TURBO INTERCOOLING

                                        INTRODUCTION

Cool Air Equals Power

Cool air is good for making power, but could hot air be even better?
Most people know that engines make more power when the inlet air is cooler. Let’s take a look at why this is true at least in most applications. We’ll also tell you right up front that this article might leave you with more questions than answers. Then again, you might be the one that provides the additional answers and takes the world to the next generation of internal combustion engines.
To understand what goes on during both the intake cycle and the power cycle when inlet air temperature is reduced, we need to consider both normally aspirated and supercharged gasoline engines, as well as turbocharged diesels. We’ll also limit this discussion to four-cycle engines.
Before we go any further, let’s define a couple of terms. For this article, we’ll say that supercharging is anything that increases the amount of oxygen available in the cylinder to support combustion of fuel above what could be expected from cylinder filling due to atmospheric pressure only. We’ll assume atmospheric pressure at sea level to be 14.7 PSI and that “normal” air contains approximately 21 percent oxygen. We’ll also exclude oxygen-bearing fuels, such as nitro methane, as a form of supercharging. This means that any form of mechanical compressor that pumps more air into an engine, such a belt- or gear-driven “supercharger”, or an exhaust- or turbine-driven “turbocharger” is included, as well as the injection of nitrous oxide, or even oxygen itself.
Gale Banks has a favorite saying, “It’s all about airflow.” Airflow helps engines make power in many ways, as explained in other articles on this site, but it is also true that the more air you can flow through an engine, the more oxygen that will be available for burning fuel. More oxygen means more fuel can be burned, and that means more power. Maybe his saying should be refined for this article to be “It’s all about oxygen content.” This is most evident when dealing with an ordinary normally aspirated gasoline engine. Many hot rodding tricks relate to getting more air (read oxygen) into the cylinder. Whether it’s by installing a less restrictive fuel injection system or carburetor, a freer flowing intake manifold, porting the cylinder head(s), increasing camshaft lift or duration, the purpose is still the same  get more oxygen into the cylinder. Now in all fairness, the hot rodder is looking at getting maximum oxygen into the cylinder at wide-open throttle for peak power (to beat the other guy). This is partly why nitrous oxide (an oxygen-rich gas) injection is so effective. Nitrous oxide effectively increases the percentage of oxygen in the working fluid (which becomes a mixture of air, nitrous oxide, and fuel) above the 21 percent oxygen in air alone. That means more fuel can be mixed into the working fluid too for greater combustion heat to expand the working fluid and increase pressure in the cylinder. Additionally, when the compressed nitrous oxide, which is stored in its pressurized container as a liquid, is injected, it depressurizes and changes state from a liquid to gas, cooling the working fluid for an accompanying density increase. Of course, it would take an incredible amount of nitrous oxide to be able to use it at all times, so as you would expect, nitrous oxide injection is only used on demand at wide open throttle. But what if we could get more oxygen into the engine at all throttle positions all the time? Then what happens?
 “Airflow – the Secret to Making Power”, we explain that the air throttle on a gasoline engine controls the density of the intake charge that enters the cylinder. We also explain how superchargers and turbochargers increase the density under boost conditions. In some regards, we can look at density as the amount of oxygen crammed into a given volume of air (the working fluid). Increased density means the molecules in the air are closer together in the same space more air mass (and oxygen) in the same space. Here’s where things can get a little muddy. We have to consider increased air density in both unconfined and confined spaces. Let’s look at an unconfined space, such as the atmosphere, because that’s the world of the normally aspirated engine. Two things affect air density in the atmosphere pressure and temperature. As atmospheric pressure goes up, indicated by higher barometric pressure on a barometer, the density increases if the temperature stays the same. In other words, at any given temperature, if the barometric pressure rises, so does the air density. By the same token, as temperature goes down, the density increases if the atmospheric pressure stays the same. Atmospheric air density is very important to normally aspirated engines. Obviously, you can’t do much to increase the atmospheric air pressure in regard to a normally-aspirated engine, but you can enhance it slightly with some form of ram air taken either from the front of the vehicle or from a dynamically high pressure area, such as the base of the windshield. More importantly, in most cases you can do something about the temperature of the inlet air. The object is to get the coolest air possible to the engine’s intake system. Many engines induct air that has passed through the radiator or over other warm areas of the engine, significantly heating the air and reducing its density. By relocating the air intakes to duct outside air that hasn’t been warmed into the engine, density is significantly increased. For example, it is not uncommon for air to increase up to 50º F. passing through the radiator and air conditioning condenser on a late model vehicle. The general rule of thumb is that for every 10º of temperature drop, the density (and oxygen content) increases 1 percent. It’s actually more like 1.8 percent. Similarly, power increases by an equal amount. So, in this example, if you can intake air that hasn’t been heated, you can gain as much as 5 to 9 percent more power. Happily, the best places to collect cool air are the same places that work for ram air, so you can get the density gains from both pressure and temperature using the same intake ducting.
To get back to our earlier question of what happens when we have cooler, or higher density, air at all throttle positions, it means that the engine is capable of producing given amounts of power at lesser throttle openings. This generally equates to better fuel economy. It also means the engine has greater power potential for accelerating or climbing grades. Cooler intake air also suppresses detonation since the working fluid doesn’t reach as high a temperature on the compression stroke again, a plus for accelerating or climbing grades.
Both gasoline and diesel engines that use superchargers and turbochargers face their own unique problems with intake air temperature. Superchargers and turbochargers significantly heat the intake air as they compress it to create boost. The higher boost pressure increases the air density, but the increased temperature of the air can largely offset this density gain. In this case, we’re talking about the affects of pressure and temperature in a confined space, the intake system. Consequently, it is desirable to cool the compressed air before it enters the engine. In most cases, especially where boost levels exceed 7 PSI, cooling the compressed air with a charge air cooler, often called an intercooler, increases the air density more than any density losses that occur due to the accompanying pressure drop due to cooling or flow restrictions through an intercooler. In other words, intercooling results in a net density increase for the air entering the cylinder.
Intercooling also provides other benefits. For supercharged or turbocharged gasoline engines, reducing the intake air temperature suppresses detonation, just as it does for normally aspirated gasoline engines. For diesel engines, intercooling not only increases charge density, it also results in lower exhaust gas temperature. Excessive exhaust gas temperature, above 1300º cannot be sustained in a diesel without eventual engine and/or turbocharger failure. Lowering intake temperature results in an almost equal reduction in exhaust temperature. For example, the air exiting the turbocharger on the Banks Sidewinder pickup was approximately 500º F. under full power. Dual air-to-water marine intercoolers, connected to a reservoir of ice water, were then used to reduce the air temperature to 100º F. before it entered the engine. With the intercooling, exhaust temperatures remained manageable for the duration of the Bonneville World Speed Record runs. Without intercooling, the exhaust temps would have been in the 1800º-1900º F. range.
The final conclusion is that regardless of whether an engine is normally aspirated or supercharged, gas or diesel, the cooler the intake air, the better.

