Design, Manufacture and Testing of Subsonic Ramjet Engine PDF

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Design, Manufacture and Testing of Subsonic Ramjet Engine Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Technology by Ishan Singh (08D10008) Under the Supervision of Prof. K.P.Karunakaran & Prof. Tanmay K. Bhandakkar Department of Mechanical Engineering INDIAN ...

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Design, Manufacture and Testing of Subsonic Ramjet Engine Submitted in Partial Fulfillment of the Requirements for the Degree of

Master of Technology by

Ishan Singh (08D10008) Under the Supervision of

Prof. K.P.Karunakaran & Prof. Tanmay K. Bhandakkar

Department of Mechanical Engineering INDIAN INSTITUTE OF TECHNOLOGY BOMBAY October 2014

Declaration I declare that this written submission represents my ideas in my own words and where others’ ideas or words have been included, I have adequately cited and referenced the original sources. I also declare that I have adhered to all principles of academic honesty and integrity and have not misrepresented or fabricated or falsified any idea/data/fact/source in my submission. I understand that any violation of the above will be cause for disciplinary action by the Institute and can also evoke penal action from the sources which have thus not been properly cited or from whom proper permission has not been taken when needed.

Ishan Singh 08D10008

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Abstract Around 86 % of helicopter crashes in India have been attributed to tail rotor failure. The purpose of the tail rotor is to counter the torque created by the engine shaft housed in the cock-pit, thus keeping the helicopter from rotating about it’s axis and spiraling out of control. However not only does this method leach energy but also jeopardizes flight safety in the event of a malfunction. In order to completely do away with the inefficient tail rotor a novel application involving Ramjet engines was first put forth by Hiller. A pair of Ramjet engines were mounted on the tips of the helicopter blade, in place of the conventional engine. Since the engine was now independent of the cock-pit, it transferred no torque to the helicopter body, hence eliminating the need for a tail rotor. Ramjet engine is of the airbreathing type with no movable parts. It consists of three regions, namely compressor, combustor and nozzle. Ideally they are deployed at supersonic velocities due to their high efficiency in this region. However, since the blade tips rotate at subsonic velocities the engines consume nearly ten times more fuel making this a serious drawback. Though attempts to militarize and commercialize the tip-jet helicopters were made in the 1950’s, they failed due to a number of reasons. Foremost being their extremely noisy operation and high visibility which ruled out stealth applications. Potential investors shied away owing to it’s high fuel consumption rate and safety concerns, which eventually ensured that although this project was a technical success, it remained a commercial failure. This project aims to revive the Tip-jet culture by addressing key issues from the previous works and by taking advantage of the advances made in engineering in the last iii

50 years. Hiller had attributed the noisy nature of his engine to it’s sheet metal build. Thus we decided to opt for an alternate method of manufacture. A CAD model of the subsonic ramjet engine was designed and sectioned into two symmetric halves. Two steel blocks were then machined to produce the internal engine contour. The two machined halves were then bolted together to obtain a hollow and empty central region in the shape of specified ramjet geometry. To test the engine a static rig has been designed. The rig involves use of a fan to generate adequate wind speed, and guide rails to direct the motion of engine. With the help of two sufficiently strong spring gauges the engine will be constrained. The deformation of the spring gauge will give us the thrust generated. The first aim of the test rig is to ensure a safe examination of the engine and then determine whether it can generates positive thrust. Subsequently it will serve to measure and improve the efficiency of the engine.

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Contents

Abstract

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Contents

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List of Figures

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List of Tables

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1. Introduction

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1.1 Why Ramjet Helicopters ?

