Diesel exhaust
Diesel exhaust is the gaseous exhaust produced by a diesel type of internal combustion engine, plus any contained particulates. Its composition may vary with the fuel type or rate of consumption, or speed of engine operation, whether the engine is in an on-road vehicle, farm vehicle, marine vessel, or stationary generator or other application. Diesel exhaust is a Group 1 carcinogen, which causes lung cancer and has a positive association with bladder cancer, it contains several substances that are listed individually as human carcinogens by the IARC. Methods exist to particulate matter in the exhaust; the primary products of petroleum fuel combustion in air are carbon dioxide and nitrogen. The other components exist from incomplete combustion and pyrosynthesis. While the distribution of the individual components of raw diesel exhaust varies depending on factors like load, engine type, etc. the adjacent table shows a typical composition. The physical and chemical conditions that exist inside any such diesel engines under any conditions differ from spark-ignition engines, because, by design, diesel engine power is directly controlled by the fuel supply, not by control of the air/fuel mixture, as in conventional gasoline engines.
As a result of these differences, diesel engines produce a different array of pollutants than spark-driven engines, differences that are sometimes qualitative, but more quantitative. For instance, diesel engines produce one-twenty-eighth the carbon monoxide that gasoline engines do, as they burn their fuel in excess air at full load. However, the lean-burning nature of diesel engines and the high temperatures and pressures of the combustion process result in significant production of gaseous nitrogen oxides, an air pollutant that constitutes a unique challenge with regard to their reduction. While total nitrogen oxides from petrol cars have decreased by around 96% through adoption of exhaust catalytic converters as of 2012, diesel cars still produce nitrogen oxides at a similar level to those bought 15 years earlier under real-world tests. Modern on-road diesel engines use selective catalytic reduction systems to meet emissions laws, as other methods such as exhaust gas recirculation cannot adequately reduce NOx to meet the newer standards applicable in many jurisdictions.
Auxiliary diesel systems designed to remediate the nitrogen oxide pollutants are described in a separate section below. Moreover, the fine particles in diesel exhaust has traditionally been of greater concern, as it presents different health concerns and is produced in significant quantities by spark-ignition engines; these harmful particulate contaminants are at their peak when such engines are run without sufficient oxygen to combust the fuel. From the particle emission standpoint, exhaust from diesel vehicles has been reported to be more harmful than those from petrol vehicles. Diesel exhausts, long known for their characteristic smells, changed with the reduction of sulfur content of diesel fuel, again when catalytic converters were introduced in exhaust systems. So, diesel exhausts continue to contain an array of inorganic and organic pollutants, in various classes, in varying concentrations, depending on fuel composition and engine running conditions; the following are classes of chemical compounds.
The following are classes of specific chemicals. §Includes all regioisomers of this aromatic compound. See ortho-, meta-, para-isomer descriptions at each compound's article. Vehicle exhaust contains much water vapor. There has been research into ways that troops in deserts can recover drinkable water from their vehicles' exhaust gases. To reduce particulate matter from heavy-duty diesel engines in California, the California Air Resources Board created the Carl Moyer Program to provide funding for upgrading engines ahead of emissions regulations. In 2008, the California Air Resources Board implemented the 2008 California Statewide Truck and Bus Rule which requires all heavy-duty diesel trucks and buses, with a few exceptions, that operate in California to either retrofit or replace engines in order to reduce diesel particulate matter; the US Mine Safety and Health Administration issued a health standard in January 2001 designed to reduce diesel exhaust exposure in underground metal and nonmetal mines.
Emissions from diesel vehicles have been reported to be more harmful than those from petrol vehicles. Diesel combustion exhaust is a source of atmospheric soot and fine particles, a component of the air pollution implicated in human cancer and lung damage, mental functioning. Moreover, diesel exhaust contains contaminants listed as carcinogenic for humans by the IARC, as present in their List of IARC Group 1 carcinogens. Diesel exhaust pollution is thought to account for around one quarter of the pollution in the air in pre
Alkyne
In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula CnH2n−2. Alkynes are traditionally known as acetylenes, although the name acetylene refers to C2H2, known formally as ethyne using IUPAC nomenclature. Like other hydrocarbons, alkynes are hydrophobic but tend to be more reactive. Alkynes are characteristically more unsaturated than alkenes, thus they add two equivalents of bromine. Other reactions are listed below. In some reactions, alkynes are less reactive than alkenes. For example, in a molecule with an -ene and an -yne group, addition occurs preferentially at the -ene. Possible explanations involve the two π-bonds in the alkyne delocalising, which would reduce the energy of the π-system or the stability of the intermediates during the reaction, they show greater tendency to oligomerize than alkenes do.
