Ideal Gas Conversions


Ideal gas conversions Carnot cycle and theoretical cycles of the reciprocating engine (Otto, diesel, hybrid, Stirling, ericsson) are divided into two main groups.

Ideal Gas Conversions

Ideal Gas Conversions

Ideal Gas Conversions

A) Carnot cycle:

This cycle is the cycle proposed by Nicolas Leonard Sadi Carnot French scientists in 1824. Heat machinery is considered as an ideal cycle. Pv and Ts diagrams of the Carnot cycle is as shown in Fig.

Carnot Cycle

cycle as shown in the figure, consists of two isentropic and two isothermal process. Article isothermal work with external business between 1-2 points (T S = constant) and is compressed as isentropic between 2-3 points; temperature and pressure increasing working substance, isothermal between 3-4 points (T H = constant) and also do business by expanding the isentropic between 4-1 points. As is known, the pressure of the compressed gas and the temperature increases, in contrast, the pressure and temperature of the expanding gas is reduced. Temperature which tends to increase due to compression in one to two points (T L) to be permanent, the cooling system that discarded heat from the system, while the ars 3-4 points, the temperature of which tends to decrease due to the enlargement (T H) for maintaining constant having the heat must be supplied to the system. Carnot cycle, in theory, be carried out in a continuous-flow closed or open system.

The amount of heat taken from my QL = Q2 = MRT L .ln (v 1 / v 2), the amount of heat given to the system in QH = Q 4 = MRT H .ln (4 v / v 3) calculated with the equation. The thermal efficiency of the cycle t = 1 to n-Q L / Q has the H correlation. Here the isentropic the thermal efficiency of the Carnot cycle for state Carnot = 1-T L / T H bond is obtained.


As shown schematically in Figure Carnot heat engine, it receives 500 kJ of heat from a heat source to heat at 627 C and 27 C in the cold source. Calculate the amount of heat supplied to the thermal efficiency of this machine and the cold source.

Carnot Cycle Example


The Carnot = 1 – (27 + 273) / (627 + 273) = 0.667 or 66.7% is located. Here, the heat quantity Q L = Q H (T S / T H) = 500 (300/900) = 166.67 kJ becomes.

B) Theoretical Cycle of Ideal Gas Reciprocating Engines

1) Constant Volume (Otto) cycle:

Constant volume cycle, the first time in 1862, but was described by Beau de Rochas, together, in the first cycle of the application olarak1876 by Nikolaus August Otto. Otto, the same year, compression, four-stroke, reciprocating internal combustion engine took first in the market. Pv is the Otto cycle and graphic Ts as shown in Fig.

Otto Cycle

Otto engine heat (thermal) efficiency n t = 1- (T4-T1) / (T2-T3) can be found from Eq. Yield compression ratio (ε), depending on n t = 1- 1 / (ε k-1) can also be specified in the form. Here v1 / v2 = ε stop. Accordingly, when a compression ratio increases yield increases.

2) Constant Pressure (Diesel) Cycle:

Rudolf Deisel 1892 has produced an engine that bears his name and was granted a patent. This cycle is called the Deisel engine cycle. compressing with air and fuel in Otto engine was being lowered the yield. Diesel engines separately compressed air and fuel efficiency increase is achieved. This motor ε = 24/1 allows to compression ratio. This cycle is a constant pressure, is composed of a fixed volume and two isentropic process. Pv and Ts diagrams of the cycle is as follows.

Diesel Cycle

volumetric compression ratio of the diesel cycle ε = v1 / v2, the rate of expansion at constant pressure (pre-expansion ratio) p (v3 / v2) = (T3 / T2) is shaped. The thermal efficiency of the Diesel cycle t = 1- 1 / (ε k-1) * (p k -1) / (k (p-1)) is found by correlation.

3) Combined Cycle:

Today’s modern diesel engines burning while close to the first stage of constant volume, the final stage is held approximately constant pressure. fixed volume of a portion of the heat to the site, called hybrid cycle to cycle is delivered at a constant pressure in the rest. PV and TS diagram of this cycle is as follows.

Mixed Cycle

volumetric compression ratio in the mixed cycle ε = v1 / v2 pressure increase at a constant volume λ = (P3 / P2) = (T3 / T2) and expansion at constant pressure (pre-expansion) ratio p = (v4 / v3) = (T4 / T3 ), respectively. The thermal efficiency in this case t = 1 1 / (ε k-1) * (λp k -1) / [(λ-1) + kλ (p-1)] is added.

4) Stirling Cycle:

r.stirling (1816) designed by, belonging to the theoretical cycle should give the outside temperature Stirling engine Pv and Ts diagrams are as shown in Fig.

Stirling Cycle

The cycle consists of two isothermal and two constant volume process. The working substance in a sealed cylinder to heat is provided by a special heat exchanger-heater. The beam is taken out from the cooling heat exchanger from the other. heat required for the motor is supplied from a special combustion chamber outside the cylinder, where they are continued from combustion. q = total heat Cv given to this site (TH-TL) + rta.ln (P2 / P1), while net heat in my work translated QNet = (TH-TL) R.ln (P2 / P1) d. In this case, a simple (regeneratörsüz) thermal efficiency of the Stirling cycle nt = QNet / q has the ratio. The Regeneratörl the Stirling cycle heat discharged by the help regenerate are brought into the system again.

q = total heat given my CV in this cycle (TH-TL) + rta.ln (P2 / P1), the work translated into net heat, QI = (TH-TL) R.ln (P2 / P1) d.

5) Ericsson Cycle:

Ericsson cycle, except that the location of the isobars izohor is no different from the Stirling cycle.This is the cycle gas turbine today is considered as an ideal cycle. PV and TS diagram Ericsson cycle is as follows.

Ericsson Cycle

If regererat added to the Ericsson cycle, storing the heat discharged by the regenerator 4-1 isobars on site throughout the data back to the system during the 2-3 isobars.

John Ericsson, Swedish his engines, the 19th century, has been made into a number value and used. These engines were heated fresh air and indirectly taken for each cycle (external combustion). It ‘s not an open system with another system. Ericsson, in 1853, designed by one of his four 2200-ton ship engine has achieved a first in this regard.

Source: Ideal Gas Conversions, Mehmet TAŞKAN, Ideal Gas Conversions Article

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