Assalam-u-alaikum and Good afternoon fellow students and respected ma’am.

I am Sana Jafar, and my other team members are Zoha Navaid, Qazi Saud and Qaisar Amin.

We are here to present five basic thermodynamic cycles i.e Carnot cycle, Rankine cycle, Otto cycle, Diesel Cycle and dual combustion cycle.

Let’s get started.

We begin by answering this simple question that:

What is a thermodynamic cycle?

A thermodynamic cycle is a series of processes where the properties of the system are the same after the cycle as they were prior. Three main properties — temperature, pressure, and specific volume — are tracked when a system undergoes a set of processes. To be considered a cycle, all three properties need to be the same at their initial state and at the end. One property could remain the same throughout any one of processes; the cycle is considered isothermal if temperature is constant, isobaric if pressure is constant, and isochoric or isometric if specific volume is constant. The most efficient type of cycle is one that has only reversible processes, such as the Carnot cycle, which is made up of four reversible processes.

A thermodynamic cycle is a series of thermodynamic processes which returns a system to its initial

state. Properties depend only on the thermodynamic state and thus do not change over a cycle.

Variables such as heat and work are not zero over a cycle, but rather depend on the process.

The first law of thermodynamics dictates that the net heat input is equal to the net work output over

any cycle. The repeating nature of the process path allows for continuous operation, making the

cycle an important concept in thermodynamics.

Example of P-V diagram of a thermodynamic cycle.

If the cyclic process moves clockwise around the loop, then it represents a heat engine, and W will

be positive. If it moves counterclockwise then it represents a heat pump, and W will be negative.

The Dual Combustion Cycle

Modern oil engines known also as diesel engine, use solid injection of the fuel.

The ideal cycle which is used as a basis for comparison is called the dual combustion

cycle or the mixed cycle, and is shown on a p-v diagram in Figure. 3.1 In this cycle, heat

is supplied in two parts; the first part at constant volume and the second in constant

pressure. Hence the name ‘dual combustion’.

Figure 3.1 : p-v diagram

3.2 The dual combustion cycle process.

1. Process 1 to 2 is isentropic compression.

2. Process 2 to 3 is reversible constant volume heating.

3. Process 3 to 4 is reversible constant pressure heating.

4. Process 4 to 5 is isentropic expansion.

5. Process 5 to 1 is reversible constant volume cooling. (rejection of heat)

V1=V5V2=V3

P3=p4

5

43

2

1

V

P

p .vγ=conts

In order to fix the thermal efficiency completely three factors are necessary.

There are the ratio of compression, rv = v1/ v2 ; the ratio of pressure, rp = p3/p2 and the

ratio of volume and cut, rc = v4/v3 .

Then it can be shown that

η=1− 1rvγ−1

[ r p×rcγ−1

(r p−1 )+σr p (r c−1 ) ]The efficiency of dual combustion cycle depends not only on the compression

ratio but also on the relative amount of heat supplied at constant volume and at constant

pressure. The best method of calculating thermal efficiency is to evaluate each

temperature throughout the cycle and then use this equation, η=1−Q2 /Q1 . The heat

supplied, Q1, is calculated using the equation,

Q1=cv (T 3−T 2)+cp (T 4−T 3)

The heat rejected, Q2 , is calculated by Q2=cv (T 5−T 1)

The dual cycle is a better approximation to the modern high speed compression ignition engine than either the Diesel cycle or the Otto cycle.