Determinationofcombustionparameters

The combustion equation looks like following:

where  - pressure build-up.

    For pre-chamber and vortex-chambered diesel engines is taken closer to the lower limit, and for engines with direct injection closer to the upper limit.

    According to the diagramU = f (t)values of the internal energy of gases in the temperature range300…900⁰С (pic. 2.1.) we find graphically for the compression temperaturet_С = Т_С – 273 = 1035 – 273 = 726⁰Сinternal energy of 1 kmole of airU_C = 4113 and internal energy of 1 kmole of combustion products for diesel fuel atα = 1,0

,

    The internal energy of 1 kmole of combustion products at a compression temperature t_C includes the internal energy of the combustion products atα = 1.0 and internal energy of excess air. that is,

,

where – relative amount of combustion products, withα = 1,0 in 1 kmole of combustion products at

α = 1,35;

– relative amount of excess air in 1 kmole of combustion products.

    Then the internal energy of 1 mole of combustion products at the compression temperaturet_С

.

    We set the value, let = 1,8.

    Then the sum of all the terms on the left side of the combustion equation

    From here .

Because , so .

    Value of s a function of the combustion temperature and heat capacity, so the last equation can be solved by the selection method, using Table 2.1 or Fig. 2.2 in the temperature ranget_Z = 1800…2100⁰С.

    Let take the valueoft_Z =2000⁰Сand find and  for this temperature.

    Giventhat

, then

.

    The values и ofair are taken from the table 2.1 for the respective temperature values.

The result is less than necessary, so we set the temperaturet_Z = 2100⁰С. When:

.

In this case: .

Since the right-hand side of the combustion equation is and it is less than , it is obvious that the desired temperature is between 2000⁰and 2100⁰С. To do this, we plot a graph (fig. 3.1) and determine the desired temperature graphically.

    It can be seen from the graph thatt_Z = 2034⁰С.

    Then the temperature at end of the combustion

.

    Maximumcombustionpressure:

.

 

18000                           

 

17500

 

17000

 

 1900                                          2000    t_Z⁰ С.

Рис. 3.1. Dependency from the temperaturet_Z⁰С.

3.6.

Calculationofexpansionparameters

1) Preliminaryexpansion

.

2) Subsequentexpansion

.

3) Expansionendpressure

; .

4) End-of-ExpansionTemperature

; .

5) Mean calculated indicated pressure of the cycle

.

6) The actual average indicated pressure, taking into account the curvature factor of the indicator diagram.

; .

 

KeyPerformanceIndicators

1) The proportion of indicated pressure used for friction and drive of auxiliary units

.

    For pre-chamber and vortex chamber diesels

.

2) Mean effective cycle pressure

;  .

3) Mechanicalefficiency

;       .

4) Specificindicatedfuelconsumption

,

гдеρ₀  –density of the charge at the inlet, ^кg / _м³,

;                      ;

l₀ – theoretically required amount of air (in kg) for combustion of 1 kg of fuel.

5) Indicatedefficiency ; .

6) Specificeffectivefuelconsumption: ; .

7) Effectiveefficiency ; .

 

 

Basicdimensionsofthe engine

1) Calculatedvolume of one cylinder

.

2) Diameter of the inner surface of the cylinder:

.

3) Pistonstroke

.

    Finally, for the convenience we round up values to integers.

    Speed  should not differ from the chosen one by more than 5...10 %, otherwise, it is necessary to recalculate the effective indicators.

 

4) Enginedisplacement .

5) Effectivepower .

6) Indicatedpower .

7) Volumetricpower .

 

8) Effective and indicated torque

;

.

 

 

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