Air Standard Cycle of an IC Engine

Air Standard Cycle (Otto Cycle)

Aim: To develop a MATLAB script that profiles the air standard cycle followed by an IC engine, as described by the traditional thermal Otto cycle, on a P-V diagram. To develop a script replicating the isentropic expansion and compression cycle of the trace volume for varying crank-angels for compression and expansion strokes. Finally, determine the thermal efficiency of the engine cycle.

Method: The Otto cycle comprises of four processes, states 1-2 represent the Isentropic compression, states 2-3 represent constant volume heat addition, states 3-4 represent Isentropic expansion, and finally, states 4-1 represent the constant volume heat rejection. Thereafter, the script fundamentally utilizes the thermodynamic relationships governed by the four processes to determine the characteristic parameters of volume, pressure, and temperature at the four key states, namely, 1,2,3, and 4.

1. Engine geometry such as bore diameter, stroke length, compression ratio, and connecting rod length were utilized to determine the swept and clearance volume of the IC engine.
2. Thereafter, fluid volume at state 1 was determined as the sum of clearance and swept volumes and volume at state two was assigned value of clearance volume.
3. Next, using input parameters of state 1 temperature and pressure, and state 3 temperature, isentropic gamma relations and ideal gas law were utilized to determine the volumes, pressures, and temperatures for the remainder of the states.
4. A function was defined to determine the trace volume for varying crank angels for the compression and expansion strokes. (180° to 0° and 0° to 180°, respectively)
5. Thereafter the function was called in the main script and a real-time profile for the trace volumes of compression and trace volumes of expansion are attained.
6. Subsequently, isentropic gamma relations are utilized to attain a real-time profile of the expansion and compression stroke pressures of the crank-shaft.
7. Consequently, the pressure and volumes of the four states were plotted, along with the real time pressure-volume profile of the compression and expansion strokes.
8. Thus, a P-V diagram for the air standard cycle and one synonymous of the Otto cycle is attained.
9. Finally, the compression ratio is utilized to compute the thermodynamic efficiency of the IC engine.

P-V Diagram:

Code:

Access code files at the following link to shared one-drive

https://drive.google.com/open?id=1gx54UXvpvHu2N7t0rpc6TxBX9B-4QR3W