Cork Institute of Technology
Higher Certificate in Engineering in Mechanical Engineering - Award
(National Certificate in Engineering in Mechanical Engineering - Award)
(NFQ – Level 6)
Summer 2005
Mechanical Technology - Thermofluids
(Time: 3Hours)
Answer 5 questions, at least two questions
from Section A and two from Section B and
one other.
Examiners: Ms. M. Kavanagh
Mr. J. Connolly
Mr. R. Simpson
SECTION A
1. Sketch and describe the P-V diagram for the Otto cycle. Sketch a typical indicator
diagram for a four-stroke cycle engine, and discuss briefly how it differs from the ideal
Otto cycle. (6 marks)
A six cylinder, four-stroke cycle, marine oil engine has cylinders of diameter 610mm
and a piston stroke 1250mm. When the engine speed is 2revs/s it uses 340kg of fuel oil
of calorific value 44.2MJ/kg in one hour. The cooling water amounts to 19200kg/hour,
entering at 15oC and leaving at 63oC. The indicated mean effective pressure is
775kN/m2 and the mechanical efficiency is 80%. Determine:
(a) The indicated power. (3 marks)
(b) The brake power. (2 marks)
(c) The percentage of energy supplied per kg of fuel lost to the cooling water.
(3 marks)
(d) The brake thermal efficiency. (3 marks)
(e) The brake mean effective pressure. (3 marks)
Take the specific heat capacity of water as 4200J/kgK.
