Question-3 a) Sketch the p-v diagrams for ideal air standard Otto and diesel cycles indicating the volume at top dead centre and bottom dead centre. (10 marks) b) How does the efficiency of an ideal air standard Otto cycle depend upon the compression ratio for the engine and what places limits are placed upon the operating conditions which limit the overall ideal efficiency of an ideal air standard Otto cycle (5 marks) c) An ideal air standard Otto cycle operates with a bore of 5cm, a swept length of 10cm and a clearance volume of 28cm3. Calculate the efficiency. (10 marks) d) If a ideal air standard Otto cycle operates at the same compression ratio as an ideal air standard Diesel cycle, which one will have the higher efficiency? What two factors result in a real Diesel engine typically having a higher efficiency than a petrol engine (5 marks) The composition of air in this question may be taken as 79% Nitrogen and 21% Oxygen. a) Petrol can be approximated as having the chemical formula of C8H18. Derive the chemical equation for this idealised version of petrol burning in a stoichiometric quantity of pure oxygen and calculate the adiabatic flame temperature rise (11 marks) b) In practice petrol is burnt in air rather than pure oxygen. Derive the chemical equation for this idealised version of petrol burning in a stoichiometric quantity of air and explain the advantages and disadvantages of burning a C8H18 with excess air (i.e. lean) (9 marks) c) Derive the chemical equation for burning C8H18 with pure 10% excess air and explain the difficulties in designing a combustor burning a lean pre-mixed mixture of fuel and air and how these can be overcome. (10 marks) 8 \begin{tabular}{|c|c|c|c|c|} \hline Product & Formul a & Structure & Heat capacity/ kJkmol1K1 & Molecula r mass/ kgkmol1 \\ \hline Water & H2O & & 75.327 & 18.02 \\ \hline air/ nitrogen & N2 & & 29.9 & 28.01 \\ \hline carbon monoxide & CO & & 28.01 & 28 \\ \hline oxygen & O2 & & 31.998 & 32 \\ \hline \end{tabular}