1. + Powering Transportation - Identify the three main types of motion - Describe the two main types of engines - Discuss electric and fluid power motors - List several alternative energy sources for transportation - Explain how design affects vehicle performance

2. + Prime Movers Prime movers supply the power (use of energy to create movement) in transportation. Engines and motors are the prime movers we will be talking about. While the terms “engine” and “motor” are often used interchangeably, which is not wrong, it is possible to be more exact: An Engine is a machine that gets its energy from fuel (which is usually burned to create heat). A Motor is a machine that gets its energy from an external source.

3. + Types of Motion There are three types of motion that engines and motors produce: Reciprocating motion is a back-and-forth oscillation. The most common form is through a reciprocating internal combustion engine, where the piston(s) move up and down or side to side. Rotary motion is circular motion. Turbines and rotors produce rotary motion and can be found in trains and large ships. Linear motion is motion in a straight line. Jet or rocket engines are examples of linear motion engines.

4. + Reciprocating Motion Most highway vehicles, some rail vehicles, propeller driven aircraft and small watercraft all use reciprocating internal combustion engines. During operation, the reciprocating motion of a piston is changed into the circular motion of the crankshaft. Engines of this type are classified by the number of piston cylinders and their arrangement. The larger the piston (in both weight and size), the slower the engine usually operates: Very large engines in trains and ships may turn at only 100-400 RPM Very small engines in model airplanes may turn at well over 20,000 RPM

5. + Pros and Cons of Reciprocating Engines There are several major advantages to using reciprocating engines: The RPM of these engines can be quickly and easily controlled, which makes it ideal for stop-and-go driving and other situations where the speed changes quickly. The cost of manufacturing a reliable engine is quite low. The cost of repairing or rebuilding an engine is also low compared to other types of internal combustion engines. As always, there are trade-offs and the disadvantages of this type of engine include: Only a limited amount of energy can be economically produced by each cylinder. This means that higher horsepower engines generally have more cylinders. They have more moving parts that other types of engines and weigh more, which reduces efficiency. The higher the RPM of the engine, the shorter its lifespan. Lastly, these engines require quick-burning fuels which tend to be more expensive.

6. + Rotary Motion In a rotary engine, the expanding gases push against a turbine or rotor, which causes it to turn. A turbine is a lot like a fan: it has a wheel with evenly spaced blades or fins attached. A rotor is a triangle-shaped part of a rotary engine that revolves in a specifically shaped combustion chamber. Rotary engines generally produce more power for the same size than reciprocating engines because the individual pieces have less mass and produce less friction. They work best when the same RPM is held for extended periods of time. Some trains use a “gas turbine” engine that powers electric generators that are then used to more it. Gas turbines are also used in large ships where the rotational motion is directly translated to the propellers of the ship.

7. + Pros and Cons of Rotary Engines Advantages include: They have fewer moving parts to maintain and cause friction. Horsepower can be increased by simply enlarging the engine, where extra pistons would have to be added in a reciprocating engine. A wide variety of fuels can be burned to produce the necessary expanding gases. A constant RPM can be maintained for very long periods of time without damage to the engine parts. Disadvantages include: Quick changes in RPM cannot be made efficiently. The cost of manufacturing and rebuilding rotary engines is larger than reciprocating engines. Because of the high maintained RPM, the engine must be kept well lubricated and in perfect balance.

8. + Linear Motion Rocket and jet engines are the most powerful types of engines. As with other forms of internal combustion engines, these engines require fuel that is burned to rapidly expand it. However, in this case, the spent fuel is simply propelled out the back of the engine and Newton’s 3 rd Law makes sure that the vehicle is propelled forward as a result. The more fuel that is burned, the faster the vehicle will accelerate. The only difference between a rocket engine and a jet engine is where the engine gets its oxygen for combustion (since oxygen is required for any kind of combustion). Jet engines use oxygen from the atmosphere by directing air into the combustion chamber from the front. Rocket engines use oxygen that is on board along with the fuel. This allows the rocket to operate outside of the Earth’s atmosphere. The fuel supply can be carried as a solid or as separate liquids that, when combined, combust in the chamber to produce the thrust.

