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Thursday, September 11, 2008

The Concept of Forced Induction:-

One of the primary factors affecting engine performance as the ability to get as much of the air and fuel mixture into the engine as possible. It can be thought of as the engines ability to "inhale". In order to produce power, an engine requires a fuel and air mixture to be mixed together and then brought into the cycle. The concept of forced induction is essentially a method wherein we literally compress the air before we bring it into the process of combustion. So basically, think of an engine as a person who is gasping for air after a long run down the street. This person is gasping because they are trying to circulate as much air as possible through their lungs. Now imagine if you were able to force more air into their lungs then they would otherwise be able to suck in on their own. This would in turn help them out very much. In fact, it would help them so much that they would probably be able to run for allot longer without having to stop in order to "catch their breath". In turn, this would yield greater performance. So basically, you can pretty much parallel this idea to an engine. The more air you get into it, the more performance you'll get out of it. This is where the concept of forced induction was derived. While different systems have been designed to achieve the same result (e.g. Superchargers and Turbo Units) the Turbo unit seems to have dominated. In brief, the two systems differ from one another in the means by which the compression process is powered. The turbo unit works by making use of exhaust gases in order to compress the intake while the supercharger mechanically translates the engines rotational power in order to do the same job.

Monday, September 8, 2008

Turbo Chargers:-

To keep it brief and simple, a turbo unit compresses the intake of the engine by means of a fan. Essentially, the fan pulls in air on one side and then it pushes it out the other ( it's referred to as the compressor wheel). A fan performs the function of moving air; however we are still left with the task of compressing the air. In order to compress the air; we must then contain it within an enclosed space (this is the compressor housing). Once the intake is compressed it gets sent out to the engine. This process of compression is what's technically referred to as "boost". When one is running more "boost" this person is essentially running more compressed air out of his turbo unit. This is usually related to the size of the unit itself. However, certain factors can limit the degree to which boost varies with the size of the unit. As this gets too technical within the scope of the article.

The Turbine Side:-

So far we understand how the compressor side allows for more air to flow into the engine, but we must now understand what it is that makes the compressor wheel turn fast enough to create the boost in the first place. In turn, we are brought into the turbine side. A turbine is a term used to describe a fan like object that gets propelled by the flow of air, water or steam. In a hydroelectric power plant, the Turbine is propelled by the flow of water which then turns a generator. Within the scope of the turbo charger, the turbine is propelled by the flow of exhaust gases that come out of the engine. So the more exhaust that flows out of the engine, the faster the turbine will turn. Again, like the intake side, pressure can only be created if the flow of air is kept within an enclosed space; for this reason, we have the turbine housing.

Ups and Downs of Turbo Chargers:-
So what does a turbo charger do then you ask? Well, it basically allows you to get more power out of a smaller engine. So in a car that would normally require 6 cylinders, you can now run 4 and still get close to the same power without the added weight and increased gas consumption.

While the turbo unit does provide ample cranking power, it is very dependant on the reciprocating process which I described earlier. This implies that we must somehow power the unit before it begins to give us anything in return. So its one of those deals where you got to give it something before it gives you anything in return. You can think of it as one of those greedy bastards you run across in life. He'll help you as long as you do something for him first. Within the framework of the article, the turbo unit requires exhaust pressure to turn before it begins to provide any added boost to the engine. As a result, what happens is that engines equipped with turbo units take a little while before they give off the power. So at lower RPM's you'll find that you don't get that instant throttle response that you would otherwise get in a naturally aspirated system. This is because the intake and exhaust functions of the engine are not intertwined much like they are in forced induction systems. However, in order to overcome this, turbo charged engines can be driven at higher RPM's. In turn, this keeps the unit constantly turning and fully ready to give off the extra pressure on demand. Of course, as most of you are already aware, this would in turn result in greater wear and tear on the engine and greater gas consumption. However, technology has allowed for many of the downsides of turbo units to be more or less overcome.
These issue that must be addressed relates to the manner in which power is delivered through a turbo charged engine. Basically, the turbo system is quite sporadic. Meaning, it's sometimes hard for more novice drivers to know where and how the power is going to be brought on. Turbo charged cars tend to take a little while before any boost is generated, so the driver may find himself pressing down pretty far on the gas under 2 500 RPM's. However, once the boost is brought on, the driver would then experience a great jolt. This jolt, if not accommodated properly can send a rear wheel drive car into a severe drift. In some set-ups, this can be very lethal. An example would be a rear engine, turbo charged rear wheel drive car, much like the older 911 Turbo's. This partially helps explain why most 911's now come equipped with all wheel drive and state of the art traction control systems.

Basic Engine Parts

Basic Engine Parts:-
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.

In an inline engine, the cylinders are arranged in a line in a single bank.
Different configurations have different advantages and disadvantages in terms of smoothness, manufacturing cost and shape characteristics. These advantages and disadvantages make the 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.

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
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.

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).


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