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1.2 Ramjet Engine

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1.3 Drawbacks of Ramjet Helicopter

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1.4 Aim of This Project

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1.5 Organization of Report

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2. Analysis of Ramjet Engine

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2.1 Thrust Generation

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2.2 Subsonic Ramjet Engine

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2.2.1 Body Structure

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2.2.2 Flame Stabilization System

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2.2.3 Flame Injection and Ignition System

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2.2.4 Choice of Fuel

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2.3 Ramjet Efficiency

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2.4 Summary

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3. Design and Manufacture of Ramjet Engine

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3.1 Procedure Adopted

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3.2 Design of Body Structure

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3.2.1 Design of Diffuser

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3.2.2 Design of Combustion Chamber

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3.2.3 Design of Exhaust Nozzle

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3.2.4 Scaling Down of Ramjet Dimensions

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3.2.5 Materials and Method of Manufacture

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3.3 Design of Flame Holder

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3.4 Fuel Consideration

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3.4.1 Fuel Consumption and Tank Size

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3.4.2 Fuel Injection Nozzle

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3.4.3 Fuel Ignition

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3.5 CAD Model of Engine

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3.6 Manufacture of Ramjet Engine

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3.7 Summary

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4. Design of Experimental Setup

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4.1 Test Rig Objectives

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4.2 First Test Rig Design

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4.3 Current Design of Test Rig

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4.3.1 High Speed Air Supply

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4.3.2 Fuel Supply to Ramjet

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4.3.3 Harness Structure

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4.4 Summary

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5. Conclusions and Future Plan

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5.1 Conclusions

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5.2 Work Done

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5.3 Future Work Plan

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Appendix I

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Literature Cited

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Acknowledgments

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List of Figures Figure 1-1 YH-32 Hiller Hornet Ramjet Helicopter......................................................................1 Figure 1-2 HJ-1 of Hiller Aircraft Operation, USA.......................................................................2 Figure 1-3 Ramjet Engine Schematic.............................................................................................2 Figure 1-4 Hiller’s 8RJ2B Engine..................................................................................................3 Figure 1-5 Plan of Action...............................................................................................................4 Figure 2-1 Schematic of Ramjet Engine showing Various Components.......................................7 Figure 2-2 Various Types of Flame Holders..................................................................................8 Figure 3-1 Flowchart showing Action Plan..................................................................................11 Figure 3-2 Ramjet Engine Mounted on Blade Tip.......................................................................12 Figure 3-3 Sketch showing Body Structure of Engine.................................................................13 Figure 3-4 Chart plotting Thrust per sq.inch of diffuser entrance area versus Ramjet Velocity..14 Figure 3-5 Curved Inner Profile of the Diffuser as per NACA ARR No. L4F26........................15 Figure 3-6 Curved Profile of the Diffuser....................................................................................16 Figure 3-7 Ramjet Body Structure: Co-relation of Different Dimensions...................................18 Figure 3-8 Ramjet Body Structure with Final Dimensions..........................................................18 Figure 3-9 Geometry of Flame Holder of Radial Type................................................................19 Figure 3-10 First Design of Flame Holder................................... ...............................................20 Figure 3-11 Specific Fuel Consumption vs Ramjet velocity.......................................................21 Figure 3-12 Thrust calculated for Ramjet Velocity of 656 ft/s....................................................21 Figure 3-13 Fuel Injection Setup..................................................................................................22 Figure 3-14 8mm Diameter Glow Plug........................................................................................23 Figure 3-15 Second Hand Glow Plug on Stand By......................................................................23 Figure 3-16 CAD Model of Ramjet Engine.................................................................................24 Figure 3-17 Section of Ramjet.....................................................................................................24 Figure 3-18 Ramjet Engine Blocks..............................................................................................25 Figure 3-19 Ramjet Block with Tool Paths Displayed................................................................26

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Figure 3-20 Assembled Ramjet Engine Block.............................................................................27 Figure 3-21 Ramjet Engine viewed from exit nozzle end............................................................27 Figure 4-1 Suspended Ramjet Harness.........................................................................................29 Figure 4-2 Schematic of Air Funnel.............................................................................................30 Figure 4-3 (a) Air Funnel made of Sheet Metal (b) Welded to Grill for Easy Mounting............30 Figure 4-4 Harness Setup.............................................................................................................31 Figure 4-5 Side View of Static Test Rig......................................................................................32 Figure 4-6 Top View of Static Test Rig.......................................................................................32 Figure 6-1 Temperature(or Enthalpy) versus Entropy Diagram for a Ramjet Engine.................38

