A Common List of Advantages and Disadvantages
Advantages of 2 Stroke Engines:
- Two-stroke engines do not have valves, simplifying their construction.
- Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost.
- Two-stroke engines are lighter, and cost less to manufacture.
- Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.
- Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost.
- Two-stroke engines are lighter, and cost less to manufacture.
- Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.
Disadvantages of 2 Stroke Engines:
- Two-stroke engines don't live as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster. Two-stroke engines require a mix of oil in with the gas to lubricate the crankshaft, connecting rod and cylinder walls.
- Two-stroke oil can be expensive. Mixing ratio is about 4 ounces per gallon of gas: burning about a gallon of oil every 1,000 miles.
- Two-stroke engines do not use fuel efficiently, yielding fewer miles per gallon.
- Two-stroke engines produce more pollution.
From:
-- The combustion of the oil in the gas. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit more oily smoke.
-- Each time a new mix of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port.
- Two-stroke engines don't live as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster. Two-stroke engines require a mix of oil in with the gas to lubricate the crankshaft, connecting rod and cylinder walls.
- Two-stroke oil can be expensive. Mixing ratio is about 4 ounces per gallon of gas: burning about a gallon of oil every 1,000 miles.
- Two-stroke engines do not use fuel efficiently, yielding fewer miles per gallon.
- Two-stroke engines produce more pollution.
From:
-- The combustion of the oil in the gas. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit more oily smoke.
-- Each time a new mix of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port.
Tips for protecting your computer from viruses
Protecting your computer from viruses and other threats isn't difficult, but you have to be diligent. Here are some actions you can take:
- Install an antivirus program. Installing an antivirus program and keeping it up to date can help defend your computer against viruses. Antivirus programs scan for viruses trying to get into your email, operating system, or files. New viruses appear daily, so set your antivirus software to install updates automatically.
- Don't open email attachments unless you're expecting them. Many viruses are attached to email messages and will spread as soon as you open the email attachment. It's best not to open any attachment unless it's something you're expecting.
- Keep your computer updated. Microsoft releases security updates that can help protect your computer. Make sure thatWindows receives these updates by turning on Windows automatic updating.
- Use a firewall. Windows Firewall (or any other firewall) can help alert you to suspicious activity if a virus or worm attempts to connect to your computer. It can also block viruses, worms, and hackers from attempting to download potentially harmful programs to your computer.
- Use your browser's privacy settings. Being aware of how websites might use your private information is important to help prevent fraud and identity theft. If you're using Internet Explorer, you can adjust your Privacy settings or restore the default settings whenever you want.
- Use a pop-up blocker with your browser. Pop-up windows are small browser windows that appear on top of the website you're viewing. Although most are created by advertisers, they can also contain malicious or unsafe code. A pop-up blocker can prevent some or all of these windows from appearing.The Pop-up Blocker feature in Internet Explorer is turned on by default.
- Turn on User Account Control (UAC). When changes are going to be made to your computer that require administrator-level permission, UAC notifies you and gives you the opportunity to approve the change. UAC can help keep viruses from making unwanted changes.
WINDOWS 7 INSTALLATION STEPS
Beginning the Installation Process
When installing on a physical computer insert your Windows 7 DVD media into your DVD drive and reboot your computer. If you're asked to press a key to boot from DVD or CD, press any key. A black window will appear momentarily while the DVD content is read.
Note: These screenshots are taken from a Windows 7 Ultimate installation performed on a virtual machine running on VMware Workstation. I will be using an .ISO file mounted on the VMs CD/DVD drive.
Next, a Starting Windows screen will appear.
Note: If the Windows installation page doesn't appear and you're not asked to press a key to start from DVD or CD, you might have to specify that your computer uses its DVD or CD drive as the startup device.
The Installation Process
Like in Windows Vista and Windows Server 2008, and unlike previous versions of Windows, Windows 7 does not have a noticeable text phase of the setup process, and it will boot directly into the Graphical User Interface (GUI) mode.
After a few moments you will see the first prompt:
Click "Next" unless you want to change some regional settings for the installation process. Hebrew users should read my "Installing Hebrew on Windows 7" article.
Click on the "Install now" button.
Note: If you're using the installation media to repair an existing installation of Windows 7 you should also read my latest article on the Windows Recovery Environment.
Next, accept the license terms and click on "Next".
