Thermodynamics Cycles

Thermodynamics Cycles

Contents

Recall the working principle of the Otto cycle with the help of p-v and T-s diagrams 1

Calculate the following parameters of the Otto cycle: i. Thermal Efficiency ii. Work done iii. Mean effective pressure iv. Compression ratio 4

Recall the working principle of the Diesel cycle with the help of p-v and T-s diagrams 5

Calculate the following parameters of the Diesel cycle: i. Thermal Efficiency ii. Work done iii. Mean effective pressure 7

Recall the working principle of Dual cycle with the help of p-v and T-s diagram 8

Recall the comparison between Otto, Diesel, and Dual Cycle 10

Recall the working principle of Reversed Carnot cycle with the help of p-v and T-s diagrams 11

Recall the working principle of Bell Coleman or Reversed Brayton cycle with the help of p-v and T-s diagrams 13

Derive an expression for COP of the Bell Coleman cycle 15

Recall the working principle of the Rankine cycle with the help of p-v and T-s diagrams 16

Derive the expression for the Efficiency of the Rankine cycle 18

Recall the working principle of the Otto cycle with the help of p-v and T-s diagrams

The Otto cycle is a type of thermodynamic cycle that describes the operation of a four-stroke internal combustion engine, such as the one used in most vehicles. The cycle consists of four processes: intake, compression, power, and exhaust. The cycle is named after Nikolaus Otto, who invented the four-stroke engine.

The working principle of the Otto cycle can be understood with the help of pressure-volume (p-v) diagrams and temperature-entropy (T-s) diagrams.

In the intake process, the piston moves down and a mixture of fuel and air is drawn into the cylinder. This process is known as the suction stroke and occurs at a constant volume. The pressure and temperature of the gas in the cylinder decrease during this process.

In the compression process, the piston moves up and compresses the fuel-air mixture. This process occurs at a constant temperature and the pressure and temperature of the gas in the cylinder increase.

In the power stroke, the compressed fuel-air mixture is ignited by a spark and undergoes a rapid expansion. This process is exothermic and releases a large amount of heat. The pressure and temperature of the gas in the cylinder increase further, causing the piston to move down and perform work.

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In the exhaust process, the piston moves up and the exhaust gases are expelled from the cylinder. This process occurs at a constant volume and the pressure and temperature of the gas in the cylinder decrease.

The Otto cycle is represented on a pressure-volume diagram as a cycle that traces out a closed loop, with the four processes represented by four distinct points on the loop. On a temperature-entropy diagram, the Otto cycle is represented by a cycle that also traces out a closed loop, with the four processes represented by four distinct points on the loop.

In conclusion, the Otto cycle is a fundamental concept in thermodynamics and is used to understand the operation of internal combustion engines. The cycle can be represented on p-v and T-s diagrams, which provide valuable insights into the thermodynamic behavior of the engine and the relationships between different thermodynamic properties.

Calculate the following parameters of the Otto cycle: i. Thermal Efficiency ii. Work done iii. Mean effective pressure iv. Compression ratio

The Otto cycle is a thermodynamic cycle that describes the operation of a four-stroke internal combustion engine. There are several parameters that can be calculated to characterise the performance of the Otto cycle, including thermal efficiency, work done, mean effective pressure, and compression ratio.

  1. Thermal Efficiency: The thermal efficiency of the Otto cycle is a measure of the amount of energy that is converted into useful work by the engine. It is calculated as the ratio of the work done by the engine to the heat added to the cycle, and is expressed as a percentage. The thermal efficiency of an Otto cycle can be calculated using the following formula:
    η = (W / Qin) * 100%

Where W is the work done by the engine and Qin is the heat added to the cycle.

  1. Work done: The work done by the engine during the Otto cycle is the amount of energy that is converted into useful work. It can be calculated using the following formula:
    W = m * R * T * ln(V2 / V1)

Where m is the mass of the working fluid, R is the ideal gas constant, T is the temperature of the working fluid, V1 is the volume at the beginning of the cycle, and V2 is the volume at the end of the cycle.

