| What is the difference between spark ignition engines and diesel engines?
Just before burning their fuels, both engines compress air inside a sealed cylinder. This compression process adds energy to the air and causes its temperature to skyrocket. In a spark ignition engine, the air that's being compressed already contains fuel so this rising temperature is a potential problem. If the fuel and air ignite spontaneously, the engine will "knock" and won't operate at maximum efficiency. The fuel and air mixture is expected to wait until it's ignited at the proper instant by the spark plug. That's why gasoline is formulated to resist ignition below a certain temperature. The higher the "octane" of the gasoline, the higher its certified ignition temperature. Virtually all modern cars operate properly with regular gasoline. Nonetheless, people frequently put high-octane (high-test or premium) gasoline in their cars under the mistaken impression that their cars will be better for it. If your car doesn't knock significantly with regular gasoline, use regular gasoline.
A diesel engine doesn't have spark ignition. Instead, it uses the high temperature caused by extreme compression to ignite its fuel. It compresses pure air to high temperature and pressure, and then injects fuel into this air. Timed to arrive at the proper instant, the fuel bursts into flames and burns quickly in the superheated compressed air. In contrast to gasoline, diesel fuel is formulated to ignite easily as soon as it enters hot air.
How does an automatic transmission in a car work?
An automatic transmission contains two major components: a fluid coupling that controls the transfer of torque from the engine to the rest of the transmission and a gearbox that controls the mechanical advantage between the engine and the wheels. The fluid coupling resembles two fans with a liquid circulating between them. The engine turns one fan, technically known as an "impeller," and this impeller pushes transmission fluid toward the second impeller. As the liquid flows through the second impeller, it exerts a twist (a "torque") on the impeller. If the car is moving or is allowed to move, this torque will cause the impeller to turn and, with it, the wheels of the car. If, however, the car is stopped and the brake is on, the transmission fluid will flow through the second impeller without effect. Overall, the fluid coupling allows the efficient transfer of power from the engine to the wheels without any direct mechanical linkage that would cause trouble when the car comes to a stop.
Between the second impeller and the wheels is a gearbox. The second impeller of the fluid coupling causes several of the gears in this box to turn and they, in turn, cause other gears to turn. Eventually, this system of gears causes the wheels of the car to turn. Along with these gears are several friction plates that can be brought into contact with one another by the transmission to change the relative rotation rates between the second impeller and the car's wheels. These changes in relative rotation rate give the car the variable mechanical advantage it needs to be able to both climb steep hills and drive fast on flat roadways.
Finally, some cars combine parts of the gear box with the fluid coupling in what is called a "torque converter." Here the two impellers in the fluid coupling have different shapes so that they naturally turn at different rates. This asymmetric arrangement eliminates the need for some gears in the gearbox itself.
Does it make sense to raise the thermostat setting on your air conditioner when you leave your house, since when you come back, you have to lower it again and the unit has to work more? Are there any energy savings?
You will save energy and money by raising the thermostat setting when you leave your home and then lower it again when you return. That's because the rate at which heat flows into your home from outside is roughly proportional to the difference between the indoor and outdoor temperatures. By letting the indoor temperature rise, you slow the heat flow into your home. With less heat flowing into your home, the air conditioner doesn't have to pump as much heat outside and that saves energy. Moreover, an air conditioner is more energy efficient when the indoor temperature is closer to the outdoor temperature, so letting the indoor air warm up saves even more energy. While the air conditioner does have to work steadily for a while when you return to your home, its efficiency is still good during that time and the energy saved while you were away more than makes up for the energy consumed when you return.
How does a catalytic converter help emissions in a car?
While the burned gases that emerge from an ideal car engine would consist only of water vapor, carbon dioxide, and nitrogen gas, a real car engine is far from ideal. In addition to these gases, a real engine emits nitrogen oxides, carbon monoxide, and various unburned hydrocarbons left over from the gasoline. Because these gases are major contributors to urban smog, car manufacturers have been forced to reduce them in various ways.
One of the most effective tools for eliminating the unburned hydrocarbons and carbon monoxide is a catalytic converter. It is essentially a pipe containing a ceramic honeycomb on which there are countless tiny particles of platinum and palladium. As the unwanted molecules pass through the honeycomb, they land on the metal particles briefly and are combined with oxygen atoms to form water vapor and carbon dioxide. The catalytic converter is burning these molecules in a controlled way, with the precious metal particles acting as catalysts to assist the burning process.