Now comes the really interesting part of this article that raises all the questions. Twenty years ago, the late, great racing mechanic and inventor Henry “Smokey” Yunick left the automotive engineers shaking their heads when he invented and patented his hot vapor engine. Based on the familiar four-cycle piston engine concept, instead of cooling the intake air to improve efficiency, he used coolant heat and exhaust waste heat to significantly warm the intake air. The purpose was to fully vaporize the fuel and to make the intake air expand in the intake system to generate positive pressure, like a supercharger. A small turbocharger was used as a “mixer” and as a check valve to prevent the expanding intake air from back flowing out of the intake system. With the heated, pressurized, homogenous mixture, the engine ran at air/fuel ratios considered impossibly lean, such as 22:1, on pump gasoline. The hot vapor engine made incredible power and was highly efficient, responsive, surprisingly emissions clean, and delivered fuel economy of 45-50 MPG in a compact car, and it did it all without computers, smog pumps or catalytic converters. Although initially denounced by the automotive world as a hoax, several prominent SAE engineers later published papers validating Smokey’s theories and design. It was no hoax to Smokey. He considered it his greatest achievement. However, the automotive giants had their own designs for increasing fuel economy and controlling emissions, and Smokey’s simple and cost-efficient engine package was ignored. Today, Smokey’s designs are buried somewhere in the U.S. Patent Office awaiting someone to take this technology to the next level.

HOW TURBO INTERCOOLER  WORKS

The drawing below shows the typical Turbo Intercooler live-circle. Please note that there are no fuel parts necessary to understand the principle.

So, how does the thing work?

1.      The engines cylinder exhaust gases travel out of the exhaust valves to the Turbo.

2.   The gases speed then drives the large Turbine Wheel and leaves the circle through          the cats and the exhaust.
3.  On the same axle as the gas-driven Turbine Wheel sits the Compressor Wheel (the axle is lubed by the engines oil).
4.  This smaller but trickier wheel has the same rpm like the Turbine Wheel and compresses the filtered and measured air.
5.  Compressing anything increases its temperature and therefore the compressed air has to be cooled down.
6.  For this we let the air travel through an Intercooler. This reduces the air temperature before going back into the engine.

Why do we need an Intercooler?
 Each engine has an optimal temperature operating range. As our different ambient conditions can vary so much, the engine computers also measure barometric pressure, air temperature and amount of air the engine sucks in. With this the optimal amount if air/fuel ratio for the current ambient is determined and the engine runs in its parameters.

