26 Jun BRIEFLY DESCRIBE THE MORSE TEST FOR MEASURING THE INDICATED POWER OF A MULTI-CYLINDER ENGINE.
a) Show that the logarithmic mean area Am of a cylinder of unit length, internal radius r1, external radius r2, thermal conductivity k, whose inside and outside surface temperature are t1 and t2 respectively are given by:
A_m=(2p(r_2-r_1))/(l_n r_2/r_1 ) (6 marks)
b) Wet steam at 20 bar is carried in a steel steam mains of outside diameter 140mm, thickness 6mm and length 8m. The mains is insulated with an inner layer of diatomaceous earth 38mm, and an outer layer of magnesia 30mm thick. The inside heat transfer coefficient is 8.5 W/m2K and that of the outside surface lagging is 18W/m2K. The thermal conductivities of the diatomaceous earth, magnesia and steel are 0.09, 0.06 and 48W/mK, respectively.
Determine:
The rate of heat loss.
The temperature of the outside surface of the lagging. (14 marks)
a) i) With the aid of a graph show how the indicated power and brake power vary with the engine speed for a variable speed engine and explain the general shape of the graph.
ii) State any FOUR advantages of super charging of an internal combustion engine. (51/2 marks)
b) Briefly describe the Morse Test for measuring the indicated power of a multi-cylinder engine. (5 marks)
c)A four-cylinder petrol engine has an output of 16.5KW at a speed of 2400 rev/min. A Morse Test is carried out and the brake torque readings are 112 N, 107N, 105N and 109N respectively. The torque arm has a length of 0.4m and the fuel consumption is 8 litres per hour. The specific gravity of the fuel is 0.8 and the calorific value is 45MJ/kg.
Determine:
The brake thermal efficiency
The specific fuel consumption on brake power basis. (91/2 marks)
a) Explain the following terms as applied to a spark ignition engine:
“rich mixture”
“weak mixture” (2 marks)
b) Distinguish between higher and lower calorific values of a fuel. (2 marks)
c)The dry exhaust gas analysis by volume during a test on an engine was 11% CO2, 1.8O2, 3.2CO and the remainder was nitrogen. The flue gases were exhausted to the atmosphere at a pressure of 1.013 bar, temperature of 3250C and at a velocity of 8m/s. The fuel had a composition by mass:- 85.8% carbon, Hydrogen 14.2%. The total mass of fuel burnt was 4kg/hr.
Determine:
The air/fuel ratio by mass
The mixture strength
The exhaust pipe diameter.
Take R=290J/kgK. (16 marks)
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