly attached to the

overhead camshaft. A new jerk type fuel injection pump was designed based on the differences

in the physiochemical properties of diesel and petrol. The characterization of the engine is done

in carburetor mode for reference purpose. A characterization of the fuel injection pump was also

carried out.

1. Introduction

The direct injection system introduces the fuel directly in the combustion chamber, which means

that only air enters the cylinder through the manifold and the mixture of air and fuel takes place inside the

combustion chamber. This system has the possibility of running in the premixed mode previously

described if the injection of the fuel is done during the admission stroke, and in a mode called stratified if

the fuel is injected at the end of the compression stroke which means that the fuel burns while being

injected. Stratified combustion has the advantage of avoiding knock, since there is no air-fuel mixture in

the front of the flame. Gasoline needs to have a special property of anti-ignition to avoid knocking when

the pressure inside an engine's combustion chamber is very high, but in the case of stratified combustion

it is not needed; even more, different kinds of fuels can be used by the same engine.

A second advantage of stratified combustion is that, since the front of the flame doesn't reach the

cylinder wall, less amount of heat is transferred to them, increasing the work transferred to the piston. The

third advantage of this type of injection is that the combustion can be controlled by the amount of fuel

being injected, living the opportunity of not using a throttle valve at all and to reduce significantly pump

losses. This also gives better control of the flame in the combustion chamber than premixed mode, as in

premixed mode the flame propagation depends heavily on the air movement inside the combustion

chamber which is not always the same, and in stratified mode the flame is always near the injector and

controlled by the injection of the fuel and the shape of the piston.

As for the two stroke engine the big advantage is that, since the fuel is being injected when the

exhaust port is closed, the short circuit problem is totally overcome. This characteristic is very important

since this problem has not permitted the two stroke engine to be further used in the automotive industry

due to the high emissions it produces

Mixing consists on the fact that there is a small amount of residual gases which remain

trapped without being expelled, being mixed with some of the new air charge. Also in traditional

two-stroke engines the fuel air mixture disperses widely within the combustion chamber leaving

a substantial amount of fuel unburned. A normal gasoline engine has a compression ratio of

about 10 to 1 (or slightly less). One problem with increased compression ratio is that fuel can

ignite prematurely causing engine knock. Also during cold starts bulk of emissions are produced.

While four strokes are found on most automobiles and street legal motorcycles, two-stroke rules

when it comes to off-road motorcycles, small boat and personal watercraft engines and many of

the motorbikes, those serve as primary transportation in developing nations. The potential of

Two- stroke engines has become more and more subject to increasing research work trying to

optimize the Power-Weight ratio as well as the pollution emissions with the development of the

high efficient Direct Injection System. The NOx issue notwithstanding, GDI engines get high

marks in particular for the cleaner emissions. It is for this reason numerous engine companies

have toiled to build two-stroke version of the gasoline direct injection engine trying to overcome

issues like short circuiting, mixing, knocking, cold starting problems etc. which are otherwise

produced in traditional two stroke gasoline engines with carburetors.

Major Objectives of GDI Engine:

Ultra-low fuel consumption that betters that of even diesel engines

Superior power to conventional MPI engines

Technical features:

Upright straight intake ports for optimal airflow control in the cylinder

Curved-top pistons for better combustion

High pressure fuel pump to feed pressurized fuel into the injectors

High-pressure swirl injectors for optimum air-fuel mixture

2. Working Principle:

Gasoline direct-injection engines generate the air/fuel mixture in the combustion

chamber. During the induction stroke, only the combustion air flows through the open intake

valve. The fuel is injected directly into the combustion chamber by special fuel injectors. The

system uses an Electronic Control Unit (ECU) and a solenoid operated fuel injector to meter the

fuel.

The ECU uses various sensors located on the engine components. It receives inputs

from sensor in the form of voltage signals which is analyzed and adjusts the air fuel ratio and

injection timing.

Various sensors used are:

Throttle position sensor located on throttle plate to sense its movement.

The engines coolant temperature sensors to sense the coolant temperature. It helps to

adjust the air fuel supply at the time of cold starting and idling.

Air flow sensor located at intake manifold to monitor the air flow rate .

Engine exhaust temperature sensor to measure O2 content in exhaust.

Manifold pressure sensor mounted on intake manifolds and it helps to adjust flow of

air-fuel ratio into the engine.

Air inlet temperature sensor mounted on intake manifolds to sense the temperature of

inlet air and helps to adjust air-fuel ratio.

Camshaft position sensor mounted on camshaft which senses the rotation of camshaft

and adjusts fuel injection timing.

Combustion process:

In the case of gasoline direct injection, the combustion process is defined as the way in which

mixture formation and energy conversion take place in the combustion chamber. The mechanisms are

determined by the geometries of the combustion chamber and the intake manifold, and the injection point

and the moment of ignition. Depending on the combustion process concerned, flows of air are generated

in the combustion chamber. The relationship between injected fuel and air flow is extremely important,

above all in relation to those combustion processes which work with charge stratification (stratified

concepts). In order to obtain the required charge stratification, the injector fuel injects the fuel into the air

flow in such a manner that it evaporates in a defined area. The air flow then transports the mixture cloud

in the direction of the spark plug so that it arrives there at the moment of ignition. A combustion process

is often made up of several different operating modes between which the process switches as a function of

the engine operating point. Basically, the combustion processes are divided into two categories: stratified-

charge and homogeneous combustion processes.