 Fact: The more heat the engine is getting the less power is produced. For design purposes it is also desired to minimize the variable "intake temperature" as much as possible. But we learned that compressing the air produces heat! And the more the air is compressed the more heat is produced. Therefore somebody had the idea to cool down the compressed air the Intercooloer was born. With this element the air is cooled down to acceptable temperatures and allows us freaks to increase the boost without the danger to loose the needed horses. Of course, cooling the engine always helps to keep it longer alive.

 
What is a waste gate?
 Its name says all a gate that is able to waste something away :) Physics tells us that the faster the turbine wheel turns the faster the compressor wheel turns and therefore the more air will be transported. Also the compression increases due to the speed. Of course, this depends on the style of the compressor wheel; housing and whatever as the boost and rpm curve are not linear together.
 The waste gate now is a device that can control the boost by releasing (wasting) some amount of the exhaust gases to the exhaust before traveling to the Turbine Wheel. Therefore the Compressor Wheels is not driven that fast and boost is reduced. A actuator, driven by air pressure, opens the waste gate. The actuator is preloaded with a spring and opens the waste gate when the pressure applied exceeds the spring’s load.

 Usually a vacuum hose to the actuator-actuator will connect the Compressors output. Therefore the bigger the boost of the compressor the more the actuator opens and the less boost will be produced. But less boost means closing the actuator more and therefore more boost will be produced. To get more control for opening and closing the waste gates, the 3000GT/Stealth are having a solenoid valve that, activated by the ECU, releaves some of the boost out of the hose that runs to the actuator actuators. This circle regulates the boost our car needs to go that fast :) This is the basic functionality for getting more boost.

HEAT EXCHANGER THEORY  AND  INTERCOOLER

An intercooler is a heat exchanger. That means there are two or more fluids that don't physically touch each other but a transfer heat or energy takes place between them. Turbo Regals made in 1986/87, Turbo TAs, GMC Syclones and Typhoons all came with intercoolers to cool down the hot compressed air coming from the turbocharger. Turbo Regals and Turbo TAs use outside air as the cooling media; Syclones and Typhoons use water. Turbo Regals made in 1985 and before did not have intercoolers as original equipment.

At wide open throttle and full boost the hot compressed air coming from a turbocharger is probably between 250 and 350 deg F depending on the particular turbo, boost pressure, outside air temperature, etc.. We want to cool it down, which reduces its volume so we can pack more air molecules into the cylinders and reduce the engine's likelihood of detonation.

How does an intercooler work? Hot air from the turbo flows through tubes inside the intercooler. The turbo air transfers heat to the tubes, warming the tubes and cooling the turbo air. Outside air (or water) passes over the tubes and between fins that are attached to the tubes. Heat is transferred from the hot tubes and fins to the cool outside air. This heats the outside air while cooling the tubes. This is how the turbo air is cooled down. Heat goes from the turbo air to the tubes to the outside air.

There are some useful equations, which will help us understand the factors involved in transferring heat. These equations are good for any heat transfer problem, such as radiators and a/c condensers, not just intercoolers. After we look at these equations and see what's important and what's not, we can talk about what all this means.

Equation 1

The first equation describes the overall heat transfer that occurs.
 Q = U x A x DTlm
Q is the amount of energy that is transferred.
U is called the heat transfer coefficient.  It is a measure of how well the exchanger transfers heat.  The bigger the number, the better the transfer.
A is the heat transfer area, or the surface area of the intercooler tubes and fins that is exposed to the outside air.
DTlm is called the log mean temperature difference.  It is an indication of the "driving force", or the overall average difference in temperature between the hot and cold fluids. The equation for this is:
DTlm = (DT1-DT2)  * F
               ln(DT1/DT2)
where DT1 = turbo air temperature in - outside air temperature out
         DT2 = turbo air temperature out - outside air temperature in
              F = a correction factor, see below

Note:

The outside air that passes through the fins on the passenger side of the intercooler comes out hotter than the air passing through the fins on the driver’s side of the intercooler.  If you captured the air passing through all the fins and mixed it up, the temperature of this mix is the "outside air temperature out".

F is a correction factor that accounts for the fact that the cooling air coming out of the back of the intercooler is cooler on one side than the other.  

To calculate this correction factor, calculate "P" and "R":

P = turbo air temp out - turbo air temp in
     outside air temp in - turbo air temp in

R = outside air temp in - outside air temp out
         turbo air temp out - turbo air temp in

Find P and R on "Fchart.jpg" (attached) and read F off the left hand side

This overall heat transfer equation shows us how to get better intercooler performance. To get colder air out of the intercooler we need to transfer more heat, or make Q bigger in other words. To make Q bigger we have to make U, A, or DTlm bigger, so that when you multiply them all together you get bigger number. More on that later.

