For example, you can have a , an , a , an or a The front set of wheels supports the front end of the locomotive, and guides it around turns. The rear set supports the rear portion. The center one or two sets are the driving wheels that are powered by the pistons. The primary tradeoff is between power and steering. This maximized its tractive force, but the downside was that it could only operate at very slow speeds. Why is this? There are two reasons. You need wheels up front that guide the locomotive back to its center position as soon as it tries to rotate sideways, and that help pull the front end to the side when negotiating a curve.
Switch engines waddle down the tracks. By midth Century, the standard locomotive was the ten-wheeler, with six driving wheels, four pilot wheels and no trailing wheels. It struck a good balance of weight between the pilot wheels and the drivers. The weight on each pair of drivers is in turn limited by the weight-bearing capacity of the rails and roadbed. The practical limit of the wheelbase is typically about 25 feet. But there were exceptions, like the Union Pacific class It worked in the prairies, where the turning radii were large, but not on the mountain routes.
To extend the wheelbase, you could use several smaller wheels or fewer larger ones.
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Locomotives with five or six drivers on each side were made, but they were rare: four on each side became standard in the latter days of steam power, each typically six feet in diameter. With more drivers, the weight of the rods connecting the wheels to the piston and to each other limits the maximum speed of the locomotive. That is why the fastest trains used locomotives with only four drivers. Other locomotives could go this fast, but were not operated at maximum speed. An older freight locomotive might have four pairs of small drivers and a pair of pilot wheels, creating a wheel configuration called a Consolidation, like the little engine that hauled my mother and me from Aberdeen to Council Bluffs that stormy night I described in an earlier essay.
The Ten-Wheeler shown earlier had four pilot wheels and six larger drivers for higher speeds, and like the Consolidation, no trailing wheels. The power of a steam locomotive also depends on how much heat can be produced in the firebox, which in turn depends on the area of the fire in the firebox. Increasing the area of the firebox made it too wide to fit between the drivers, requiring a trailing truck to carry its weight see the Atlantic, above.
Here is another tradeoff, this time between traction and power. The more weight carried by the trailing truck, the less weight on the drivers. The first trailing trucks had two wheels, with four becoming standard in later locomotives. On most locomotives, the firebox was set entirely behind the drivers, but on articulated locomotives, the firebox typically extended over the rear-most drivers — a result of the longer boiler and commensurately larger firebox.
This problem was eliminated by turning the locomotive around. The distinctive cab-forward design was possible because they burned oil which could be piped to the front. The 4-wheeled truck under the firebox now became the pilot truck. A typical steam locomotive can be dissected into a few major components: a boiler to produce steam; steam engines to rotate driving wheels; a fuel and water supply; a cab and the engineer and fireman housed therein; all carried by a frame supported by a system of wheels. Most of the information on the web applies to British locomotives, as steam locomotives are still popular across the pond.
However, the basic principles hold true for all steam locomotives. In clips of Big Boys in action, smoke and steam are artificially exaggerated for visual effect. The purpose of the boiler is to create the pressurized steam that powers the engines. It is a cylindrical tank filled with water, lying on its side. At the back is a firebox in which the fuel is burned, while at the front is a chamber called the smokebox. There spent steam from the engines, still under pressure, mixes with the hot gases from the fire and rushes out the smokestack, creating the draft that keeps the fire burning.
The firebox is also immersed in the boiler water, and together with the firetubes, heat the water to create the steam that powers the engines. The steam is typically at a pressure of to pounds per square inch. On each side of each set of drivers is a steam engine. Its job is to move the main rod back and forth. So a locomotive will always have two engines, one on each side, and will have four if it has two sets of drivers, like the Big Boys. Each engine consists of a main cylinder within which a piston is alternatively pushed back and forth by the pressurized steam created in the boiler.
Above the main cylinder is a smaller cylinder housing a valve that has three functions.
