MASTER'S THESIS Performance Prediction of a Valved and Valveless Pulse-jet Engine Running on Alternative Fuel Johanna Åstrand 2014 Master of Science in Engineering Technology Space Engineering Luleå University of Technology Department of Computer Science, Electrical and Space Engineering Master's Thesis Performance Prediction of a Valved and Valveless Pulse-jet Engine Running on Alternative Fuel JOHANNA ASTRAND˚ Master of Science Programme in Space Engineering Aerospace Engineering Lule˚aUniversity of Technology Department of Computer Science, Electrical and Space Engineering Lule˚a,Sweden Monash University Department of Mechanical and Aerospace Engineering Melbourne, Australia October 21, 2014 - To Johan - 3 March 2014 iii Abstract Pulse-jet engines have gone from being developed by engineers and scientist for military use to being developed in home workshops to power model aircraft. The interest for the pulse-jet have in the last years increased and are now researched in companies and at university's to find out if its suitable for UAV's. The modern pulse-jet is cheap to manufacture but has the disadvantage of being very fuel insufficient and the performance could be improved. The valved engine usually runs on liquid fuel such as petrol, which is expensive and is quite bad for the environment there for researching if the engine could run on a cheaper and more environment friendly fuel without redesigning the engine is highly attractive. The valveless engine are usually designed to be running on gas such as propane. This project aims to investigate how Dynajets Redhead engine and the Lady Anne Boleyn engine, designed by Larry Cottrill, performance is affected when running on alternative fuel. The fuels tested were petrol mixed with different amount of ethanol and propane as gas alternative. To predict the performance of the engines two different model were made to fit each of the engine designs. The models were built up with Helmholtz resonators and frequency in pipes equations to predict the combustion frequency. Performance parameters for each blend where collected during experimental runs using several monitors and readers. The collected performance parameters is the frequency, exhaust temperature, thrust and fuel flow. The Redhead engine were ordered from a retailer and the Lady Anne Boleyn engine were designed and manufactured in-house. An experimental test rig where built and on it all monitors and readers was installed, also designed was a liquid fuel delivery system and for the gas an existing delivery system were used. During the project it was concluded that Helmholtz resonator and pipe equations worked to predict the frequency of the Redhead engine but no conclusion could be made for the Lady Anne Boleyn engine due to lack of successful runs. With low percentage of ethanol added to the petrol the Redhead engine almost kept its maximum performance and also lowered the fuel flow in comparison with when running on pure petrol. v Contents 1 Introduction 1 1.1 Pulse-jet History . .2 1.2 Engine Theory . .2 1.2.1 Valved Pulse-jet . .3 1.2.2 Valveless Pulse-jet . .3 1.3 Design Variations . .4 1.3.1 In-line Systems . .4 1.3.2 Linear Systems . .5 1.3.3 U-shape Systems . .5 1.3.4 Effects . .6 1.4 The Project . .6 1.4.1 Project Definition . .6 1.4.2 Project Goals . .7 1.4.3 Project Process . .7 2 Theory 8 2.1 Basic physical concepts . .8 2.1.1 The Vena Contracta Effect . .9 3 Method 11 3.1 Engine Design . 11 3.1.1 Valveless . 11 3.1.2 Valved . 14 3.2 Ignition System . 15 3.3 Air Start-up System . 16 3.4 Fuel System . 16 3.4.1 Liquid Fuel . 16 3.4.2 Gas Fuel . 17 3.4.3 Fuel mixtures . 19 3.5 Measuring Instruments . 19 3.5.1 Load Cell . 19 3.5.2 Microphone . 20 vii 3.5.3 Thermocouple . 21 3.6 Engine run procedure and data collection . 22 3.6.1 Starting the engine . 22 3.6.2 Collecting data . 22 3.6.3 Engine shut down procedure . 22 3.7 Processing recorded data . 22 3.7.1 Experimental data post-processing . 22 3.7.2 Prediction model . 23 4 Results 24 4.1 Valved Redhead Engine . 24 4.1.1 Experimental results . 24 4.1.2 Numerical results . 31 4.2 Valveless Lady Anne Boleyn Engine . 