Question

QUESTION 2 You are a Project Engineer in a well-known engineering consulting company. One of your clients, Dato' Ang Chun Kit is very keen to sponsor a group of UCSI students to represent Malaysia in an Innovative Gas Power Cycle Competition, to be held in Japan. The main objectives are to build a prototype which operates at promisingly high and stable efficiencies, but at the same time can be economically and/or environmentally attractive. In your first meeting with Dato' Ang, you have presented the conceptual ideas of the prototype to be operated on cycles below: Stirling Cycle Ericsson Cycle Brayton Cycle By analysing all three cycles above in terms of working principles, advantages, and disadvantages, identify the most suitable cycle for Dato' Ang's sponsorship. With reasonable arguments, justify why the prototype operated on that cycle is proposed, and how the cycle can fulfil all the objectives.

Answer 1

Stirling Cycle: In Stirling cycle, Carnot cycle's compression and

expansion isentropic processes are replaced by two constant-volume

regeneration processes. During the regeneration process heat is transferred

to a thermal storage device i.e. regenerator during one part and is

transferred back to the working fluid in another part of the cycle.

The cycle consist of 4 different processes namely:

• 
  Isothermal expansion process (1-2): During this heat addition from
  
  external source takes place.
  
• 
  Constant volume heat transfer (2-3): During this internal heat transfer
  
  from gas to regenerator takes place.
  
• 
  Isothermal compression (3-4): During this heat rejection to the external
  
  sink takes place.
  
• 
  Constant volume heat transfer (4-1): During this internal heat transfer
  
  from the regenerator to the gas takes place.
  

T P TH v=const. 2 Qin QRE Th=const. v=const. Qres 3 4 TL 4 Qout Qout ذرا TL = =const.

Advantages:

• 
  Few moving parts.
  
• 
  Limiting wear on components.
  
• 
  Low emissions of NOx and unburned fuel.
  
• 
  Fuel versatility.
  

Disadvantages:

• 
  High cost and reliability issues.
  
• 
  Low electrical efficiency.
  

Performance, Efficiency and Suitability:

• 
  Stirling cycle has high theoretical efficiencies.
  
• 
  Current operational efficiencies of Stirling cycle is around 12 to 20 percent,
  
  due to material and design limitations.
  
• 
  Stirling engines are suitable for residential or portable applications.
  
  The small size and quiet operation means that they would integrate
  
  well into a domestic environment.
  
• 
  The high costs and small size of Stirling engines limits the applicability
  
  of this technology in developing regions.
  

Ericsson Cycle: The Ericsson cycle is an altered version of the Carnot

cycle in which the two isentropic processes featured in the Carnot cycle

are replaced by two constant-pressure regeneration processes.

The cycle consist of 4 different processes namely:

• 
  Isothermal expansion process.
  
• 
  Constant pressure or isobaric heat rejection process.
  
• 
  Isothermal compression process.
  
• 
  Constant pressure or isobaric heat absorption process.
  

T3=T4 Isothermal Pressure Isothermal Temperature Constant Pressure Constant Pressure T2=1 2 Volume Entropy

• 
  The theoretical efficiencies of both, Ericsson and Stirling cycles acting
  
  in the same limits are equal to the Carnot efficiency for same limits.
  

Brayton Cycle: According to the principle of the Brayton cycle, air

is compressed in the turbine compressor. The air is then mixed with

fuel, and burned under constant pressure conditions in the combustor.

The resulting hot gas is allowed to expand through a turbine to perform work.

The Brayton cycle consists of four basic processes:

• 
  Isentropic compression process.
  
• 
  Constant pressure heat addition process.
  
• 
  Isentropic expansion process.
  
• 
  Constant pressure heat rejection process.
  

P 2 3 S = const. S = const. 4 T P =const. N 4 P=const. S

Advantages:

• $\textup{It has great reliability especially where power output required is high.}$
• $\textup{It requires low cost and consumption of lubricating oil.}$
• $\textup{It can make use of different forms of fuel ranging from synthetic oil to}$$\textup{natural oil.}$
• $\textup{It emits low toxic emission.}$

$\textbf{Dis-advantages:}$

• 
• $\textup{It is less responsive to demand of change in power.}$