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DESIGN AND DEVELOPMENT OF PULSE JET ENGINE Divyesh B. Patel

1, Jayesh R. Parekh

2

Assistant professor, Mechanical Department, SNPIT & RC, Umrakh, Gujarat, India1

Assistant professor, Mechanical Department, SNPIT & RC, Umrakh, Gujarat, India 2

Abstract: A pulse jet engine (or pulsejet) is a type of jet engine in which combustion occurs

in pulses. Pulsejet engines can be made with few or no moving parts, and are capable of

running statically. Pulsejet engines are characterized by simplicity, low cost of construction

but high vibrations and noise levels. Pulsejet fuel efficiency is a topic for hot debate, as

efficiency is a relative term. While the thrust-to-weight ratio is excellent, thrust specific

fuel consumption is generally very poor.

Keywords: Combustion, fuel efficiency, jet engine, Pulsejet.

INTRODUCTION

Pulse Jet Engine is also known as Pulse Detonation Engine (PDE). A pulse jet

engine (or pulsejet) is a very simple type of jet engine in which combustion occurs in

pulses. It contains neither compressor nor turbine & equipped with or without valve.

The concept of the first pulsed jet can be traced back to an 1882 Publication by

Nikolai Egorovich Zhukovsky. His paper, „On the reaction force of in-and-out

oscillating flowing liquid‟, is the first reference to the „Vapor Pulse Jet‟. The subject of

the paper was developed in two subsequent editions published in 1885 and 1908.

Stating a general method used for the determination of the motion of a body and fluid

inside it, he investigated Helmholtz‟s problem and augmented it by the new problem of

the motion of a closed tube filled with fluid. He studied this last problem with the aid of

the theory of pipes of Poiseuille, and its solution was verified by a special experiment

performed by him (Zamyatina, 1986).

Nine years later, in 1906, Russian engineer Vladimir V. Karavodin experimented

with pulsejets in basic research to find the effects of varying tube length and diameter

had on he cycle pulse frequency, stability and thrust produced. The jet tube he used

was straight and of constant diameter. He obtained a patent for an air breathing pulse-

jet engine. In 1907 he built a working engine based on his invention (Gwynn, 2005).

Basically the system produced a high velocity pulsed gas jet generated by a cyclic

combustion of a liquid Hydrocarbon fuel / air mixture.

The most infamous pulsejet was developed by German Paul Schmidt (Foa, 1960;

Reynst 1961) in conjunction with a German manufacturer, Argus, in 1939. That

pulsejet used a series of one-way valves at the intake end of the tube to intake a fresh

volume of air to mix with the atomized fuel prior to ignition. This jet was used to power

the V-1 “Buzz Bomb” shown in Figure 1−3. The V-1 had a mass of 4750 lbs and

produced 650 lbs of thrust at an altitude of 3000 ft and at a cruise speed of 400 mph

(Reynst, 1961; Zaloga, 2005). Once the motor had reached operating temperature and

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had been accelerated to minimum air flow velocity ( launched using a steam catapult )

the air / fuel pulsejet no longer needed its electrical ignition system and continued to

run thanks to reflected pressure waves from the jet output nozzle that opened the

valves, compressed the new intake charge, and ignited it.

The Russians are also believed to have built copies of the V-1, and the French

operated a target drone based on the V-1 and designated the “Arsenal 5.501” well into

the 1950s, though it differed from the original design in having twin tailfins and was

radio controlled (Goebel, 2005). After World War II was over, there were many new

engines to choose from. The jet age was born. Pulsejets were placed on the shelf as the

gas turbine engine took over due to its reliability and significantly better specific fuel

consumption. While the race to the moon was nearing an end, there was a desire for

jetpacks and hovering vehicles. Lockwood and Hiller performed a small study on the

jets.