The resulting polymers, called polyacetylenes are conjugated and can exhibit semiconducting properties. In acetylene, the H–C≡C bond angles are 180°. By virtue of this bond angle, alkynes are rod-like. Correspondingly, cyclic alkynes are rare. Benzyne is unstable; the C≡C bond distance of 121 picometers is much shorter than the C=C distance in alkenes or the C–C bond in alkanes. The triple bond is strong with a bond strength of 839 kJ/mol; the sigma bond contributes 369 kJ/mol, the first pi bond contributes 268 kJ/mol and the second pi-bond of 202 kJ/mol bond strength. Bonding discussed in the context of molecular orbital theory, which recognizes the triple bond as arising from overlap of s and p orbitals. In the language of valence bond theory, the carbon atoms in an alkyne bond are sp hybridized: they each have two unhybridized p orbitals and two sp hybrid orbitals. Overlap of an sp orbital from each atom forms one sp–sp sigma bond; each p orbital on one atom overlaps one on the other atom, forming two pi bonds, giving a total of three bonds.
The remaining sp orbital on each atom can form a sigma bond to another atom, for example to hydrogen atoms in the parent acetylene. The two sp orbitals project on opposite sides of the carbon atom. Internal alkynes feature carbon substituents on each acetylenic carbon. Symmetrical examples include 3-hexyne. Terminal alkynes have the formula RC2H. An example is methylacetylene. Terminal alkynes, like acetylene itself, are mildly acidic, with pKa values of around 25, they are far more acidic than alkenes and alkanes, which have pKa values of around 40 and 50, respectively. The acidic hydrogen on terminal alkynes can be replaced by a variety of groups resulting in halo-, silyl-, alkoxoalkynes; the carbanions generated by deprotonation of terminal alkynes are called acetylides. In systematic chemical nomenclature, alkynes are named with the Greek prefix system without any additional letters. Examples include octyne. In parent chains with four or more carbons, it is necessary to say. For octyne, one can either write oct-3-yne when the bond starts at the third carbon.
The lowest number possible is given to the triple bond. When no superior functional groups are present, the parent chain must include the triple bond if it is not the longest possible carbon chain in the molecule. Ethyne is called by its trivial name acetylene. In chemistry, the suffix -yne is used to denote the presence of a triple bond. In organic chemistry, the suffix follows IUPAC nomenclature. However, inorganic compounds featuring unsaturation in the form of triple bonds may be denoted by substitutive nomenclature with the same methods used with alkynes. "-diyne" is used when there are two triple bonds, so on. The position of unsaturation is indicated by a numerical locant preceding the "-yne" suffix, or'locants' in the case of multiple triple bonds. Locants are chosen. "-yne" is used as an infix to name substituent groups that are triply bound to the parent compound. Sometimes a number between hyphens is inserted before it to state which atoms the triple bond is between; this suffix arose as a collapsed form of the end of the word "acetylene".
The final" - e" disappears. Commercially, the dominant alkyne is acetylene itself, used as a fuel and a precursor to other compounds, e.g. acrylates. Hundreds of millions of kilograms are produced annually by partial oxidation of natural gas: 2 CH4 + 3/2 O2 → HC≡CH + 3 H2OPropyne industrially useful, is prepared by thermal cracking of hydrocarbons. Most other industrially useful alkyne derivatives are prepared from acetylene, e.g. via condensation with formaldehyde. Specialty alkynes are prepared by dehydrohalogenation of vicinal alkyl dihalides or vinyl halides. Metal acetylides can be coupled with primary alkyl halides. Via the Fritsch–Buttenberg–Wiechell rearrangement, alkynes are prepared from vinyl bromides. Alkynes can be prepared from aldehydes using the Corey–Fuchs reaction and from aldehydes or ketones by the Seyferth–Gilbert homologation. In the alkyne zipper reaction, alkynes are generated from other alkynes by treatment with a strong base. Featuring a reactive functional group, alkynes participate in many organic reactions.
