Tag: automobiles

What will be the source of energy for vehicles 50 years from now? — AW, Karachi, Pakistan

When the earth’s petroleum supply has been depleted to point where it becomes too precious and expensive to burn, electric vehicles will probably take over. While it’s possible to synthesize chemical fuels, I don’t think it will be worth the trouble. The bigger question is where the electricity needed to charge the batteries will come from. I’ll bet on solar power. Right now, electric cars don’t save fossil fuels or keep the air significantly cleaner because the electricity those cars use is obtained by burning fossil fuels. But the electric cars of the future will probably obtain their electric power from the sun. Nuclear fission and fusion are also possibilities, but fission power has its drawbacks and its not clear when or even if fusion power will be available.

Why are there pistons in an engine? — T, Enola, PA

The pistons in a gasoline engine compress the fuel and air mixture before ignition and then extract energy from the burned gases after ignition. When the engine is operating, each piston travels in and out of a cylinder with one closed end many times a second. The piston makes four different strokes during its travels. In the first or “intake” stroke, the piston travels away from the closed end of the cylinder and draws the fuel and air mixture into the cylinder through an opened valve. During the second or “compression” stroke, the piston travels toward the closed end of the cylinder and compresses the fuel and air mixture to high pressure, density, and temperature. The spark plug now ignites the fuel and air mixture and it burns. During the third or “power” stroke, the piston travels away from the closed end of the cylinder and the expanding gases do work on the piston, providing it with the energy that propels the car forward. During the fourth or “exhaust” stroke, the piston travels toward the closed end of the cylinder and pushes the burned gases out of the cylinder through another opened valve.

How does an internal combustion engine work? — RT, Kitchener, Ontario

An internal combustion engine burns a mixture of fuel and air in an enclosed space. This space is formed by a cylinder that’s sealed at one end and a piston that slides in and out of that cylinder. Two or more valves allow the fuel and air to enter the cylinder and for the gases that form when the fuel and air burn to leave the cylinder. As the piston slides in and out of the cylinder, the enclosed space within the cylinder changes its volume. The engine uses this changing volume to extract energy from the burning mixture.

The process begins when the engine pulls the piston out of the cylinder, expanding the enclosed space and allowing fuel and air to flow into that space through a valve. This motion is called the intake stroke. Next, the engine squeezes the fuel and air mixture tightly together by pushing the piston into the cylinder in what is called the compression stroke. At the end of the compression stroke, with the fuel and air mixture squeezed as tightly as possible, the spark plug at the sealed end of the cylinder fires and ignites the mixture. The hot burning fuel has an enormous pressure and it pushes the piston strongly out of the cylinder. This power stroke is what provides power to the car that’s attached to the engine. Finally, the engine squeezes the burned gas out of the cylinder through another valve in the exhaust stroke. These four strokes repeat over and over again to power the car. To provide more steady power, and to make sure that there is enough energy to carry the piston through the intake, compression, and exhaust strokes, most internal combustion engines have at least four cylinders (and pistons). That way, there is always at least one cylinder going through the power stroke and it can carry the other cylinders through the non-power strokes.

How does a steam engine work? — MP, New Fairfield, CT

Like the internal combustion engines used in automobiles, a steam engine is a type of heat engine—a device that diverts some of the heat flowing from a hotter object to a colder object and that turns that heat into useful work. The fraction of heat that can be converted to work is governed by the laws of thermodynamics and increases with the temperature difference between the hotter and colder objects. In the case of the steam engine, the hotter the steam and the colder the outside air, the more efficient the engine is at converting heat into work.

A typical steam engine has a piston that moves back and forth inside a cylinder. Hot, high-pressure steam is produced in a boiler and this steam enters the cylinder through a valve. Once inside the cylinder, the steam pushes outward on every surface, including the piston. The steam pushes the piston out of the cylinder, doing mechanical work on the piston and allowing that piston to do mechanical work on machinery attached to it. The expanding steam transfers some of its thermal energy to this machinery, so the steam becomes cooler as the machinery operates.