The Lockwood-Hiller design, a valveless variant, was patented in 1963 (Lockwood,

1963). This variant works off of the same principles of the Marconnet design, however

the tube was bent into a U-shape to have thrust going in the same direction from both

the inlet and exhaust. An example of this can be seen in Figure 1−4.In August of 1944,

the USAAF placed an order for 1,000 JB-2s, these JB-2s‟ had an improved guidance

system when compared with that of the V-1. Ford built the PJ-31 pulse-jet engine and

Republic built the airframe. Other manufacturers built the control systems, launch

rockets, launch frames, and remaining components. At the end of World War II there

where parallel development programs undertaken in Russia, France, and the United

States to produce new pulsejet rockets (Goebel, 2005).

The JB-2s were launched off of a rail with a solid rocket booster, compared to the

steam catapult system that the Germans used. The USAF then experimented with air-

launching the JB-2. Most of the launches were from a B-17 bomber, though some were

performed from B-24s and B-29s. The Air Force was so enthusiastic with the results

that they increased the order for JB-2s to 75,000 in January 1945. However, the end of

the war in August dampened enthusiasm for the weapon, and the program was

terminated in September of that year. 1,200 JB-2‟s had been built (Goebel, 2005). The

US Navy also experimented with its own V-1 variant, the “KUW-1 Loon”. The Loon

weighed 5000 lbs and cruised at 425 mph. Two submarines, the USS Carbenero and the

USS Cusk, and a surface vessel, the USS Norton Sound, were modified to launch the

KUW-1. In February 1947, the Cusk successfully launched a Loon (Goebel, 2005). The

flying bomb was stored in a watertight hanger on the deck of the submarine, and

assembled and launched by solid rocket boosters while the submarine was on the

surface. Today the US Navy uses Tomahawk cruise missiles in a similar manner;

however they are stored in torpedo tubes or converted ballistic missile tubes.

WORKING CYCLE

Pulse Jet Engine works on Newton’s 3rd

law of motion that is Forces of action and

reaction between two bodies are equal and in opposite direction. It generally works on two

cycles. Lenoir cycle and Humphery cycle.

A. Lenoir cycle

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A pulsejet’s operation can be explained by combining two-cycles: the Lenoir Cycle which

consists of isentropic compression followed by constant volume heat addition and then

adiabatic expansion and the Humphrey Cycle, which operates similarly but has an isentropic

compression added to the cycle. Pulsejets typically have a very small compression ratio that

reaches a maximum at around 1.7. The Lenoir three cycle process can be seen below in Fig-

1.

Figure 1: Lenoir cycle

B. Humphery cycle

Figure 2: Humphery cycle

It consists of the intake of air and fuel at point a, isochoric combustion from a to b, and an

adiabatic expansion to c. The humphrey Cycle is shown in Fig-2 and adds a small amount of

compression before combustion, step a to b. This holds true for both valved and valveless

models.

There are three stages in this engine to complete a whole cycle, they are

1. Inlet (Exhaust)

2. Combustion

3. Exhaust (Suction)

1. Inlet Stage:

To understand this stroke there are two situations to complete this stage

i. Starting of engine

ii. During running condition

When engine is to be started it is necessary to pass compressed air from inlet which will

help to provide enough mixture to start the engine.

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When engine is running, suction force generated due to exhaust thrust will lead to fuel

injection. So vacuum generated in chamber will automatically operate the valve and the air-

fuel mixture will enter the combustion chamber.

Figure 3: Inlet Stage

2. Combustion stroke:

During this stroke spark plug will ignite the fuel mixture and high amount of pressure and

temperature will be generated. These combustible gases will be blocked by valve to enter the

inlet head and will have to pass through the exhaust cone.

3. Exhaust stroke:

Combustible gases will pass through cone and thrust pipe. Due to gradual decrease in area

of passage volume will decrease and pressure will increase which will generate thrust at

outlet of the thrust pipe. As exhaust gases will be released to the environment in combustion

chamber vacuum will be generated which will again help to suck the mixture for next stroke.

Figure 4: Outlet Stage

COMPONENTS DISCRIPTION

The different components in the experimental setup is described below.

