Some info on the New External Emissions
in the Common Rail 09 Jetta TDI. This stuff all comes out of the Bosch Diesel Engine Managemnt manual/text and VW factory mechanic manuals and basically applies to all new Tier 2 BIN 5 technology in the US. Since this is the wave of the future I figured I'd try and be first to set it all down on paper because I wanted to know and help everyone out. Feel free to add to it or point out any errors. Sorry its so complicated.
Active and Passive Regeneration in the 09 Jetta.
Overview of 2009 Jetta Common Rail External Exhaust Emissions System
A system can be described as a structure of logically and functionally related components. The strength and weakness of the external emissions system in the 09 Jetta with the Common Rail Diesel and CBEA 2.0 liter is its complexity and interrelated character. The old tuning concept of combining balanced performance components to achieve certain power goals is now duplicated in the internal and external subsystems of our new emissions system.
Understanding this system without mentioning the ECU, the Sensors, all the Exhaust Catalysts, and some of the chemistry involved is impossible. Keep in mind each of these subjects has entire books written on it. Passive Regenerations occur in the DOC and DPF. Active Regenerations occur in the DPF, NOx, and H2S catalysts.
The engine internal emissions functions: EGR, Closed/Open Loop, Fuel Injection Measures, Intake Duct Modulation, etc., are left for another thread or for someone else if they want. The information in this thread is compiled from Bosch: Diesel Engine Management and VW Self Study Program 826803 and some others without direct quotes except for standard component names and generic chemical formulas.
In general
Regeneration, passive and active occurs continuously throughout the entire exhaust in the 4 separate catalysts. It requires temperatures maintained at certain levels in the exhaust for each components. To do this among other things the ECU will retard injection timing and add injection events which are not preset but “need” calculated depending on several factors. One of the main factors is EGT (Exhaust Gas Temperature). The ECU will also restrict free (fresh) air and restrict exhaust and increase Low Pressure EGR to keep the charge burn at the right volume and level and temperature and add or decrease fuel to facilitate burnoff. At the same time the chief requirement for the ECU is to maintain the same TORQUE, so the driver never knows all this is going on. Several different temperatures are maintained at once from the point of combustion clear back to the H2S catalyst to keep the emissions chemistry balanced.
Maximum efficiency (Torque) is sacrificed in both the internal (engine) and external (exhaust) emission measures to keep emissions low. So we burn more fuel to make less noxious fumes.
Processor Overview
In general the electronic computerized system in all modern automobiles follows this pattern: Input (some sensor) Processing (ECU Electronic Control Unit) Output (Actuator or action) (If/Then/Else). The 2009 Jetta, the EDC17, has 8 chips or ECMs in the ECU.
The processer uses sensor input to evaluate and calculate the correct actuator output. The engine management processor in the 09 ECU, the Bosch EDC17 (Electronic Diesel Control) evaluates signals from at least 14 different sensors and “set point generators” (speed, rpm) pertaining to emissions and engine control in its ECM (Engine Control Module) chip which is one of the eight chips in the ECU. The ECM or chip is the “J623”. (There are at least 27 sensors reporting to J623 - around 14 dealing with emissions.)
The EDC17 receives input from programming modules attached to the blue 16 pin CAN (Control Area Network) BUS connector located under the dash on the driver’s side of the Mk5 Jetta through J533, the (Data Bus Diagnostic Interface) chip (#7 below). J533 also interfaces factory diagnostic equipment and the RossTech VAGCOM operating by laptop computers through the CAN port over pins 2 and 10 for North America (SAE J 1850) and 7 and 15 for European (ISO 9141-2). (p. 434)
The other 6 chips appear in the list below (1-6):
8 Chips in the EDC 17 ECU by Bosch.
1. J104 ABS Control
2. J217 Transmission Control Module (TCS)
3. J234 Airbag Control Module
4. J285 Instrument Cluster Control Module
5. J519 Vehicle Electrical Control Module
6. J527 Steering Column Electronic Systems Control Module
7. J533 Data Bus Diagnostic Interface
8. J623 Engine Control Module
In summary the J623 chip manages the engine performance and ALL of the emissions functions of the engine over the CAN BUS. The CAN supports serial data transmission over a linear bus system to reduce multiple data line requirements using a 0 to 8 bit data code.
