Overview of Gas Turbine and Reciprocating Engine Cycles

Reciprocating Engines

A 4-stroke engine operates with the following strokes: Intake, Compression, Expansion, Exhaust.

Air-Standard Otto Cycle

An idealized cycle assuming an ideal gas and omitting suction and part of the exhaust stroke, consisting of: 1-2: Isentropic compression, 2-3: Constant volume heating, 3-4: Isentropic expansion, 4-1: Constant volume cooling.

Modeling Gas Turbine Power Plants

Gas turbines can operate in two configurations: Open Gas Turbine, Closed Gas Turbine.

Air-Standard Brayton Cycle

An idealized cycle with air as an ideal gas, assuming reversible processes: 1-2: Adiabatic compression (isentropic) through the compressor, 2-3: Constant pressure heating, 3-4: Adiabatic expansion (isentropic) through the turbine, 4-1: Constant pressure cooling.

Cold Air-Standard Analysis for Brayton Cycle

Neglects temperature variation and assumes constant specific heats for simplification. Efficiency depends on the compressor-pressure ratio.

Effect of Compressor-Pressure Ratio

Efficiency increases as the pressure ratio (p2/p1) across the compressor increases. High pressure ratios are limited by the maximum allowable temperature at turbine blades (T3). A higher pressure ratio increases cycle efficiency but may reduce cycle work.

Regenerative Gas Turbine

A regenerator uses exhaust gas heat to preheat air entering the combustion chamber, which: Reduces fuel consumption, Increases efficiency (h), Leaves turbine work unchanged.

Gas Turbines for Aircraft Propulsion

In turbojet engines, ideal analyses assume: Isentropic processes for a-1, 1-2, 3-4, and 4-5. Constant pressure processes for 2-3 and 5-a.