Overview on turbo systems
Overview on turbo systems
this was on 350zmotoring.com. It is pretty good for people new to FI.
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.
Turbo Chargers
How The Turbo Unit Works
The Compressor Side
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 (see diagram A, here 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, I will leave it to a later discussion.
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.
Turbochargers Explained: The Wastegate
Without a wastegate, the amount of boost that a turbocharger creates varies with the pressure of the engine's exhaust. This happens because exhaust pressure varies with relation to the engine's speed (measured in RPM's). This implies that as an engine reaches higher RPM's, increasing amounts of boost will be created by the turbocharger. The problem with this is that an engine can only accomodate a given amount of boost. Most stock engines are only meant to take about 10 PSI if not less. In order to regulate the amount of boost that comes into the engine, a wastegate acts as a door only allowing a given amount of exhaust to hit the turbocharger's exhaust turbine. Once the engine starts producing more exhaust pressure then the wastegate system will allow, a flap is opened to redirect excess exhaust away from the turbine blades. In turn, this is where a wastegate gets it's name. It's a gate to carry away waste. In order to regulate when a wastegate opens, a boost conroller can be used.
There are two types of wastegates. The first one is an internal wastegate (see picture A). An internal wastegate is a component on the turbo unit itself. The gate is opened via an actuator which is a diaphram type system (see picture B). Excess exhaust is then fed directly into the exhaust system. We also have what is called an external wastegate (left), unlike an internal wastegate, it is seperate from the turbo unit and does not require an actuator. Excess exhaust can either be fed into the exhaust system or it can be vented straight out and into the atmosphere. High performance set-ups typically follow the latter alternative. Most stock systems come with an internal wastegate as this set-up is better suited for low boost applications. However most aftermarket systems perform better with an seperate external wastegate assembly making it an ideal choice for those generating boost in the range of 20-30 PSI.
The Blow Off Valve (BOV) and the Diverter or Bypass Valve
Ever wonder why rally cars make that sound you hear when you open a bottle of pop? Well, maybe not exactly like that but more or less similar to the sound of air being released (air, not gas!). You usually hear this when you let off the throttle, sorta sounds like a woosh!. In effect, what you are hearing is the sound of built up boost pressure being released from the intake system. The reason for this is that the turbocharger will keep spinning even after you let off the gas. So as you close the throttle plate, allot of pressure builds up in the intake system. This becomes problematic in that this excess pressure can cause the turbines to seize. Ultimately, this would destroy the turbo unit. For this reason, we incorporate BOV's, bypass or diverter valves. These mechanism work because on the other side of the throttle plate, vacuum gets built up in the intake manifold. Blow off valves, diverter and bypass valves all work by detecting this vacuum. Having done so, they use this vacuum to mechanically open a valve in order to relieve unnecessary boost from the other side of the throttle plate.
Now let us differentiate BOV's, diverter and bypass valves. First, a blow off valve (see picture A) is common to high performance applications in that it provides the least bit of compromise. A BOV essentially releases this pressure straight out into the atmosphere. Quite often you will find that these units take on particular shapes, making them resemble musical instruments. I guess some people out there really like to flaunt their gadgets. A bypass or a diverter valve can also be used (see picture B). These units essentially redirect this pressure back behind the compressor causing the net flow of air to remain constant. This in turn gradually slows the turbine down.
The Boost Controller
It is important to note that stock systems with a wastegate actuator operated by means of boost pressure do not come equipped with a boost controller. When you have a boost pressure operated actuator, the actuator itself is the mechanism limiting your boost. In essence, the actuator opens your wastegate when boost levels reach the predetermined PSI level. Now in order to get more boost from your turbo system in this sort of set-up, you need to install a boost controller (see picture A). A boost controller limits the amount of pressure that gets sent to the wastegate actuator. In a sense, it fools it to think that less boost is being created in the system. In turn, it will open the wastegate at higher levels of boost. On the other hand, we have a wastegate actuator operated by means of a solenoid. In this sort of set-up, the system is tied into your engine management system. Boost pressure is detected by an air flow sensor, this signal is then sent to your ECU and your ECU will regulate boost pressure accordingly. In such a set-up, you do no install a mechanical boost controller. In the latter case, people typically reprogram their engine management system to allow for more boost. A more intricate set-up will employ a boost controller which is electronically tied into your ECU. An example of this sort of set-up is the G-Reddy E-01 (see picture B). This unit offers the option to adjust your turbo system to suit driving conditions. As for those of you with a conventional system, electronic boost control conversions are available.