32 5 Summary and Conclusions 34 6 Future Work 35 A Drawings 36 B MATLAB code 40 C Result tables 48 viii Preface This thesis is the final project for the Master of Science in Space Engineering degree focusing in Aerospace Engineering at the Department of Computer Sci- ence, Electrical and Space Engineering (SRT) at Lule˚aUniversity of Technology (LTU). This project was conducted in Melbourne, Australia, at the Department of Mechanical and Aerospace Engineering at Monash University. The supervisor for the project was Associate Professor Damon Honnery, Monash university. The examiner at LTU was Associate Professor Lars-G¨oranWesterberg. I would like to thank A/Prof. Damon Honnery for the opportunity to conduct my project at Monash University and for all the guidance and help he has given me. I want to give extra thanks to Edward Kuo for all the help at the lab and support during the project. A big thank to Juliann Pavlekovich-Smith for all the help on my arrival to the university and for the help to finding accommodation for my last weeks in Melbourne. Furthermore I would like to thank Angpannefreningens˚ Forskningsstiftelse, Sven Molin for all the help and Helen Fox at Monash HR Imigration for helping me with my visa. Finally, I would like to thank my family and friends for all their encourage- ment and support, its because of them that i have come this far. Special thanks to my mum Inga and Heinze for taking the long trip to Australia to visit me so we could share some of the adventure. Johanna Astrand˚ Melbourne, Australia ix List of Figures 1.1 Marconnet's valveless engine design.[2] . .2 1.2 Cross-section of a valved pulse-jet engine. .3 1.3 Combustion cycle for a valveless pulse-jet engine[4]. .4 1.4 Schubert in-line valveless pulse-jet design [5]. .5 1.5 Chinese CS valveless pulse-jet design[5]. .5 1.6 Lockwood-Hiller U-shape pulse-jet engine [5]. .6 2.1 Streamline patterns for Vena contracta for two different intakes. 10 3.1 CAD image of the modified focussed wave engine called Lady Anne Boleyn. In the image it can be seen a hole to the left where the spark plug is to be mounted. 12 3.2 Combustion chamber with lid. 13 3.3 Intake with flare etc. 13 3.4 Exhaust pipe designed as a divergent-convergent-divergent nozzle to increase the gas flow velocity. 14 3.5 Redhead pulse-jet engine with its typical red intake. 15 3.6 Engine intake with the fuel flow regulator with the fuel pipe con- nected. 15 3.7 Liquid fuel system set-up . 17 3.8 Gas fuel system: 1. Solenoid valve, 2. Flow readers, 3. Switches for ignition and power to valve and 4. Air and fuel regulators . 18 3.9 Set-up of the air and gas lines to the intake of the valveless engine. 18 3.10 Calibrations with known weights pulling in the load-cell . 20 3.11 G.R.A.S 46BE 1/4" free-field microphone. 21 4.1 Fuel tank mass and thrust recordings from one run plotted against each other. 25 4.2 Exhaust temperature for different fuel blends . 26 4.3 Frequency peak to the left and two harmonic peaks to the right. 27 4.4 Combustion frequency for different fuel blends . 28 4.5 Close-up on recorded thrust data from the load-cell . 29 4.6 Average thrust for different fuel blends . 30 xi 4.7 The fuel flow for three different fuel blends. 31 4.8 Experimental recorded frequency and numerical frequency. 32 xii List of Tables 3.1 Dimensions of the manufactured valveless pulse-jet engine ..... 12 3.2 G.R.A.S 46BE features ........................ 21 4.1 Numerical prediction of combustion frequency for Valveless Lady Anne Boleyn Engine running on Propane .............. 33 xiii Nomenclature Abbreviations FAR Fuel-Air Ratio FFT Fast Fourier Transformation FWE Focused Wave Engine LTRAC Laboratory for Turbulence Research in Aerospace and Combustion LTU Lule˚aUniversity of Technology SRT Department of Computer Science, Electrical and Space Engineering UAV Unmanned Aerial Vehicles VTOL Vertical take-off and landing Commonly used symbols c Speed of sound [m/s] f Frequency [Hz] F Average thrust [N] γ Heat capacity ratio [-] L Length [m] m_ Air mass flow rate [kg/s] m_ f Fuel mass flow rate [kg/s] p Static pressure [Pa] R Specific gas constant [J/kgK] ρ Density [kg/m3] S Cross-section area [m2] T Temperature [K] V Combustion chamber volume [m3] Indexes burnt Burnt fuel/air mixture cold Cold fuel/air mixture e Exhaust i Intake v Valved engine vl Valveless engine Constants γcold 1.4 - R 287 [J/kgK] Rg 290.9 [J/kgK] 3 Vv 0.00031004 [m ] 3 Vvl 0.00031920 [m ] xiv Chapter 1 Introduction The first air breathing pulse-jet engine was invented in 1906 and from that time the pulse-jet has change its shape and size several times. Today the pulse-jet is used in several areas such as military, industrial and hobby models. For military use the engine mostly propels target drones but Boeing is talking about using the Pulse Ejector Thrust Augmentor (PETA) that is a new developed design of the pulse-jet engine to propel crafts in a vertical direction both for military and commercial VTOL use [1].