In many ways, N43/N53 series engine is a leader of BMW technologies.
It’s control system MSD80/81 can work in several operation modes:
1. Homogeneous mixture mode. Injection happens in expansion cycle, VANOS accordingly to this mode, multi-point ignition: sequential, no separation in time.
2. Stratified charge. Works with very lean mixture. In this mode Lambda can reach 3, 0 .. 3,5. Most advanced/general mode, which makes N43/N53 so different comparing to all other BMW engines. VANOS and ignition: totally different, multi-point ignition within 1 .. 3 times, exactly before ignition.
3. Transitional mode: Homogeneous lean. In this mode Lambda is closer to 1 (1,4 .. 1,6), for additional reduction of exhaust gas an EGR system is used. The fuel is injected in expansion cycle AND just before ignition, creating mixture close to homogeneous till the moment of ignition.
Briefly, when each mode is used:
In the picture – typical distribution of performance modes for N43/N53 series direct injection petrol engine.
Performance modes of N53B30.
Injection strategy for N53. Technical material of BMW AG.
Injection strategy for N53B30. Test results from third party measurements of performing engine.
Homogeneous mixture is used at middle/high load; cold engine; for warmed up engine – in case, if error readings of NOx catalytic converter or/and NOx sensor are present; in time, when calibration of wide-band Lambda sensor or individual mixture correction for cylinders is in progress. If the engine determine incorrect performance of NOx catalytic converter and/or sensor and store errors about these exhaust components – this mode (Homogeneous charge) is alternative (actually – an emergency ignition mode) and provides limited performance: higher fuel consumption, clumsy operation, error message recordings regarding fuel trim, uneven idle, troubles starting engine in cold weather etc. Engine power is adjusted with throttle opening (amount of air), but fuel mixture is adjusted by changing (amount) of fuel injection time.
In high load – basic operation mode of engine.
Stratified charge: for warmed up engine, if there is no error readings regarding NOx system, in steady load conditions and if NOx sensor is Online (description in topic of NOx sensor). Engine power is adjusted by changing amount of fuel (injection time). Throttle – almost or fully open. Mixture suitable for combustion (rich enough) is created in near vicinity of spark plug, in other areas – mixture is very lean.
Homogeneous lean (transitional mode): in case of increased load, in stage between Stratified charge and Homogeneous mode and if uneven performance and/or insufficient efficiency of NOx catalytic converter is determined.
Stratified charge. Lambda depends of RPM and load of the engine.
Marked cells: Stratified charge and Homogeneous lean injection mode (Lambda is significantly higher than 1,0).
NOx catalytic converter and it’s regeneration on Stratified charge mode.
Basic parameters of N43 and N53 series engines in Stratified charge mode:
- Phase of regeneration ~3 seconds, Lambda (before CO catalytic converter): ~ 0,8 (within 1 second for each bank, sequentially), after NOx catalytic converter ~ 0,90 .. 0,95;
- Phase of Stratified charge: 10 .. 60 seconds (with step of 5 seconds), depending of load, RPM, NOx level in exhaust;
- Lambda in Stratified phase: 1,8 .. 3,5 (Homogeneous lean: 1,4 .. 1,6).
Remark: BMW in their training material points out, that regeneration phase for NOx catalytic converters happens alternately for each of 2 banks. Detailed inspection shows that regeneration happens sequentially within 3 second period of regeneration phase.
In case uneven running is detected (in conditions of even load and RPM short-term changes in speed of flywheel is detected), Lambda (for a while) is being reduced from 2,6 .. 3,2 to 1,4 .. 1,6: engine turns to Homogeneous lean operation mode. If uneven running continues, engine switches to Homogeneous mode. If in (downgraded Lambda) Homogeneous lean mode no unevenness is observed, after a while (changing driving conditions or starting a new driving session: in period of 5 .. 15 minutes) the engine tries to restore full Stratified charge mode (Lambda till 2,6 .. 3,2).
Working in idle, the engine can use following operating modes: (exact data for N53, but by idea the same states for N43 also):
1. Stratified charge with Lambda 1,8 .. 2,2 (up to 2,7 on latest software releases). This mode is chosen by MSD80, if till moment of idle running the Stratified charge was operational. In idle, MSD80 don’t performs analysis of NOx and don’t regenerates catalytic converter;
2. Homogeneous mode. MSD80 switches to this mode, if the idle (parking) mode lasts more than 2 .. 3 minutes. When the movement resumes, Stratified charge mode is on again. If the parking mode lasts longer than 10 .. 15 minutes, the NOx sensor switches off. When the movement resumes, it switches on, and after 2 minutes, when it’s ready, engine switches to Stratified charge mode. This mode is switched on also when uneven running of engine is detected and Stratified charge has been switched off for a while (error message 3104: uneven run with active status), and also if there are error reading regarding NOx system.