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Folder 5 ENGINES

Engines

It has only been in the last century that people have been given the ability to move around the globe at will and it was the invention of an engine that gave people this wonderful opportunity. In hindsight we have, perhaps, been too greedy with our gift as the environment is greatly suffering from our insatiable appetite for global travel and transportation of goods. Future generations will not be so fortunate.

(Although the subject of transportation and the word "Locomotion" is strongly connected with "Engines" this folder is specifically about how engines work and the study of the vast subject of locomotion/ transport has to be sought elsewhere-e.g., for the UK, the text by Bagwell and Lyth, Transport in Britain - from Canal lock to Gridlock, is a very informative read.)

The story of engines is, of course, a fascinating part of our heritage and the following account gives a brief story of steam engines and the development of internal combustion and jet engines which superseded them.

Steam engines

Introduction to steam power

The history of the steam engine dates back as far as the first century. Hero of Alexandria, AD 20 - 62, produced an "engine of sorts" as illustrated below.

Water in the cauldron is heated to form steam and this is fed into a sphere where the steam is expelled through jets causing the sphere to spin rapidly.

Though many other curiosities were invented in subsequent years the need for engines became acute at the start of the industrial revolution. Mines for coal or minerals were inoperable most of the time due to flooding and man-power or horse-power could not pump the large quantities of water from these mines. In 1698 Thomas Savery (1650-1715) was the first to build a pumping engine and this was quickly followed in 1712 by Thomas Newcomen (1664-1729). In 1769, James Watt (1736-1819) improved the Newcomen fundamentally with the addition of a separate steam condenser. The development in the later parts of the 1700's was rapid and engines were used for many industrial processes as well as pumping water from mines. They were all stationary engines and, quickly, this form of power replaced water or wind power for industry. The latter sources of power were too intermittent for the new industrialist.

Around 1800 Richard Trevithick and, separately, Oliver Evans introduced engines using high pressure steam. These were much more powerful for a given cylinder size then the previous engines and therefore could be made small enough for transport applications.

The 1800's was most definitely the century of steam locomotion. Most notable was The Rocket designed and built by George Stephenson with the help of his son, Robert, and Henry Booth. In 1829 the Rainhill Trials were held, by the Liverpool and Manchester Railway Company, to find the best locomotive engine for a railway line that was being built to serve these two English cities. On the day of the Trials, some 15,000 people came along to see the race of the locomotives. During the race, the Rocket reached speeds of

24 mph during the 20 laps of the course. This was due to several new design features. It was the first locomotive to have a multi-tube boiler - with 25 copper tubes rather than a single flue or twin flue. The blast pipe also increased the draught to the fire in the firebox by concentrating exhaust steam at the base of the chimney. This meant that the boiler generated more power (steam), so the Rocket was able to go faster than its rival, and thus secure its place in history.

So, what is the magic behind steam power? How does it work?

How a steam locomotive work

The steam engine is a machine for converting heat energy into work. The operation is illustrated below with two diagrams showing how steam is alternately injected into chambers at the front and back of the piston to move it.

Left Hand Diagram Steam enters at "In1" and pushes the piston from left to right - excess steam behind the piston is expelled at orifice marked "Out".

Right Hand Diagram Valve is moved to close off "In1" and " In2" is then opened . The piston is forced to the left and excess steam passes through the orifice "Out" again.

There is clearly an exact timing between the piston and valve movements and this is best shown in the animation at

http:/www.animatedengines.com

Select the "steam engine" from the list of engines and note that the valve and piston movements are approximately 90 degrees out of phase.

It now remains to see how a source of steam is produced.

A firebox and boiler are shown below:

The numbers indicate the principle parts:

1. Chimney; 2. Smokebox; 3. Blastpipe as outlet from valve; 4. Steam pipe as inlet to valve; 5. Boiler barrel; 6. Dome; 7. Regulator valve; 8.Outer firebox; 9. Safety valves

10. Regulator handle; 11. Boiler compartment with fire tubes leading from firebox to chimney --- blue colour signifies water, pink area represents steam above the water.

