The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. The engine described above has one cylinder. That is typical of most lawn mowers, but 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 (also known as horizontally opposed or boxer), as shown in the following figures.
Figure 2. Inline - The cylinders are arranged in a line in a single bank.
Figure 3. V - The cylinders are arranged in two banks set at an angle to one another.
Figure 4. Flat - The cylinders are arranged in two banks on opposite sides of the engine.
Different configurations have different advantages and disadvantages in terms of smoothness, manufacturing cost and shape characteristics. These advantages and disadvantages make them more suitable for certain vehicles.
Let's look at some key engine parts in more detail.
Spark plug
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.
Valves
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.
Piston
A piston is a cylindrical piece of metal that moves up and down inside the cylinder.
Piston rings
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:
• They 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.
Connecting rod
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.
Crankshaft
The crankshaft turns the piston's up and down motion into circular motion just like a crank on a jack-in-the-box does.
Sump
The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).
Sabtu, 14 Mac 2009
Engine Problems
So you go out one morning and your engine will turn over but it won't start... What could be wrong? Now that you know how an engine works, you can understand the basic things that can keep an engine from running. Three fundamental things can happen: a bad fuel mix, lack of compression or lack of spark. Beyond that, thousands of minor things can create problems, but these are the "big three." Based on the simple engine we have been discussing, here is a quick rundown on how these problems affect your engine:
Bad fuel mix - A bad fuel mix can occur in several ways:
• You are out of gas, so the engine is getting air but no fuel.
• The air intake might be clogged, so there is fuel but not enough air.
• The fuel system might be supplying too much or too little fuel to the mix, meaning that combustion does not occur properly.
• There might be an impurity in the fuel (like water in your gas tank) that makes the fuel not burn.
Lack of compression - If the charge of air and fuel cannot be compressed properly, the combustion process will not work like it should. Lack of compression might occur for these reasons:
• Your piston rings are worn (allowing air/fuel to leak past the piston during compression).
• The intake or exhaust valves are not sealing properly, again allowing a leak during compression.
• There is a hole in the cylinder.
The most common "hole" in a cylinder occurs where the top of the cylinder (holding the valves and spark plug and also known as the cylinder head) attaches to the cylinder itself. Generally, the cylinder and the cylinder head bolt together with a thin gasket pressed between them to ensure a good seal. If the gasket breaks down, small holes develop between the cylinder and the cylinder head, and these holes cause leaks.
Scott Olson/Getty Images
Doing regular engine maintenance can help you avoid future repairs.
Lack of spark - The spark might be nonexistent or weak for a number of reasons:
• If your spark plug or the wire leading to it is worn out, the spark will be weak.
• If the wire is cut or missing, or if the system that sends a spark down the wire is not working properly, there will be no spark.
• If the spark occurs either too early or too late in the cycle (i.e. if the ignition timing is off), the fuel will not ignite at the right time, and this can cause all sorts of problems.
Many other things can go wrong. For example:
• If the battery is dead, you cannot turn over the engine to start it.
• If the bearings that allow the crankshaft to turn freely are worn out, the crankshaft cannot turn so the engine cannot run.
• If the valves do not open and close at the right time or at all, air cannot get in and exhaust cannot get out, so the engine cannot run.
• If someone sticks a potato up your tailpipe, exhaust cannot exit the cylinder so the engine will not run.
• If you run out of oil, the piston cannot move up and down freely in the cylinder, and the engine will seize.
In a properly running engine, all of these factors are within tolerance.
As you can see, an engine has a number of systems that help it do its job of converting fuel into motion. We'll look at the different subsystems used in engines in the next few sections.
Bad fuel mix - A bad fuel mix can occur in several ways:
• You are out of gas, so the engine is getting air but no fuel.
• The air intake might be clogged, so there is fuel but not enough air.
• The fuel system might be supplying too much or too little fuel to the mix, meaning that combustion does not occur properly.
• There might be an impurity in the fuel (like water in your gas tank) that makes the fuel not burn.
Lack of compression - If the charge of air and fuel cannot be compressed properly, the combustion process will not work like it should. Lack of compression might occur for these reasons:
• Your piston rings are worn (allowing air/fuel to leak past the piston during compression).