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List of Tables Table 1-1 Comparison of Fuels..............................................................................................10 Table 3-1 Problem Specifications.............................................................................................12 Table 5-1 Summary of Work Completed in Phase I...............................................................33 Table 5-2 Time Line for Completion of Remaining Work in Phase II...................................35

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Chapter 1

Introduction

Figure 1-1 YH-32 Hiller Hornet Ramjet Helicopter

“ Necessity is the Mother of Invention “ ~ Plato

1.1 Why Ramjet Helicopters ? Ramjet helicopters are an innovative offshoot from the conventional tail rotor helicopters in use today and as is the case with all inventions and innovations, its conceptualization was preceded by a significant necessity. Traditional helicopters despite their tremendous success have a few shortcomings. The foremost being it’s dependence on a tail rotor. As the engine is located within the cock-pit, a shaft transmits torque to the blades. This system inadvertently results in the application of a counter-torque which acts to rotate the helicopter about it’s own axis, driven by the law of conservation. To check this event of instability, a tail rotor was deployed. Though it manages to successfully keep the helicopter stable, it comes at a certain price. Firstly this rotor ends up leaching fuel, thus reducing flight distance. Then there is the need to provide a sufficiently long ‘tail boom’ to mount it. This is done to reduce it’s energy dependence so as to generate the same amount of anti-torque at lower rpm. This results in an unnecessary increase in size. Last but not least, it may even be considered the ‘Achilles Heel’ of

this aerial warrior. Severe damage inflicted to this part more or less ensures an out of control machine spiraling to the ground. In fact around 86% of all helicopter crashes have been attributed to tail rotor failure. This figure just by itself is alarming enough to question it’s use. All these were the factors which led Stanley Hiller to innovate and eliminate the very need to depend on tail rotors. He used a novel approach by which he removed the engine from the fuselage and replaced it with a pair of ramjet engines, that were mounted onto the tips of the helicopter main rotor blades. This one step eliminated the counter-torque experienced by the helicopter, and hence also the tail rotor. Hiller started the development of the first ramjet helicopter in 1948 and its first successful flight was in 1950 followed by it’s introduction to public in 1954. His goal was to develop an affordable sport helicopter for $5000. He subsequently built 18 machines for US Army and Navy. The ramjet 8RJ2B he developed for this helicopter was certified by CAA. However the project was shelved before 1960 mainly because Hiller’s attention diverted to more important and lucrative post WW-II defence projects.

Figure 1-2 HJ-1 of Hiller Aircraft Operation, USA

1.2 Ramjet Engine Ramjet was invented by René Lorin of France in 1913. It is probably the simplest of all power plants that mankind has developed so far. It has absolutely no moving part. It is simply a conduit in which the air rushing in due to its forward velocity is compressed by a diffuser, fuel is injected and burnt and the resulting hot gases exit at high velocity from the rear nozzle thus pushing the engine forward. As there are no moving parts, ramjet is very small and light with high reliability. It can use a variety of solid, liquid and gaseous fuels including Castrol. The only requirement of a ramjet is a sufficiently high forward velocity (> 0.5M). So ramjet is not yet suitable for transport aircraft and has largely been limited to the super/hyper-sonic flights of missiles.

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Figure 1-3 Ramjet Engine Schematic

Mounting ramjets at the blade tips of helicopter is a very innovative idea. It provides the necessary forward velocity even while hovering (a 7m diameter rotor at 1500 rpm gives about 1.7 Mach and it is about 1 Mach for 4m diameter rotor). Unlike a fixed-wing system, the rotor speed can be kept constant so that the duct of the ramjet can be nicely optimized. Another significant advantage as mentioned above is the absence of the counter-torque of the rotor. The blades are large enough to hold the fuel. There is no need for a fuel pump too as the centrifugal force will pump it. So, the rotor of a helicopter with ramjets at the blade tips such as HJ-1 is simply a self-contained flying saucer with a payload hanging from its center.