First, it controls when steam is sent to the pistons, the job done in an automobile engine by the timing mechanism. Third, it controls whether the locomotive goes backward or forward. If the locomotive has a brain, it is the valve gear. The linkage is connected to the main driving wheels, and also to a rod controlled by the engineer that adjusts the position of the gear. The dancing, rocking motion of the valve gear is fascinating to watch and adds a delicate grace to the muscular behavior of a locomotive.
Judge any attempt at accurate depiction by how the artist draws the valve gear. Superheating raises the steam temperature above the boiling point of the water, greatly increasing efficiency. At the typical boiler pressure of psi the boiling point is somewhat above degrees F: superheating can raise the temperature another or degrees. The downside is the expense of maintaining the complex tubing required.
Superheating became ubiquitous around Diesel-electric locomotives are about twice as efficient. Some locomotives burned wood, but most burned coal, and in the west, oil. Whatever the fuel, it was was typically carried in the forward section of a water-filled tender towed behind the locomotive.
Slow-moving switching locomotives that need to put all their weight on the driving wheels carried their own water and fuel — Thomas the Tank Engine, for example.
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In early locomotives, the fireman fed wood or coal into the firebox. As locomotives became larger, automatic feed devices were needed, leaving the fireman to tend the fire and adjust the water supply. The cab is a weather-protected space in which the engineer and fireman stand or sit.
In nearly all locomotives, it was at the rear end of the locomotive, between the tender and the firebox. In that essay I also cover the frame, suspension and wheel arrangements. I think we need this for its own sake, and in order to home in on where steam locomotives fit into the scheme of things.
Engines, motors and turbines convert a source of energy into rotary or reciprocating back and forth motion. Energy is quite difficult to define because it takes many forms, and we are most interested in its transformations from form to form. The sources of the energy we use on earth are nuclear fission within the earth and nuclear fusion within the sun. And of course, the ultimate source of everything, including energy, is the Big Bang.
To take one example: nuclear fusion within the sun creates electromagnetic radiation that strikes the earth and heats bodies of water; the water evaporates to form clouds; rain condenses out of the clouds to fill reservoirs; the potential energy of the elevated water is converted into rotary mechanical energy in turbines; the turbines rotate generators that create electrical energy; the electrical energy is converted back into rotary kinetic energy by an electric motor; and this energy does useful work by moving a vehicle, spinning a saw blade, or performing any of the myriad tasks for which we use electric motors.
The example is typical of an energy cascade in having many steps where energy is changed in form. Another example would be solar energy transforming chlorophyll into sugar, which powers the growth of plants, which become food that we consume either directly or via domestic animals and transform into sugar, which powers our muscles to do useful work. At each transformation of the source energy, some is lost and dissipated into the environment as diffuse heat. Only a fraction of the original source energy ends up doing what we call useful work, although some processes are much more efficient than others.
Engines that operate by burning fuel come in two varieties: internal and external combustion. Both types can further be subdivided into reciprocating piston engines and gas turbines. In an internal combustion piston engine, air and fuel burn in one or more enclosed cylinders, creating heat that expands the air, pushing on pistons that turn a crankshaft to power autos, trucks, motor vessels, small aircraft and equipment.
In an internal combustion gas turbine, fuel and air are burned in an open-ended chamber to create a continuing flow of expanding gas that moves turbine blades attached to a rotating shaft. The turbine blades expend some of their work in compressing the air entering the turbine. In a commercial turbofan or turbojet engine, the maximum amount of energy is extracted by the turbine blades to drive a propeller, with the residual used to provide additional thrust.
In the illustration, the fan really a big propeller in a housing shown on the left is turned by the turbine blades shown at the right, in the area colored red. Much of the air from the fan escapes around the engine, shown by the dark blue pointed shapes, while the air in the center passes through the multistage compressor, which is also turned by the turbine blades. The compressed air is mixed with fuel in the combustion chamber, creating hot gas that turns the turbine.
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Residual hot gas exits as a jet exhaust. The turbines blades in a military jet engine only extract the amount of energy needed to run the compressor blades; the rest of the expanding gas roars out the jet exhaust, its kinetic energy thrusting the aircraft forward.