Such use was pioneered by Ralph Raphael, who in 1955 wrote the first book describing their versatility as intermediates in synthesis. Alkynes character
Exhaust gas
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, petrol, biodiesel blends, diesel fuel, fuel oil, or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack, or propelling nozzle, it disperses downwind in a pattern called an exhaust plume. It is a major component of motor vehicle emissions, which can include: Crankcase blow-by Evaporation of unused gasolineMotor vehicle emissions contribute to air pollution and are a major ingredient in the creation of smog in some large cities. A 2013 study by MIT indicates that 53,000 early deaths occur per year in the United States alone because of vehicle emissions. According to another study from the same university, traffic fumes alone cause the death of 5,000 people every year just in the United Kingdom; the largest part of most combustion gas is nitrogen, water vapor, carbon dioxide. A small part of combustion gas is undesirable, noxious, or toxic substances, such as carbon monoxide from incomplete combustion, hydrocarbons from unburnt fuel, nitrogen oxides from excessive combustion temperatures, particulate matter.
Exhaust gas temperature is important to the functioning of the catalytic converter of an internal combustion engine. It may be measured by an exhaust gas temperature gauge. EGT is a measure of engine health in gas-turbine engines. During the first two minutes after starting the engine of a car that has not been operated for several hours, the amount of emissions can be high; this occurs for two main reasons: Rich air-fuel ratio requirement in cold engines: When a cold engine is started, the fuel does not vaporize creating higher emissions of hydrocarbons and carbon monoxide, which diminishes only as the engine reaches operating temperature. The duration of this start-up phase has been reduced by advances in materials and technology, including computer-controlled fuel injection, shorter intake lengths, pre-heating of fuel and/or inducted air. Inefficient catalytic converter under cold conditions: Catalytic converters are inefficient until up to their operating temperature; this time has been much reduced by moving the converter closer to the exhaust manifold and more so placing a small yet quick-to-heat-up converter directly at the exhaust manifold.
The small converter handles the start-up emissions, which allows enough time for the larger main converter to heat up. Further improvements can be realised in many ways, including electric heating, thermal battery, chemical reaction preheating, flame heating and superinsulation. Comparable with the European emission standards EURO III as it was applied on October 2000 In 2000, the United States Environmental Protection Agency began to implement more stringent emissions standards for light duty vehicles; the requirements were phased in beginning with 2004 vehicles and all new cars and light trucks were required to meet the updated standards by the end of 2007. In spark-ignition engines the gases resulting from combustion of the fuel and air mix are called exhaust gases; the composition varies from petrol to diesel engines, but is around these levels: The 10% oxygen for "diesel" is if the engine was idling, e.g. in a test rig. It is much less. Exhaust gas from an internal combustion engine whose fuel includes nitromethane will contain nitric acid vapour, corrosive, when inhaled causes a muscular reaction making it impossible to breathe.
People exposed to it should wear a gas mask. In aircraft gas turbine engines, "exhaust gas temperature" is a primary measure of engine health; the EGT is compared with a primary engine power indication called "engine pressure ratio". For example: at full power EPR there will be a maximum permitted EGT limit. Once an engine reaches a stage in its life where it reaches this EGT limit, the engine will require specific maintenance in order to rectify the problem; the amount the EGT is below the EGT limit is called EGT margin. The EGT margin of an engine will be greatest when the engine has been overhauled. For most airlines, this information is monitored remotely by the airline maintenance department by means of ACARS. In jet engines and rocket engines, exhaust from propelling nozzles which in some applications shows shock diamonds. Flue gas Flue gas emissions from fossil fuel combustion In steam engine terminology the exhaust is steam, now so low in pressure that it can no longer do useful work. Mono-nitrogen oxides NO and NO2 react with ammonia and other compounds to form nitric acid vapor and related particles.
