2 CarsHave you ever opened the hood of your car and wondered what was going on in there?A car engine can look like a big confusing jumble of metal, tubes and wires to the uninitiated.
3 CarsToday’s discussion will concern the basic idea behind an engine and then go into detail about how all the pieces fit together, what can go wrong and how to increase performance.The purpose of a gasoline car engine is to convert gasoline into motion so that your car can move.Currently the easiest way to create motion from gasoline is to burn the gasoline inside an engine.Therefore, a car engine is an internal combustion engine -- combustion takes place internally.
4 Cars The principle behind any internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas.You can use that energy to propel a potato 500 feet.In this case, the energy is translated into potato motion. You can also use it for more interesting purposes.For example, if you can create a cycle that allows you to set off explosions like this hundreds of times per minute, and if you can harness that energy in a useful way, what you have is the core of a car engine!
5 CarsAlmost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion.The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in The four strokes are:Intake strokeCompression strokeCombustion strokeExhaust stroke
6 CarsYou can see in the figure that a device called a piston replaces the potato in the potato cannon.The piston is connected to the crankshaft by a connecting rod.As the crankshaft revolves, it has the effect of "resetting the cannon."
7 Cars Here's what happens as the engine goes through its cycle: The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work.Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful.When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down.Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tailpipe.
8 CarsNow the engine is ready for the next cycle, so it intakes another charge of air and gas.Notice that the motion that comes out of an internal combustion engine is rotational, while the motion produced by a potato cannon is linear (straight line).In an engine the linear motion of the pistons is converted into rotational motion by the crankshaft.The rotational motion is nice because we plan to turn (rotate) the car's wheels with it anyway.Now let's look at all the parts that work together to make this happen, starting with the cylinders.
9 CarsThe core of the engine is the cylinder, with the piston moving up and down inside the cylinder.Most cars have more than one cylinder (four, six and eight cylinders are common).In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, V or flat.
10 Cars Let's look at some key engine parts in more detail. The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly.The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.A piston is a cylindrical piece of metal that moves up and down inside the cylinder.Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes:
11 CarsPiston rings prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion.They keep oil in the sump from leaking into the combustion area, where it would be burned and lost.Most cars that "burn oil" and have to have a quart added every 1,000 miles are burning it because the engine is old and the rings no longer seal things properly.The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates.The crankshaft turns the piston's up and down motion into circular motion just like a crank on a jack-in-the-box does.The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).
12 Mental Quiz… How many strokes are there in a typical car engine? Four What is the first stroke of this cycle?IntakeWhat does the engine take in?Air and gasoline mixture.What is the second stroke of the cycle?Compression.What is the third stroke?Combustion.What provides the ignition?Spark Plug.Name some products of incomplete combustion.CO2, H2O, CO, NOx and small carbon chains.What is the last stroke in the Otto Cycle?Exhaust
13 How Gasoline WorksIn the United States and the rest of the industrialized world, gasoline is definitely a vital fluid.It is as vital to the economy as blood is to a person.Without gasoline (and diesel fuel), the world as we know it would grind to a halt.The U.S. alone consumes something like 130 billion gallons of gasoline per year!
14 How Gasoline Works Gasoline is known as an aliphatic hydrocarbon. In other words, gasoline is made up of molecules composed of nothing but hydrogen and carbon arranged in chains.Gasoline molecules have from seven to 11 carbons in each chain.Here are some common configurations:
16 How Gasoline WorksWhen you burn gasoline under ideal conditions, with plenty of oxygen, you get carbon dioxide (from the carbon atoms in gasoline), water (from the hydrogen atoms) and lots of heat.A gallon of gasoline contains about 1.32x108 J of energy.
17 How Gasoline WorksIf you took a 1,500-watt space heater and left it on full blast for a full 24-hour day, that's about how much heat is in a gallon of gas.If it were possible for human beings to digest gasoline, a gallon would contain about 31,000 food calories.The energy in a gallon of gasoline is equivalent to the energy in about 110 McDonalds hamburgers!
