a$)$ State three $(3)$ essential differences between the processes of the ideal Otto cycle and those of an actual spark $-$ ignition intermal combustion engine. $(6$ marks$)$

b$)$ In a petrof engine, compression starts with a pressure of $1\mathrm{.}035$ bar and temperature of $40C$ and finishes with a pressure of $14$ bar $.$ The compression ratio is $7.$ The maximum pressure in the cycle is $30$ bar. Assuming the gas in the cylinder to have properties of air and using a $p-v$ diagram find;

i$)$ the index $($ n $)$ to the lavy of compression of form $p{v}^{**}=$ constant and,

ii$)$ the heat release to the gas during combustion per kg of gas.

$(7$ marks$)$

$(7$ matro$)$

Assume the specific heat at constant volume for air as$,c,=0\mathrm{.}718k\frac{J}{k}g.$