EURO 4-5 Diesel Exhaust Pollutant After- · PDF fileLow pressure EGR (EURO 5 / 6...

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Transcript of EURO 4-5 Diesel Exhaust Pollutant After- · PDF fileLow pressure EGR (EURO 5 / 6...

  • Ing. Antonio Cofano - [email protected] 1

    EURO 4-5 Diesel Exhaust Pollutant After-Threatment

    EURO4-5 Common Rail

  • Ing. Antonio Cofano - [email protected] 2

    Exhaust gas recirculation EGR fundamentals:

    AFR: Air to Fuel Ratio. This parameter is used to define the ratio between fuel (petrol, diesel LPG, CNG etc) and air during a combuston process

    Lambda: is defined as the ratio between the intake air quantity and the optimal air quantity necessary to reach a stoichometric combustion

    = Airintake

    / Airideal

    Lambda is an adimensional parameter and is independent from the fuel used in the combustion process

    Positive ignition engines work with a lambda value always close to 1

    Direct injection diesel engines work work with a variable lambda always > 1

    Almost all of the positive ignition engines on the market have a compression ratio (10/1) < CR < (12/1)

    Almost all of the diesel engines on the market have a compression ratio (16,5/1) < CR < (17,5/1)

    Due to this higher compression ratio, in the diesel engines combustion chamber there's a continuous oxidation of nitrogen gas, especially during idle and partial load operation (when >>1)

    As several differenr Nitrogen oxides are generated during combustion, it is assumed to name the whole composites as NOx. Diesel engines produce therefore high quantity of NOx emissions

    Since the end of the '90s the first and main solution adopted was to avoid to fulfill the cylinder of free air: so variable quantities of exhaust gases are recirculated into the combustion chamber

  • Ing. Antonio Cofano - [email protected] 3

    Exhaust gas recirculation

    EGR fundamentals:

    EURO4-5 applications have an high pressure EGR only, with position feedback analog signal

    EURO5-6 applications have an high pressure EGR and a low pressure EGR with position feedback

    In order to optimize the EGR flow through the intake manifold, an EGR throttle is also implemented

    In order to reduce the exhaust gas temperature, an EGR cooler with a bypass valve is also present

    EGR control is feeded-back by the intake mass air flow information.

    A target map into the software is used to determine the optimal air value in all the conditions

  • Ing. Antonio Cofano - [email protected] 4

    Exhaust gas recirculation

    EGR control map: values are expressed in (mg/strk)

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    Exhaust gas recirculation

    EGR system valves on the engine

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    Exhaust gas recirculation

    EGR system valves on the engine

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    Exhaust gas recirculation

    Manifold Throttle valve

    Latest NOx reduction techniques implement the modulation of the intake air into the manifold

    A throttle valve upstream the EGR valve reduces the amount of fresh air into the manifold

    In some operating conditions throttle valve determines a pressure gap suitable to improve the exhaust gas recirculation

    As all the other ECU controlled valves on the engine, throttle body has an embedded position sensor

    Manifold Throttle valve pin-out

    Throttle valve power supply (12V)

    Throttle valve PWM control (GND control)

    Feedback sensor power supply (5V)

    Feedback sensor analog signal (0,5V- 4,5V)

    Feedback sensor GND

  • Ing. Antonio Cofano - [email protected] 8

    High Pressure EGR and Low Pressure EGR

    High pressure EGR (EURO 3 / 4 implementation)

    Low pressure EGR (EURO 5 / 6 implementation)

  • Ing. Antonio Cofano - [email protected] 9

    High Pressure EGR and Low Pressure EGR

    High pressure EGR (EURO 3 / 4 implementation)

    The HP EGR system fetches the exhaust gas upstream of the turbocharger and enters them again in the system downstream of it. This system minimizes the pressure drop of the exhaust gases along the path of re-entry. This also prevents the passage of exhaust gases through the compressor which could lead to a rapid deterioration of this organ. Various strategies have been used to increase the pressure difference between the intake and exhaust ducts to facilitate a greater flow of EGR to the engine. We've already examinated the throttle valve implementation.

