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.
Overview
The demand for higher-power spark-ignition
engines, combined with the requirement
for reduced fuel consumption, were
behind the “rediscovery” of gasoline direct
injection. The principle is not a new one.
As far back as 1937, an engine with mechanical
gasoline direct injection took to the air
in an airplane. In 1951 the “Gutbrod” was
the first passenger car with a series-production
mechanical gasoline direct-injection
engine, and in 1954 the “Mercedes 300 SL”
with a four-stroke engine and direct injection
followed.
At that time, designing and building a direct-
injection engine was a very complicated
business.Moreover, this technology made
extreme demands on the materials used. The
engine’s service life was a further problem.
These facts all contributed to it taking so
long for gasoline direct injection to achieve
its breakthrough.
Method of operation
Gasoline direct-injection systems are characterized
by injecting the fuel directly into the
combustion chamber at high pressure (Fig. 1).
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 (Fig. 2, Pos. 19)
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 (Fig. 1, Pos. 6).
118 Gasoline direct injection Overview, method of operation
Gasoline direct injection
Fig. 1
1 Piston
2 Intake valve
3 Ignition coil and
spark plug
4 Exhaust valve
5 High-pressure
fuel injector
6 Fuel rail
6
5
2
3
4
1
1 Gasoline direct injection (engine section)
æ UMK1917-1Y
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.
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 (Fig. 3a), 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.Homogeneous concepts are therefore
set out to be emission-reducing concepts.
Gasoline direct injection Method of operation, combustion process 119
Fig. 2
1 Hot-film air-mass
meter
2 Throttle device
(ETC)
3 Intake-manifold
pressure sensor
4 High-pressure pump
5 Charge-flow control
valve
6 Fuel rail with highpressure
injector
7 Camshaft adjuster
8 Ignition coil with
spark plug
9 Camshaft phase
sensor
10 Lambda sensor
11 Primary catalytic
converter
12 Lambda sensor
13 Exhaust-gas
temperature sensor
14 NOX accumulatortype
catalytic
converter
15 Lambda sensor
16 Knock sensor
17 Engine-temperature
sensor
18 Speed sensor
19 Fuel-supply module
with electric fuel
pump
16 12
18
19
17
13
15
14
1
2
3
4
5
6
7 8
9
10
11
2 Components of gasoline direct-injection system
æ UMK2076Y
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.
Overview
The demand for higher-power spark-ignition
engines, combined with the requirement
for reduced fuel consumption, were
behind the “rediscovery” of gasoline direct
injection. The principle is not a new one.
As far back as 1937, an engine with mechanical
gasoline direct injection took to the air
in an airplane. In 1951 the “Gutbrod” was
the first passenger car with a series-production
mechanical gasoline direct-injection
engine, and in 1954 the “Mercedes 300 SL”
with a four-stroke engine and direct injection
followed.
At that time, designing and building a direct-
injection engine was a very complicated
business.Moreover, this technology made
extreme demands on the materials used. The
engine’s service life was a further problem.
These facts all contributed to it taking so
long for gasoline direct injection to achieve
its breakthrough.
Method of operation
Gasoline direct-injection systems are characterized
by injecting the fuel directly into the
combustion chamber at high pressure (Fig. 1).
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 (Fig. 2, Pos. 19)
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 (Fig. 1, Pos. 6).
118 Gasoline direct injection Overview, method of operation
Gasoline direct injection
Fig. 1
1 Piston
2 Intake valve
3 Ignition coil and
spark plug
4 Exhaust valve
5 High-pressure
fuel injector
6 Fuel rail
6
5
2
3
4
1
1 Gasoline direct injection (engine section)
æ UMK1917-1Y
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.
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 (Fig. 3a), 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.Homogeneous concepts are therefore
set out to be emission-reducing concepts.
Gasoline direct injection Method of operation, combustion process 119
Fig. 2
1 Hot-film air-mass
meter
2 Throttle device
(ETC)
3 Intake-manifold
pressure sensor
4 High-pressure pump
5 Charge-flow control
valve
6 Fuel rail with highpressure
injector
7 Camshaft adjuster
8 Ignition coil with
spark plug
9 Camshaft phase
sensor
10 Lambda sensor
11 Primary catalytic
converter
12 Lambda sensor
13 Exhaust-gas
temperature sensor
14 NOX accumulatortype
catalytic
converter
15 Lambda sensor
16 Knock sensor
17 Engine-temperature
sensor
18 Speed sensor
19 Fuel-supply module
with electric fuel
pump
16 12
18
19
17
13
15
14
1
2
3
4
5
6
7 8
9
10
11
2 Components of gasoline direct-injection system
æ UMK2076Y