Like all catalysts, these particles are not consumed in the process of burning the gases, but they can easily be contaminated. That's why it's so important not to put leaded gasoline in a car with a catalytic converter--one tank of leaded gas is all it takes to lead-coat the tiny platinum and palladium particles and to render them useless. Another interesting note is that the catalytic converter is usually located on the underside of the car, protected only by a thin metal shield. The converter becomes very hot in operation, both because hot exhaust gas is passing through it and because the controlled combustion taking place inside it heats it up. Don't park a car with a catalytic converter over a pile of leaves! Many an autumn car fire has started when a hot catalytic converter ignited the pile of leaves beneath it.
I heard some time ago about a car that uses microwaves to heat the air in front of it so that it creates a vacuum. The relatively higher pressure behind then pushes it forward. Is this possible?
Even if microwaves were effective at heating air, which they are not, this heating would not propel the car forward. The air in front of the car would become hot, but its pressure would remain almost unchanged. Instead, the air would expand to occupy a larger volume and would then be lifted upward by the cooler air around it ("hot air rises"). Cooler air would flow in to replace the escaping hot air and the car would simply sit there with a steady stream of hot air rising in front of it.
Could you suspend a car on hot air produced below it?
For the buoyancy of hot air to suspend a car, you would need a lot of it--in effect you would have to turn the car into a hot air balloon. That's because the lifting force experienced by hot air is really supplied by the cooler air around it and this upward buoyant force is proportional to the volume of hot air being lifted. Since a car is pretty heavy, the volume of hot air required will be enormous.
However, if you trap the air underneath the car, so that its volume can't increase, and then heat that air, its pressure will rise. This increased pressure below the car would produce an overall upward pressure force on the car and could support the car's weight. In effect, you would be creating a ground-effect hovercraft in which the elevated pressure of trapped hot air supports the weight of the vehicle. But it would be easier and less energy-intensive to pump air underneath your hovercraft with a big fan. That's what most ground-effect vehicles do. They pack extra air molecules underneath themselves and then allow those molecules to support their weight. Furthermore, because air molecules are always leaking out from beneath the vehicle, you'll need a fan to replace them anyway.
How much steam is required to produce a unit of power?
There is no easy answer to this question, but for an interesting reason. First, "power" is a measure of energy per time (e.g. joules per second or BTUs per hour) so any answer would have to involve the amount of steam per time (e.g. kilograms per second or cubic meters per hour). But even recognizing that requirement, I can't answer the question. First, I'd need to know the temperature of the steam. The hotter the steam, the more thermal energy it contains and the more energy it could provide. For more complicated reasons, I'd also have to know the pressure of the steam. But there is a fourth issue: even knowing the amount of steam involved and the temperature and pressure of that steam, the amount of useful energy that can be extracted from that steam depends on the existence of a colder object. You can't turn thermal energy--the type of energy that steam contains--directly into useful work or into electric energy in a continuous manner. You must use the steam in a "heat engine", converting a fraction of its thermal energy into work as that thermal energy flows as heat from the hot steam to a colder object. This requirement is established by the laws of thermodynamics and there is no way to get around it. The hotter the steam and the colder the object, the larger the fraction of the steam's thermal energy you can convert to work. However, there is no way to convert all of the steam's thermal energy into work continuously.
I understand that for a steam engine to produce useful work, you need a difference in temperatures. My question is whether the difference in temperatures between cold glacier ice and the warmer air could be used to drive a steam engine and generate electricity.
As you clearly recognize, any heat engine--a machine that converts thermal energy into work--can only do its job while heat is flowing from a hotter object to a colder object. That limitation is imposed by the second law of thermodynamics--a statistical law that observes that the disorder of an isolated system can never decrease. A heat engine's theoretical efficiency at turning thermal energy into work improves as the temperature difference between its hotter and colder objects increases. Since the air temperature is hotter than the glacier temperature, there is the possibility to convert some of the air's thermal energy into work as heat flows from the air to the glacier. In short, what you suggest could be done.