9. + Pros and Cons of Linear Engines +: Very high horsepower or thrust can be achieved for an amount of fuel. Several different types of solid or liquid fuels can be used to make the expanding gases. There are no moving parts to transfer power to the vehicle so there is no power lost to friction or in making the internals move. This also means that there are fewer things that can break. -: Solid fuels cannot be “turned off” once they are started. They will burn until all of the fuel is gone. Manufacturing and rebuilding costs are quite high despite the lack of moving parts. Rocket engines designed for space can only be used once (for now). Changing the direction of motion is nearly impossible from the engine, so other structural components must be used.

10. + Systems of Internal Combustion Engines ICEs are the most common form of engine. They power almost all vehicles you would use in your everyday life. The hallmark of an ICE is the fact that the fuel is burned within the engine itself. Most engines have 9 subsystems that include: Mechanical system: these are the moving parts of the system (e.g. the piston, crankshaft, driveshaft, etc.) Lubrication system: The goal of this system is to reduce friction so that more power can go into motion. Air induction system: Since oxygen is required for combustion, this system directs air into the combustion chamber Fuel system: This system directs the combustible fuel into the chamber. Ignition system: This system ignites the air/fuel mixture at exactly the right moment. Charging system: This system is used to store energy in the battery to supply electrical current for many other systems. Starting system: The starting system starts the engine. It may be a simple rope on a pulley for a lawnmower, or it may use a motor and electricity from a storage battery. Once the engine is started, however, the starting system must stop operating. Cooling system: All engines produce heat and that heat must be controlled. Small engines are air-cooled, but larger engines may be water-cooled. Exhaust and emissions system: The exhaust system vents spent gases through a tailpipe. This usually includes a place (the catalytic converter in cars) where emission pollutants are reduced before actually moving out into the atmosphere.

11. + Internal Combustion Engine Operation Reciprocating ICEs are either a four-stroke or two-stroke design. Almost all automobiles, and large motorcycles use four-stroke engines. A four-stroke engine has, obviously, 4 strokes in one combustion cycle: Intake Stroke: where the air/fuel mixture is taken into the combustion chamber. Compression Stroke: where the gases are squeezed by the momentum of the piston. Power Stroke: where the sparkplug fires and the gases are ignited. The ensuing rapid expansion forces the piston down giving the engine its power. Exhaust Stroke: where the piston comes back up, pushing the spent gases out of the combustion chamber.

12. + Diagram of a 4-Stroke ICE

13. + 2-Stroke and Diesel Engines Two-Stroke Engines: A two-stroke engine combines the intake and exhaust strokes into the power stroke from the four-stroke engine which requires only one stroke each of up and down to complete the cycle. Two-stroke engines have fewer moving parts and a shorter cycle, which makes them cheaper and able to run at higher RPM. Unfortunately, they also produce a lot more pollution because the lubricating oil gets mixed in with the fuel and air and gets burned and expelled. Diesel Engines: A diesel engine can be either a four-stroke or a two-stroke engine. The main difference is the lack of a sparkplug for ignition. Instead of using a spark to ignite the air/fuel mixture, diesel fuel auto-ignites when it’s squeezed because it gets so hot. However, because of the high pressures necessary, diesel engines tend to be heavier. Diesel engines are quite common in larger applications like highway trucks, delivery trucks and some personal light trucks/cars. Diesel fuel costs less to produce than gasoline, it burns more completely than gasoline, which means better mileage. Advances in emission control systems and fuel engineering have reduced emissions of CO 2 to below levels found in gasoline emissions. Emissions of other, more dangerous, gases are quite a bit higher in diesel than in gasoline.