Figure 1-4 Hiller’s 8RJ2B Engine

1.3 Drawbacks of Ramjet Helicopter There are three main reasons due to which ramjet helicopters were found unsuitable for defense related purposes: i. High fuel consumption ii. Very noisy operation iii. High night time visibility 3

The massive fuel consumption placed a severe limitation on the flight distance as well as the payload whereas the noise and visibility issues barred it from any stealth related operation.

1.4 Aim of this Project This project aims to take help of the engineering advances made in the last half a century to manufacture and test a ramjet engine, which is more efficient as well as silent compared to it’s predecessors. An iterative process will be followed as shown below in Figure 1-5.

Figure 1-5 Plan of Action

Key Objectives of this project include: 1. Design and Manufacture of a miniature ramjet engine. 2. Design and Assembly of a flame holder and fuel system. 3. Design and Assembly of a static test rig to test and measure performance. 4. Analysis and interpretation of test results to improve engine performance.

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1.5 Organization of Report This chapter dealt with a brief history of how ramjet helicopters were born, and examined the drawbacks that have stopped them from becoming commercially viable. It also spelled out the scope of work and key objectives of this project. Chapter 2 reviews existing literature on ramjet engines. This chapter contains more detailed information on the ramjet and it’s various components. Chapter 3 gives a detailed account of the design and manufacture of the engine carried out in this investigation. The chapter begins by laying out the procedure adopted and then explicitly describes how engine dimensions were obtained. This chapter also contains snapshots of the machined ramjet body structure along with a flame holder. Chapter 4 discusses the testing process that will come into play once the ramjet along with it’s smaller components are fully prepared. It describes the reason why a static test rig was preferred to a dynamic one. Finally the current test rig plan is presented. Chapter 5 rounds the topic up with conclusions, work done and future work remaining. A Time line for the completion of future work is specified. Appendix I contains a formula which is used to arrive at the curved conical profile of a diffuser. It also contains the Ideal Cycle Analysis which will be needed to calculate the engine efficiency as well as thrust generated.

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Chapter 2 Analysis of Ramjet Engine 2.1 Thrust Generation Thrust is the force that moves an aircraft through the air and is generated by the propulsion system of the aircraft. Different types of engines develop thrust in different ways, although thrust is usually generated through some application of Newton's Third Law. A gas is accelerated by the propulsion system, and the reaction to this acceleration produces a force on the engine. A general derivation of the thrust equation shows that the amount of thrust generated depends on the mass flow through the engine and the exit velocity of the gas. In the early 1900's some of the original ideas concerning ramjet propulsion were first developed in Europe. Thrust is produced by passing the hot exhaust from the combustion of a fuel through a nozzle. The nozzle accelerates the flow, and the reaction to this acceleration produces thrust. To maintain the flow through the nozzle, the combustion must occur at a pressure that is higher than the pressure at the nozzle exit. In a ramjet, the high pressure is produced by "ramming" external air into the combustor using the forward speed of the vehicle. The external air that is brought into the propulsion system becomes the working fluid, much like a turbojet engine. In a turbojet engine, the high pressure in the combustor is generated by a piece of machinery called a compressor. But there are no compressors in a ramjet. Therefore, ramjets are lighter and simpler than turbojets. Ramjets produce thrust only when the vehicle is already moving; ramjets cannot produce thrust when the engine is stationary or static. Alternate propulsion system must be used to accelerate the vehice to a speed where the ramjet begins to produce thrust. Until aerodynamic losses become a dominant factor, the higher the speed, the better the performance of a ramjet. The thrust equation for a ramjet contains three terms: gross thrust, ram drag, and a pressure correction. If the free stream conditions are denoted by a "o" subscript and the exit conditions by an "e" subscript, the thrust (F) is equal to the mass flow rate (ṁ) times the velocity (V) at the exit minus the fre...