If the compression ratio of an engine working on Otto cycle is Increased from 5 to 7, find the percentage increase in thermal efficiency.
5. (a) If the compression ratio of an engine working on Otto cycle is
Increased from 5 to 7, find the percentage increase in thermal
efficiency.
(b) Derive an expression for thermal efficiency of ideal Brayton cycle.
(c) In an engine working on the ideal Otto cycle, the pressure and
temperature at the beginning of compression are 100 kPa and 40 °C
respectively. The ratio of specific heat capacities is 1.4. If the airstandard efficiency of the engine is 50%, determine
(i) The compression ratio.
(ii) The pressure and temperature at the end of adiabatic
compression.
(6a) Explain and discuss in your own words, the following three concepts in
combustion: stoichiometric mixture of air and fuel, weak mixture and rich
mixture. Explain their importance in combustion applications.
(6b) A gas fuel has the following volumetric composition:
Propane C3H8: 73 %
Butane C4H10: 5 %
Ethane, C2H6: 3%
Nitrogen N2: 19%
(i) Write out the complete combustion equations for all the
combustible constituents individually.
(ii) Calculate the stoichiometric air to fuel (A/F) ratio on a volume
basis. Explain all steps of your work.
(iii) Determine the wet volumetric analysis of the combustion
products when 20% excess air is supplied. Explain all steps of
your work.
(iv) Determine the dry volumetric analysis of the combustion
products when 20% excess air is supplied. Explain all steps of
your work.
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