But before the piston actually leaves the steam engine’s cylinder, the valve stops the flow of steam and opens the cylinder to the outside air. The piston can then reenter the cylinder easily. In many cases, steam is allowed to enter the other end of the cylinder so that the steam pushes the piston back to its original position. Once the piston is back at its starting point, the valve again admits high-pressure steam to the cylinder and the whole cycle repeats. Overall, heat is flowing from the hot boiler to the cool outside air and some of that heat is being converted into mechanical work by the moving piston.

I’ve heard of people using moonshine as fuel for cars and pick up trucks. Is that possible and, if it is, how well does it work?

Yes, it’s probably possible. Moonshine (and any distilled spirits) is a mixture of ethanol (ethyl alcohol) and water. Depending on how picky you are during the distilling process, the water content may be as low as 10% (you can’t do better by distilling because 4.4% water and 95.6% ethanol form an azeotrope—a low boiling point mixture blend that can’t be separated by distilling). Ethanol burns nicely and should make a pretty good fuel. Obviously, the less water the better, because water doesn’t burn and may impede the combustion of ethanol. Ethanol is often included in gasoline to reduce exhaust emissions, but only at about the 10% level. Unfortunately, ethanol is also more corrosive than normal gasoline, so people worry about it damaging their engines.

What is the purpose of pistons in an engine?

The piston moves in an out of a cylinder, moving the air, fuel, and exhaust about and extracting work from the burned fuel and air. Without the piston, there would be no way to obtain energy from the gasoline.

What’s the difference with a Mazda rotary engine?

The rotary engine was supposed to revolutionize automobiles when it was first introduced several decades ago. Instead of a piston and cylinder, it has a triangular shaped object that wobbles around the inside of a hollow chamber. This object traps a fuel and air mixture, compresses it, ignites it, extracts energy from it, and releases it into the outside air, just as a normal engine does. But it uses the wobbling motion of the triangle, rather than the reciprocating motion of the piston and cylinder. The rotary engine has fewer moving parts to wear out, but it evidently has other issues that have prevented its wide adoption.

Why do I need a choke?

When an engine is cold, it runs better with a rich mixture (more fuel, less air). Years ago, the choke pinched off the airflow to the cylinder (hence the name “choke”) and was operated manually. Later it was operated automatically (often turning off too soon and causing the car to stall a few minutes after starting). In modern cars, there is no choke, just the computer controlling the fuel and air mixture on a moment-by-moment basis.

Why is it good to put premium gas in your car during the winter? If premium gas does not burn easily, does it also not freeze easily?

I’m not sure that it is better to put premium gas in your car during the winter. If you car operates properly on regular during the summer, then it should also operate properly on regular during the winter. Actually, summer gasoline and winter gasoline are slightly different. When it’s cold outside, gasoline doesn’t evaporate as easily so it needs to be reformulated to make it more volatile. During the winter, the gasoline manufacturers add more small molecules to the mixture so that it turns into a gas more easily. But they try to retain the same resistance to ignition in each of their gasoline grades. In any case, gasoline doesn’t freeze at normal temperatures, so that’s not a problem. Only water that condenses in your gas tank will freeze and can plug your gas line.

How do certain mufflers provide more horsepower?

A muffler’s job is to control the flow of exhaust from the cylinders to the outside air, so that the abrupt fluctuations in pressure created by the opening cylinders are smoothed away by the time the exhaust leaves the car’s tail pipe. The pressure fluctuations create sound and, by smoothing them away, the muffler quiets the engine. But the easiest ways to smooth away the pressure fluctuations also impede the flow of exhaust from the cylinders. The result is that some exhaust is trapped in the cylinders and interferes with the operation of the engine. The car’s gas mileage drops. A good muffler smoothes out exhaust pressure without impeding its flow and without reducing gas mileage.