• The intake or exhaust valves are not sealing properly, again allowing a leak during compression.
• There is a hole in the cylinder.
The most common "hole" in a cylinder occurs where the top of the cylinder (holding the valves and spark plug and also known as the cylinder head) attaches to the cylinder itself. Generally, the cylinder and the cylinder head bolt together with a thin gasket pressed between them to ensure a good seal. If the gasket breaks down, small holes develop between the cylinder and the cylinder head, and these holes cause leaks.
Scott Olson/Getty Images
Doing regular engine maintenance can help you avoid future repairs.
Lack of spark - The spark might be nonexistent or weak for a number of reasons:
• If your spark plug or the wire leading to it is worn out, the spark will be weak.
• If the wire is cut or missing, or if the system that sends a spark down the wire is not working properly, there will be no spark.
• If the spark occurs either too early or too late in the cycle (i.e. if the ignition timing is off), the fuel will not ignite at the right time, and this can cause all sorts of problems.
Many other things can go wrong. For example:
• If the battery is dead, you cannot turn over the engine to start it.
• If the bearings that allow the crankshaft to turn freely are worn out, the crankshaft cannot turn so the engine cannot run.
• If the valves do not open and close at the right time or at all, air cannot get in and exhaust cannot get out, so the engine cannot run.
• If someone sticks a potato up your tailpipe, exhaust cannot exit the cylinder so the engine will not run.
• If you run out of oil, the piston cannot move up and down freely in the cylinder, and the engine will seize.
In a properly running engine, all of these factors are within tolerance.
As you can see, an engine has a number of systems that help it do its job of converting fuel into motion. We'll look at the different subsystems used in engines in the next few sections.
Engine Questions and Answers
Here is a set of engine-related questions from readers and their answers:
• What is the difference between a gasoline engine and a diesel engine?
In a diesel engine, there is no spark plug. Instead, diesel fuel is injected into the cylinder, and the heat and pressure of the compression stroke cause the fuel to ignite. Diesel fuel has a higher energy density than gasoline, so a diesel engine gets better mileage. See How Diesel Engines Work for more information.
• What is the difference between a two-stroke and a four-stroke engine?
Most chain saws and boat motors use two-stroke engines. A two-stroke engine has no moving valves, and the spark plug fires each time the piston hits the top of its cycle. A hole in the lower part of the cylinder wall lets in gas and air. As the piston moves up it is compressed, the spark plug ignites combustion, and exhaust exits through another hole in the cylinder. You have to mix oil into the gas in a two-stroke engine because the holes in the cylinder wall prevent the use of rings to seal the combustion chamber. Generally, a two-stroke engine produces a lot of power for its size because there are twice as many combustion cycles occurring per rotation. However, a two-stroke engine uses more gasoline and burns lots of oil, so it is far more polluting. See How Two-stroke Engines Work for more information.
• You mentioned steam engines in this article -- are there any advantages to steam engines and other external combustion engines?
The main advantage of a steam engine is that you can use anything that burns as the fuel. For example, a steam engine can use coal, newspaper or wood for the fuel, while an internal combustion engine needs pure, high-quality liquid or gaseous fuel. See How Steam Engines Work for more information.
• Are there any other cycles besides the Otto cycle used in car engines?
The two-stroke engine cycle is different, as is the diesel cycle described above. The engine in the Mazda Millenia uses a modification of the Otto cycle called the Miller cycle. Gas turbine engines use the Brayton cycle. Wankel rotary engines use the Otto cycle, but they do it in a very different way than four-stroke piston engines.
• Why have eight cylinders in an engine?
Why not have one big cylinder of the same displacement of the eight cylinders instead? There are a couple of reasons why a big 4.0-liter engine has eight half-liter cylinders rather than one big 4-liter cylinder. The main reason is smoothness. A V-8 engine is much smoother because it has eight evenly spaced explosions instead of one big explosion. Another reason is starting torque. When you start a V-8 engine, you are only driving two cylinders (1 liter) through their compression strokes, but with one big cylinder you would have to compress 4 liters instead.
• What is the difference between a gasoline engine and a diesel engine?
In a diesel engine, there is no spark plug. Instead, diesel fuel is injected into the cylinder, and the heat and pressure of the compression stroke cause the fuel to ignite. Diesel fuel has a higher energy density than gasoline, so a diesel engine gets better mileage. See How Diesel Engines Work for more information.
