By contrast, a V-type engine arrangement may require other considerations. Running a single turbo on a Vengine will require you to route the exhaust from one side to the other unless your vehicle, like Indy cars, has sufficient room to place the turbo aft of the engine. The length of the manifold tubing and the total increase in heat load will likely require the use of expansion joints to eliminate the cracks from thermal expansion and contraction.
Applying two smaller units will solve most of these plumbing and fitment problems. The engine room at Gale Banks engineering and another twin turbo system and engine build underway. Historically, the major interest in using twins has been to help reduce the turbo lag during engine acceleration. This is especially true for highperformance street engines. Two small turbines have a lower total polar moment of inertia than a single large turbine.
Moment of inertia is the resistance of a body to change in speed, up or down. Remember your basic physics: a body in motion tends to stay in motion, and a body at rest tends to stay at rest also a couch-potato definition. The radius of gyration is the distance from the axis of rotation to a point in the body that would have the same I as the body itself.
This will not be equal to the radius of the rotational diameter of the turbine wheel because turbines are designed to keep as much of their mass as close to the axis of rotation as possible.
The turbine wheel hub is much more massive than the outer areas of the blades. Therefore, K will almost always be less than one-half the rotational diameter. The formula demonstrates the value of keeping the turbine wheel material near the outer diameter to a minimum to reduce K, because the moment of inertia varies as the square of K.
This can be functionally illustrated by applying the formula to see how two turbos will cut the moment of inertia by more than half, which indicates a gain in potential rotor acceleration since two turbos will each have exactly half the exhaust energy as compared to what a single turbo unit would see on the same engine.
If the alternative best match single unit turbine wheel had a diameter of 3. This would be 2. There are many factors aside from moment of inertia that will affect turbo system response time.
Turbine efficiency is another important consideration. An often overlooked and rarely recognized concept is that the turbine wheel running clearance the space between the wheel and the housing is a loss feature to turbine efficiency. In the above examples, both turbine wheels would likely have the same turbine wheel contour clearance between the turbine housing and turbine wheel. The total turbine wheel clearance contained in two turbines will therefore be a higher percentage of total turbine flow, thereby potentially lowering the total turbine efficiency in a twin unit arrangement.
Packaging and abstract efficiency discussions aside, it may make the most sense for the intended use of the vehicle to help you decide between a big single and twins. Drag racing vehicles today make good use of tuning features such as anti-lag systems ALS discussed in greater depth in Chapter 8. Once the vehicle with a big single unit is launched using such tuning mechanisms, the higher system efficiency takes over and the single unit will pay dividends in lower ETs.
Regardless of whether you plan to make a competition or high-performance street machine, the air intake is an extremely important consideration. Note the Lexus GS gets its intake air right through the hood. Note how the wastegate dumps nicely parallel to the turbine outlet path. The leading edge from where you get your air is the same as in a competition vehicle, but you have two other primary considerations: filtration of small dirt particles and rain. Do not use paper air filter elements in a turbocharged vehicle.
While many companies market performance intake systems already designed for your vehicle, be cautious because they have a filter element sized for its stock naturally aspirated state. This will likely be undersized for your turbocharged motor and can cause problems. This keeps the pressure drop and resulting pumping loss during intake to a minimum. It also creates excess flow capacity to allow dirt to be more easily separated from the air stream and become trapped, while still having the capacity to flow enough air for the desired performance.
The filters are pleated to allow more surface area within a given diameter for packaging purposes. Now, to help you choose a filter, determine the diameter that will fit your installation, and then use the following formula to determine the filter length or height, depending on orientation. Note that this calculation is for round filters. Consequently, in the above example if you had room for a inch diameter filter it would require a filter height of about 3 inches.
If this seems large to you, then you now understand the value of a properly sized air filter assembly and the value of knowing how to design your own turbo system. If you have a few feet to navigate, keep your tubing diameter as large as room will allow.
This reduces tubing line loss. There is some confusion in terminology between aftercooler, intercooler, and charge-air cooler. In the past, aircraft engines would run turbochargers in stages where the first stage compressor would feed the inlet of the second stage compressor, which would further compress the air before it enters the engine. Due to the extremely high boost pressures, an air cooler was positioned between the first and second-stage compressors. That cooler was called the intercooler.
Another cooler would be positioned after the second stage, which was the final compressor stage, and that was referred to as the aftercooler. The aftercooler was the cooler whose outlet fed the engine. The Banks twin-turbo 6. While multi-stage turbocharger systems are still in-use in some tractor pull classes, selected high-performance diesels, and late-model commercial diesels, the term intercooler and aftercooler are used synonymously today.
The term intercooler is used today to mean a cooler in-between the turbo and the engine. So feel free to use whichever term you are comfortable with. The subject of aftercoolers is one that could fill an entire book. And does anyone really stick to running just 7 psi?
While the air density enhancement is not as dramatic at this mild boost level, a cooler air charge will still raise the fuel detonation threshold and keep you running safe.
An aftercooler on a commercial application such as this can drop the intake charge temperature as much as degrees F. However, above that 5 to 7 lbs boost level the benefits are indeed worth the trouble. In addition to dramatically increasing air density, the aftercooler removes a significant amount of thermal stress that would otherwise be seen by the engine.
But perhaps the biggest benefit is that an aftercooled charge is less likely to detonate, which will dramatically reduce power and can quickly destroy your engine. The cooler keeps the air charge temperature lower without loss in engine thermal efficiency. As a general rule, each one degree F reduction of intake air temperature will also reduce exhaust temperatures by one degree F.
