Direct Petrol Injection System with Bosch Motronic MED 7 - Volkspage

More documents

Recommendations

Info

Fundamentals Mixture formation process In stratified charge mode, a crank angle of only 40° - 50° is available for mixture formation. This is a decisive factor influencing the ignitability of the mixture. If the interval between injection and ignition is shorter, the mixture is not ignitable because it has not been sufficiently prepared. A longer interval would lead to further homogenisation throughout the combustion chamber. Area of mixture formation This is why a highly ignitable atomised mixture forms around the spark plug at the centre of the combustion chamber. This is enveloped by an outer layer which is ideally composed of fresh air and recirculated exhaust gas. 253_040 The air-fuel ratio throughout the combustion chamber is between λ=1.6 and 3. Combustion process The ignition cycle commences when the air-fuel mixture is positioned exactly in the area of the spark plugs. Only the atomised mixture is ignited, while the other gases act as an insulating envelope. Thus, heat losses through the cylinder wall are reduced and the engine's thermal efficiency is increased. The ignition point lies <strong>with</strong>in a narrow crankshaft window because of the retarded injection end point and the time available for mixture formation at the end of the compression stroke. Area of combustion 253_041 In this operating mode, torque developed by the engine is determined only by the injected fuel quantity. Intake air mass and ignition advance angle are minor factors here. 12
Homogeneous lean charge mode This is located in the mapped area between stratified charge mode and homogeneous charge mode. A homogeneous lean mixture is present throughout the combustion chamber. In this mode, the air-fuel ratio is approximately λ = 1.55. The same conditions apply here as to stratified charge mode. Intake process As in stratified charge mode, the throttle valve is opened as far as possible and the intake manifold flap is closed. This firstly reduces throttle losses and, secondly, produces an intensive air flow in the cylinder. Throttle valve Intake manifold flap 253_037 <strong>Injection</strong> cycle Fuel is injected directly into the cylinder approximately 300° before ignition TDC during the intake stroke. The injection quantity is regulated by the engine control unit in such a way that the air-fuel ratio is approximately λ = 1.55. Injected fuel spray Air flow 253_106 Mixture formation process Due to the advanced injection point, more time is available for pre-ignition mixture formation, resulting in a homogeneous mixture distribution in the combustion chamber. Lean mixture distribution 253_138 Combustion process As in homogeneous charge mode, the ignition point can be selected freely due to the homogeneous air/fuel mixture distribution. The combustion process takes place throughout the combustion chamber. Area of combustion 253_045 13
Page 1 and 2: Service. Self-Study Programme 253 D
Page 3 and 4: Table of Contents Introduction . .
Page 5 and 6: Why has Volkswagen waited until now
Page 7 and 8: Homogeneous operation at high exhau
Page 9 and 10: Combustion process The term "combus
Page 11: Injection cycle Fuel is injected du
Page 15 and 16: Mixture formation process By inject
Page 17 and 18: Motronic control unit J220 Fuel pum
Page 19 and 20: Torque-based engine management syst
Page 21 and 22: Intake system In comparison with th
Page 23 and 24: This is how it works The driver inp
Page 25 and 26: Intake manifold flap actuated In st
Page 27 and 28: Air-mass flow meter G70 and intake
Page 29 and 30: This is how the exhaust gas recircu
Page 31 and 32: Fuel system The fuel system is divi
Page 33 and 34: This is how it works The fuel flows
Page 35 and 36: The fuel pressure regulating valve
Page 37 and 38: This is how it works Inlet with fin
Page 39 and 40: Activated charcoal canister system
Page 41 and 42: Exhaust system This was adapted to
Page 43 and 44: Broadband lambda probe (G39) The br
Page 45 and 46: Exhaust gas temperature sender (G23
Page 47 and 48: NOx sensor control unit (J583) This
Page 49 and 50: Function of the NOx sender The func
Page 51 and 52: Sulphur regeneration is a technical
Page 53 and 54: Variable valve timing Inner exhaust
Page 55 and 56: Positive terminal GND Input signal
Page 57 and 58: Notes 57 Solutions to questions on
Page 59 and 60: 5. What is the signal from the inta

Direct Petrol Injection System with Bosch Motronic MED 7 - Volkspage

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?