1. Combustion chamber,2. Thrust pipe, 3.Valve cap, 4.Butterfly valve, 5.Partition, 6.

Screw, 7.Cone, 8.Inlet Head, 9.Butane Cylinder, 10.Fuel supply pipe, 11.Inlet pipe, 12. Air

Blower, 13.Fuel injector Pump, 14. Spark Plug, 15.Ignition Circuit

1. Combustion chamber:

Figure 5: Combustion Chamber and Thrust Pipe

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It hold the spark plug, providing earthing. In combustion it intakes the fuel and air

mixture and ignites it with the help of spark plug. It is necessary to consider that chamber

walls are capable to withstand the amount of pressure going to be generated when

combustible gases are produced, and should be capable to withstand against the temperature.

Combustion Chamber is made from steel. Reason for choosing this material is because of

availablity and simplicity in machining.

2. Thrust Pipe (Nozzle):

Thrust Pipe is used to increase pressure by decreasing volume generated in combustion

chamber. It should also be capable to withstand high pressure and temperature.It is made of

steel because material availablity and simplicity in machining.

3. Valve Cap:

Valve cap is made of mild steel, it’s surface in contact with valve is chamfered at angle

of 5 t’s main function is to lock the angular movement of valve o, it holds the valve and

prevents the breakage of the valve.

Figure 6: Cap, Valve, Partition, Bolt, Cone

4. Butterfly Valve:

Figure 7: Butterfly Valve Diagram

This valve has to deal with very high temperature and pressure. It should be made of

Spring Steel material according to its functional requirements. It works as one way valve, by

allowing gases and air mixture to enter the combustion chamber and preventing combustible

gases to go to Inlet Head.

5. Partition:

Figure 8: Partition

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It is made from MS bar and consist of 8 holes. It provides passage for inlet air and fuel

mixture to enter the combustion chamber from inlet head. This componant also withstands

the temperature and pressure.

6. Screw:

It holds Valve cap, Butterfly valve, Partition and Cone.Here cone helps by acting as nut.

7. Cone:

Figure 9: Cone inside inlet head

Cone’s function is to diverge the air direct to the inlet holes of the partition Thus cone

will also increase thrust of input by direct impacting the charge to the inlet holes.It is made of

MS.

8. Inlet Head:

It is made of Stainless Steel. t’s main function is to increase the inlet pressure of air To

increase pressure it is shaped as venture tube so first its diameter will decrease gradually and

then increase as shown in figure.

Figure 10: Inlet Head

9. Gas Cylinders:

They are used as fuel for testing purpose.

Figure 11: LPG cylinders

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10. Fuel Supply pipe and Inlet Pipe:

Fuel supply pipe supply the fuel to fuel inlet pipe from tank(Gas tank/ Petrol tank). Inlet

pipe is copper pipe which injects the fuel almost nearer at the inlet hole. Amount of fuel

injected is controlled manually.

Figure 12: Fuel Supply pipe and Inlet Pipe.

11. Air Blower:

As pulse jet engine can not start at an atmospheric temperature initially high pressurised

air is required. So, it is used to provide high pressurised air to start the engine.

Figure 13: Air Blower

12. Fuel Injector Pump:

It is used to inject the fuel from supply tank.

Figure 14: Fuel injector Pump

13. Spark Plug:

It is used to ignite the mixture entered in chamber. It is placed in combustion chamber

through a hole grounding is provided to the chamber wall so spark occurs between spark plug

and chamber surface. Rate of spark required is 180/min

14. Ignition Circuit:

It generates such higher voltage that can pass current from spark gap with the help of

Transformer and Capacitor.

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Figure 15: Ignition Circuit

DESIGN CALCULATION

a. Pulsejet operation equations:

Air-Fuel ratio is taken nearly about 12-13. This means that we need 12-13 kg of air to

burn 1 kg fuel at ground. A fact to be considered is that the gas exit velocity never goes above

speed of sound in this engine.