Small particles can penetrate into sensitive lung tissue and damage it, causing premature death in extreme cases. Inhalation of NO species increases the risk of colorectal cancer, and inhalation of such particles may cause or worsen respiratory diseases such as emphysema and bronchitis and heart disease. In a 2005 U. S. EPA study the largest emissions of NOx came from on road motor vehicles, with the second largest contributor being non-road equipment, gasoline and diesel stations; the resulting nitric acid may be washed into soil, where it becomes nitrate, useful to growing plants. When oxides of nitrogen and volatile organic compounds react in the presence of sunlight, ground l
Diesel engine
The Diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel, injected into the combustion chamber, is caused by the elevated temperature of the air in the cylinder due to the mechanical compression. Diesel engines work by compressing only the air; this increases the air temperature inside the cylinder to such a high degree that atomised Diesel fuel injected into the combustion chamber ignites spontaneously. With the fuel being injected into the air just before combustion, the dispersion of the fuel is uneven; the process of mixing air and fuel happens entirely during combustion, the oxygen diffuses into the flame, which means that the Diesel engine operates with a diffusion flame. The torque a Diesel engine produces is controlled by manipulating the air ratio; the Diesel engine has the highest thermal efficiency of any practical internal or external combustion engine due to its high expansion ratio and inherent lean burn which enables heat dissipation by the excess air.
A small efficiency loss is avoided compared with two-stroke non-direct-injection gasoline engines since unburned fuel is not present at valve overlap and therefore no fuel goes directly from the intake/injection to the exhaust. Low-speed Diesel engines can reach effective efficiencies of up to 55%. Diesel engines may be designed as either four-stroke cycles, they were used as a more efficient replacement for stationary steam engines. Since the 1910s they have been used in ships. Use in locomotives, heavy equipment and electricity generation plants followed later. In the 1930s, they began to be used in a few automobiles. Since the 1970s, the use of Diesel engines in larger on-road and off-road vehicles in the US has increased. According to Konrad Reif, the EU average for Diesel cars accounts for 50% of the total newly registered; the world's largest Diesel engines put in service are 14-cylinder, two-stroke watercraft Diesel engines. In 1878, Rudolf Diesel, a student at the "Polytechnikum" in Munich, attended the lectures of Carl von Linde.
Linde explained that steam engines are capable of converting just 6-10 % of the heat energy into work, but that the Carnot cycle allows conversion of all the heat energy into work by means of isothermal change in condition. According to Diesel, this ignited the idea of creating a machine that could work on the Carnot cycle. After several years of working on his ideas, Diesel published them in 1893 in the essay Theory and Construction of a Rational Heat Motor. Diesel was criticised for his essay, but only few found the mistake that he made. Diesel's idea was to compress the air so that the temperature of the air would exceed that of combustion. However, such an engine could never perform any usable work. In his 1892 US patent #542846 Diesel describes the compression required for his cycle: "pure atmospheric air is compressed, according to curve 1 2, to such a degree that, before ignition or combustion takes place, the highest pressure of the diagram and the highest temperature are obtained-that is to say, the temperature at which the subsequent combustion has to take place, not the burning or igniting point.
To make this more clear, let it be assumed that the subsequent combustion shall take place at a temperature of 700°. In that case the initial pressure must be sixty-four atmospheres, or for 800° centigrade the pressure must be ninety atmospheres, so on. Into the air thus compressed is gradually introduced from the exterior finely divided fuel, which ignites on introduction, since the air is at a temperature far above the igniting-point of the fuel; the characteristic features of the cycle according to my present invention are therefore, increase of pressure and temperature up to the maximum, not by combustion, but prior to combustion by mechanical compression of air, there upon the subsequent performance of work without increase of pressure and temperature by gradual combustion during a prescribed part of the stroke determined by the cut-oil". By June 1893, Diesel had realised his original cycle would not work and he adopted the constant pressure cycle. Diesel describes the cycle in his 1895 patent application.