Unfortunately, most practical heat engines work best when the hotter object is really hot. For example, a steam engine works best when the hotter object is hot enough to produce very high temperature, high pressure steam. To operate a steam engine with outside air as the hotter object and cold ice as the colder object, the steam engine would have to operate at very low pressure. In fact, it would operate well below atmospheric pressure in a carefully sealed environment. Steam might not even be the best choice for a working fluid--you might do better with a refrigerant such as the various Freon replacements. In effect, your heat engine would be an air conditioner run backward--providing electric power rather than consuming it. Although this could be done, it would probably not be cost effective. The heat exchangers needed to obtain heat from the air and to deliver most of that heat to the glacier, as well as all the machinery of the heat engine itself, would probably make the electricity you generated too expensive. Just because something can be done doesn't mean that it's worth doing. Until other sources of energy become more expensive, this one won't pay for itself.
What is the difference between internal and external combustion engines?
External combustion engines burn a fuel outside of the engine and produce a hot working fluid that then powers the engine. The classic example of an external combustion engine is a steam engine. Internal combustion engines burn fuel directly in the engine and use the fuel and the gases resulting from its combustion as the working fluid that powers the engine. An automobile engine is a fine example of an internal combustion engine.
How much electric current is there in an automobile spark plug?
Without measuring it directly, I would guess that the current passing through a spark plug during a spark is about 10 milliamperes. I base that guess both on a calculation--assuming sensible values for the energy, voltage, and duration of the spark--and on my experience with electric sparks. If I have a chance to measure the current directly--I have the equipment but not the time--I'll put a more specific value here.
What will be the source of energy for vehicles 50 years from now?
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?
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?
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?
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.
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.
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.
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.
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.
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.
I've heard about a car (I think some type of Ferrari) that has a clutch-less manual transmission.
According to Bryan Tiedemann, Ferarri makes a computer-shifted manual transmission. It begins with a standard manual transmission (gears, input/output shafts, synchronizers) that's similar to that of many "stick-shift" cars of today. However, instead of having a driver-controlled clutch and shift lever, a computer regulates the actual mechanical clutch movement and it also shifts gears via servos and motors. The driver uses a "shift paddle" on the steering wheel to shift, and the computer does the actual shifting. The automatically controlled manual is better than a normal automatic because manual transmissions give better performance than automatics and no energy is lost as heat in hydraulic couplings.
In modern car alarm systems, people can start the engine with a push of a button from a remote. How is this done?
This question has a long answer, because there's lots going on. First, there is a radio transmission from the key chain to the car when you push the button. That transmission is carefully encoded so that no one else can trigger your car (the car's receiver checks for the proper authorization code when it receives the radio transmission). I won't describe the transmission/reception process in detail, because that's a whole story in its self. The receiver than activates the car's electric system, which was cut off when the driver last turned off the car. The electric system is now ready to provide sparks at the proper moments when the engine turns. Finally, the receiver starts the engine turning by activating the starter motor. An electromagnetic solenoid (a coil of wire with a piece of iron inside) pushes the starter motor or a gear from the starter motor against the car's flywheel (a huge gear attached to the engine's crankshaft) and power is supplied to the starter motor. The motor begins turning and it turns the engine. The electric system provides sparks and the engine starts up.
How does using better spark plugs make your car run more efficiently? Is it worth paying extra for those spark plugs? Would it improve your car's performance?
According to several readers of this web site, there is a difference between standard and high performance spark plugs. The high performance spark plugs produce a more intense spark and ignite the fuel and air mixture more reliably than standard plugs. That would indicate that igniting the fuel and air mixture at just the right moment isn't as straightforward as it seems. If the plugs don't fire reliably and don't light the gasoline at exactly the right moment every single time the cylinder is supposed to fire, the car's efficiency will suffer.
How does a nitrous kit on a car make it go faster?
According to David Ingham, a nitrous kit is a system that injects nitrous oxide into the air intake. This technique was developed during WWII as a way to obtain short bursts of extra power from gasoline engines. Keith Spillman points out that the nitrous oxide is injected as a dense liquid so that it greatly increases the number of oxygen atoms inside the cylinder at the moment the fuel ignites. Since nitrous oxide breaks down into nitrogen and oxygen at high temperatures, it supports combustion and allows more fuel to burn during each engine cycle. The engine thus produces more power. The liquid nitrous oxide also provides an "intercooling" effect when it evaporates--it cools the gases in the cylinder prior to compression so that there is less possibility of knocking.
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.
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