Gas Power Cycle | Sahithyan's Notes

Working fluid stays in gas phase throughout the cycle. Used in IC engines and gas turbines using the air-standard assumption.

Air Standard Assumptions

Used to simplify real IC engine analysis.

Working fluid = air behaving as an ideal gas.
Air circulates in a closed loop.
Combustion = external heat addition.
Exhaust = heat rejection.
All processes internally reversible.

Cold Air Standard Assumption

$\gamma$ is assumed to be constant.

Reciprocating Engine

An engine where a piston reciprocates (moves back and forth) inside a cylinder, and that linear motion is converted into rotary motion using a crankshaft.

Intake Valve

A valve that opens to admit the fresh charge (air or air-fuel mixture).

Exhaust Valve

A valve that opens to release combustion products from the cylinder during the exhaust stroke.

Top Dead Centre

Aka. TDC. Minimum volume inside chamber.

Bottom Dead Centre

Aka. BDC. Maximum volume inside chamber.

Stroke

Maximum distance the piston can move. Distance between TDC and BDC.

Displacement Volume

$\text{Displacement Volume} = \text{Piston Area} \times \text{Stroke}$

Clearance Volume

Volume at TDC.

Swept Volume

Volume displaced by the piston as it moves from TDC to BDC.

Compression Ratio

Denoted by $r$ .

r = \frac{V_{max}}{V_{min}}

Mean Effective Pressure

Aka. MEP. A fictitious uniform pressure that gives the same net work as real cycle.

\text{MEP} = \frac{w_\text{net}}{v_\text{max} - v_\text{min}}

Analysis

P-V diagram is used.

Thermal Efficiency

\eta = 1 - \frac{1}{r^\gamma -1}

Here: $\gamma=C_p/C_v$ .