This is because with the two-stroke cycle, there are twice as many combustion events which produce the power per revolution. It turns out that the diesel two-stoke engine is really much more elegant and efficient than the two-stroke gasoline engine.
You might be thinking, if this engine is about 24 times the size of a big V-8 car engine, and uses a two-stroke instead of a four-stroke cycle, why does it only make about 10 times the power? The reason is that this engine is designed to produce 3, hp continuously, and it lasts for decades.
If you continuously ran the engine in your car at full power, you'd be lucky if it lasted a week. This giant engine is hooked up to an equally impressive generator.
It is about 6 feet 1. At peak power, this generator makes enough electricity to power a neighborhood of about 1, houses! So where does all this power go? It goes into four, massive electric motors located in the trucks. The trucks are the heaviest things on the train -- each one weighs 37, pounds 16, kg. The trucks do several jobs.
They support the weight of the locomotive. They provide the propulsion, the suspensions and the braking. As you can imagine, they are tremendous structures.
The traction motors provide propulsion power to the wheels. There is one on each axle. Each motor drives a small gear, which meshes with a larger gear on the axle shaft. This provides the gear reduction that allows the motor to drive the train at speeds of up to mph. The trucks also provide the suspension for the locomotive. The weight of the locomotive rests on a big, round bearing , which allows the trucks to pivot so the train can make a turn.
Below the pivot is a huge leaf spring that rests on a platform. The platform is suspended by four, giant metal links , which connect to the truck assembly. These links allow the locomotive to swing from side to side. The weight of the locomotive rests on the leaf springs , which compress when it passes over a bump. This isolates the body of the locomotive from the bump.
The links allow the trucks to move from side to side with fluctuations in the track. The track is not perfectly straight, and at high speeds, the small variations in the track would make for a rough ride if the trucks could not swing laterally.
The system also keeps the amount of weight on each rail relatively equal, reducing wear on the tracks and wheels.
Braking is provided by a mechanism that is similar to a car drum brake. An air-powered piston pushes a pad against the outer surface of the train wheel. In conjunction with the mechanical brakes, the locomotive has dynamic braking.
In this mode, each of the four traction motors acts like a generator, using the wheels of the train to apply torque to the motors and generate electrical current. The torque that the wheels apply to turn the motors slows the train down instead of the motors turning the wheels, the wheels turn the motors.
The current generated up to amps is routed into a giant resistive mesh that turns that current into heat.
A cooling fan sucks air through the mesh and blows it out the top of the locomotive -- effectively the world's most powerful hair dryer. On the rear truck there is also a hand brake -- yes, even trains need hand brakes.
Since the brakes are air powered, they can only function while the compressor is running. If the train has been shut down for a while, there will be no air pressure to keep the brakes engaged. Without a hand brake and the failsafe of an air pressure reservoir, even a slight slope would be enough to get the train rolling because of its immense weight and the very low rolling friction between the wheels and the track. The hand brake is a crank that pulls a chain.
It takes many turns of the crank to tighten the chain. The chain pulls the piston out to apply the brakes. You don't just hop in the cab, turn the key and drive away in a diesel locomotive. Starting a train is a little more complicated than starting your car.
The engineer climbs an 8-foot 2. He or she engages a knife switch like the ones in old Frankenstein movies that connects the batteries to the starter circuit. Then the engineer flips about a hundred switches on a circuit-breaker panel, providing power to everything from the lights to the fuel pump. Next, the engineer walks down a corridor into the engine room. He turns and holds a switch there, which primes the fuel system, making sure that all of the air is out of the system.
He then turns the switch the other way and the starter motor engages. The engine cranks over and starts running. Next, he goes up to the cab to monitor the gauges and set the brakes once the compressor has pressurized the brake system. He can then head to the back of the train to release the hand brake. Finally he can head back up to the cab and take over control from there. Once he has permission from the conductor of the train to move, he engages the bell , which rings continuously, and sounds the air horns twice indicating forward motion.