Rockets are yet another kind of internal combustion engine. Instead of using the oxygen in air to create combustion, they carry their own oxidizing material such as liquid oxygen and can operate in a vacuum. A diesel-electric locomotive uses a diesel internal combustion engine to turn a generator, which creates electricity to power motors that turn the wheels. Steam is the working fluid of choice in most cases because changing water into steam stores energy equivalent to raising its temperature 1, degrees F. Today nearly all external combustion engines are steam turbines, where steam drives turbine blades to create rotary kinetic energy.
The turbine either drives a generator or rotates the screws in a nuclear-powered ship.
Turbines have the great advantage of having few moving part, but the turbine blades must be of a high-strength material carefully machined, and were not available until late in WWII, when working jet engines were finally developed. At the very end of the age of steam locomotives, both internal and external combustion turbines were used briefly by a few railroads. They were no match for the diesel-electric. Finally, we get to the steam engine! The classic design, invented in the late 18th Century, uses steam created by external combustion to move a piston back and forth, creating a reciprocating motion that does work by cranking a shaft or turning a wheel.
- STEAM LOCOMOTIVE.
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Such a device was possible in the 18th Century, using the iron-based technology of the time, and burning wood or coal. For me they are living creatures and I love them as others love women or horses. Since early childhood, I have adored trains. Later, I fell in love with steam locomotives, after reaching an age where the terror of the belching monsters changed slowly over to thrill, but at age 5 or 6, diesels were fine with me — I loved diesel switch engines then as now, if they are the proper kind.
My true love affair with steam locomotives really started in the summer of , just before my 8th birthday. Route It was a flag stop on the Milwaukee mainline, in the section of the line between Aberdeen and Mobridge, where — no surprise — the railroad crossed the Missouri River. Aberdeen seemed very far away to a 7-year-old, and Mobridge, 70 miles to the west, was just a legend. There was a traditional Main Street running north-south, with a classic one-block downtown complete with ice cream parlor and movie theater. Another significant source of diesel idle emissions can be railway locomotives.
Unlike trucks, most locomotive engines do not use anti-freeze in their cooling systems. Motor coach buses are another vehicle category that can experience long periods of idling of their main propulsion engine. This is primarily to maintain a comfortable interior compartment for passengers heat or air conditioning.
While not as numerous as trucks, coaches have attracted attention because, due to their large interior compartment, maintaining a comfortable interior temperature requires substantially more idling time than the typical long-haul truck or personal passenger vehicle . Long-duration idling of truck, locomotive and other diesel engines can have several negative impacts on the environment and economy, as follows:.
In North America, a large portion of onroad diesel fuel is used by Class 8 tractor trailers hauling goods. Other estimates suggest maximum idle times of up to 8 hours per day . It is therefore informative to examine the case of idling long-haul highway trucks to estimate the proportion of total daily emissions and fuel consumption that can be attributed to idling from these vehicles. The contribution of idle emissions to the total emissions from laden highway trucks can be estimated based on data from several CRC studies  .
This estimate will assume an extreme case where a truck idles for 8 hours a day and spends 10 hours on the road cruising at highway speed. Table 2 outlines the results of this estimate based on the average of the emissions and fuel consumption for 36 heavy-duty trucks. Emission factors were estimated from the average values for tests carried out at idle with no accessory loads and on the cruise mode of the HHDDT cycle.
The data in Table 2 could be used to estimate the relative contribution of idling to total emissions for the considered example. In a different approach, one can first estimate the relative idling contribution for each vehicle and then average these values. This allows a better estimate of the range of values for the idling contribution. Figure 1 shows the results of this estimate. While the averaged daily idling contribution is similar to the proportion that would be estimated from the averaged data of Table 2, the results are not necessarily identical. Range of contributions of idling to total daily emissions and fuel consumption for a truck idling for 8 hours a day.
The contribution of all emissions from idling exceeds the contribution of fuel consumption. These estimates assume no accessory loads and a low speed idle. If cab heat, air conditioning or a significant electrical load is required, the idling proportion will increase. Two factors could account for the disproportionately high CO and HC emissions at idle.