Notice that there is no longer a mention of compression temperatures exceeding the temperature of combustion. Now it is stated that the compression must be sufficient to trigger ignition. "1. In an internal-combustion engine, the combination of a cylinder and piston constructed and arranged to compress air to a degree producing a temperature above the igniting-point of the fuel, a supply for compressed air or gas. See US patent # 608845 filed 1895 / granted 1898In 1892, Diesel received patents in Germany, the United Kingdom and the United States for "Method of and Apparatus for Converting Heat into Work". In 1894 and 1895, he filed patents and addenda in various
Nanoparticle
Nanoparticles are particles between 1 and 100 nanometres in size with a surrounding interfacial layer. The interfacial layer is an integral part of nanoscale matter, fundamentally affecting all of its properties; the interfacial layer consists of ions and organic molecules. Organic molecules coating inorganic nanoparticles are known as stabilizers and surface ligands, or passivating agents. In nanotechnology, a particle is defined as a small object that behaves as a whole unit with respect to its transport and properties. Particles are further classified according to diameter; the term "nanoparticle" is not applied to individual molecules. Ultrafine particles are the same as nanoparticles and between 1 and 100 nm in size, as opposed to fine particles are sized between 100 and 2,500 nm, coarse particles cover a range between 2,500 and 10,000 nm; the reason for the synonymous definition of nanoparticles and ultrafine particles is that, during the 1970s and 80s, when the first thorough fundamental studies with "nanoparticles" were underway in the USA and Japan, they were called "ultrafine particles".
However, during the 1990s before the National Nanotechnology Initiative was launched in the USA, the new name, "nanoparticle," had become more common. Nanoparticles can exhibit size-related properties different from those of either fine particles or bulk materials. Nanoclusters have at least one dimension a narrow size distribution. Nanopowders nanoparticles, or nanoclusters. Nanometer-sized single crystals, or single-domain ultrafine particles, are referred to as nanocrystals. According to ISO Technical Specification 80004, a nanoparticle is defined as a nano-object with all three external dimensions in the nanoscale, whose longest and shortest axes do not differ with a significant difference being a factor of at least 3; the terms colloid and nanoparticle are not interchangeable. A colloid is a mixture; the term applies only if the particles are larger than atomic dimensions but small enough to exhibit Brownian motion, with the critical size range ranging from nanometers to micrometers. Colloids can contain particles too large to be nanoparticles, nanoparticles can exist in non-colloidal form, for examples as a powder or in a solid matrix.
Although nanoparticles are associated with modern science, they have a long history. Nanoparticles were used by artisans as far back as Rome in the fourth century in the famous Lycurgus cup made of dichroic glass as well as the ninth century in Mesopotamia for creating a glittering effect on the surface of pots. In modern times, pottery from the Middle Ages and Renaissance retains a distinct gold- or copper-colored metallic glitter; this luster is caused by a metallic film, applied to the transparent surface of a glazing. The luster can still be visible if the film has resisted other weathering; the luster originates within the film itself, which contains silver and copper nanoparticles dispersed homogeneously in the glassy matrix of the ceramic glaze. These nanoparticles are created by the artisans by adding copper and silver salts and oxides together with vinegar and clay on the surface of previously-glazed pottery; the object is placed into a kiln and heated to about 600 °C in a reducing atmosphere.
In heat the glaze softens, causing the copper and silver ions to migrate into the outer layers of the glaze. There the reducing atmosphere reduced the ions back to metals, which came together forming the nanoparticles that give the color and optical effects. Luster technique showed; the technique originated in the Muslim world. As Muslims were not allowed to use gold in artistic representations, they sought a way to create a similar effect without using real gold; the solution they found was using luster. Michael Faraday provided the first description, in scientific terms, of the optical properties of nanometer-scale metals in his classic 1857 paper. In a subsequent paper, the author points out that: "It is well known that when thin leaves of gold or silver are mounted upon glass and heated to a temperature, well below a red heat, a remarkable change of properties takes place, whereby the continuity of the metallic film is destroyed; the result is that white light is now transmitted, reflection is correspondingly diminished, while the electrical resistivity is enormously increased."