14. + Diagram of a 2-Stroke Engine

15. + External Combustion Engines As the name implies, ECEs burn their fuel outside of the engine. They can provide either reciprocating or rotary motion, but not linear. Almost all of the ECEs used in transportation are steam-driven; that is, they use their fuel to boil steam which is then used to spin a turbine or drive a piston. The fuel used can come from many different sources: In the earliest stages, coal was burned. Oil is now much more common. Nuclear fuel has been used in modern military vehicles for some time. The main disadvantages to ECEs are: that the boiler apparatus takes up a very large amount of space. Steam is also dangerous to handle, and the water corrodes metals. Continuous care and preventative maintenance are required.

16. + Diagram of an External Combustion Engine

17. + Electric Motors Electric motors have been used for many years to power urban mass-transit vehicles. These get their electricity from hanging wires or a “hot” third rail on the ground. Cars, on the other hand, rely on batteries to power their electric motors. Batteries are heavy, require frequent recharging, and can lose power under cold conditions. Although the cars don’t generate any pollution themselves, the electricity used to charge the batteries could be generated using any number of sources, and those could be polluting.

18. + Fluid-Powered Motors and Motor & Diesel Engine Combinations Fluid-Powered Motors: Fluid-powered motors can be either hydraulic or pneumatic. They can generate considerable power, but tend to be very low speed in application. Because of this, they are often used in heavy machinery and other slow-moving vehicles. Both hydraulic and pneumatic motors use increases and decreases in pressure to drive the application. Motor-Diesel Engine Combinations: Most modern locomotives use a diesel engine to power an electric motor. These work just like rotary engines except that the rotors are used to turn an electric generator instead of being used for propulsion. The generator produces the electricity needed to power the motor.

19. + Alternative Power One of the biggest problems facing transportation is finding inexpensive power sources that are plentiful in supply and that do not harm the environment. Wind Power has been used for centuries to power ships, though recently something called turbosails have been developed that can generate up to 4 times the thrust of traditional sails. Solar Power for transportation is almost exclusively in the form of photovoltaic cells that then use the electricity to charge batteries. The batteries then power an electric motor. Alternative Fuels are defined by the EPA as a fuel that is substantially not petroleum and yields substantial environmental benefits and energy security. Examples include: natural gas, ethanol, methanol, biodiesel, and hydrogen. These fuels are further expanded upon in the earlier notes “Energy Sources and Conversions”.

20. + Alternative Power (cont.) Magnetic Levitation, or maglev, propulsion systems are rail systems on the principle that like poles of a magnet repel each other. These systems are near frictionless, quiet, smooth, and very fast, reaching speeds of up to 300 mph. The first commercial maglev train was built in Shanghai, China by a German company in 2004. As of now, there are only 3 maglev passenger systems in operation in the world (China, Japan, South Korea). Fuel Cells are, in many ways, much like a battery. They store energy for a later use, usually through electricity. The most common fuel cells combine Hydrogen and Oxygen to create water and electrical current. Hybrid Power is anything that uses more than one source. We commonly use the term today to mean gasoline engines in combination with electric motors. At low speeds, these cars use the electric motor, while at higher speeds, the gasoline engine propels the car as well as charges the batteries. This can significantly increase gas mileage depending on driving habits.

21. + Diagrams of 2 different Maglev Systems Electromagnetic Suspension (EMS) Electrodynamic Suspension (EDS)

22. + Power From Vehicle Design Design can make vehicles more efficient, more economical, and safer. Today, most design considerations involve aerodynamics, size and weight, materials, and electronics. Aerodynamics is the science of the interaction between the air and moving objects. The fast objects travel through air, the stronger the aerodynamic drag force is. Engineers design vehicle shapes to reduce this drag. A basic principle of Physics is that the lower an objects mass, the lower the energy required to get it moving. Steel, while strong, is also somewhat heavy. With an increased focus on energy consumption and emissions, producing lighter cars and trucks without sacrificing space has shifted materials away from steel. That being said, steel still accounts for roughly 60%, on average, of a car’s curb weight. Aluminum, plastics like carbon fiber, and composite materials cost more, but at some point, it is likely that the benefits will outweigh those increased costs.