• What is the difference between a two-stroke and a four-stroke engine?
Most chain saws and boat motors use two-stroke engines. A two-stroke engine has no moving valves, and the spark plug fires each time the piston hits the top of its cycle. A hole in the lower part of the cylinder wall lets in gas and air. As the piston moves up it is compressed, the spark plug ignites combustion, and exhaust exits through another hole in the cylinder. You have to mix oil into the gas in a two-stroke engine because the holes in the cylinder wall prevent the use of rings to seal the combustion chamber. Generally, a two-stroke engine produces a lot of power for its size because there are twice as many combustion cycles occurring per rotation. However, a two-stroke engine uses more gasoline and burns lots of oil, so it is far more polluting. See How Two-stroke Engines Work for more information.
• You mentioned steam engines in this article -- are there any advantages to steam engines and other external combustion engines?
The main advantage of a steam engine is that you can use anything that burns as the fuel. For example, a steam engine can use coal, newspaper or wood for the fuel, while an internal combustion engine needs pure, high-quality liquid or gaseous fuel. See How Steam Engines Work for more information.
• Are there any other cycles besides the Otto cycle used in car engines?
The two-stroke engine cycle is different, as is the diesel cycle described above. The engine in the Mazda Millenia uses a modification of the Otto cycle called the Miller cycle. Gas turbine engines use the Brayton cycle. Wankel rotary engines use the Otto cycle, but they do it in a very different way than four-stroke piston engines.
• Why have eight cylinders in an engine?
Why not have one big cylinder of the same displacement of the eight cylinders instead? There are a couple of reasons why a big 4.0-liter engine has eight half-liter cylinders rather than one big 4-liter cylinder. The main reason is smoothness. A V-8 engine is much smoother because it has eight evenly spaced explosions instead of one big explosion. Another reason is starting torque. When you start a V-8 engine, you are only driving two cylinders (1 liter) through their compression strokes, but with one big cylinder you would have to compress 4 liters instead.
asas penjagaan kenderaan anda
banyak sudah yang berkereta sekarang tetapi bukan semua menjaga keretanya sendiri.percayakah anda,kereta yang dimiliki lelaki lebih bersih daripada kereta yang dimiliki oleh perempuan?hahahaha....itu adalah fakta
memiliki sebuah kereta adalah satu tanggungjawap,bukan sekadar membayar harga ansuran tetapi tanggungjawap untuk menjaganya untuk 9 tahun,itupun kalau tidak terlimpas niat untuk menjual semula.
mari kita lihat tips untuk penjagaan kenderaan anda.
1. sebelum anda memulakan sesuatu perjalanan atau pegi kerja,periksa keadaan kereta anda terutamanya enjin.periksa minyak motor,mana tau ada kebocoran.lihat level minyak motor,samada level enjin hidup dan enjin mati.periksa juga air radiator,kalau enjin terlalu cepat panas padahal tiada kebocoran,cuba-cubalah mencampurkan air radiator anda dengan cecair penyejuk radiator(biasanya berwarna hijau).hidupkan enjin kereta anda sebelum memulakan perjalanan selama lebihkurang 3 minit dan juga semua lampu berfungsi sebelum anda menekan trotle ke tempat kerja.
2. jikalau ada masa,periska juga minyak brek anda kadang-kadang,mana tau kering sudah.tengo-tengokan tayar sekali,jangan dibiarkan terlalu botak.
3. jika anda mau kereta anda kelihatan sentiasa bersih,rajin-rajinlah cuci kereta,kalau malas,hantar saja pegi car wash.cuci kereta bukan susah.kalau badan kereta anda terpalit oleh tar(kerana anda baru melalui jalan berturap),anda perlu mencuci kerta anda terlebih dahulu sebelum menyembur cecair penaggal tar(tar remover) ke bahagian yang dikotori tar.jangan sesekali guna thiner!kalau mau cuci enjin,pastikan lubang-lubang yang terdedah itu disumbat dahulu dengan kain atau plastik seperti lubang penapi udara(air filter).bagi kereta yang bertransmisi outomatik,anda harus diingatkan supaya membalut dengan plastik kotak tansmisi auto di diri dan kanan(ada sesetengahnya begitu).sembur enjin anda dengan penanggal gris(degreaser) sebelum anda menyabunnya.pastikan cecair penanggal gris tidak terkena bahagian luar badan kereta anda.kalau terkena,cepat bersihkan bahagian yang terkena itu.