Next, unless you're upgrading an existing Windows installation, press the Custom (Advanced) installation type button. Note that in this case, the Upgrade button is disabled because this specific installation if performed on a new computer without any previous operating system on it.
The next phase is to pick the installation partition. Since this computer has a new hard disk that hasn't been formatted before, you will only have the option to create a new partition on it.
If you don't want to specify a specific partition to install Windows on, or create partitions on your hard disk, click Next to begin the installation. If you already have another existing partition with enough free space and want to install the Windows 7 on that partition to create a multiboot configuration, select the partition you want to use, and then click Next to begin the installation. If you want to create, extend, delete, or format a partition, click Drive options (advanced), click the option you want, and then follow the instructions.
Since I don't need to perform any additional task I will just click on the "Next" button. The installation process will then create a partition on all the available disk space, and format it.
The setup process will now begin to copy files from the installation DVD media to the hard disk.
Process could take a while depending on the type of hardware your computer uses. In my VM test sample I've used for this demo, the entire process finished before I could finish writing the previous 3 paragraphs, so it could be pretty quick.
The computer will reboot, and the next thing you'll see is the prompt to set the user's and computer's name. By default, the computer's name will be username-PC, where username is the username you've entered.
Note: The user you're creating will be the only user currently available on the system. Like Vista, the built-in Administrator's account is disabled. Read my article on how to enable the Windows 7 Administrator's account article for more information.
Click on "Next".
Enter the user's password. Remember this password, as it will be the ONLY user on the system, and unless you create an additional user or enable the built-in administrator account, if you forget this password you'll need to crack it to gain access to the system. The best option would be to choose a complex password made of at least 7 characters or more (something like Pssw0rd or MYpa$$w0rd). You must also enter a password hint.
Click on "Next".
Next, type in your product key. If you do not have the product key at hand you can still click "Next", and proceed with the installation. You will be asked to enter the product key after Windows is installed.
Choose what sort of protection your computer gets. The recommended settings are best for someone that doesn't plan to hide their computer behind a corporate firewall (and even then, in some cases, this would be the best option). If you plan to install a 3rd-party firewall later you can opt to be prompted later. Note that this setting will also have effect on how the computer uses the Microsoft Windows Update
WINDOWS 8 INSTALLATION STEP BY STEP SCREENSHOTS
Getting started
After booting from the DVD that I created from my download, the first thing I encountered was the new light blue Windows logo on a black background, as shown in Figure A. This image remained on the screen for a few moments while Setup was initializing. I was kind of hoping that the flag would be animated, but the only animation was the dots spinning in a circle.
Figure A
The new light blue Windows flag is introduced.
After a few minutes, you’ll see the Windows Setup screen shown in Figure B and you will specify your language settings before clicking Next. When you do, Setup will perform some more initialization tasks in the background.
Figure B
The first step in the installation is to specify your language settings.
As soon as the initial steps are taken care of, you’ll see the Windows Setup screen shown inFigure C and will click the Install Now button.
Figure C
To get started, just click the Install now button.
Collecting Information
Once you click the Install now button, you’ll see the beginning of the information collection phase of the installation procedure. As you can see in Figure D, the first step here is to input the Windows 8 product key.
Figure D
You’ll enter your product key to start the information collection phase of the installation procedure.
The next step is to acknowledge that you accept the license terms, as shown in Figure E. If you take the time to read through them, you will see that Microsoft has indeed radically overhauled EULA as Ed Bott over at ZDNet wrote about in a recent column.
Even if you don’t take the time to read the license terms during the installation, once you have installed Windows 8, you can find the Microsoft Software License Agreement in the Windows Help and Support system - just search with the term License. Not only is the license shorter in length, but it is also much clearer and easier to read.
Figure E
The new EULA is much easier to read that previous versions.
When you are prompted to choose which type of installation you want to perform, as shown inFigure F, you’ll choose Custom: Install Windows only (advanced) type in order to perform a clean install of Windows 8.
Figure F
In order to perform a clean install of Windows 8, you’ll select the Custom option.
When you are prompted to choose where you want to install Windows, as shown in Figure G, you’ll see a list of any partitions that are currently on your hard disk. As you can see in my example system there are actually four separate partitions. You may have a different combination depending on your system.
