72736 - Aeronautical and Space Propulsion

Learning outcomes

The objective is to give to students the information required to understand the behavior of all the airbreathing propulsion systems.

Course contents

Introduction
Thrust, power, propulsion efficiency. Evaluation with respect the ratio between the vehicle speed and the gas speed exiting the engine.

The propeller
When use of the propeller is preferable. Pitch, geometric pitch angle of the propeller and the angle of attack Skew and rake. Propeller efficiency.
Constant, adjustable and controllable pitch propellers.
Variation of the thrust produced with the rotational speed and propeller diameter. Number of blades.
Matching between propeller and engine.

Reciprocating engines
Introduction to reciprocating engines for aeronautics applications. Theoretical model: Otto and Sabathe cycles. Thermodynamic efficiency variations with compression ratio.
Mean exhaust temperature evaluation for turbo-charging applications.
Torque and power evaluation. Introduction to important engine performance parameters: brake and indicated mean effective pressures, mean piston velocity, stroke/bore ratio.
Combustion model: flame propagation speed and its variation with engine speed.
Knock phenomenon and its implications over the engine design and operation capabilities: limitations to the maximum displacement per cylinder. Fuels and knock: leaded and unleaded fuels, Octan Numbers RON and MON.
Evaluation of the pressure gradient inside the combustion chamber through a combustion model. Variation of the Spark Advance with the engine speed.
Multi-cylinder engines: instantaneous torque production variations and related problems when connecting the engine to a propeller.
Inertia forces evaluation varying the engine architecture (L2, B2, V2).
Engine cooling, knock, inertia forces for the different architecture investigated.
Limitations to the maximum power that can be produced using reciprocating engines.
Supercharging and turbocharging.
Matching between propeller and engine.
Electronic injection and main corresponding control strategies: speed-density, alfa-speed, maf. Maps to bi stored into the Electronic Control Unit (ECU). Advantages related to the electronic injection.
Emissions: catalysts and aftertreatments. EGR. Canister.
Lubrication for reciprocating engines.

Gas turbine engines
Introduction to the main gas turbine engine architectures: turbojet, turbofan and turboprop.
Thrust for airbreathing engines. By-pass ratio. Thrust for engines with high by-pass ratio.
Thermodynamic, propulsion and total efficiencies. Take off thrust and maximum range. Performance, Thrust Specific Fuel Consumption: typical values for ramjet, turbojet, turbofan and turboprop.
Thermodynamics of gas turbine: Optimization of the Brayton cycle, compression ratio variation effects on efficiency and specific work produced, maximum cycle temperature influence on cycle efficiency. Isentropic and polytropic efficiencies for compression and expansion.
Gas turbine engines static components: Intake (sub-sonic and super-sonic), nozzle, combustion chamber.
Matching between compressor and turbine characteristics. Off-design performance evaluation.
Single-shaft and double-shaft engine configurations.

Rockets
Rocket propulsion introduction. Chemical rockets configurations: liquid and solid propellants.

Readings/Bibliography

Recommended readings:
Bettocchi, R., Spina, P.R., - Propulsione aeronautica con turbogas - 2a ed. - Pitagora, 2002.
E. BENINI - Propulsione aerea - Ed. CLEUP
Cohen H., Rogers G.F.C., Saravanamuttoo H.I.H. - Gas Turbine Theory – 5th Ed. – Prentice Hall, 2001

Other readings:
Hill & Peterson - Mechanics and Thermodynamics of Propulsion - Addison-Wesley Publishing Company - New York
Sandrolini S., Borghi M., Naldi, G. – Turbomacchine termiche. Turbine – Pitagora, 1992.
Sandrolini S., Naldi G. – Macchine 1. Fluidodinamica e termodinamica delle turbomacchine – Pitagora, 1997.
Sandrolini S., Naldi G. – Macchine 2. Le turbomacchine motrici e operatrici, Pitagora,1998.

Teaching methods

Theaching is organized in class lectures and numerical exercises.

Attendance is strongly recommended for an improved learning of concepts and notions, but does not affect the final evaluation process.

Assessment methods

The assessment methods consist of an oral part lasting about 1 hour, during which the student must answer three questions covering the entire program.

The evaluation, expressed in thirtieths, will be higher if the student is:

• autonomous in articulating responses to the three questions;
• exhaustive in explaining the arguments;
• precise in representing the functionality of the free-hand sketches.

The module of Propulsione aeronautica e spaziale T (6 CFU) is one of the two that, together with Turbomacchine T (6 CFU), constitutes the integrated course of Propulsione Aerospaziale T (12 CFU). The vote that will be recorded will be calculated with the arithmetic average of the single votes that the student will have obtained in the two modules. If the result of the average presents the decimal number 0.5, the vote will be rounded in excess.

In order to obtain the "30 cum laude" final evaluation, the student must be in one of the following two cases:

• receiving "30 cum laude" in both modules
• obtaining "30 cum laude" in one module and 30 in the other.

The exam dates are comunicated in advance through the AlmaEsami web platform of the University of Bologna.

At the time of the exam the student must carry an identification document.

Teaching tools

The slides used by the teacher are available.
Practical examples and engines are shown in the lab facilities.

Office hours

See the website of Fabrizio Ponti