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Common Rail controlling algorithm development


      Fuel injection systems with microprocessor controlling make it possible to reduce an air pollution emission of diesel engine. However, development of controlling algorithm for these systems is a problem which requires a large expenditure. The development of first approach of this algorithm by means of computer simulation and optimization is the issue of the day. Sequence of actions and some results of research in this direction performed in Bauman Moscow State Technical University are presented below.

Step: 1.   

      Calibration of calculation model for high-speed diesel in 10…11 points of operating range.

                            Euro II operating range.gif (4113 bytes)

Fig. 1. Diesel operating range. % inside a ring means a contribution of the point in overall emission level. Green points was add to increase accuracy on external curve.

      In each marked point of operating range the injection profiles of Bosch VE was calculated with INJECT software intended for fuel injection system simulation. These injection profiles were included into data file of DIESEL-RK software. In the each marked point diesel was calculated with DIESEL-RK and results were compared with experimental ones. There were compared:
-    Power [kW] and SFC [g/kW h],
-    Maximum cylinder pressure p_max [bar],
-    Air flow rate [kg/sec],
-    NO emission [ppm],
-    Smoke emission [Hartridge].

      DIESEL-RK was calibrated to achieve high accuracy of high-speed engine simulation over the whole operating range with identical coefficients. Results of simulation and comparision calculated data with experimental ones are presented in fig. 2.

HighSpeedDieselCalibration.gif (127425 bytes)

Fig. 2. Results of simulation of high speed diesel over whole operating range and comparision of calculated data with experimental ones.
m_air is an air flow rate, kg/s;
SFC, g/kW h;     NO, ppm,
Smoke is a Smoke Bosch Number. 


Step: 2. 

         Modeling of Common Rail injection profiles with INJECT software.  In the 9 points of operating map the CR injection profiles were calculated to obtain individual sections of injection profile beginning and ending. These sites are marked by rectangles in figure 3. Lately, at optimization of injection duration on each operating mode, optimized injection profile includes these sites connected with line. Thus injection duration is alone factor, which describes injection profile on current operating mode (injection velocity curve is calculated as a function of cycle fuel mass, injection duration and shape of injection profile). Actual injection profile has a same shape but scaled to provide fixed cycle fuel mass and specified injection duration.

   Inj profile of CR.gif (41699 bytes)

Fig. 3. Injection profile of CR system. Marked sites are calculated for each operating point with especial software.


  Step: 3.  

       Optimization of Injection Duration fi and Injection Timing qi to decrease both NO and smoke emission. In 9 points of operating map there were performed optimizations by 2D scan method. Goal of optimization is finding of fi  and qi  combination provided minimum of sum emission SE. The points where optimization was carried out are marked by orange in diagrams of operating maps (fig. 4, 5, 6).

      Complex of air pollutant: Summary Emission (SE) of PM and NOx calculated as:

SE = Cpm (PM / 0.15) + Cno (NOx / 7.);

where: PM is a specific particulate matter emission,
            NOx is a specific nitrogen oxides emission,
            Cpm is an empiric line factor for Particulate Matter emission (0.5);
            Cno is an empiric line factor for Nitrogen Oxides emission (1.0).
The coefficients: Cpm and Cno have to be calibrated for each type of engine.

      In each of 9 operating points the 2D map of scanning results were obtained with using DIESEL-RK software. Taking into account limitations (restrictions) p_max < 130 bar; p_inj max < 1650 bar, optimum values of fi  and qi were founded to achieve minimum level of SE. Results are presented in fig. 4. Allowable area is yellow filled; optimal area with minimum emission level is blue-green filled. Selected point for controlling algorithm forming is marked with black rhomb.

      At full load (fig. 4. pic. 1) the allowable area is not crossing with optimal area. On other operating points (fig. 4, pics. 2-6) there are common sites of allowable area and optimal area. Thus, the results point at full load has to be selected as a near to optimal area.

Fig. 4. Results of Injection pressure 2D approximation over whole operating range on a base of emission level optimization performed in each point in view of limitations (p_max < 130 bar; p_inj max < 1650 bar).
fi is Injection Duration [CA];   qi
 is Injection Timing [CA before TDC].
Allowable area is yellow filled; optimal area with minimum emission level is blue-green filled. Selected point for controlling algorithm forming is marked with black rhomb. Injection pressure p_inj is a pressure before nuzzles. Accumulator pressure is more due to losses in cone. One may be calculated with software for fuel injection simulation.

Enlarge 2D scanning results pictures...and explain them.

Step: 4.   

       Common Rail controlling parameters maps forming. Parameters of fuel injection corresponding with minimal summary emission or minimal SFC, (if strongly marked minimum of SE was not founded), were get into operating map (fig. 4.).

      In fig. 4 only six 2D scanning maps are presented. Actually in every orange point 2D scanning was performed and results of optimization were got into operating maps.

      After, the obtained Injection Pressure p_inj, optimal Injection Duration fi and optimal Injection Timing qi  were approximated in whole operating map as functions of RPM and fuel mass (mf ). Results of approximation are presented in figure 5.

     Phi_inj.gif (5957 bytes)  
a) Optimal Injection Duration fi as a function of RPM and fuel mass.

     Theta_i.gif (10079 bytes) 
b) Optimal Injection Timing qi as a function of RPM and fuel mass.

Fig. 5. Injection duration fi and injection timing qi as functions of RPM and fuel mass per cycle mf. Results of 2D approximation.

      Obtained character of controlling algorithm maps is available for only achieving minimum of air pollution. If other goal will be formulated, for example to achieve minimum of SFC, the maps of injection parameters will be different because minimum of SE disagrees with minimum of SFC in map with axis: fi  and qi.


Step: 5.    

       Comparison of emission levels of engine with obtained controlling algorithm on the one hand and of engine with base configuration on the other hand is presented in table below. Emission levels were calculated for both engine configurations with using of contributions of each operating mode presented in fig.1. Base engine parameters are accepted as 100%.

Engine configuration NO PM
Base: Bosch VE  100%    100%
Common Rail with developed algorithm 88% 46%



  1. The designed technique of computational making of base control algorithm for Common Rail allows decrease expenditure on development of diesel control system .
  2. The number of points where optimization was carried out (9) is not sufficient for correct and smooth approximation. It seems, that the amount of points should be enlarged up to 12...13.
  3. Computational making of optimal controlling algorithm for main fuel injection parameters with DIESEL-RK software allows resolving the problems of decrease NO and PM emissions in diesel. 


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