Integral parameters, curves of heat release, curves of pressure during combustion and gas exchange. The analysis of calculation results of   injected fuel allocation in the characteristic zones.

    Experience of use of the program DIESEL-2/4t for engines of different size and purpose has shown that the program needs no preliminary set-up of used factors for the concrete engine. However, to obtain authentic calculation results, if you search for the ways of improvement of the engine performances or the ways of decrease of harmful materials emission, etc., it is expedient to carry out the comparison between calculated and measured data for a base engine configuration at several regimes. If necessary, it can carry out the additional set-up for a number of empirical coefficients. The amount of empirical coefficients is not great, and they are strictly constant for any operating regimes of engine and for any its configuration.

    In present site, the comparison of calculated and experimental data for the truck diesel KamAZ -7405 is given. The data for comparison are taken for regimes of the speed performance.
     The values of all empirical coefficients are strictly identical.
     The experimental data are given by the KamAZ R&D Center.
     Measurement and processing of data were carried out with AVL equipment.

Main structural data

Piston bowl design and fuel jets orientation.

Amount of identical jets:                         4 х 0.33 Angle b:                                                    0 Angle a:                                                   60 deg. External diameter, dc:                                64 mm Radius of sphere in centre, rc:                    20 mm Radius of hollow chamfer in periphery, rp:  5 mm Depth of bowl in centre, hc:                     23.2 mm Depth of bowl in periphery, hp:                23.2 mm Inclination angle of bowl forming    to a plane of the piston crown, g:            90 deg. Piston crown - cylinder head clearance, h clr:1 mm Displacement of a spray from bowl axis, si:    0 Displacement of a spray from the bottom    of a cylinder head,  hi:                              2 mm

Let  H  be a swirl number defined as a relation between swirl angular velocity ws (in the cylinder at the end of intake) and rotation velocity wr.:                                                    1.586

The results of calculation

Analysis and visualization of mixture formation

     The software DIESEL-2/4t includes "Fuel Jet Visualization" code. This code allows in a pictorial form to analyze the animation picture of interaction of fuel jets with combustion chamber walls, with swirl and among themselves.  Observation of the development of fuel jets and their interaction  with a swirl and walls offers possibility to find directions of nozzles orientation and configuration of piston bowl walls which would provide the best combustion conditions.
     The " Fuel Jet Visualization" code with data files for different diesels can be sent free of charge to the interested persons and organizations.
     The figure presented below is generated by this code.

Full capacity: rpm=2200,  BMEP=9.7 bar.

     As a result of calculation of a development of each fuel jet, the amount of fuel allocated in each  characteristic zone is evaluated. Characteristic zones:
- environment of free jet and of wall surface flow;
- core of free jet;
- core of wall surface flow on the piston wall;
- zone of intersections of wall surface flows on the piston wall;
- surface of the cylinder head;
- surface of the cylinder wall.
  There are approximately identical conditions of fuel evaporation inside one characteristic zone. In different zones, fuel evaporation velocities differ critically.

The table contains distribution of fuel of each jet in characteristic zones   including a zone of crossing of wall surface flows (WSF) of two close placed jets, is displaced into output file. The table contains data for the whole period of the injection.

The allocation of fuel in the zones  (at the end of injection). 
KamAZ - 7405: rpm=2200, BMEP = 9.7 bar

Num. of jet	Environment of jet and of wall surface flow	Free jet core	Core of wall surface flow of the piston	Zone of intersection of wall surface flows	Surface of the cylinder head	Surface of the cylinder wall
1	74.90 %	2.90 %	22.20 %	0.0	0.0	0.0
Sum	74.90 %	2.90 %	22.20 %	0.0	0.0	0.0

    The analysis of calculation data presented on the special page. 
      If the fuel jets develop in the different conditions, the table contain data for each jet. (See examples)