  1. Mean effective pressure: The mean effective pressure (MEP) is a measure of the average pressure exerted by the engine over one cycle. It is calculated as the average of the maximum and minimum pressures in the cylinder during the cycle. The MEP is an important parameter in the design of internal combustion engines and is used to determine the size and power of the engine.
  2. Compression ratio: The compression ratio of an Otto cycle is the ratio of the volume of the cylinder at the end of the compression process to the volume of the cylinder at the beginning of the compression process. It is a measure of the degree of compression of the fuel-air mixture in the cylinder and is an important parameter in the design of internal combustion engines. The compression ratio can be calculated using the following formula:
    r = Vmax / Vmin

Where Vmax is the maximum volume of the cylinder and Vmin is the minimum volume of the cylinder.

In conclusion, these parameters are key measures of the performance of an Otto cycle and provide valuable insights into the thermodynamic behaviour of internal combustion engines. The thermal efficiency, work done, mean effective pressure, and compression ratio are all important considerations in the design and optimization of internal combustion engines.

Recall the working principle of the Diesel cycle with the help of p-v and T-s diagrams

The Diesel cycle is a thermodynamic cycle that describes the operation of a four-stroke internal combustion engine, named after the German inventor Rudolf Diesel. The working principle of the Diesel cycle is based on the compression of air in the cylinder to a high pressure, followed by the injection of fuel into the compressed air, which ignites and drives the engine. The Diesel cycle is characterized by its high compression ratio, which allows for a more efficient conversion of heat into useful work.

The Diesel cycle can be represented on a pressure-volume (p-v) diagram and a temperature-entropy (T-s) diagram. The p-v diagram shows the pressure and volume of the working fluid in the engine over one cycle, while the T-s diagram shows the temperature and entropy of the working fluid over one cycle.

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In the Diesel cycle, the four strokes of the engine are:

  1. Intake stroke: During this stroke, the piston moves downward and air is drawn into the cylinder. The pressure in the cylinder decreases and the volume increases.
  2. Compression stroke: During this stroke, the piston moves upward and compresses the air in the cylinder. The pressure and temperature of the air increase, while the volume decreases.
  3. Combustion stroke: During this stroke, fuel is injected into the cylinder and ignites, driving the engine. The pressure and temperature of the working fluid increase, while the volume remains constant.
  4. Exhaust stroke: During this stroke, the piston moves downward and the exhaust gases are expelled from the cylinder. The pressure and temperature of the working fluid decrease, while the volume increases.

In conclusion, the Diesel cycle is a thermodynamic cycle that describes the operation of a four-stroke internal combustion engine. The high compression ratio and efficient conversion of heat into useful work make the Diesel cycle an important consideration in the design and optimization of internal combustion engines. The p-v and T-s diagrams are useful tools for visualizing and understanding the thermodynamic behavior of the Diesel cycle.

Calculate the following parameters of the Diesel cycle: i. Thermal Efficiency ii. Work done iii. Mean effective pressure

The Diesel cycle is a thermodynamic cycle that describes the operation of a four-stroke internal combustion engine, and it is characterized by its high compression ratio and efficient conversion of heat into useful work. To understand the performance of the Diesel cycle, it is important to calculate certain parameters that describe its thermodynamic behavior. These parameters include:

  1. Thermal Efficiency: Thermal efficiency is the ratio of the useful work done by the engine to the amount of heat added to the working fluid. It is a measure of how efficiently the engine converts heat into useful work, and it is an important factor in determining the fuel efficiency of the engine. The thermal efficiency of the Diesel cycle can be calculated using the formula:

η = (Wout / Qin) * 100%

Where Wout is the work done by the engine, and Qin is the heat added to the working fluid.

  1. Work done: Work done is the amount of useful work performed by the engine over one cycle. It is an important parameter in determining the engine’s power output. The work done in the Diesel cycle can be calculated using the formula:

Wout = (V2 – V1) * Pavg

Where V1 and V2 are the volumes of the working fluid at the beginning and end of the cycle, and Pavg is the average pressure during the cycle.

  1. Mean Effective Pressure: Mean Effective Pressure (MEP) is a measure of the average pressure of the working fluid during one cycle, and it is an important parameter in determining the engine’s power output. The MEP can be calculated using the formula:

MEP = (Wout / VT)

Where VT is the total volume of the working fluid during one cycle.