Homogeneous combustion process:

In the case of the homogeneous combustion process, usually a generally stoichiometric mixture is

formed in the combustion chamber in the engine map, i.e. an air ratio of λ = 1 always exists. In this way,

the expensive exhaust-gas treatment of NOX emissions which is required with lean mixtures is avoided.

Major characteristics of the GDI engine

1. Lower fuel consumption and higher output

Optimal fuel spray for two combustion mode:

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 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.

Ultra-lean Combustion Mode

Under most normal driving conditions, up to speeds of 120km/h, the Mitsubishi

GDI engine operates in ultra-lean combustion mode for 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 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 combustion by

ensuring a homogeneous, cooler air-fuel mixture that minimized the possibility of

engine knocking.

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-fuel mixture. The High Pressure Fuel Pump

supplies the high pressure needed for direct in-cylinder injection. And 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 of the development objectives, which were fuel

consumption lower than those of diesel engines and output higher than those of

conventional MPI engines. The methods are shown below.

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 strong reverse tumble

for optimal fuel injection.

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.

Method of Operation:

Gasoline direct-injection systems are characterized by injecting the fuel directly into the

combustion chamber at high pressure. As in a diesel engine, air/fuel-mixture formation takes

place inside the combustion chamber (internal mixture formation). High-pressure generation The

electric fuel pump delivers fuel to the high-pressure pump (4) at a presupply pressure of 3.5 bar.

The latter pump generates the system pressure depending on the engine operating point

(requested torque and engine speed). The highly pressurized fuel flows into and is stored in the

fuel rail.

The fuel pressure is measured with the high-pressure sensor and adjusted via the pressure-control

valve (in the HDP1) or the fuel-supply control valve integrated in the HDP2/HDP5 to values

ranging between 50 and 200 bar. The high-pressure fuel injectors (5) are mounted on the fuel

rail, also known as the “common rail”. These injectors are actuated by the engine ECU and spray

the fuel into the cylinder combustion chambers.

Advantages:

Improves volumetric efficiency of the engine.

Improves atomization and vaporization of fuel and it is independent of reduce gap

spacing speed.

Ease of cold starting and low load running.

Specific fuel consumption is reduced i.e. it gives better vehicle mileage.

Variation of air fuel ratio is reduced.

Exhaust emissions are reduced.

Gives better performance on gradients.

Improved Volumetric Efficiency Increased Compression Ratio

Better Engine performance Vehicle Acceleration

Disadvantages

Although Direct Injection provides more power and efficiency, a carbon build-up occurs in the

intake valves that over time reduces the airflow to the cylinders, and therefore reduces power.

Fuel contains various detergents and can keep the intakes clean. When fuel is no longer being

sprayed in the intake valves, small amounts of dirt from intake air cakes on the intake walls, even

with air filters that prevent most of the dirt from entering the cylinder. This build-up can become

severe enough that a piece can break off and has been known to burn holes in catalytic

converters. It can also cause sporadic ignition failures. These problems have been known for

some time and technologies have been improved to reduce the carbon build-up.

Intake Valve Deposits

Applications:

1. The Mitsubishi GDI Combustion System

2. Toyota GDI Combustion System

3. Nissan GDI Combustion System

4. Mercedes-Benz GDI Combustion System

5. Mazda GDI Combustion System

Conclusion

Engine performance compared to conventional engines of a comparable size, the GDI engine

provides approximately 10% greater outputs at all speed. In high output mode, GDI engines

provide outstanding acceleration. Frequent operation in stratified mode reduces CO2 production

by nearly 20% and also improves the brake specific fuel consumption. Smooth transition

between operating modes is achieved. The gasoline direct injection engine provides improved

torque and fulfils future emission requirements. GDI is simple to implement and can be

retrofitted in two stroke engines. Fuel consumption was reduced by 15-20%. Higher torque 5-

10% was produced. Also good and spontaneous throttle response behavior was obtained. Best

features of all the above are expected to increase more in short term.

3. Future Scope

The development of direct injection system in petrol engine is beneficial in numerous fields like

agricultural, heavy duty works and applications where the operating conditions vary with load.

The scarcity of fossil fuels has urged the use of alternative fuels which are less costly and less

harmful to the environment. As biofuels are eco-friendly their use in direct injection engines can

lead to additional advantages in the time of high price of petroleum based fuels. The biofuels like

ethanol, methanol, butanol and their blends with petrol can be successfully used in direct

injection engines. With the use of biofuels in direct injection engines the pollution can be

reduced and efficiency can be increased. The existing two stroke engines in market can be

redesigned with direct fuel injection system instead of existing carburetor system. This is going

to replace the carburetor with combination of injector, fuel pump, crank angle encoder and

electronic control unit beside with various sensors.

4. References:

1. Internal Combustion Engine Fundamentals. McGraw Hill. 1988

2. Dave Gerr. Propeller Handbook. International Marine. 2001.@ Google Books

3. www.wikipedia.com

4. SAE Technical Paper