Otto cycle

Definition

The Otto cycle is a thermodynamic cycle that describes the functioning of a typical spark ignition piston engine, commonly found in automobiles. It consists of two isochoric (constant volume) and two adiabatic (no heat transfer) processes.

5 Must Know Facts For Your Next Test

1. The Otto cycle includes four stages: isochoric compression, adiabatic expansion, isochoric heat rejection, and adiabatic compression.
2. The efficiency of the Otto cycle depends on the compression ratio and the specific heat ratios of the working fluid.
3. The thermal efficiency formula for an ideal Otto cycle is given by $\eta = 1 - \frac{1}{r^{\gamma-1}}$, where $r$ is the compression ratio and $\gamma$ is the specific heat ratio.
4. In real engines, deviations from the ideal Otto cycle occur due to factors like friction, non-instantaneous combustion, and heat losses.
5. The P-V diagram of an Otto cycle forms a distinct loop representing work done during each stage.

Review Questions

• What are the four stages of the Otto cycle?
• How does the compression ratio affect the efficiency of an Otto cycle?
• Write down the thermal efficiency formula for an ideal Otto cycle.

Related terms

Compression Ratio: The ratio of the maximum to minimum volume in a cylinder during a complete engine cycle. Higher ratios generally lead to better efficiency.

Adiabatic Process: A process in which no heat is transferred to or from the working fluid. In an ideal gas undergoing an adiabatic process, $PV^{\gamma} = \text{constant}$.

Thermal Efficiency: A measure of how well an engine converts heat energy into work. For cyclic processes like the Otto cycle, it’s calculated as $\eta = \frac{W_{out}}{Q_{in}}$.