4. jangan lupa untuk menyerbis kereta anda bila maximum perjalanan kereta telah sampai untuk diserbis.
5. jangan biarkan kereta anda melepak tanpa bunyi melebihi 2 hari,nanti piston kereta anda bertagar..haha..
6. jangan kedekut untuk dihampagas kereta anda,banyak tu habuk sana dalam,kerusi pun kalau kamu tepuk,laaagi banyak habuk.
7. yang pakai jentera berat seperti traktor,eskavator dan kopiting...hehhe..periksa,level gris,level minyak hidraulik(minyak 10 atau minyak 68 bagi escavator hitachi).periksa minyak klutch dan minyak stereng(minyak 40).periksa juga level minyak sproket(minyak 90) bagi traktor.dan...pastikan jentera anda dihidupkan selama 5 minit atau lebih sebelum memulakan kerja berat anda.
memiliki sebuah kereta adalah satu tanggungjawap,bukan sekadar membayar harga ansuran tetapi tanggungjawap untuk menjaganya untuk 9 tahun,itupun kalau tidak terlimpas niat untuk menjual semula.
mari kita lihat tips untuk penjagaan kenderaan anda.
1. sebelum anda memulakan sesuatu perjalanan atau pegi kerja,periksa keadaan kereta anda terutamanya enjin.periksa minyak motor,mana tau ada kebocoran.lihat level minyak motor,samada level enjin hidup dan enjin mati.periksa juga air radiator,kalau enjin terlalu cepat panas padahal tiada kebocoran,cuba-cubalah mencampurkan air radiator anda dengan cecair penyejuk radiator(biasanya berwarna hijau).hidupkan enjin kereta anda sebelum memulakan perjalanan selama lebihkurang 3 minit dan juga semua lampu berfungsi sebelum anda menekan trotle ke tempat kerja.
2. jikalau ada masa,periska juga minyak brek anda kadang-kadang,mana tau kering sudah.tengo-tengokan tayar sekali,jangan dibiarkan terlalu botak.
3. jika anda mau kereta anda kelihatan sentiasa bersih,rajin-rajinlah cuci kereta,kalau malas,hantar saja pegi car wash.cuci kereta bukan susah.kalau badan kereta anda terpalit oleh tar(kerana anda baru melalui jalan berturap),anda perlu mencuci kerta anda terlebih dahulu sebelum menyembur cecair penaggal tar(tar remover) ke bahagian yang dikotori tar.jangan sesekali guna thiner!kalau mau cuci enjin,pastikan lubang-lubang yang terdedah itu disumbat dahulu dengan kain atau plastik seperti lubang penapi udara(air filter).bagi kereta yang bertransmisi outomatik,anda harus diingatkan supaya membalut dengan plastik kotak tansmisi auto di diri dan kanan(ada sesetengahnya begitu).sembur enjin anda dengan penanggal gris(degreaser) sebelum anda menyabunnya.pastikan cecair penanggal gris tidak terkena bahagian luar badan kereta anda.kalau terkena,cepat bersihkan bahagian yang terkena itu.
4. jangan lupa untuk menyerbis kereta anda bila maximum perjalanan kereta telah sampai untuk diserbis.
5. jangan biarkan kereta anda melepak tanpa bunyi melebihi 2 hari,nanti piston kereta anda bertagar..haha..
6. jangan kedekut untuk dihampagas kereta anda,banyak tu habuk sana dalam,kerusi pun kalau kamu tepuk,laaagi banyak habuk.
7. yang pakai jentera berat seperti traktor,eskavator dan kopiting...hehhe..periksa,level gris,level minyak hidraulik(minyak 10 atau minyak 68 bagi escavator hitachi).periksa minyak klutch dan minyak stereng(minyak 40).periksa juga level minyak sproket(minyak 90) bagi traktor.dan...pastikan jentera anda dihidupkan selama 5 minit atau lebih sebelum memulakan kerja berat anda.
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