Sensors
The names and order of the exhaust mounted emissions sensors are these:
1. First Exhaust Gas Temperature Sensor - At the Turbo Outlet, DOC Inlet.
2. First Lambda O2 sensor – On top of the DOC. Signals from the DPF Lambda sensor set the initial air model value in the ECU in initial startup.
3. Second Exhaust Gas temperature sensor – Between DOC and DPF.
4. Before and after the DPF - Two Pressure sensors – measure pressure differential according to soot load.
5. Second Broadband Lambda O2 Sensor – after the NOx storage catalyst.
The Exhaust System
The exhaust is composed of 4 Catalytic Modules, an Exhaust Throttle Valve, a Muffler and a Resonator and the sensors listed above.
The Catalytic Modules
1. Diesel Oxidation Catalytic Converter (DOC)
2. Diesel Particulate Filter (DPF)
3. Nitrogen Oxide Catalytic Converter (NOx)
4. H2S Catalytic Converter
1. The DOC or Diesel Oxidation Catalyst is mounted close to the turbocharger in order to insure rapid “lightoff” in cold start situations. It has a metal case and a sintered metal medium coated with aluminum oxide coated with palladium and platinum catalytic material for hydrocarbons (HC) and carbon monoxide (CO.
2. The DOC is an integral unit with the DPF and has a honeycombed ceramic medium of aluminum titanide. The filter walls are coated with aluminum oxide which is coated with catalytic platinum. The honeycomb cells are blind so the soot is captured in them and kept there until regeneration.
DPF Regeneration
is done in possible 5 stages in the 09 Jetta depending on engine operating state and sensor input. (There are three other kinds of DPF regeneration we will address later: 1. SCR (“Selective Catalytic Reduction” - used in European VAG cars and Commercial Vehicles),
2. Regenerative Fuel Additives, and, 3. Electric Burnoff.
I. Warm-up stage – achieved by a secondary injection event after the main injection on startup. Quickly brings the DOC/DPF up to operating temperature and holds them there. Secondary injection stops after temperature is maintained for a given time interval.
II. Passive Regeneration – requires no action by ECM J623. Occurs best in higher load situations like highway driving. Gas flows through the DOC which converts NOx to NO2 into the DPF where NO2 oxidizes (burns) soot in passive regeneration. Soot combusts with NO2 reliably at temperatures around 300 to 450C at ratios of 8:1, NO2:Soot. NO2 is converted in this process back to NOx and continues the process until expelled from the DPF where it is reconverted back to NO2 and captured in the NOx storage catalyst. Passive regeneration works best in high sustained load applications like heavy trucks, generators, locomotives, and marine applications, but works sufficiently well to aid the soot removal in autos.
III. Active Regeneration – Accomplished at degrees 550 C to 650 C. Triggered by sensor measured Soot Load (SL) across the DPF and initiated by ECM J623. SL is calculated by 3 load model MAPs in J623.
A. Model One – calculated by driver profile and signals from Exhaust Gas Temperature (EGT) sensors and Heated O2 Sensors (HO2S)
B. Model Two – from the flow resistance of the DPF. Calculated by signals across the 2 Exhaust Pressure Sensors (EPS), Exhaust Gas Temperature (EGT), and Mass Air Flow Sensor (MAF).
C. Model Three - Distance Regeneration – done by the J623 according to a preprogrammed distance regardless of soot levels.
ECM J623 has five ways to increase the exhaust gas temperature for active regeneration.
1. Regulate intake air – MAP sensor regulates Throttle Valve Control Module and Exhaust Valve Control Module to increase/decrease free air and stoichiometric control.
2. Shut off EGR to increase combustion temperature and increase free oxygen in combustion chamber.
3. Delay Main Injection and initiate early Secondary Injection.
4. Initiate late Secondary Injection to create Hydrocarbon vapor in cylinder and push to exhaust.
(Injection Quantity Calculated by EGT sensor signal from between DOC and DPF.)
