One method of reducing the maximum temperature in an engine is to run with a rich mixture. A spark-ignition engine with a compression ratio of 10:1, operating on the Otto cycle, runs on a rich mixture of octane and air, with an equivalence ratio of 1.2. The trapped conditions are 1 bar and 300 K and the index of compression is 1.4. Calculate, taking into account dissociation of the carbon dioxide and water vapour, how much lower the maximum temperature is under this condition than when the engine was operated stoichiometrically. How has dissociation affected the products of combustion? What are the major disadvantages of operating in this mode? (See Chapter 10, P10.8.)
P10.8:
A mixture of propane and air with an equivalence ratio 0.9 (i.e. a weak mixture) is contained in a rigid vessel with a volume of 0.5 m3 at a pressure of 1 bar and 300 K. It is ignited and after combustion the products are at a temperature of 2600 K and a pressure of 9.06 bar. Calculate
(a) the amount of substance in the reactants;
(b) the amount of substance in the products and
(c) the amount of substance in the products per unit amount of substance supplied in the fuel.