    Unfortunately, the HP EGR system reduces the flow of gas through the turbocharger. If we increase the degree of EGR (increasing the passage section of the EGR valve) the flow rate processed by the turbine decreases: so at equal expansion ratio, the speed of the turbocharger increases. Also decreases the power transferred to the turbine and then to the compressor which consequently develops a lower flow rate and moves the operating point toward the surge line. Consequently, it determines a reduction of power output from the engine while increases the specific fuel consumption.

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    High Pressure EGR and Low Pressure EGR

    Low pressure EGR (EURO 5 / 6 implementation)

    The LP Loop is a well-known system that offers an alternative to overcome the limitations of the high pressure system: first of all the introduction of a substantial percentage of EGR during engine high loads operation. The exhaust gases are taken downstream of the turbine and introduced upstream of the compressor.

    Prior to the introduction into the market of the diesel particulate filter (DPF), the entire intake system, including the compressor, would be subject to rapid corrosion. This was one of the reasons that has limited the application of such a system. Introducing the DPF all the exhaust gases can pass through the turbine while preserving the performance and durability of the turbo.

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    High Pressure EGR Vs. Low Pressure EGR

    LP EGR advantages Potential lower specific fuel consumption as a result of the improved performance of the turbine and of a

    greater flexibility in the management of the turbine, no longer tied to the operation of the EGR system.

    Faster dynamic response of the engine system: a change of the operating point of the engine causes smaller changes of the speed of the turbine for the most constancy in the capacity of both the exhaust gases passing through the turbine and the mixture that passes through the compressor.

    The beginning of the transient phase decreases the fraction of EGR (the EGR flow is roughly constant) while increasing the content of fresh air in the mixture sucked by the compressor.

    Possibility to avoid the throttle valve on the suction. That component is required in the HP EGR to reduce the amount of air introduced at medium loads (high flow rate through the turbine), in order to maintain an high EGR rate.

    Lower fluid losses and simplification of the control system.

    The compressor provides a better mixing of the fresh air charge with the EGR that is distributed in the same proportions in each cylinder.

    Improved durability of the components downstream of the compressor and the lubricants for the reduced content of soot present in the exhaust gases that are going to mix with the fresh charge intake

    Reduced obstruction of the flow of EGR to the presence of soot deposits.

    The path followed by the recirculated exhaust gases to return to the engine is longer, and then determines a greater heat release before going into the engine. Lower temperatures while maintaining the operating conditions of the chiller.

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    High Pressure EGR Vs. Low Pressure EGR LP EGR drawbacks

    The increased volume and the greater length of the recirculation branch determine a delay in the achievement of the desired percentage of EGR in the combustion chambers.

    An unwanted increase of NOx in transient conditions

    The particulate filters, even the most efficient, let pass a small portion of the soot that can corrode long time the blades of the compressor particularly at high rotation speed.

    In the presence of a heat exchanger upstream of the compressor is possible condensation of water droplets which affect the turbocharger components.

    Increase of the losses due to the greater length of the path traveled by gas recirculation

    Hybrid HP +LP EGR Loop (VAG Euro5 implementation) The LP EGR gasses are filtered before being sent through the cooler and back into the intake. The HP

    gases go straight from the exhaust manifold to the EGR valve and into the intake. The LP EGR is used more at higher engine rpm and load.

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    Diesel Particulate ReductionDiesel engines up to now have been realized using the direct injection tecnique: this way the AFR

    changes dramatically with any load variation. Therefore particulate soot emissions were considered

    an unavoidable drawback of this generation of engines. In order to comply with emission regulations

    two different approaches have been developed:

    Diesel Particulate Filters with additive Diesel Particulate Filters without additive

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    Diesel Particulate Filter system with additive

    General architecture DPF system have been introduced with EURO4 regulations, when limitations imposed PM not go over 0,5

    g/km. As the same engine will produce different soot quantities, depending on the car, the use of DPF began to be mandatory.

    1 Instrument Cluster 9 Turbocharger

    2 Engine Cont