18 Where Does Gasoline Come From? Gasoline is made from crude oil.The crude oil pumped out of the ground is a black liquid called petroleum.This liquid contains hydrocarbons, and the carbon atoms in crude oil link together in chains of different lengths.
19 Where Does Gasoline Come From? It turns out that hydrocarbon molecules of different lengths have different properties and behaviors.For example, a chain with just one carbon atom in it (CH4) is the lightest chain, known as methane.Methane is a gas so light that it floats like helium. As the chains get longer, they get heavier.
20 Where Does Gasoline Come From? The first four chains -- CH4 (methane), C2H6 (ethane), C3H8 (propane) and C4H10 (butane) -- are all gases, and they boil at -107, -67, -43 and -18C.The chains up through C18H32 or so are all liquids at room temperature, and the chains above C19 are all solids at room temperature.
21 Where Does Gasoline Come From? The different chain lengths have progressively higher boiling points, so they can be separated out by distillation.This is what happens in an oil refinery -- crude oil is heated and the different chains are pulled out by their vaporization temperatures.
22 Where Does Gasoline Come From? The chains in the C5, C6 and C7 range are all very light, easily vaporized, clear liquids called naphthas.They are used as solvents -- dry cleaning fluids can be made from these liquids, as well as paint solvents and other quick-drying products.
23 Where Does Gasoline Come From? The chains from C7H16 through C11H24 are blended together and used for gasoline.All of them vaporize at temperatures below the boiling point of water. That's why if you spill gasoline on the ground it evaporates very quickly.Next is kerosene, in the C12 to C15 range, followed by diesel fuel and heavier fuel oils (like heating oil for houses).
24 Where Does Gasoline Come From? Next come the lubricating oils.These oils no longer vaporize in any way at normal temperatures.For example, engine oil can run all day at 121 C without vaporizing at all.Chains above the C20 range form solids, starting with paraffin wax, then tar and finally asphaltic bitumen, which used to make asphalt roads.All of these different substances come from crude oil. The only difference is the length of the carbon chains!
25 What is Octane? Cars use four stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug.The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites.
26 What is Octane?When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine.Knocking can damage an engine, so it is not something you want to have happening.Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.
27 What is Octane? The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths.These different chain lengths can then be separated from each other and blended to form different fuels.
28 What is Octane?For example, methane, propane and butane are all hydrocarbons.Methane has a single carbon atom.Propane has three carbon atoms chained together.Butane has four carbon atoms chained together.
29 What is Octane?Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.It turns out that heptane handles compression very poorly.Compress it just a little and it ignites spontaneously.
30 What is Octane?Octane handles compression very well -- you can compress it a lot and nothing happens.Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane).It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.
31 What about Diesel Engines? Diesel's story actually begins with the invention of the gasoline engine.Recall Nikolaus August Otto had invented and patented the gasoline engine by 1876.This invention used the four-stroke combustion principle, also known as the "Otto Cycle," and it's the basic premise for most car engines today.
32 What about Diesel Engines? In its early stage, the gasoline engine wasn't very efficient, and other major methods of transportation such as the steam engine fared poorly as well.Only about 10 percent of the fuel used in these types of engines actually moved a vehicle.The rest of the fuel simply produced useless heat.
33 What about Diesel Engines? In 1878, Rudolf Diesel was attending the Polytechnic High School of Germany (the equivalent of an engineering college) when he learned about the low efficiency of gasoline and steam engines.This disturbing information inspired him to create an engine with a higher efficiency, and he devoted much of his time to developing a "Combustion Power Engine."By 1892 Diesel had obtained a patent for what we now call the diesel engine.
34 What about Diesel Engines? If diesel engines are so efficient, why don't we use them more often?You might see the words "diesel engine" and think of big, hefty cargo trucks spewing out black, sooty smoke and creating a loud clattering noise.
