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Gasoline direct injection

Thảo luận trong 'Thùng rác diễn đàn' bắt đầu bởi tnhan_ph, 7/11/10.

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    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 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
    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
    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
    2 Throttle device
    3 Intake-manifold
    pressure sensor
    4 High-pressure pump
    5 Charge-flow control
    6 Fuel rail with highpressure
    7 Camshaft adjuster
    8 Ignition coil with
    spark plug
    9 Camshaft phase
    10 Lambda sensor
    11 Primary catalytic
    12 Lambda sensor
    13 Exhaust-gas
    temperature sensor
    14 NOX accumulatortype
    15 Lambda sensor
    16 Knock sensor
    17 Engine-temperature
    18 Speed sensor
    19 Fuel-supply module
    with electric fuel
    16 12
    7 8
    2 Components of gasoline direct-injection system
    æ UMK2076Y

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