**4. Modelling of injection process in gasoline direct injection engine by kiva 3v**

In up-to-date combustion engines the fuel is injected directly into the cylinder, where the load has a raised temperature. The evaporation is better than at the injection into the inflow duct. With regard to a very short time lapse between the start of injection and the ignition during the mixture stratification in recent gasoline engines with direct fuel injection into the cylinder the presentation of a precise mathematical model describing evaporation of fuel drops is necessary.

During fuel injection disintegration of drops, falling into smaller and smaller ones, takes place. They are subjected to aerodynamic forces which are the direct cause of their disin‐ tegration. The presentation of a precise mathematical model of the process of drop move‐ ment, disintegration, and evaporation is, so far, not possible. However, a number of models based upon aero- and thermodynamic laws and experimental investigations have already been built. As a rule, reciprocal collision of drops is not considered. In some models only one kind of drop contact with the wall (rebouncing or spilling) is assumed. The best known, at present, models of fuel evaporation are the models given by Spald‐ ing [6] and included in the module GENTRA in the programme *Phoenics* of the firm CHAM and programme *KIVA*.

Mathematical models considered in these programmes are more suitable for numerical sim‐ ulation of the fuel injection process in gasoline engines. Apart from it, the mathematical model given by Hiroyasu [4] and the PICALO model should also be considered.

In program *KIVA 3V* make use of complicated mathematical models describing the behav‐ iour of the fuel injected into the engine cylinder, and so: shaping of the fluid jet (Reitz model [5]), fuel drops breakup (TAB - Taylor Analogy of Breakup procedure [3]), evaporation of fuel drops (Spalding model [6]), resistance and movement forces (Amsden model [2]), tur‐ bulence of the charge in the combustion chamber (two - equation κ- ε model [8]).

#### **4.1. Geometry of the calculation model**

<sup>800</sup> <sup>1000</sup> <sup>1500</sup> <sup>2000</sup> <sup>3000</sup> <sup>4000</sup> <sup>5000</sup> <sup>6000</sup> <sup>7000</sup> <sup>8000</sup>

**Figure 15.** The total time which the fuel stream takes to go from the injection to the moment when it reaches the sparking plug, depending on the crank angle and the rotational speed of the engine, at constant injection pressure 5 [MPa]

From the calculated values of the angle by which the crankshaft revolts during the jet travel the value of the advance angle of injection with consideration of the advance angle of igni‐

It has to be emphasized that the actual injection angle has to be increased by the ignition

**Figure 16.** The actual injection advance angle as a function of rpm for different values of injection pressure.

0-0,001 0,001-0,002 0,002-0,003 0,003-0,004 0,004-0,005 0,005-0,006

**Crankshaft speed [rpm]**

advance angle what is superposed and presented in *Fig. 16*.

0

0,001

0,002

0,003

**Time t1** 

tion is calculated.

0,004

0,005

0,006

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**Angle of fuel injection before TDC**

> The program for computer modelling and simulation of combustion engine *KIVA 3V* pos‐ sesses a large, developed, graphic interface which may additionally consider the inflow and outflow system and create complicated curved surfaces describing, as in our case, the head of piston. For such a complicated system as the combustion chamber Mitsubishi GDI the commercial program *KIVA 3V* in the Laboratory Los Alamos describes fully the physical and thermodynamical processes inside the cylinder. In *Fig.17* shows a geometrical model of a piston of a gasoline engine type 4G93GDI of the firm Mitsubishi.

> In the case of an irregular combustion chamber calculation of the size of the contact surface of flame and cylinder walls and head can be performed applying division of the w hole sur‐ face above the piston into a number of elementary volumes. This method should be applied at irregular shapes of the combustion chamber.