In conclusion, the parameters of thermal efficiency, work done, and mean effective pressure are important in determining the performance of the Diesel cycle. Understanding these parameters is important in optimising the design and operation of internal combustion engines based on the Diesel cycle.

Recall the working principle of Dual cycle with the help of p-v and T-s diagram

The Dual cycle, also known as the Brayton cycle, is a thermodynamic cycle that describes the operation of a continuous flow heat engine, such as a gas turbine. The cycle is characterized by its high efficiency and its ability to produce high power outputs. To understand the working principle of the Dual cycle, it is important to analyze the cycle using pressure-volume (p-v) and temperature-entropy (T-s) diagrams.

The Dual cycle consists of four processes:

  1. Isentropic Compression: The working fluid, usually air, is drawn into the compressor where it is compressed isentropically, meaning that the entropy of the fluid remains constant during the process. This process increases the pressure and temperature of the fluid, which is shown as a vertical line on a p-v diagram and a horizontal line on a T-s diagram.
  2. Heat Addition: The compressed air is then heated by combustion of fuel in a combustor. This process increases the temperature and entropy of the fluid, which is shown as a curved line on a T-s diagram.
  3. Isentropic Expansion: The heated fluid then expands through a turbine, where it performs work on the turbine and its entropy remains constant during the process. This process decreases the pressure and temperature of the fluid, which is shown as a vertical line on a p-v diagram and a horizontal line on a T-s diagram.
  4. Heat Rejection: Finally, the cooled fluid is rejected to the environment, typically through a heat exchanger or a radiator, where it gives up the remaining heat that was not converted into useful work. This process decreases the temperature and entropy of the fluid, which is shown as a curved line on a T-s diagram.

In conclusion, the Dual cycle is a highly efficient thermodynamic cycle that is used to power gas turbines, and it is characterized by its isentropic compression and expansion processes and its heat addition and rejection processes. Understanding the working principle of the Dual cycle is important in the design and optimization of gas turbine systems.

Recall the comparison between Otto, Diesel, and Dual Cycle

The Otto cycle, Diesel cycle, and Dual cycle are three commonly studied thermodynamic cycles in the field of internal combustion engines. Each cycle has its own unique characteristics and operating principles, and a comparison between the cycles can provide insight into their relative performance and efficiency.

  1. Otto Cycle: The Otto cycle is a thermodynamic cycle that describes the operation of a spark-ignition internal combustion engine, such as a gasoline engine. It is characterized by a constant-volume heat addition process and an isentropic compression and expansion process. The Otto cycle has a high compression ratio, typically between 8:1 and 12:1, which allows for efficient combustion of the fuel and air mixture.
  2. Diesel Cycle: The Diesel cycle is a thermodynamic cycle that describes the operation of a compression-ignition internal combustion engine, such as a diesel engine. It is characterized by a constant-volume heat rejection process and an isentropic compression and expansion process. The Diesel cycle has a lower compression ratio, typically between 14:1 and 20:1, which allows for the air to be compressed to a high enough pressure for spontaneous ignition of the fuel.
  3. Dual Cycle: The Dual cycle, also known as the Brayton cycle, is a thermodynamic cycle that describes the operation of a continuous flow heat engine, such as a gas turbine. It is characterized by isentropic compression and expansion processes and heat addition and rejection processes. The Dual cycle has a relatively low compression ratio, typically between 2:1 and 6:1, and relies on high-temperature combustion of fuel to drive the turbine.

In conclusion, each of the three cycles has its own strengths and weaknesses, and the choice between cycles depends on the specific application and design requirements. The Otto cycle is well-suited for gasoline engines, the Diesel cycle is well-suited for diesel engines, and the Dual cycle is well-suited for gas turbines. Understanding the differences between the cycles is important for the design and optimization of internal combustion engines and gas turbine systems.

Recall the working principle of Reversed Carnot cycle with the help of p-v and T-s diagrams

The Reversed Carnot cycle is a theoretical thermodynamic cycle that operates in reverse of the Carnot cycle. The Reversed Carnot cycle can be used to understand the maximum possible efficiency of a heat engine that operates between two temperature reservoirs.