__Constant Volume Cycle- __

At point 1, the air in the cylinder is initially corresponding to P_{1}, V_{1, } and T_{1 }(pressure, volume, and absolute temperature). The piston compresses the air adiabatically during the compression stroke; and at point 2 let the condition of air be P_{2}, V_{2}, T_{2}. The air now occupies the clearance volume of the cylinder. A hot body is then brought into contact with the cylinder end such that the heat is supplied at a constant volume. This increases the pressure and temperature of the air, corresponding to P_{3}, and T_{3}. Here V_{3 }= V_{2}.

_{4}, V

_{4}, and T

_{4}. A cold body is then brought in contact with the cylinder end such that the pressure drops at constant volume, corresponding to the conditions P

_{1}, V

_{1}, and T

_{1}. Here V

_{4}= V

_{1}. Thus, The air finally returns to its original condition and the cycle is complete. For a given compression ratio, the Otto cycle is more efficient than the Diesel cycle.

__The efficiency of the Constant Volume Cycle- __

The working medium is pure air which does not undergo any chemical change. It is simply heated and cooled to undergo a cycle, which consists of the following operations —

1-2 Adiabatic compression.

The operation of the Otto cycle is as follows. Let the air is filled in the cylinder and the condition of air (pressure, volume, and absolute temperature) initially at point 1 are P_{1},

V_{1}, and T_{1}. The piston compresses the air adiabatically from V_{1 }to V_{2}. At the end of compression at point 2, the conditions of air are P_{2},

V_{2}, and T_{2}. Here the air occupies the clearance volume of the cylinder. Now, the air is heated at constant volume by bringing a hot body in contact with the cylinder. This causes to rise the pressure from 2 to 3. At point 3, the conditions of air are P_{3},

V_{3}, and T_{3.} Note that V_{2}

= V_{3}. Now, the hot body is removed and the air expands adiabatically from point 3 to 4. At point 4, the conditions of air are P_{4},

V_{4}, and T_{4}. Now, the air is cooled at constant volume by bringing a cold body in contact with the cylinder. This causes to drop in the pressure from point 4 to 1. At point 1, the air finally returns to its original conditions P_{1},

V_{1}, and T_{1}. Here V_{1}

= V_{4. }Thus, the cycle is complete.

Note that in an adiabatic process (also known as an isentropic process) no heat is supplied or rejected, i.e., the gas neither receives nor gives out heat. The gas expands thereby doing external work. For an adiabatic expansion, the following three conditions must be satisfied :

In an adiabatic expansion PV^{Y }= constant.

__Characteristics of the Otto Cycle- __

The efficiency depends on:

- Compression ratio,
*r.* - The ratio of the specific heats,
*y*.

*pv.*

### Assumptions:

1. The working fluid is not subjected to any chemical reaction. It is simply heated and cooled and used over and over again.

4. The working fluid is a perfect gas following the gas laws and has constant specific heat.

5. The heating and cooling strictly take place at constant volume.

6. The suction and exhaust take place at atmospheric pressure.

Do comment here