Cylinder was divided into 20 400 cells (30x34x20) and each 4 pipes into 1900 cells. Total number of cells of whole system when piston is in BDC amounted 29680 cells. The grid consists of a cyl‐ inder 17 of horizontal layers. 13 layers of equal thickness falls to 80% of piston stroke starting from the bottom dead centre. The remaining 4 layers around the top dead centre was concen‐ trated to obtain more advantageous terms of the simulation of combustion process that takes place there (combustion chamber). Mesh of one cylinder with two inlet and two exhaust pipes and pent-roof combustion chamber is shown in *Fig.18*. In order to determine of engine thermo‐ dynamic parameters it required a special division of cylinder layers along the wall and more complex grid inside of combustion chamber. Cross section of the cylinder along symmetric ax‐ is (*Fig.19)* shows also a bowl in the piston and layers adopted both to the pent-roof chamber and piston head. Piston head was created by CAD system and transformed to pre-processor file. For this reason a special algorithm of interpolation was written to adopt in Lagrange coordi‐ nates. Mesh of the cylinder changes during piston moving and movement of valves also takes effect on creation of mesh in every time step. Mesh of combustion chamber at 27 deg after TDC

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when inlet valves are opened is shown in *Fig.20*.

**Figure 19.** Cross section in axis symmetry of Mitsubishi GDI engine

**Figure 17.** Geometrical model of a piston of a GDI engine

**Figure 18.** Complex mesh of Mitsubishi GDI engine

Cylinder was divided into 20 400 cells (30x34x20) and each 4 pipes into 1900 cells. Total number of cells of whole system when piston is in BDC amounted 29680 cells. The grid consists of a cyl‐ inder 17 of horizontal layers. 13 layers of equal thickness falls to 80% of piston stroke starting from the bottom dead centre. The remaining 4 layers around the top dead centre was concen‐ trated to obtain more advantageous terms of the simulation of combustion process that takes place there (combustion chamber). Mesh of one cylinder with two inlet and two exhaust pipes and pent-roof combustion chamber is shown in *Fig.18*. In order to determine of engine thermo‐ dynamic parameters it required a special division of cylinder layers along the wall and more complex grid inside of combustion chamber. Cross section of the cylinder along symmetric ax‐ is (*Fig.19)* shows also a bowl in the piston and layers adopted both to the pent-roof chamber and piston head. Piston head was created by CAD system and transformed to pre-processor file. For this reason a special algorithm of interpolation was written to adopt in Lagrange coordi‐ nates. Mesh of the cylinder changes during piston moving and movement of valves also takes effect on creation of mesh in every time step. Mesh of combustion chamber at 27 deg after TDC when inlet valves are opened is shown in *Fig.20*.

**Figure 19.** Cross section in axis symmetry of Mitsubishi GDI engine

**Figure 17.** Geometrical model of a piston of a GDI engine

104 Advances in Internal Combustion Engines and Fuel Technologies

**Figure 18.** Complex mesh of Mitsubishi GDI engine

**Figure 20.** Engine mesh at 27 deg ATDC

#### **4.2. Parameters of the calculation model**

During compression stroke fuel of high pressure is delivered by injector located between two intake pipes. Fuel is injected towards the piston bowl and is turned by its wall to the spark plug. However injection time should be strictly defined in dependence of engine speed and ignition angle[3]. Parameters of fuel injection are shown in Table 1.

**Figure 21.** Participation of the gaseous phase in combustion chamber in stratified charge mode at 2400 rpm at 600

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**Figure 22.** Participation of the gaseous phase in combustion chamber in stratified charge mode at 2400 rpm at 110

before TDC (Top Death Center)

before TDC


#### **Table 1.**

Equal temperature of the combustion chamber walls about 500 0 K, and a lower temperature of the cylinder walls about 480 0 K and the piston 550 0 K can be adopted.

#### **4.3. Analysis of participation of the gaseous phase**

In the enclosed illustration (*Fig.21-22*) changes participation of the gaseous phase inside the cylinder of the gasoline direct injection engine from the moment of injection till the moment of ignition.