5. Hydrocarbons are ignited in the DOC raising EGT to degrees 650 C in the DPF.
Boost pressure is increased so driver does not notice torque change during regeneration.
IV. Required Regeneration Drive – DPF Indicator Light displays in instrument panel. Have to drive the car at a certain speed for certain time.
V. Service regeneration – has to be done at “workshop”. DPF indicator and Glow plug Indicator and “Check Engine _ Service Shop”. Above a certain level of obstruction/saturation (45 grams) DPF replaced. (Probably just ash deposits that can be cleared by sucking or blowing through the DOC/DPF.)
3. The NOx (Nitrogen Oxide Storage Catalytic Converter) is placed away from the DOC/DPF to prevent heat damage and take advantage of preoxidation products of CO, HC, and H2 in the DPF which serve as the combustion material for NO2. Physically it is a honey combed catalyst coated with barium carbonate (BaCO3) as the storage medium and it reacts with exhaust NO and forms nitrates in this reaction:
BaCO3 + 2NO2 + ½ O2 = Ba(NO3)2 + CO2
Active storage takes place in this compound: Ba(NO3)2, mostly between degrees 250 to 450 C. Below degrees 250 C, NO resists becoming NO2 and above degrees 450 C, NO2 becomes destabilized to NO + O. Storage takes place in the normal lean exhaust environment regulated by signals from the first Lambda sensor before the DOC. Full volume accumulation takes from 30 seconds to 5 minutes depending on engine operation.
In the normal lean exhaust environment, (NO3)2 clings to the surface of the Barium catalyst in an electrochemical bond as Ba(NO3)2 until the catalytic medium is saturated. Active Regeneration is initiated by the ECU from signals produced by the Lambda sensor downstream of the NOx (aft) catalyst which measures the following:
1. In the Storage cycle, the amount of oxygen in NOx that is escaping storage due to saturation of the Barium storage medium.
2. In the Regeneration cycle, the amount of oxygen not used in combustion because of cycle completion.
In the Storage cycle, once oxygen content above a certain level registers to the second Lambda O2 sensor a decreased stoichiometric (rich) mixture is set by the ECU by the following process:
The Lambda sensor detects increased oxygen due to NOx level increase, converts the physical reading to an electrical signal, and sends a signal to the ECU. The J623 chip signals the MAP sensor, which closes the IMTV (Intake Manifold Throttle Valve) a precise amount to decrease the amount of free air available for combustion. At the same time the ETV (exhaust throttle valve) (behind the NOx catalyst) closes a precise amount increasing the “back” pressure in the exhaust system. The Low Pressure EGR valve is opened and recirculating exhaust from behind the DPF provides cylinder volume to replace the free air choked off by the IMTV. The EGR charge fills the cylinders in an O2 deprived environment which restricts combustion allowing unburned hydrocarbons to flow back through the system to the NOx catalyst where combustion is forced with HC, CO, H2 in the fuel enriched environment with the Ba(NO3)2 molecules converting NO2 to CO2 and NO which is then processed by a Rhodium catalyst to N2 and CO2.
When burnoff is complete the reducing mediums of HC, CO, and H2 increase because they are no longer consumed in the process. So the Lambda O2 signal goes to rich and the process begins over. The NOx storage cycle begins again.
Each of the preoxidation products of CO, HC, and H2 produced in the DPF and used to oxidize NO2 has its own reaction and produces acceptable emissions products.
One of the problems with the NOx storage catalysts is that the Barium coating has a greater affinity to Sulfur than to NO2 and is stored as Sulfate. As a result the sulfur is has to be burned off in a process similar to Active Regeneration in the DPF. It accumulates slowly over time using ULSD and is burned out at degrees 650 C for about 5 minutes every several thousand miles. Using LSD or off road fuel will shorten the life of the catalyst considerably.
5. The H2S catalyst is installed to convert the potential poisonous gaseous byproduct of sulfate reduction, H2S to its harmless constituents.
Understanding this system will help us keep our cars running longer at less expense and prevent us being at the mercy of you-know-who.
