More about basic operating principles of NOx catalytic converter you can read in N53 series engine after-sales training material or in any description of non-BMW engine, which performs in Stratified charge mode.
Here I will pay attention to observations from “real life”, which quite essentially differs from official newsletters.
Regeneration of NOx catalytic converter
As we see, if the average driving speed is 80 km/h, average period between regeneration phases is between 50 and 55 seconds. This period of time corresponds to maximal period for Stratified charge and is typical to perfect (brand new) NOx catalytic converter.
Engineers from Corean Machine and Materials institute performed a test: placed on the stand most powerful version of N53 series engine. This engine was used for 2 years and during test decreased Lambda below maximally possible (at 3000 RPM and 2bar BMEP) – it means, that performance of NOx catalytic converter was identified as insufficient. N43 series engine with little mileage (as indicated, sufficient for NOx catalytic converter to go in working condition) in tests, performed by Oak Ridge lab engineers in USA, showed following Stratified cycle length: 15 .. 35 seconds (minimal period of 15 second at 22% load and 3500 RPM).
My experience (inspecting significant number or N43 and N53 series engines with mileage till 150’000 km) shows, that, unfortunately, performance of NOx catalytic converter for N43 and N53 engines already after 50’000 .. 70’000 km is much more modest than as indicated in promo material from BMW. 25 .. 30 seconds is more realistic period for Stratified charge period in such speed (80 km/h). On speed 100 .. 110 km/h usually the period of Stratified charge drops down to minimum cycle (10 .. 15 seconds, depending of MSD80 software release).
Desulfation of NOx catalytic converter
The sulfur, which contains fuel, “poisons” the NOx catalytic converter, and it’s performance is reduced. The greater the sulfur content, the faster NOx catalytic converter looses it’s ability to absorb the NOx ions.
According to this curve, the typical desulfation phase turns on after each 7’000 km (actually – this is the interval for brand new NOx converter. More realistic intervals are: 3000 .. 4000km and even 1000 .. 1500 km for NOx converters with reduced efficiency).
The new INPA loader 2.023 has option to evaluate “poisoning” level of NOx catalytic converter.
Real observations suggest, that MSD80 calculates the “poisoning”, using virtual cumulatively counted fuel amount, which has flown through catalytic converter. Even in case of perfect fuel (when/if performance of NOx catalytic converter in reality is not decreased) MSD80 calculates the amount of flown through fuel and “grows” the level of poisoning (obviously, in calculations the reference data of allowed amount of sulfur in fuel in EU market are used) with speed ~ 0,4 .. 0,6 mg/km. The allowable quantity of sulfur in EU is 50 mg/kg, which means, that MSD80 believes, that approximately 20% of maximally allowed norm stays in catalytic converter. Accordingly, if the amount of sulfur will be close to max, total poisoning of NOx catalytic converter will happen much faster and quicker (it is indirectly confirmed with significant decrease of performance after already 50’000 .. 80’000 km). If the MSD80 suspects not-perfect performance of NOx catalytic converter, the speed of poisoning grows inversely proportional to catalytic converter’s performance (it means, that time to desulfation regeneration is decreased).
The desulfation profile in the image is quite far away from real situation. It can correspond to situation, when till max allowed level (4000 mg) catalytic converter’s desulfation cycles are not possible.
In real life – when the sulfur accumulation level reaches around 10% (for NOx converter with poor/moderate performance) till ~ 20 .. 25 % (for NOx converter with good/perfect efficiency) from maximum level (4000 mg), MSD80 will attempt to start desulfation sessions.
In the process of desulfation (VANOS exhaust shaft is turned to necessary position), partly burned fuel is being discharged to exhaust system with Lambda 0,93 .. 0,96 (the temperature of exhaust system reaches 550 .. 650 oC according to data from temperature sensor). In this period, MSD80 mathematically counts the “renewal dose”, which is proportional to regeneration time (distance traveled).
Typical speed of desulfation, driving with speed 115 .. 120 km/h, is around 40 .. 50 mg/km on catalytic converter poisoned by 2000 mg and around 15 mg/kg, if the poisoning is around 500 mg (the curve of purification is exponential, speed of purification decreases, when the absolute level of poisoning decreases).
Regeneration starts on speed over 110 .. 115 km/h (if sulfur counter shows more than 2000 mg), lower speed does not regenerates the catalytic converter (even in forced cycle), which means – the poisoning level of NOx catalytic converter continuous to increase. If the poisoning overreaches 1000 .. 1500 mg (for NOx converter with reduced efficiency) till 3000 .. 4000 mg (for brand new NOx converter), but regeneration has not happened (for example, if the driving speed 90 .. 100 km/h is respected), MDS80 will record the error message 30EA and will stop the Homogeneous lean and Stratified charge modes.