Firebox (numbers 12 to 24) may vary from engine to engine:

12 Firebox interior; 13. Roofing bar; 14. Stays; 15. Fusable plug; 16.Brick arch;

17. Firedoor for coal input; 18. Throat plate; 19.Firebox backplate; 20. Stays;

21. Firegrate; 22. Ashpan; 23. Damper; 24. Washout plug.

Boilers in the early locomotives were very simple. Only one tube passed from the firebox to the chimney and this proved to be an inefficient way to transfer heat to the water. It was soon realized that a large number of small tubes gave much greater heat transfer and therefore this design was adopted early in the 1800's. Most boilers have a dome where the regulator is fitted. This means that relatively dry steam enters the steam pipe before going into the piston. Some illustrations from the "Pender" engine, housed at the Manchester Museum of Science and Industry (MOSI) will now be included.

(Pender was built in 1873 by the Beyer Peacock Company of Gorton, Manchester for the Isle of Man Railway and was in use until 1950. The locomotive was initially used on the very first railway on the Isle of Man, which ran from Douglas to Peel. Later, Pender had to be fitted with a bigger water tank and boiler so that it could have enough steam to power it up the hills and on the longer routes to Port Erin and Ramsey. It pulled 7 coaches containing 400 people at 30mph. Pender exemplifies the essential elements present in steam locomotives from the development of Stephenson's Rocket in the 1820s onwards. The key features are a multi-tubular boiler, a blast pipe to increase the combustion of coal in the firebox and near horizontal pistons directly driving the wheels.)

View from FireBox end

Piston

Steam is taken from the dome:

Dome showing regulator valve

Steam feeding into, and away from, sliding valve and piston

The illustrations show that most of "Pender" is a Firebox and Boiler. The large tanks on either side of the boiler hold many litres of water to produce steam and behind the driver's cab is the coal bunker containing coal for the fire. The motive power comes from a small section at the front where steam is fed into the piston chambers via the valves and where the used steam passes up the chimney.

Even though steam is taken from the dome, it contains small droplets of water which collected in the cylinders. This has to be periodically drained otherwise the engine operates very inefficiently.

The introduction of superheating was the single most important development for the steam locomotive. Superheating increases the power output of a locomotive by up to 25%, with equivalent savings in coal and water, over non-superheated engines. Its widespread use from 1910 coincided with railway operators needing to have heavier, highly efficient, trains to haul more carriages at higher speeds.

The first design for a locomotive superheater were put forward in 1850. Previous ideas utilized a steam drying process which raised the temperature of the steam by a few degrees to overcome the moisture within the steam. Contact with the metal surfaces of the pipes and cylinders cools the steam, resulting in the formation of water droplets. This condition also causes frictional resistance in the movement of the pistons and a fall in pressure. The use of a superheater, however, was not advanced for another 50 years when, after developments in metallurgy and lubricating oils capable of withstanding the severe cutting action of highly superheated steam, made superheating a practical proposition. Success was achieved largely due to the work of Dr. Wilhelm Schmidt, assisted by Dr. Robert Garbe, Chief Mechanical Engineer of the Berlin division of the Prussian State Railways and Jean Baptiste Flamme, Chief Mechanical Engineer of the Belgian Railways.

Even with these gains in efficiency the days the steam engine were numbered. The start- up time of a steam engine is an insurmountable problem. Two or three hours would be needed to start up "Pender" from cold and in a world of "instant" action this is totally unacceptable.

A few technical points must be mentioned.

If the engine happened to stop so that the valve slide was in an unfortunate position of leaving both "In1" and "In2" valves partially open then, on opening up the regulator valve, steam would be admitted to the front and back of the piston. The net force would be zero and the piston would not move. However, all steam locomotive have two pistons, one on each side of the boiler, and the valve sliding mechanisms are positioned at different parts of the cycle so that at least one piston will provide motive power.