As I mentioned, performing a clean install means blowing away all existing partitions. The first partition in this list is labeled System Reserved and it was created automatically during the Windows 7 installation. A new System Reserved partition will be created by Windows 8, so you can remove existing one. The partition labeled Recovery contains the OEM recovery for Windows 7. I created the recovery DVDs soon after I got the new system. It won’t do me any good going forward with Windows 8 anyway, so I will remove that partition too. The partition labeled WIN7 contains the Windows 7 installation that I am replacing, so it is definitely going. The partition labeled DATA contains all of my data that I copied to an external hard disk, so it is safe to blow that one away too.
Figure G
On you example system there are four partitions that I will be blowing away.
To begin blowing away partitions, you start by clicking Drive options (advanced). When you do so, you’ll see a list of commands for managing partitions, as shown in Figure H.
Figure H
When you click Drive options (advanced), you’ll see a list of commands for managing partitions.
Now, you’ll select each of the partitions, one by one, and select the Delete command. When you do, you’ll see a confirmation prompt like the one shown in Figure I. Just click OK to delete the partition.
Figure I
As you delete each partition, you’ll be prompted to confirm the operation.
Once you delete each of the existing partitions, you’ll see that all of the space will be combined together in one chunk labeled Unallocated Space, as shown in Figure J. While you could create a new partition and format it, you don’t have to. Windows 8 will automatically take care of that in the next step. So just go ahead and click Next.
Figure J
All of the space will be combined together in one chunk labeled Unallocated Space.
Installing Windows
When you click Next, Setup creates the partition, formats it, and then instantly moves into the Installing Windows phase which begins with copying and getting files ready for the installation, as shown in Figure K. This process will take a while to progress though, so you can sit back and relax a bit.
Figure K
The Installing Windows stage begins with copying files from the DVD to the hard disk.
When this phase of the process is complete, Windows will alert you that it is going to restart in order to continue, as shown in Figure L. If you are really impatient and really quick, you can click the Restart now button.
Figure L
Windows will restart after the first part of the process is complete.
Upon restarting you’ll see the black screen with the blue Windows logo and see that Setup is getting devices ready, as shown in Figure M. As soon as that part of the process is complete, Windows will alert you that it is going to restart again, as shown in Figure N.
Figure M
Windows Setup will get all installed devices ready to work with Windows 8.
Figure N
Windows will restart again.
Configuring Windows
When the system restarts, you’ll be prompted to choose a color scheme for Windows 8 and a PC name, as shown in Figure O. I chose a light blue color scheme for now. I can change it later.
Figure O
You can choose a color schema and name your computer.
When the Settings screen appears, as shown in Figure P, you can choose to customize these settings or you can allow Windows to use the express settings. If you are unsure, you can click the Learn more link and get more details. I chose to use the express settings. I can change any or all of these setting later if I want.
Figure P
You can customize the settings or just go the express route.
On the next screen, you’ll choose how you want to sign on to Windows 8, as shown in Figure Q. While you can choose to sign in with a local account, I would recommend that you use an existing Microsoft (email) account, such as a Hotmail.com or a Live.com account. If you don’t have a Microsoft account, you can sign up for one or you can use any email address that you want and Windows 8 will create an account for you.
Figure Q
It will be to your advantage to use an existing Microsoft account or to create one.
The advantage of using an existing Microsoft account or creating one is that you will be able to instantly use the Windows Store, will be able to easily sync settings between multiple Windows 8 computers, and be able to easily take advantage of other Windows 8 features. I already have a Microsoft account, so I entered it here.
After filling the details of your account on the next couple of screens, you’ll eventually see a screen that changes color as it alerts you the Setup is getting your PC ready. The green version of this screen is show in Figure R.
Figure R
While this screen changes color often, it will remain for a few minutes while Setup works in the background.
As you may know, Windows 8 comes with a host of native apps for the Start screen interface that replace and add to the group of applications that used to come with previous versions of Windows. The screen shown in Figure S indicates that Setup is installing those apps.
Figure S
As the last step in the installation, Windows 8 installs its set of native apps.
Once the apps are installed, you’ll see the Start screen, as shown in Figure T, and can begin using Windows 8.
Figure T
The Start screen appears when the installation procedure is complete.
Gnome Rotary Engine
The Gnome was one of several rotary engines popular on fighter planes during World War I. In this type of engine, the crankshaft is mounted on the airplane, while the crankcase and cylinders rotate with the propeller.
The Gnome was unique in that the intake valves were located within the pistons. Otherwise, this engine used the familiar Otto four stroke cycle. At any given point, each of the cylinders is in a different phase of the cycle. In the following discussion, follow the master cylinder with the green connecting rod.