Assuming following variable

V = tube volume (litre.)

f = pulsejet engine operation frequency. (Hz)

Va = gas exit average velocity. (m/s)

F = force, thrust (N, Newton)

fc = fuel consumption (gram/second)

m = mass in kg

t = time in second.

F= m*a

Where a= Va/t

So, F = m* Va/t

F*t = m*Va

b. Thrust pipe:

With increase in length it generates low resonance frequency; the engine can run by

itself hort pipe, high frequency and the engine can’t run without external input airflow

According to Dave Brill, the length has little effect on output power as long as the condition

for resonance sequence is met. Because in a low frequency the fuel charge are larger than

higher frequency. Low frequency and larger explosions becomes equal to higher frequency

and smaller explosions. So, if you increase tube volume, you will increase fuel mixture and

this gives us larger explosions And it’s also easy to prove that the length has nothing to do

with the output power for a tube chapped as a pipe.

Figure 16: Thurst pipe

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Equation to use is m*v=F*t. m = mass = X % air volume of the total volume in the pipe.

This is

m= X * (D2 * π* L) / 4

T = to 1 second, during 1 second explosions occur,

f = frequency.

F = V/(L*2).

This are put together and ends up with

F (Newton) = (X * D2 * π* L * V

2 )/(L * 8)

c. Size of combustion Chamber:

To determine the volume of chamber following assumption are to be made

Valve operating pressure = Pv

Exhaust volume = Ve

Unit volume of thrust pipe= Vt

Suction pressure = Ps

Now after cycle when exhaust gas will be thrown say of volume ‘Ve’, suction

generated in chamber will be of same amount but if still there is burnt pressurized gases are

there remaining in thrust pipe it will also increase suction as they are travelling towards exit

so length of pipe and size of combustion chamber should be so taken that will create suction

pressure to operate valve as well as to suck the mixture.

EXPERIMENTAL SETUP

Firstly by sequencing cap, valve, partition and cone and screwing them assembly is

prepared. This assembly is inserted in Inlet Head groove. Next is combustion chamber and

thrust nozzle which are welded, are to be mounted from the side of the valve to complete the

whole basic assembly. Fuel input is through the Inlet head.Initial air pressure is provided by

the Air blower.

First start blower and injector and spark plug. As mixture will formed and enter the

chamber, spark plug will ignite it. Here it is necessary to maintain the fuel supply and air

flow as we are not using carburettor/ air fuel mixture.

RESULT & DISCUSSION

Different material to manufacture butterfly valve was tried. Two partition, one with

10mm dia., 8 holes another with 8mm dia., 8 holes were also tried. 8mm dia., 8 hole partition

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was found to be more efficient. Two type of exhaust cone were tested. Cone 1 is rapid angled

so it generates high blasts at exhaust so its function is noisy. Second shaped cone 2 is

efficient as it is gradually angled. It works with lesser noise then the cone 1.

Figure 17: Cone shape 1 & 2

As a fuel we used LPG gas and Petrol and we conclude that LPG gives low thrust then

the petrol and the reason is the volume of the fluid.

t was noticed that due to combustion heat doesn’t reaches to the partition and

cone.

Components beside spark plug get heated.

Air-fuel ratio to be maintained is about 12-13.

Butterfly valve should be so flexible that can bend and open the port when suction

is generated in combustion chamber.

Effect of exit cone shape is very effective on all over efficiency.

Thrust pipe should be so long that can reduce the frequency and can maintain the

suction required in combustion chamber.

Further improvement in design of butterfly valve, partition and in cone is required.

REFERENCES

[01] www.Wikipedia.com

[02] Experimental Investigations Into The Operational Parameters Of A 50 Centimeter Class

Pulsejet Engine report by Robert Lewis Ordon.

[03] Inside the pulsejet engine by Fredrik Westberg.

[04] Russian Pulso-1 design.

[05] United States Patent, Patent No. 5,87,2079Verlag, 1998.

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