As water evaporates into steam the water level in the boiler is reduced and water has to be replenished. But the pressure in a low pressure boiler ( for Pender it would be 200 psi or about 1.5 Mpa ) means that an injector has to be used. This device uses the steam pressure and a series of nozzles to force the water into the boiler.

Despite the steam engine being the workhorse for transport for many years the Internal Combustion engine quickly replaced it. With much theoretical knowledge accumulated in the period 1850 to 1900 the transformation of heat into work was well understood many of the newer internal combustion engines were ready and waiting.

Steam engines for agricultural use were developed at the same time as locomotives. Invariably, they have a single cylinder as shown below.

The main body of the engine is the boiler and the firebox is beneath the flywheel. Water is stored underneath the standing platform; the coal bunker being adjacent to the break.

For single cylinder engines, the technical point made earlier about zero net force on the piston is very relevant and often the flywheel has to be moved manually to change the valve settings.

Steam is taken directly from the top of the boiler since there is no dome to provide an elevated steam pipe exit with regulator valve, as in the case of "Pender". Thus, a little more time is needed in warm up and several initial "blow-off's" of steam are recommended to make sure that a "so-called" dry steam (without water droplets) enters the cylinder. Whereas locomotives are expected to travel on relatively level tracks, the traction engine may have to move up or down terrain with steep gradients. The water level in the boiler has to allow for this and ensure that the fuseable plug is being covered with water at all times. Steering, of course, is a vital necessity on a traction engine and the front axel is orientated with a chain mechanism.

Many of these engines are still in working order and lovingly cared for by their owners.

Internal combustion engines

The internal combustion engine (ICE)is an engine in which the combustion of a fuel (normally a hydrocarbon) occurs with an oxidizer (usually air) within a combustion chamber. This rapid expansion of the high-temperature and high-pressure gases produced by combustion apply a direct force to some component of the engine. The force is applied typically to pistons, turbine blades, or a nozzle. The piston, say, moves over a distance, transforming chemical energy into useful mechanical energy.

The first commercially successful internal combustion engine was created by Joseph Étienne Lenoir in 1859 and almost a decade later, Nikolaus Otto produced a similar engine working on the "so called" Otto cycle. The marked distinction of these engines with reference to a steam engine was that there was immediate action after the first firing in the cylinder. Also, as they use air as a working fluid there is no need to carry a tank of water around. The popularity of ICE's was assured and it was only a matter of time before they replaced steam engines.

Whereas the development of the early steam engines was largely empirical, the ICE's relied on the theoretical work of several scientists most notably Joule and Carnot. We all know that rubbing one's hands together gets them warm and Joule showed (1845) that for a given amount of work done there was always a precise amount of heat generated.

Carnot was interested in the reverse idea - the conversion of heat into work. He showed (1823) that, by subjecting an ideal gas to expansions and contractions, heat can most certainly be converted to work.

Carnot's theory is based on subjecting an ideal gas to the following cycle - a-b, b-c, c-d and d-a. All temperatures need to be measured in °K ( °K = 273 + °C). Work on the gas and heat applied to the gas will be considered positive whereas work done by the gas and heat given out by the gas will be negative.

So the "engine" has the following description

A very artificial "engine" was envisaged for this cycle, just a cylinder and a piston. This assembly was moved bodily from a cold plate to an insulating plate and then to a hot plate and finally to the insulating plate. One must remember that we are still in the realms of a theoretical world.

One can understand the energy involvement by looking at the following diagram:

In any cyclic process the internal energy of the gas must return to the starting point and hence the red line, after stage d - a , returns to the original level. However it can be calculated that more work is given out by the gas, stage c-d, than the work done on the gas in stage a-b so we do have an engine capable of doing work. To provide this work there must be an input of heat energy and one can see that the heat in for stage c-d is much more than the heat out in stage a-b. After a little algebra, the efficiency of converting heat to work can be found to be:

efficiency = 1 - T(cold)/T(hot)

Whereas the conversion of work to heat gives 100% transfer ( as shown by Joule ) the reverse process - heat to work - can only give a partial conversion and the Carnot efficiency is the maximum achievable. Thus, quite a lot of heat is left as heat energy and for a electrical power station, for example, only about one third of the heat is usefully used.