This is without a detrimental effect upon BMEP, which is the force that drives the piston down the cylinder to produce power. An aftercooler is nothing more than a heat exchanger. The air leaving the turbocharger is hot. The higher the boost pressure, the more the air is compressed, and the more heat that is compacted into that intake air.
You can increase the effectiveness of the intercooler by placing it in vehicle frontal airflow, which brings more cool ambient air over the cooling fins. Its main function is to further increase air density beyond what the turbocharger has produced. Its secondary functions are reduced thermal load and lowered detonation threshold. The goal of your turbocharger system is not to create excessive boost pressure—you want increased air density for enhanced engine performance.
Boost pressure is important to the enhancement of VE, but excessive pressure can result from super-heated air if the compressor is operating outside of its range of efficiency. The absence of an intercooler will cause excess thermal stress and detonation. During the act of cooling the air, the aftercooler must actually reduce boost pressure slightly, by about 1 to 2 lbs, because of ideal gas law requirements.
Most well made aftercoolers tend to run between 60 and 75 percent efficiency. The efficiency of an aftercooler basically measures the comparison of the heat removed by the aftercooler as a function of the heat added from compression. If you end up measuring an efficiency of less than 60 percent, it might be time for an upgrade. Assume an ambient temperature of 75 degrees F T1 , compressor discharge of degrees F T2 , and an aftercooler discharge temperature of degrees F T3.
This is the formula for predicting T3 aftercooler discharge temp when adding an aftercooler with a known efficiency. Assume a compressor discharge temperature of degrees F T2 , an aftercooler efficiency of 70 percent, and an ambient temperature of 75 degrees F T1. In this example, your intake manifold temperature drops from to just degrees—a degree improvement. This would decrease your exhaust temperature by about the same amount and likely eliminate your detonation problem.
Assuming about a pressure ratio, or 15 lbs boost, along with a 70 percent compressor efficiency, you could expect to be able to produce about 15—18 percent more power at the same engine speed while making about one psi less boost. One important consideration relative to a retrofit of a cooler is that the dramatically lower EGT in Example 2 could lower the available energy driving the turbine. When this occurs it may become necessary to use a slightly smaller turbine housing to maintain desired boost level.
However, if your turbine housing was a bit on the small side and the boost actuator was set to actuate very early, your match may not require a change. Combined density ratio chart shows the density ratio of both nonaftercooled and aftercooled density ratios for the same compressor efficiencies.
Note how the two groups of lines diverge as boost pressure rises. In more recent years Garrett has introduced turbos with ball bearings to support the turbine shaft. As you can imagine the reduced drag of ball bearings in the turbo enhances several aspects.
First, the spool time is quicker. Second, the maximum RPM of the turbine is increased at full boost. Third, the cost of the turbo is enhanced too, about double that of the older style T3 and T4 type turbos with oil-lite bearings.
This lets you use a smaller turbine for the target horsepower you want to achieve. The smaller turbine means less mass, which results in a quicker spool time. So a T3 sized turbine with ball bearings GT35 can pump more air volume, similar in volume to a larger T4 which has a slower spool time , because the ball bearings allow the turbine to spin so much faster.
So the addition of ball bearings make the trade-off of spool time versus max horsepower less of an issue. You might be thinking….. The answer to that is Then an aficionado will dynomometer tuning for correct fueling with maximize horsepower and torque. The rewards can priceless, or result in catastrophic failure due to mistakes. Good luck! Your email address will not be published.
Your Website. Save my name, email, and website in this browser for the next time I comment. This site uses Akismet to reduce spam.
Learn how your comment data is processed. Summit Racing Equipment. Compressor Stage After determining realistic power level, selecting the proper compressor stage is the first step in turbocharging an engine. Rotating Assembly The compressor wheel and turbine wheel are connected via a steel shaft. Wastegate Assembly The wastegate is the control device for the turbocharger.
Author: Doug Erber. David Daugherty says: January 20, at am. Leo Gallegos says: April 26, at pm. L Hamilton says: August 22, at am. Wilbur says: March 1, at am. If ever there was a mechanical marriage made in heaven, it is a diesel engine and a turbocharger. On the farm, this union is found in everything from a pickup truck to a combine. The two methods of forced induction differ in how they are powered. A turbocharger, on the other hand, uses the exhaust gas exiting the cylinder to operate, and it requires no power from the engine.
The turbocharger accomplishes two things. It fills the cylinder bore with more air, and it causes turbulence in the cylinder. This latter effect greatly improves combustion. Thus, a turbocharger makes a diesel more powerful, lets it run cleaner, and gives it the potential to use less fuel.
The standard used to measure cylinder fill is called volumetric efficiency VE , and it is read as a percentage. That pressure, by the way, is read in the intake manifold as boost. The gauge on a dashboard reads this as pressure per square inch, but it is really the amount of pressure over the atmosphere.
If atmospheric pressure is Thus, the effective size of the engine can be considered doubled for every In theory, a liter engine 1 liter is approximately 61 cubic inches when exposed to approximately 15 psi of boost in pressure is the equivalent of a liter engine that breathes naturally.
What is wonderful about turbocharging is that the power gain it offers is passive. In other words, the gain is only there when you need it, such as the times an engine is called on to work hard. When the load is low, the engine operates at its mechanical size. When more power is needed, the turbocharging helps the engine to respond as if it were larger in displacement. Many turbocharging applications also employ a heat exchanger, which is identified as either an intercooler or charge air cooler CAC.
The purpose of the CAC is to cool charged air, which, in turn, increases the density of the air being sent to the cylinders. The CAC also helps to reduce the heat caused by the act of turbocharging.
Hotter air is undesirable to engine performance as it contains fewer oxygen molecules than cooler air. A turbocharger incorporates an exhaust-driven turbine wheel.
0コメント