What to do?
In perfect scenario: time by time drive with speed over 110 km/h. If the NOx catalytic converter will be with cumulative (mathematically counted) sulfur accumulation over 1000 mg, it will be regenerated. For prevention purposed, after 5’000 .. 10’000 km connect INPA (for example, after oil change) and evaluate the poisoning level of NOx catalytic converter. If necessary, turn on the forced regeneration and find the possibility to drive on 110+ km/h for a while.
P.S. To activate forced desulfation process, the fuel tank should be filled by (at least) 50%!!!
Desulfation of NOx catalytic converter – how it happens in real conditions.
Disclaimer: the manufacturer don’t gives any information, according what algorithms the MSD80 performs. Functionality described below is explored during several thousands of driving sessions. Different software releases can have differences from described.
If the content of sulfur in NOx catalytic converter, calculated by MSD80, is not above approximately 1000* mg, in normal conditions MSD80 will not start desulfation sessions.
If the calculated content of sulfur reaches over 1000* mg, MSD80 tries to initialize desulfation sessions, in addition, the bigger the content of sulfur, the lower speed and less amount of time is needed to keep the exact speed to start the process of desulfation. For example, if the content of sulfur is around 1000* mg, the necessary speed is around 140 km/h, it must be maintained for 10 .. 15 minutes (until desulfation begins), some aggressive driving would be required. In turn, if the content is above 2000 .. 2500 mg, required speed drops down to 110 .. 115 km/h, also the required amount of time is much shorter (only several minutes) for MSD80 to start the process of desulfation of NOx catalytic converter.
*value for brand new NOx catalytic converter. If NOx converter efficiency, measured by MSD, shows lowered efficiency, desulfation treshold also is lowered.
Content of sulfur, calculated by MSD80 in NOx catalytic converter, displayed in the image. Example.
1. below the value of 1000 mg in normal conditions MSD80 don’t initializes desulfation sessions, not depending of driving mode;
2. the content of sulfur grows with speed around 0,5 mg/km (initial value 0: catalytic converter registered just now);
3. after two driving periods, each 15 minutes, with speed 140 .. 145 km/h the session of desulfation has been started; its stops, because the speed drops below 110 .. 115 km/h for more than 30 .. 40 seconds; sulfur level average decrease speed 30 mg/km;
4. the content of sulfur grows with speed around 0,5 mg/km;
5. driving with speed above 125 .. 130 km/h, the session of desulfation starts. lt stops, because the speed drops below 100 .. 115 km/h; sulfur level average decrease speed 35 mg/km;
6. the content of sulfur grows with speed around 0,5 mg/km, in this stage the driving speed don’t exceeds 100 km/h;
7. the driving speed exceeds 100 .. 115 km/h longer than 10 min, the session of desulfation starts; it stops, because the speed drops down 100 km/h for longer than 2 minutes; sulfur level average decrease speed 45 mg/km;
8. the content of sulfur grows with speed around 0,5 mg/km;
9. the driving speed exceeds 110 km/h longer than 5 minutes, the session of desulfation starts; sulfur level average decrease speed 48 mg/km.
Assuming the car is operating under conditions, where driving (very often) is along the highways (for example: Germany, France), the current algorithm works flawlessly. But, if the vehicle is operated in countries, where only on some roads max 110 .. 130 km/h is allowed, the situation becomes much worse. Only when the content of sulfur is close to max allowed, the desulfation sessions are started on speed 110 .. 115 km/h. If in this stage (2000 .. 3000 mg or around 2000 km) the car don’t drives with speed required, the content of sulfur reaches over 3000 mg and the error message 30EA is recorded soon, Stratified charge mode is turned off, the performance of creation of long-term trims is stopped, etc.
In countries, where is no possibility to drive with speed above 110 km/h, the situation is even worse. In this case, after driving 6000 .. 7000 km, the error message 30EA inevitably will be recorded, and officially there is no solution to solve this problem.
The fact that no interface has been created by BMW between MSD80 and CCC/CIC (multimedia unit), makes situation even worse. If the driver would receive information, that the NOx filter will require purification, in time – in many cases would be possible to avoid the 30EA error message and following problems of engine performance. Unfortunately, the user don’t knows the pollution level and has no way to avoid threatening problems.
Values during desulphation (../F9/Shift+F3/F1):
- exhaust temperature around +600 oC;
- target values of Lambda: 0.94 .. 0.96