Nanoparticles are of great scientific interest as they are, in effect, a bridge between bulk materials and atomic or molecular structures. A bulk material should have constant physical properties regardless of its size, but at the nano-scale size-dependent properties are observed. Thus, the properties of materials change as their size approaches the nanoscale and as the percentage of the surface in relation to the percentage of the volume of a material becomes significant. For bulk materials larger than one micrometer, the percentage of the surface is insignificant in relation to the volume in the bulk of the material; the interesting and sometimes unexpected properties of nanoparticles are therefore due to the large surface area of the material, which dominates the contributions made by the small bulk of the material. Nanoparticles possess unexpected optical properties as they are small enough
InterCity 125
The InterCity 125 is a diesel-powered passenger train built by British Rail Engineering Limited between 1975 and 1982. Each is made up of one at each end of six to nine Mark 3 carriages; the name is derived from its top operational speed of 125 mph. The sets were classified as Classes 253 and 254; as of July 2018, InterCity 125s remained in service with CrossCountry, East Midlands Trains, Great Western Railway, London North Eastern Railway and Network Rail. Most of those operating with GWR and LNER will be replaced by Class 800, 801 and 802s by December 2019. In the 1950s and early 1960s, the British Transport Commission was modernising its rail network. In particular, it wanted to increase intercity speeds, so that the railways could compete more with the new motorways; the government was unwilling to fund new railways, so the BTC focused its attention on increasing line speeds through the development of new trains and minor modifications to the existing infrastructure. A team of engineers was assembled at the Railway Technical Centre in Derby in the early 1960s, with the aim of designing and developing an Advanced Passenger Train, that would be capable of at least 125 miles per hour and incorporate many features not seen on British railways—such as tilting to allow higher speeds on curves.
The APT project had suffered repeated delays, in 1970, the British Railways Board decided that it was not sufficiently developed to be able to provide modernisation of the railways in the short term. Thus, at the instigation of Terry Miller, Chief Engineer, the BRB authorised the development of a high-speed diesel train for short-term use until the APT was able to take over. An operational prototype of this train was to be built by 1972; the prototype high-speed diesel train, to become the InterCity 125, was to be formed of a rake of passenger coaches sandwiched between two power cars, one at each end. The decision to use two power cars was taken early in the project as design engineers had calculated that the train would need 4,500 horsepower to sustain the required speed of 125 miles per hour on the routes for which it was being designed, it was established that no single "off-the-shelf" diesel engine was capable of producing such power. A factor in the decision was that the use of two locomotives, operating in push–pull formation, would cause less wear on the rails than a single, much heavier, locomotive.
The framework of the new locomotive, classified British Rail Class 41, was built at Crewe Works before being transferred to Derby Litchurch Lane Works for completion. The design of the locomotive incorporated a driving desk fitted around the driver, a sound-proofed door between the cab and the engine room, unusually, no side windows; the prototype became the first diesel locomotive in British railway history to use AC alternators in place of a DC generator, with the output converted to DC when used for traction. The prototype train of seven coaches and two locomotives was completed in August 1972 and by the autumn was running trials on the main line; the following year, high-speed testing was being undertaken on the "racing stretch" of the East Coast Main Line between York and Darlington. The set had been reduced to two power cars and five trailers, there seems to have been a concerted attempt to see how fast the train would go. On 6 June 1973 131 mph was reached, this maximum was raised as the days passed.
By 12 June a world diesel speed record of 143.2 mph was achieved. The drivers believed that 150 mph was possible but the BRB issued instructions for the high speed tests to cease, it was believed at the time that this was because the BRB wanted to promote the APT as the future of high speed rail travel in the UK. The fixed-formation concept was proven in trial running between 1973 and 1976, British Rail decided to build 27 production HSTs to transform InterCity services between London Paddington, Bristol and Swansea; the first production power car, numbered 43002, was delivered in late 1975, with a different appearance from the prototype. The streamlined front end lacked conventional buffers, the drawgear was hidden under a cowling; the single cab front window was much larger than the prototype's, side windows were included. There was no driving position at the inner end; the appearance of the train is the work of British designer Kenneth Grange. Grange was approached just to design the livery for the train, but under his own impetus decided to redesign the body, working with aerodynamics engineers.
As he put it, " It was rather quite brutal, rather clumsy. I thought,'Oh I'd like to get my hands on that', although the brief was nothing to do with the shape not at all." He went on to persuade them to adopt it. An InterCity 125 consists of two Class 43 diesel-electric power cars, each powered by 2,250 bhp Paxman Valenta engines, a set of six to nine Mark 3 coaches. Key features of the design are the high power-to-weight ratio of the locomotives, which were purpose-built for high-speed passenger travel, improved crashworthiness over previous models, bi-directional running avoiding the need for a locomotive to run around at terminating stations; until the HST's introduction, the maximum speed of British trains was limited to 100 miles per hour. The HST allowed a 25% increase in
. Encyclopedia Americana. 1920.