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.
Turbo Chargers
How The Turbo Unit Works
The Compressor Side
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 (see diagram A, here 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, I will leave it to a later discussion.
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.
Turbochargers Explained: The Wastegate
Without a wastegate, the amount of boost that a turbocharger creates varies with the pressure of the engine's exhaust. This happens because exhaust pressure varies with relation to the engine's speed (measured in RPM's). This implies that as an engine reaches higher RPM's, increasing amounts of boost will be created by the turbocharger. The problem with this is that an engine can only accomodate a given amount of boost. Most stock engines are only meant to take about 10 PSI if not less. In order to regulate the amount of boost that comes into the engine, a wastegate acts as a door only allowing a given amount of exhaust to hit the turbocharger's exhaust turbine. Once the engine starts producing more exhaust pressure then the wastegate system will allow, a flap is opened to redirect excess exhaust away from the turbine blades. In turn, this is where a wastegate gets it's name. It's a gate to carry away waste. In order to regulate when a wastegate opens, a boost conroller can be used.
There are two types of wastegates. The first one is an internal wastegate (see picture A). An internal wastegate is a component on the turbo unit itself. The gate is opened via an actuator which is a diaphram type system (see picture B). Excess exhaust is then fed directly into the exhaust system. We also have what is called an external wastegate (left), unlike an internal wastegate, it is seperate from the turbo unit and does not require an actuator. Excess exhaust can either be fed into the exhaust system or it can be vented straight out and into the atmosphere. High performance set-ups typically follow the latter alternative. Most stock systems come with an internal wastegate as this set-up is better suited for low boost applications. However most aftermarket systems perform better with an seperate external wastegate assembly making it an ideal choice for those generating boost in the range of 20-30 PSI.
The Blow Off Valve (BOV) and the Diverter or Bypass Valve
Ever wonder why rally cars make that sound you hear when you open a bottle of pop? Well, maybe not exactly like that but more or less similar to the sound of air being released (air, not gas!). You usually hear this when you let off the throttle, sorta sounds like a woosh!. In effect, what you are hearing is the sound of built up boost pressure being released from the intake system. The reason for this is that the turbocharger will keep spinning even after you let off the gas. So as you close the throttle plate, allot of pressure builds up in the intake system. This becomes problematic in that this excess pressure can cause the turbines to seize. Ultimately, this would destroy the turbo unit. For this reason, we incorporate BOV's, bypass or diverter valves. These mechanism work because on the other side of the throttle plate, vacuum gets built up in the intake manifold. Blow off valves, diverter and bypass valves all work by detecting this vacuum. Having done so, they use this vacuum to mechanically open a valve in order to relieve unnecessary boost from the other side of the throttle plate.
Now let us differentiate BOV's, diverter and bypass valves. First, a blow off valve (see picture A) is common to high performance applications in that it provides the least bit of compromise. A BOV essentially releases this pressure straight out into the atmosphere. Quite often you will find that these units take on particular shapes, making them resemble musical instruments. I guess some people out there really like to flaunt their gadgets. A bypass or a diverter valve can also be used (see picture B). These units essentially redirect this pressure back behind the compressor causing the net flow of air to remain constant. This in turn gradually slows the turbine down.
The Boost Controller
It is important to note that stock systems with a wastegate actuator operated by means of boost pressure do not come equipped with a boost controller. When you have a boost pressure operated actuator, the actuator itself is the mechanism limiting your boost. In essence, the actuator opens your wastegate when boost levels reach the predetermined PSI level. Now in order to get more boost from your turbo system in this sort of set-up, you need to install a boost controller (see picture A). A boost controller limits the amount of pressure that gets sent to the wastegate actuator. In a sense, it fools it to think that less boost is being created in the system. In turn, it will open the wastegate at higher levels of boost. On the other hand, we have a wastegate actuator operated by means of a solenoid. In this sort of set-up, the system is tied into your engine management system. Boost pressure is detected by an air flow sensor, this signal is then sent to your ECU and your ECU will regulate boost pressure accordingly. In such a set-up, you do no install a mechanical boost controller. In the latter case, people typically reprogram their engine management system to allow for more boost. A more intricate set-up will employ a boost controller which is electronically tied into your ECU. An example of this sort of set-up is the G-Reddy E-01 (see picture B). This unit offers the option to adjust your turbo system to suit driving conditions. As for those of you with a conventional system, electronic boost control conversions are available.
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