The Carnot engine is completely hypothetical but the main elements of an IC engine can be explained with the Otto engine.

This engine has valves and pistons in much the same way as a steam engine but the crank (turning linear motion to rotating motion) is within the engine rather than on the wheels as with steam trains. Both "two stroke" and "four stroke" engines are available but the four stroke engine is described here.

The first "stroke" ( piston move from top to bottom ) has "In" open and draws in fuel and air. In the next "stroke" the piston moves back to the top and both valves are closed. The fuel/air mixture is compressed as it cannot escape from the cylinder. A little before the piston reaches the top a spark ignites the fuel and, by the time a full explosion ensues, the piston is racing down again. This "stroke" is called the ignition "stroke" and generates power - again both valves are closed. On the final "stroke" the "Out" valve is opened to allow the combustion gases to escape.

The whole sequence is then repeated - intake, compression, ignition/explosion (power stroke) and exhaust. Note - the pressure at ignition in an IC engine is typically 10 Mpa or about 1500 psi compared to the low pressure steam boiler with pressures of 1.5 Mpa or about 200 psi .The Otto cycle is shown in the diagram:

The path A-B is the power stroke. Even thought the cylinder is metallic, and a good thermal conductor, the process is adiabatic since the gas has not sufficient time to acquire the cylinder temperature ( this is the power stroke). At B the exhaust valve opens and the gas is discharged into the atmosphere (exhaust stroke). On reaching C the exhaust valve is closed and the inlet valve is opened. The path C to B is the intake stroke which is followed by the compression stroke B to A. The cycle depicted on a pressure versus volume graph is therefore two isobaric (constant volume) lines cutting two adiabatic curves. Note ---- that the work done per cycle must be divided by 2 as the exhaust and intake strokes do not contribute to any power development. Calculations also show that the Otto cycle is less efficient than the Carnot cycle but at least a practical engine can be realised with this cycle. (see www.animatedengings.com)

An illustration of an actual engine is given below, clearly, it is a more complex mechanism than the steam engine.

As the illustration shows, there are more than one cylinder in this engine. Four cylinder are a popular choice so that the pistons in each cylinder are on successive strokes - intake/induction - compression - ignition - exhaust. A spark plug in each cylinder causes the ignition and the high voltage, which causes this, has to be "distributed" to the correct cylinder at the right time. This is the role of the distributor. The correct fuel/ air mixture is supplied by the so called, carburetor. This device is attached to the engine on the opposite side to the distributor. It may be thought that a distributor would be needed for this supply. However, the carburetor is attached to all the cylinders in parallel and it is the opening of the inlet valve which dictates which cylinder is supplied with the fuel/ air mixture .The animated engine sequence can be re-visited to get the flavor of the vastness of engine technology in today's world. Those engines based on the Otto and Diesel cycles have stood the test of time but recent development may include other cycles as flexible fuel may be needed in the future. The illustration is given of a Stirling engine --- and who knows ? steam may be back in a revised form.

Many textbooks have been written about the Stirling engine so only a short paragraph will be given here. The PV cycle is very similar to the Carnot diagram:

With a device called a regenerator any heat lost along the left hand side constant volume path is regained along the right hand side path so that the engine has an efficiency of a Carnot engine. Of course, the regenerator is not 100% effective so that the Stirling engine is rather less efficient than a Carnot engine.

There are NO valves in this engine and thus it is a very quiet engine suitable for use in Combined Heat and Power installations in the home. A simple demonstration Stirling engine is shown below:

From a commercial standpoint the OTTO Cycle has been displaced by the DIESEL Cycle which is remarkably similar

This is a four stroke engine with inlet of AIR ONLY from D to C. Adiabatic compression takes place from C to A so producing a massive temperature rise in the air. A to B is the injection of FUEL which immediately IGNITES in the hot air, B to C is the power stroke. Exhaust then takes place from C to D. It must be noted that the compression ratio (volume piston down/ volume piston up) for the Diesel cycle can be very high (15 to 20) as air will not self-ignite until fuel is injected. This is not the case for the OTTO cycle as BOTH fuel and air are compressed. If too high a compression is used then ignition occurs even without a spark and the engine exhibits a severe "Knocking" which would eventually lead to destruction. A typical ratio for an Otto engine is 8 .With its high ratio, the Diesel cycle give efficiencies greater than the Otto cycle and therefore a diesel will always be a prefered choice of engine as it leads to greater savings in fuel consumption.

