In an I.C. engine operating on the dual cycle (limited pressure cycle), the temperature and pressure of the working fluid (air) at the beginning of compression are 27°C and 1 bar. The ratio of the maximum and minimum pressures of the cycle is 70 and the compression ratio is 15. The amounts of heat added at constant volume and at constant pressure are equal. Compute the air standard thermal efficiency of the cycle. State three main reasons why the actual thermal efficiency is different from the theoretical value.