35 What about Diesel Engines? This negative image of diesel trucks and engines has made diesel less attractive to casual drivers in the United States –although diesel is great for hauling large shipments over long distances, it hasn't been the best choice for everyday commuters.This is starting to change, however, as people are improving the diesel engine to make it cleaner and less noisy.
36 What about Diesel Engines? In theory, diesel engines and gasoline engines are quite similar.They are both internal combustion engines designed to convert the chemical energy available in fuel into mechanical energy.This mechanical energy moves pistons up and down inside cylinders.The pistons are connected to a crankshaft, and the up-and-down motion of the pistons, known as linear motion, creates the rotary motion needed to turn the wheels of a car forward.
37 What about Diesel Engines? Both diesel engines and gasoline engines covert fuel into energy through a series of small explosions or combustions.The major difference between diesel and gasoline is the way these explosions happen.In a gasoline engine, fuel is mixed with air, compressed by pistons and ignited by sparks from spark plugs.
38 What about Diesel Engines? In a diesel engine, however, the air is compressed first, and then the fuel is injected.Because air heats up when it's compressed, the fuel ignites.
39 What about Diesel Engines? The diesel engine uses a four-stroke combustion cycle just like a gasoline engine. The four strokes are:Intake stroke -- The intake valve opens up, letting in air and moving the piston down. Compression stroke -- The piston moves back up and compresses the air.
40 What about Diesel Engines? Combustion stroke -- As the piston reaches the top, fuel is injected at just the right moment and ignited, forcing the piston back down. Exhaust stroke -- The piston moves back to the top, pushing out the exhaust created from the combustion out of the exhaust valve.
41 What about Diesel Engines? Remember that the diesel engine has no spark plug, that it intakes air and compresses it, and that it then injects the fuel directly into the combustion chamber (direct injection).It is the heat of the compressed air that lights the fuel in a diesel engine.
42 Diesel FuelPetroleum fuel, or crude oil, is naturally found in the Earth.When crude oil is refined at refineries, it can be separated into several different kinds of fuels, including gasoline, jet fuel, kerosene and, of course, diesel.
43 Diesel FuelIf you have ever compared diesel fuel and gasoline, you know that they are different.They certainly smell different.Diesel fuel is heavier and oilier.Diesel fuel evaporates much more slowly than gasoline -- its boiling point is actually higher than the boiling point of water.You will often hear diesel fuel referred to as "diesel oil" because it is so oily.
44 Diesel Fuel Diesel fuel evaporates more slowly because it is heavier. It contains more carbon atoms in longer chains than gasoline does (gasoline is typically C9H20, while diesel fuel is typically C14H30).It takes less refining to create diesel fuel, which is why it used to be cheaper than gasoline.
45 Diesel FuelSince 2004, however, demand for diesel has risen for several reasons, including increased industrialization and construction in China and the U.S.Diesel fuel has a higher energy density than gasoline.On average, 1 gallon (3.8 L) of diesel fuel contains approximately 1.55x108 J, while 1 gallon of gasoline contains 1.32x108 J.
46 Diesel FuelThis, combined with the improved efficiency of diesel engines, explains why diesel engines get better mileage than equivalent gasoline engines.
47 Diesel FuelThink about how important diesel is to the economy -- without its high efficiency, both the construction industry and farming businesses would suffer immensely from investments in fuels with low power and efficiency.About 94 percent of freight -- whether it's shipped in trucks, trains or boats -- relies on diesel.
48 Biodiesel FuelBiodiesel is made from vegetable oil or animal fat (triglycerides) reacted with methanol or ethanol and a catalyst (lye), yielding biodiesel (fatty acid methyl or ethyl esters) and glycerin as a by-product.It can be used in any diesel engine without modifications — diesel engines run better and last longer with biodiesel. And it can easily be made from a common waste product: used cooking oil.
49 Biodiesel FuelBiodiesel is a much cleaner fuel than conventional fossil-fuel petroleum diesel ("dinodiesel").Biodiesel burns up to 75% cleaner than petroleum diesel fuel.Biodiesel reduces unburned hydrocarbons (93% less), carbon monoxide (50% less) and particulate matter (30% less) in exhaust fumes, as well as cancer-causing PAH (80% less) and nitrited PAH compounds (90% less).