The throttle control has eight positions, plus an idle position. Each of the throttle positions is called a " notch. To get the train moving, the engineer releases the brakes and puts the throttle into notch 1. In this General Motors EMD series engine, putting the throttle into notch 1 engages a set of contactors giant electrical relays.
These contactors hook the main generator to the traction motors. Each notch engages a different combination of contactors, producing a different voltage. Some combinations of contactors put certain parts of the generator winding into a series configuration that results in a higher voltage. Others put certain parts in parallel, resulting in a lower voltage.
The traction motors produce more power at higher voltages. As the contactors engage, the computerized engine controls adjust the fuel injectors to start producing more engine power.
The brake control varies the air pressure in the brake cylinders to apply pressure to the brake shoes. Trains get traction because of the immense weight of the locomotives, and the friction generated between the wheel and rail head.
Furthermore, in less than ideal weather conditions, sand is sprayed on the rail head to reduce wheel slip. There are many factors that must come into play in order for a train to get enough traction to move heavy loads.
To assist with gaining traction, many modern locomotives are equipped with traction control systems, which will control the amount of tractive effort applied to the rail head. Weight and the skill of the engineer also come into play, as more experienced locomotive engineers are more adept in getting the train rolling faster.
Furthermore, the free rolling bearings on rolling-stock significantly contribute to momentum keeping the train rolling. A modern diesel electric locomotive weighs around , lbs, and has a tractive effort of roughly 60, lbs, thus, there is massive force on the rail head. Some modern locomotives, such as the ES44AC, are ordered with extra weight for additional tractive effort.
In short, the heavier the locomotive, the greater the tractive effort. Aerodynamic drag is also a key factor in how trains are able to gain tractive force. Trains have very little friction between the wheel and the rail-head, thus, allowing trains to move at quicker speeds on level ground than cars, which have rubber tires, thus, aerodynamic drag is greatly increased.
Contrary to popular belief, the surface of the wheel that makes contact with the rail-head is merely the size of a small coin. When the train reaches its maximum speed, the aerodynamic drag is equal to the tractive force.
Although trains can operate efficiently on level surfaces, traction is greatly affected by oil substances on the tracks caused by crushed leaves and other slippery substances, however, appropriate precautions are taken. However, when a train begins to climb a significant gradient, the weight of the locomotive produces drag and slows it down.
This is where a car with tires has an advantage, as it creates more friction, and allows the car to crest the gradient without issue. To combat this lack of traction on grades, locomotives are coupled to the rear of the train in order to push it over the hill. The amount of tractive effort supplied by a locomotive depends on the locomotive. For example, back in the days of steam, wheel slip was much more prominent than in the current age of the diesel and electric locomotive.
The only way would be to just overcome a large frictional force would be to get one car moving at at time. Once a car is moving, the axle-wheel interaction changes to kinetic friction with a lower coefficient. This is really what I wanted to do - make a model that shows these cars starting to move.
Ok, let me tell you how I am going to cheat to model this train to car coupling force. My first idea was to use a spring, but I decided against that not sure why. My plan is to just have a constant coupling force. If the distance between cars is greater than some value, there is a force pulling it forward. If the distance between cars is too small, there will be a force pushing them apart. It's that simple.
Of course, I need to add a frictional force also. For the cars, there will be some maximum static frictional force to keep it stationary. After it starts to move, this will be replaced with a constant kinetic friction. Before I start, I have to pick some values for things. I don't know why, but I decided to model this as a small train model. I don't think it really matters too much. Also, I have the coefficient of friction on the driving wheels at 0. View Iframe URL.
That is in slow motion so you can see the different cars moving at different time. Here is a plot of the position of each car relative to its starting position. In this model, the train just keeps on accelerating. Really, I should put a velocity dependent drag force on the train engine so it looks more realistic.
However, there is something pretty cool in the above plot. Look at the time difference between each car starting. It looks to be evenly spaced out in starting times. This seems to agree with the sound of a real starting train. This starting train problem is one of those weird things.
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