Gas Turbine Engine – Turbojet

Uses for Gas Turbine Engines

Gas Turbine Ideal Thermodynamic Cycle IDEAL SITUATION Ideal Brayton Cycle P Gas turbine engine again acts as a ‘heat engine’. Heat added to gas through combustion is converted to useful work. Work Out Work In V

Gas Turbine Thermodynamic Cycle Inlet + Compressor P Turbine + Nozzle Work Out Work In Combustor V

Types of Gas Turbine Engines Axial Centrifugal

Turbine ● Engine thermal efficiency is optimized by increasing the turbine inlet temperature, but there is a limit. ● Current turbine exhaust temperatures ~ 1350° C ● Special materials and active cooling used to prevent melting of blades. TURBINE BLADES

Port Fuel Injected 4-Stroke Overall Comparison BSFC: Brake Specific Fuel Consumption (lb fuel / hour / hp) TYPE CATEGORY BSFC DIESEL Industrial / 4-Stroke 0.26-0.34 Other 4-Stroke 0.28-0.36 2-Stroke 0.32-0.38 SI-ENGINE Automotive Port Fuel Injected 4-Stroke 0.40-0.48 Carbureted 4-Stroke 0.48-0.60 Automotive 2-Stroke 0.55 + GAS TURBINE Sample – Rolls Royce MT30 0.35

Thermal Efficiencies Better Efficiency at High Power Output? Thermal 50% Gas Turbine Diesel 25% Otto, Rankine % Full Power 50% 100%

Gas Turbine Performance Advantages Disadvantages Large power-to-weight ratio (ideal for aircraft) Small size (compared to diesel at same power output) High RPM – advantage for power generation Provides high speed exhaust – ideal for high- speed air travel. Expensive Difficult to design and maintain Operates only at high RPMs – gas guzzler !! Not good for rapid changes in load / speed

MiniLabTM Gas Turbine Power System (1) Start Procedure https://www.youtube.com/watch?v=kzGAAP3GcYc

MiniLabTM Gas Turbine Power System (2) Compressor Analysis – compressor pressure ratio, power required, rotational speed and compressor efficiency Turbine Analysis – work and power developed, expansion ratio and turbine efficiency Brayton Cycle Analysis – mass flow rate, inlet and exit velocity, station temperature and pressures, combustion and thermal efficiency, specific fuel consumption and power/thrust developed Combustion Analysis – excess air and fuel-air ratio General Analysis – diffuser and nozzle performance and efficiency

SR-30 – Compact Turbojet Engine Single Stage Centrifugal Flow Compressor Reverse Flow Annular Combustor Engine Diameter: 17 cm Engine Length: 27 cm Single Stage Axial Flow Turbine

Engine Sensor Locations Design Max. RPM: 87,000 Mass Flow: 0.5 kg/s Design Max. Thrust: 178 N (40 lbf)

Control Panel and Data Acquisition All data needed for the analysis assignments can be downloaded into an Excel file. You must bring a thumbdrive to save your data to.

Brayton Cycle Analysis

Experimental and Requirements – Brayton Cycle Thrust Specific Fuel Consumption (TSFC) Analysis: Select at least four RPM settings (from low to highest operating RPM in the range of 40,000‒80,000 RPM) for your run. Calculate Thrust Specific Fuel Consumption at each RPM setting. Determine the power settings that offer the best and worst TSFC. System Analysis: For a chosen RPM, conduct Brayton cylce analysis. Determine the state of each cycle point the specific work done by the compressor the specific energy added by the fuel the specific work of the turbine the specific work done by the cycle the thermodynamic efficiency of the cycle

Things to Study* Air-Standard Otto Cycle and Brayton Cycle Work Mean Effective Pressure and Back Work Ratio Thermal Efficiency Effect of Compression Ratio Reacting Mixtures and Combustion Complete Combustion Stoichiometric Coefficients Air-Fuel Ratio Enthalpy of Formation Enthalpy of Combustion Higher and Lower Heating Values Determination of Adiabatic Flame Temperature *: M.J. Moran and H.N. Shapiro, Fundamentals of Engineering Thermodynamics, Chapters 9 &13.