50 Biodiesel FuelSulphur dioxide emissions are eliminated (biodiesel contains no sulphur).Biodiesel is plant-based and using it adds no extra CO2 greenhouse gas to the atmosphere.The ozone-forming (smog) potential of biodiesel emissions is nearly 50% less than petro-diesel emissions.Nitrogen oxide (NOx) emissions may increase or decrease with biodiesel but can be reduced to well below petro-diesel fuel levels.
51 Biodiesel FuelBiodiesel exhaust is not offensive and doesn't cause eye irritation (it smells like French fries!).Biodiesel is environmentally friendly: it is renewable, and more biodegradable than sugar and less toxic than table salt.Biodiesel can be mixed with petro-diesel in any proportion, with no need for a mixing additive.
52 Biodiesel FuelBiodiesel is a much better lubricant than petro-diesel and extends engine life -- even a small amount of biodiesel means cleaner emissions and better engine lubrication: 1% biodiesel added to petro-diesel will increase lubricity by 65%.
53 Biodiesel FuelWith slight variations depending on the vehicle, performance and fuel economy with biodiesel is the same as with petro-diesel.Biodiesel can be used in any diesel engine without modification.A U.S. Department of Energy study at the University of California at Davis found that using pure biodiesel instead of petro-diesel reduced cancer risks from exhaust emissions by 93.6%.
54 The ProcessBiodiesel is made from vegetable and animal fats and oils, or triglycerides.Chemically, triglycerides consist of three long-chain fatty acid molecules joined by a glycerin molecule.
55 The Process--Transesterification The biodiesel process uses a catalyst (lye) to break off the glycerin molecule and combine each of the three fatty-acid chains with a molecule of methanol, creating mono-alkyl esters, or Fatty Acid Methyl Esters—biodiesel.The glycerin sinks to the bottom and is removed.
56 The Process--Transesterification First, vegetable or animal fats and oils are triglycerides, composed of three chains of fatty acids bound by a glycerin molecule.Triglycerides are esters.Esters are acids, such as fatty acids, combined with an alcohol, and glycerin (glycerol) is a heavy alcohol.
57 The Process--Transesterification The transesterification process converts triglyceride esters into alkyl esters (biodiesel) by means of a catalyst (lye) and an alcohol reagent, usually methanol, which yields methyl esters biodiesel -- the methanol replaces the glycerin.
58 The Process--Transesterification In transesterification the triglyceride molecule is broken into three separate methyl ester molecules plus glycerin as a by-product.The lye catalyst breaks the bond holding the fatty acid chains to the glycerin, the glycerin falls away, the fatty acid chains then bond with the methanol.
59 The Process--Transesterification It happens in three stages.First, one fatty acid chain is broken off the triglyceride molecule and bonds with methanol to form a methyl ester molecule, leaving a diglyceride molecule—two chains of fatty acids bound by glycerin.Then a fatty acid chain is broken off the diglyceride molecule and bonded with methanol to form another methyl ester molecule, leaving a monoglyceride molecule.
60 The Process--Transesterification Finally the monoglycerides are converted to methyl esters—completion.The problem is that the process can run out of reagent or catalyst before it gets that far, or agitation, temperature or processing time may be inadequate.
61 The Process--Transesterification The result is some unconverted or partly converted material remaining in the biodiesel.Well, so what if the process isn't completed?SVO (straight vegetable oil) is a good fuel anyway, so what's it matter if some of it is unreacted?But it's not just unreacted material that's the problem so much as the partly-reacted stuff.
62 The Process--Transesterification Diglycerides and monoglycerides are bad things to put in your diesel.Diglycerides don't burn well and lead to coking problems, monoglycerides can lead to corrosion and other problems—bad fuel.We must be careful when we make our biodiesel.