What seems to be only minor changes in shape between the Diesel and Otto cycles has resulted in a world wedded to mass transport as explained by Mark Evans in his BBC4 TV documentary Timeshift program "The Engine that powers the World".

Shortly after viewing the program, Sept 23rd 2015, the motor industry was awakened to the VW saga and the guardian report, 26th Sept 2015, is included below:

Pollution from road vehicles is a major problem today and this was not highlighted in the Mark Evans' programme. It is true that the inventor, Diesel, anticipated that his engine would use vegetable oil (biodiesel) but now the first demand on this oil is for FOOD products and mineral diesel is mostly used in vehicles.

The Jet Engine

Sir Frank Whittle's jet engine transformed aviation and has allowed global travel on a massive scale with the highest of safety standards. Although OTTO engines were used for several decades the jet engine has proved to be far superior.

In 1922 Frank Whittle presented to the Air Ministry a design for a jet engine. They were unimpressed and rejected his idea. Regardless of this set-back, Whittle still patented his "turbojet engine" in 1930. His design appeared to solve the problem that had baffled inventors for some years - how do you create a chamber strong enough to house an engine that would create a lot of heat and vast directed thrust ? Many combustion chambers had simply been too weak to cope and had exploded under the strain.

Whittle's engine had ten combustion chambers which produced impressive thrust : rather than having just one large chamber which would produce a volatile and potentially uncontrollable reaction, his engine effectively divided up the combustion created into the ten chambers but still did not decrease the power of the engines.

Increasing fears about problems in Europe, lead to the government having second thoughts about Whittle's jet engine. In 1936, he went to Cambridge University, but he left and set up a company called Power Jets Ltd.

In 1937, using newly available alloys that were strong and light, he produced the first viable jet engine to be successfully tested in a laboratory. Now it had to be put onto a plane for field trials and carry out safety tests.

In 1941, a new jet fighter-prototype flew. Its successor, the Gloster Meteor, entered service with the RAF in 1944. However, the Gloster Meteor was not the first jet fighter. This claim goes to the Heinkel He 178 which first flew on August 24th 1939.

With World War II ended , it seemed logical to apply this new invention to passenger planes. Journeys became quicker and the more powerful jet engine allowed passenger planes to get bigger so that more people could be carried on them.

The first jet powered passenger airliner is considered to be the De Haviland Comet whose maiden flight from London to South Africa took place in 1952. This came into operation in a blaze of publicity. Within two years, it was withdrawn from service after a series of tragic accidents which killed many. This, however, was not due to its jet engines but to a fault in its fuselage which lead to the aircraft breaking up in flight.

Boeing then took over the lead in jet-powered airliners. The Boeing 707 entered service in 1958. It was safe and allowed people to travel distances at speeds that would had been impossible just 10 years earlier. The intervening years have seen Concorde speeding across the Atlantic at Mach2. The journey time was just 3 hours and this service, commencing in 1976, was continued until 2003. The airlines AirFrance and British Airways finally decided that the service was uneconomic and the aviation industry has now settling down on the side of size rather than speed with the Jumbo Jets (Boeing 747 operating since 1970) and the Airbus A380 's (operating since 2005).

Now "How does a jet engine works?"

A simplified diagram, below, shows you the process through which a jet engine converts the energy in fuel into kinetic energy that makes an aircraft fly:

1. For a typical jet aircraft , the engine is moving through the air at about 1000 km/h (600 mph). We can think of the engine as being stationary and the cold air moving toward it at this speed.

