The air standard Otto cycle consists of
Two constant volume and two isentropic processes
Understanding the Air Standard Otto Cycle Processes
The air standard Otto cycle is a thermodynamic cycle that models the process in a typical spark-ignition internal combustion engine. It is an idealized cycle, meaning it makes certain assumptions to simplify the analysis, such as assuming air is the working fluid and combustion is instantaneous heat addition.
The air standard Otto cycle consists of four distinct processes:
- Isentropic Compression (Process 1-2): The piston moves from bottom dead center (BDC) to top dead center (TDC), compressing the air. This process is assumed to be reversible and adiabatic (isentropic), meaning there is no heat transfer and no irreversibilities.
- Constant Volume Heat Addition (Process 2-3): At TDC, the volume is constant. Heat is added to the working fluid, simulating the combustion of the fuel-air mixture. This causes a rapid increase in pressure and temperature.
- Isentropic Expansion (Process 3-4): The hot, high-pressure gas expands, pushing the piston from TDC back down to BDC. This is the power stroke. Like compression, this process is assumed to be reversible and adiabatic (isentropic).
- Constant Volume Heat Rejection (Process 4-1): At BDC, the volume is constant. Heat is rejected from the working fluid, simulating the opening of the exhaust valve and blowdown. This causes the pressure to drop back to the initial state.
Thus, the air standard Otto cycle is composed of two constant volume processes (heat addition and heat rejection) and two isentropic processes (compression and expansion).
We can summarize the processes:
| Process | Description | Type |
|---|---|---|
| 1-2 | Compression | Isentropic (Constant Entropy) |
| 2-3 | Heat Addition | Constant Volume |
| 3-4 | Expansion | Isentropic (Constant Entropy) |
| 4-1 | Heat Rejection | Constant Volume |
Based on this breakdown, the air standard Otto cycle includes two constant volume processes and two isentropic processes.
Important Questions from Otto Cycle
Otto cycle is a constant ________ cycle.
In an air standard Otto cycle, the compression ratio is 7. Find the cycle efficiency
Which of the following statements is incorrect?
Which of the following cycle is used in spark ignition (SI) engine?
In actual four-stroke petrol engine ignition takes place when the piston approaches.
