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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2011
Module Title: Thermofluids
Module Code: MECH 6033
School: Mechanical and Process Engineering
Programme Title: Bachelor in Engineering in Mechanical Engineering Bachelor in Engineering (Honours) in Sustainable Engineering
Programme Code: EMECH_7_Y2, ESENT_8_Y
External Examiner(s): Dr. E. Ahearne, Mr. M. McKeon Internal Examiner(s): Ms. Maria Kavanagh, Mr. Michael Walsh
Instructions: Answer any 3 questions. Please tick off which questions you attempt on the front of your script
Duration: 2 Hours
Sitting: Autumn 2011
Requirements for this examination: Steam Tables, Log Tables
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination. If in doubt please contact an Invigilator.
Q1 Combustion a) Sketch a typical indicator diagram for a 4 stroke petrol engine and label each stroke of the cycle on the diagram. Identify the work in and work out processes Identify the process that can be considered a constant volume process and state why this is. (10 marks)
b) A 4 cylinder, 4 stroke petrol engine has a bore diameter of 100mm and stroke of 135mm. During a test with an engine speed of 16.5revs/sec the fuel consumption was recorded to be 2.5kg/hr. The calorific value of the fuel is 45.5MJ/kg, the indicated mean effective pressure is 550kN/m^2 and the mechanical efficiency is 80%
Determine: i) The indicated power and brake power of the engine (11 marks) ii) The brake specific fuel consumption (4 marks) iii) The thermal efficiency on a brake and on an indicated power basis (8 marks)
Q2 Expansion and Compression of Gases
0.15M^3 of air is compressed from a pressure of 100kN/M^2 and a temperature of 20°C to a pressure of 1.5MN/M^2 according to the law PV1.2=C Sketch this on a PV diagram (3 marks)
Find i) The work done during compression. Is the work done by or on the gas? (10 marks) ii) The mass of the gas in the cylinder? (5 marks) iii) The change in internal energy (10 marks) iv) The heat transferred during compression Is this heat supplied or rejected? (5 marks)
cv = 7180 J/kgK and R=2870 J/kgK