Stratified Charge Combustion in a Spark-Ignition Engine With Direct Injection System http://dx.doi.org/10.5772/53971 107

**Figure 20.** Engine mesh at 27 deg ATDC

**4.2. Parameters of the calculation model**

106 Advances in Internal Combustion Engines and Fuel Technologies

Way of injection sinusoidal

Mass of the injected fuel per cycle 0,0255 g Position of the injector γ = 60 deg

Global coefficient of air excess λ = 1,512

**4.3. Analysis of participation of the gaseous phase**

of the cylinder walls about 480 0

**Table 1.**

of ignition.

Ignition moment 10 deg before TDC

Equal temperature of the combustion chamber walls about 500 0

K and the piston 550 0

In the enclosed illustration (*Fig.21-22*) changes participation of the gaseous phase inside the cylinder of the gasoline direct injection engine from the moment of injection till the moment

During compression stroke fuel of high pressure is delivered by injector located between two intake pipes. Fuel is injected towards the piston bowl and is turned by its wall to the spark plug. However injection time should be strictly defined in dependence of engine

**Parameters of fuel injection**:

K, and a lower temperature

K can be adopted.

speed and ignition angle[3]. Parameters of fuel injection are shown in Table 1.

Direct fuel injection 75 deg crank angle before TDC Total time of injection duration 32 deg crank angle (2 ms)

**Figure 21.** Participation of the gaseous phase in combustion chamber in stratified charge mode at 2400 rpm at 600 before TDC (Top Death Center)

**Figure 22.** Participation of the gaseous phase in combustion chamber in stratified charge mode at 2400 rpm at 110 before TDC

We can see a turning of fuel jet to the spark plug, but concentration of fuel is observed on piston bowl. Near TDC some of liquid fuel flows to the squish region and sometimes cannot be burned. During motion of jet fuel vaporize and on its boundary is more vapours than in‐ side of jet. Because of restricted volume of this paper it cannot be presented distribution of equivalence fuel-air ratio. However near spark plug air excess coefficient is enough to begin of combustion process. Ignition of spark plug took place 10 deg before TDC.

#### **4.4. Analysis of temperature distribution in the cylinder GDI engine**

In the enclosed illustration (*Fig.23-24*) changes of temperature inside the cylinder the GDI engine from the moment of injection till the end of the combustion process are shown.

During injection process there is observed decrease of temperature of charge where is liquid fuel and is caused by vaporization process. When piston is near TDC temperature of charge in a squish region is higher than in the centre of combustion chamber. The process of com‐ bustion during stratified charge mode is irregular, as a result of conductivity of fuel and gas, first of all ignite the regions with fuel vapour surrounding liquid fuel. It can be observed also during visualization process. The distribution of temperature shows the whole process of combustion and it proceeds in another way than in conventional engine with homogene‐ ous charge. Just at the end of this process the charge in the middle of combustion chamber burns as a result of higher temperature and vaporization of fuel jet.

**Figure 24.** Temperature distribution in the cylinder for 130 before TDC

Test bed investigations were divided into two basis stages:

of ignition until the end of the combustion process [7].

kWh]. The fuel injection took place for 780

**1.** The first stage includes elaboration of the visualization process of fuel injection and combustion of stratified charges for various loads and chosen rotational speeds of

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By use of a VideoScope 513 D of the firm AVL the movement of fuel jet will be followed from the moment of injection, fuel rebouncing from the piston head, up to the moment of its entering under the ignition plug, and subsequently spreading of the flame from the moment

**2.** The second stage includes carrying out of test bed investigations aiming at determina‐

The carried out visualization concerned the process of injection and combustion during en‐ gine work on stratified mixture [10]. The recording was carried out for rotational speed of the engine 2400 [rpm] for partial load. The value of specific fuel consumption was 238 [g/

CA before TDC.

tion of increase in total efficiency of a Gasoline Direct Injection Engine.

**5.1. Visualization of injection combustion process during engine work on stratified**

**5. Test bed investigation**

engine.

**mixture**

**Figure 23.** Temperature distribution in the cylinder for 590 before TDC

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**Figure 24.** Temperature distribution in the cylinder for 130 before TDC