         To achieve a good mixture formation, fast combustion and low level of fuel consumption one should directed each jet so that the maximum amount of fuel was allocated in zones with good conditions of evaporation. First of all, it is zone of environment of a jet and, to a lesser degree, core of a wall surface flow. It is necessary to avoid allocation of fuel in zones of intersection of wall surface flows, and also the settlement of fuel on a wall of the cylinder and on the head of the cylinder, especially, if the head is made of aluminium alloy and has low temperature.
      In the given construction these guidelines are fulfilled.
However, to reduce a level of NOx emission it is necessary to realize other operations, which cause intersection of wall surface flows of adjacent jets, settlement of fuel on a surface of the cylinder head, reduction of combustion and increase of soot emission. The software  DIESEL - 2/4t and built-in "Fuel Jet Visualization" code allows to coordinate these opposite tendencies and to find the favorable compromises.

 

Comparison between calculated and experimental data.

Integrated parameters of engine

Parameter of engine	rpm=2200		rpm=1400		rpm=1000
	Experiment	Calculation	Experiment	Calculation	Experiment	Calculation
Ne is capacity, kW	192.3	193.6	140.1	138.8	92.6	92.5
ge -is specific fuel consumption, g/(kW h)	213.7	212.4	201	202.8	212	212.2
Рe   is BMEP, bar	9.66	9.72	11.06	10.96	10.24	10.22
Pi  is indicator  pressure, bar	11.74	11.7	12.51	12.03	11.18	11.05
Ps  is inlet manifold mean pressure, bar	1.97	1.97	1.51	1.52	1.29	1.28
Ts is inlet manifold mean temperature, K	390	390	353	354	336	338
Gira is air flow rate, kg/s	0.346	0.346	0.178	0.182	0.110	0.112
Pz is max. cylinder pressure, bar	130.7	129.5	116.8	121.	105.2	107.9
Pinj is max. injection pressure, bar	672	665	540	532	355	349
Hartridge   is level of soot emission	7.0	7.8	20.	15.9	41.	38.
Pt is mean pressure before turbine, bar	1.89	1.89	1.37	1.36	1.19	1.2
Tt*   is mean temperature before turbine, K	768	764	798	753	788	752
Thead is mean temperature of cylinder head flame surface, K	454	459	436	439	416	430
Pо is mean pressure before compressor, bar	0.95		0.974		0.978
Ptо   is mean pressure in the tail pipe, bar	1.004		0.993		0,988
qc is portion of fuel per cycle, g	0.0778		0.0838		0.0818
Fi_inj   is injection timing, deg.	21.2		15.35		14.05
Fi_lead is lead of injection, deg.	14.		12.4		12.

     As can seen from the table, the program allows to obtain the high accuracy results.

     The difference between calculated  and measured gas temperatures in front of the turbine Tt* is caused by well known circumstance: the measurement of temperature of a pulsing flow by the thermocouple gives overestimated results. The error of this measurement increases when the relation between pulse pressure difference and average value of pressure increases.

Smoke emission, max. cylinder pressure and fuel consumption at the different operating regimes

     The comparison between calculated and measured functions of pressure in the cylinder as a function of the a crank angle is placed below.
     The "measured" heat release was obtained by processing   measured values of pressure (by code of AVL).
     Dependencies of injection velocity on crank angle was obtained experimentally and are the input data for calculation.

Curves of cylinder pressure, heat release and injection velocity are shown in figures below.

 

Gas exchange phenomena are shown in figures below.

Notation:

Cylinder pressure: a is the calculated pressure;  h is the measured pressure; b is exhaust manifold pressure; c is inlet manifold pressure; d is effective square of a flow section of outlet valves; e is effective square of a flow section of inlet valves; gas velocity: f for the exhaust port; g for the inlet port.

     A good agreement between calculated and experimental data both for combustion processes and gas exchange allows to make conclusion about adequacy of mathematical model of engine and about possibility to carry out the optimization of engine parameters with help of this program.