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Log Graphs 1


Car: 2009 Impreza 2.0 Turbo Diesel, 110 kW / 148 hp / 150 PS, European domestic market, Euro 4 spec.

Important: Newer Boxer Diesel generations (Euro 5/6) may show different behaviour!

ECU firmware: patched ROM for unlimited logging, otherwise stock.
Protocol: SSM2 via CAN
More than 120 items had been logged, plenty of RAM variables (*) plus standard SSM2 items at roughly 170 ms interval.


I prepared two graph images plotting some interesting parameters, click picture for full resolution:

Image 1/2


Image 2/2


Additional details

… at specific time positions:

#1: State before active regeneration

Time @ ~ 33 ½ min
Cruise Control: active
Vehicle Speed*: 110 km/h
Engine Speed: 2300 rpm
Gear: 5
Coolant Temperature: 93 °C
Injections: 2 (pre + main)
Soot Accumulation Ratio: 64 %
DPF Pressure Difference: ~ 5 kPa
Exhaust Gas Temperature (EGT) Catalyst Inlet: 345 °C
EGT DPF Inlet: 370 °C
Intake Air Amount: 430 mg/cyl
Mass Air Flow: 33.8 g/s
Manifold Absolute Pressure (MAP)*: 126 kPa
Inlet Air Temperature: 25 °C
Manifold Air Temperature: 48 °C
Fuel Temperature: 58 °C
Throttle Opening Angle: 79 deg
EGR Valve Opening Angle: 38 deg
Final Oil Dilution Rate*: -1.9 mg/s (evaporation)
Oil Dilution Amount: 282.0 g (4.6 %)

#2: Soot 65%, preparing for DPF regeneration

@ 33 ¾ min
Soot Accumulation Ratio* reaches 65%, this triggers active regeneration preparations. Note: I am referring to the actual RAM value, diagnostic parameter may indicate 65% earlier due to rounding.
Apparently ECU now does 3 injections (pre + main + after) when power demand is high enough, no post injections yet

#3: Active Regen ON

@ 34:04; = 20 seconds after #2, DPF Regeneration Switch turns ON
EGR valve closes instantly, 0 deg
Manifold Air Temperature dropping
Boost Control opens VGT immediately, from 52 to 25%
Manifold Absolute Pressure* dropping
pilot-injection kicks in, 2 injections (pilot C + main)
post-injections begin to fade in but not active yet

#4: Post-Injections

@ 33 seconds after #2, post-injections A + B become operational (injection amount > 0)
oil dilution rising
EGTs climbing
Manifold Absolute Pressure*: 75 kPa (~ 25 below ambient), varying, stays below ambient most of the time during regen at low power demand
EGT Catalyst Inlet: 340 °C
EGT DPF Inlet: 320 °C
injections: 4 (pilot C + main + post A + post B)

#5: Coasting Fuel Cut-Off During Regen

Example @ 35:12
EGR valve opens instantaneously, 70 deg; EGR behaves rather digitally during regen – either fully closed (0 deg, for max EGT) or max opened (70 deg, less fresh air)
Throttle Opening Angle: rising up to 31 deg
injections: 0
Fuel Consumption*: 0 mm³/s
oil dilution going down slowly due to estimated evaporation
EGT Catalyst Inlet: decreases fast, EGT at DPF inlet (> 600 °C) follows with a delay
Engine Speed: gear change from 5th to 6th to reduce engine braking effect

#6: Idling with Active Regen ON

@ 45:30
Engine Speed: 800 rpm
Post A Injection Amount*: 0
Post B Injection Amount*: ~ 8 mm³/st
Apparently while idling the ECU prefers the 2nd post-injection (“B”), otherwise during driving it’s rather mixed
Final Oil Dilution Rate: ~ 20 mg/s (medium)
Boost Control: 25 % (VGT fully open)
Manifold Absolute Pressure*: 74 kPa
Throttle Opening Angle: 5.5 deg
EGR Valve Opening Angle: 0 deg
Intake Air Amount: 370 mg/cyl
Mass Air Flow: 9.8 g/s

#7: DPF Regeneration OFF

@ 46:15, decision is based on elapsed time from #2, achieved soot level does not matter (!)
DPF Regeneration SW had been ON for 12.2 minutes
all post-injections off
Oil Dilution Amount*: 299.6 g (4.9 %) = + 0.3 % during regeneration
EGR back to normal operation
Boost Control: 65 % instantly (max speed, spooling up turbo)
MAP rising
EGT Catalyst Inlet: 270 °C
EGT DPF Inlet: 490 °C

Oil Dilution Graph

Shown graph contains a complete DPF active regeneration process – the rising section (750 seconds duration = 12.5 minutes).
Basically, oil dilution is driven by:

  1. post-injections during active DPF regeneration
  2. estimated diesel fuel evaporation

According to internal algorithm and logged data, normal operation does not increase dilution. Oil dilution slowly decreases as the ECU estimates fuel evaporation out of engine oil. (On Euro 4 at least, this algorithm is also running if ignition is on, engine not running but coolant temperature warm enough).
Active regeneration however uses one or more post-injections (small additional late injections – during exhaust stroke) in order to heat up the DPF, raising oil dilution amount, at much higher rate therefore winning over evaporation.
Notice these short intermittent steps during regeneration – these are caused by coasting – ECU suspending all injections, including post-injections.
Wouldn’t coasting cool down the DPF then by pushing rather cold air through the system? To mitigate this, the software fully opens EGR valve (70 deg). As soon as injections resume, EGR valve is being closed again. Normally, during active regeneneration it is in fully closed position (0 deg) helping to increase exhaust temperature (more oxygen).
If you look carefully, you can spot more evaporation going on after regeneration had finished compared to before it started. This is mainly due to higher engine temperature, having reached normal operating conditions of around 90 °C. For evaporation to get going it needs temperatures beyond 30 °C, the higher the better.
Also take a look at post “Estimated Distance to Oil Change” for additional information.