Intake
During this portion of the stroke, a vacuum forms in the cylinder, forcing the intake valve open and drawing the fuel-air mixture in from the crankcase.
Compression
The mixture is compressed during this phase. The spark plug fires toward the end of the compression stroke, slightly before top dead center.
Power
The power stroke happens here. Note that the exhaust valve opens early—well before bottom dead center.
Exhaust
This engine has a fairly long exhaust stroke. In order to improve power or efficiency, engine valve timing often varies from what one might expect.
When I first learned how these engines worked, I thought the only person crazier than the engine designer was the one who paid money for it. At first glance it seems ridiculously backwards.
Nonetheless, a number of engines were designed this way, including the Gnome, Gnome Monosoupape, LeRhone, Clerget, and Bentley. It turns out there were some good reasons for the configuration:
Balance
Note that the crankcase and cylinders revolve in one circle, while the pistons revolve in another, offset circle. Relative to the engine mounting point, there are no reciprocating parts. This means there’s no need for a heavy counterbalance.Air Cooling
Keeping an engine cool was an ongoing challenge for early engine designers. Many resorted to heavy water cooling systems. Air cooling is quite adequate on rotary engines, since the cylinders are always in motion.No flywheel
The crankcase and cylinders provided more than adequate momentum to smooth out the power pulses, eliminating the need for a heavy flywheel.
All these factors gave rotary engines the best power-to-weight ratio of any configuration at the time, making them ideal for use in fighter planes. Of course, there were disadvantages as well:
Gyroscopic effect
A heavy spinning object resists efforts to disturb its orientation (a toy gyroscope demonstrates the effect nicely). This made the aircraft difficult to maneuver.Total Loss Oil system
Centrifugal force throws lubricating oil out after its first trip through the engine. It was usually castor oil that could be readily combined with the fuel. The aircraft’s range was thus limited by the amount of oil it could carry as well as fuel. Most conventional engines continuously re-circulate a relatively small supply of oil.
Most of my information on the Gnome came out of Air board Technical Notes
Diesel Engine
The diesel engine was first patented in 1892 by Rudolph Diesel.
The diesel is similar to the four stroke, but uses a different method to ignite the fuel.
Intake
The intake valve opens, and fresh air (containing no fuel), is drawn into the cylinder.
Compression
As the piston rises, the air is compressed, causing its temperature to rise. At the end of the compression stroke, the air is hot enough to ignite fuel.
Injection
Near the top of the compression stroke, the fuel injector drives fuel into the cylinder. The fuel immediately ignites upon contact with the hot compressed air.
Power
As the fuel burns, the gas in the cylinder heats and expands, driving the piston.
Exhaust
The exhaust valve opens, and the exhaust is driven out of the cylinder.
Valve detail
The valves are operated by a variety of mechanisms on diesel and four stroke engines. The engine illustrated here features dual overhead camshafts, sometimes abbreviated DOHC. These are usually driven by a chain or cog belt as shown here.
With his first practical engine in 1897, “Diesel proved to the world that his was the most efficient engine ever built.”8 Diesels are still among the most energy efficient engines available. They are widely used in large trucks, boats, earthmoving machinery, etc.
Two Stroke Engine
The two stroke engine employs both the crankcase and the cylinder to achieve all the elements of the Otto cycle in only two strokes of the piston.
Intake
The fuel/air mixture is first drawn into the crankcase by the vacuum that is created during the upward stroke of the piston. The illustrated engine features a poppet intake valve; however, many engines use a rotary value incorporated into the crankshaft.
Crankcase compression
During the downward stroke, the poppet valve is forced closed by the increased crankcase pressure. The fuel mixture is then compressed in the crankcase during the remainder of the stroke.
Transfer/Exhaust
Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well.
Compression
The piston then rises, driven by flywheel momentum, and compresses the fuel mixture. (At the same time, another intake stroke is happening beneath the piston).
Power
At the top of the stroke, the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle. (At the same time, another crankcase compression stroke is happening beneath the piston.)
Since the two stroke engine fires on every revolution of the crankshaft, a two stroke engine is usually more powerful than a four stroke engine of equivalent size. This, coupled with their lighter, simpler construction, makes the two stroke engine popular in chainsaws, line trimmers, outboard motors, snowmobiles, jet-skis, light motorcycles, and model airplanes.
Unfortunately, most two stroke engines are inefficient and are terrible polluters due to the amount of unspent fuel that escapes through the exhaust port.