2. A fan at the front sucks the cold air into the engine.

3. A second fan called a compressor squeezes the air (increases its pressure) by about eight times. This slows the air down by about 60 percent and it's speed is now about 400 km/h (240 mph).

4. Kerosene (liquid fuel) is injected into the engine from a fuel tank in the plane's wing.

5. In the combustion chamber, just behind the compressor, the kerosene mixes with the compressed air and burns fiercely, giving off hot exhaust gases. The burning mixture reaches a temperature of around 900°C (1650°F).

6. The exhaust gases rush past a set of turbine blades, spinning them like a windmill.

7. The turbine blades are connected to a long axle (represented by the middle gray line) that runs the length of the engine. The compressor and the fan are also connected to this axle. So, as the turbine blades spin, they also turn the compressor and the fan.

8. The hot exhaust gases exit the engine through a tapering exhaust nozzle. The tapering design helps to accelerate the gases to a speed of over 2100 km/h (1300 mph). So the hot air leaving the engine at the back is traveling over twice the speed of the cold air entering it at the front-and that's what powers the plane. Military jets often have an after burner that squirts fuel into the exhaust jet to produce extra thrust.

The Jet Engine has proved to be an ideal engine for the aviation industry and is most definitely here to stay. (Animation www.animatedengines.com )

Conclusion

Within less than two centuries engines have become a dominant force in our lives. On the positive side they have taken the toil out of work and allowed technology and industrialization to develop at an alarming rate. The IC and Jet engines do, however, rely on a plentiful supply of refined fossil fuels. This supply will come to an end and then engines which do not rely on internal combustion may well have to be revived - Steam power, Stirling engines, etc

As regards mass transport it is imperitive to have efficient engines so Steam power could be refined in the future. The Industrial Revolution, which made Britain the Workshop of the World and underpinned its empire, was made possible by the improved roads and new canals of the eighteenth century, and by the railway network of the nineteenth. As cities grew, transport continued to be central to Britain's economy, yet its infrastructure became steadily inadequate. Faced by too many cars in too small an area, and by an urgent need to spend vast sums to modernize the public system, transport has now become one of the most pressing and controversial issues for our time. Even air-space is beginning to get congested. Aircraft density around major airports of the world are reaching dangerous levels and it is inevitable that more accidents are likely to occur in the future.

If one were to pose the question "where would society be without the engine?" it is likely that we would still have a society based on agriculture. Perhaps at the end of the current century we will have to embrace that kind of lifestyle again. We know from past experiences that it has the great advantage of being sustainable.

Features and texts for reading

Transport in Britain - from Canal lock to Gridlock ---Philip Bagwell and Peter Lyth, Hambledon Press 2002 ISBN Number 1 85285 263 1 Chapter 9, pages 143 - 158, gives a good account of how Technology and Transport are interwoven.

On the move - essays in Labour and Transport History --- Ed Chris. Wrigley and John Shepherd, ( these essays were presented to Philip Bagwell in appreciation for his work in transportation and the Labour movement) Hambledon Press 1991 ISBN Number 1 85285 060 4 ( Note. The Aisgill accident of 1913, page 123 - 154 shows how Driver William Nicholson and Fireman James Metcalf were so busy feeding water into the train's boiler with a faulty injector that they failed to see a red signal. This oversight was compounded by the fact that the driver of the broken down train had failed to put detonators on the line as an added warning to any approaching locomotive. The time of the accident was 3:00 am on a dark rainy September morning just half a mile before the Aisgill signal box.)

Industrial Steam Locomotives ---Geoffrey Hayes, Shire Publications Ltd, 2ndEd. 1998

Internal Combustion Engines , Mc Graw Hill, 1994 -----------V. Ganesan page 16 gives a comparison table between "two stroke" and "four stroke engines.

Available as Google book.

Introduction to Internal Combustion Engines, Oxford Press, 3rd Ed 1998 R. Stone

Locomotion -History of Railways --------TV BBC2 ------------ Dan Snow

How Britain worked TV Ch 4 ------------------------------------Guy Martin