Equation 2

We also have an equation for checking the amount of heat lost or gained by the fluid on one side of the heat exchanger (i.e., just the turbo air or just the outside air):

                      Q = m x Cp x DT


Q is the energy transferred.  It will have the exact same value as the Q in the first equation.  If 5000 BTU are transferred from turbo air to outside air, then Q = 5000 for this equation AND the first equation.

m is the mass flow rate (lbs/minute) of fluid, in this case either turbo air or outside air depending on which side you're looking at.
Cp is the heat capacity of the air.  This is a measure of the amount of energy that the fluid will absorb for every degree of temperature that it goes up.  It is about 0.25 for air and 1.0 for water.  Air doesn't do a great job of absorbing heat.  If you put 10 BTU into a pound of air the temperature of it goes up about 40 degrees.  If you put 10 BTU into a pound of water, the temperature only goes up about 10 degrees!  Water is a great energy absorber.  That's why we use water for radiators instead of some other fluid.

DT is the difference in temperature between the inlet and outlet.  If the air is 200 deg going in and 125 deg coming out, then DT = 200 - 125 = 75.  Again, on the cooling air side the outlet temperature is the average "mix" temperature.

If you know 3 of the 4 main variables on one side of the exchanger (the amount of heat transferred, the inlet and outlet temperatures, and the fluidís  flow rate) then this equation is used to figure out the 4th.  For example, if you know the amount of heat transferred, the inlet temperature, and the flow rate you can calculate the outlet temperature.  Since you can’t measure everything, this equation is used to figure out what you don’t
Pressure Drop
Another aspect of intercoolers to be considered is pressure drop. The pressure read by a boost gauge is the pressure in the intake manifold. It is not the same as the pressure that the turbocharger itself puts out. To get a fluid, such as air, to flow there must be a difference in pressure from one end to the other. Consider a straw that is sitting on the table. It doesn't having anything moving through it until you pick it up, stick it in your mouth, and change the pressure at one end (either by blowing or sucking). In the same way the turbo outlet pressure is higher than the intake manifold pressure, and will always be higher than the intake pressure, because there must be a pressure difference for the air to move.

The difference in pressure required for a given amount of air to move from turbo to intake manifold is an indication of the hydraulic restriction of the intercooler, the up pipe, and the throttle body. Let's say you are trying to move 255 gram/sec of air through a stock intercooler, up pipe, and throttle body and there is a 4 psi difference that is pushing it along (I'm just making up numbers here). If your boost gauge reads 15 psi, that means the turbo is actually putting up 19 psi. Now you buy a PT-70 and slap on some Champion heads. Now you are moving 450 gm/sec of air. At 15 psi boost in the intake manifold the turbo now has to put up 23 psi, because the pressure drop required to get the higher air flow is now 8 psi instead of the 4 that we  had before. More flow with the same equipment means higher pressure drop. So we put on a new front mount intercooler. It has a lower pressure drop, pressure drop is now 4 psi, and so the turbo is putting up 19 psi again. Now we add the 65 mm throttle body and the pressure drop is now 3 psi. Then we  add the 2.5" up pipe, and it drops to 2.5 psi. Now to make 15 psi boost the turbo only has to put up 17.5 psi. The difference in turbo outlet temperature between 23 psi and 17.5 psi is about 40 deg (assuming a constant efficiency)! So you can see how just by reducing the pressure drop we can lower the temperatures while still running the same amount of boost.

Pressure drop is important because the higher the turbo discharge pressure is the higher the temperature of the turbo air. When we drop the turbo discharge pressure we also drop the temperature of the air coming out of the turbo. When we do that we also drop the intercooler outlet temperature, although not as much, but hey, every little bit helps. This lower pressure drop is part of the benefit offered by new, bigger front mount intercoolers; by the Duttweiler neck modification to stock location intercoolers; by bigger up pipes; and by bigger throttle bodies. You can also make the turbo work  less hard by improving the inlet side to it. K&N air filters, free flowing MAF pipes, removing a screen from the MAF, removing the MAF itself when switching to an aftermarket fuel injection system, the upcoming 3" and 3.5" MAFs from Modern Muscle, these all reduce the pressure drop in the turbo inlet system which makes the compressor work less to produce the same boost which will reduce the turbo discharge temperature (among other, and probably greater, benefits).
What about  Intercooler?
Wondering if your intercooler is up to snuff? The big test: measure your intercooler outlet temperature! When I did this I got a K type thermocouple,  the thin wire kind, slid it under the throttle body/up pipe hose and down into the center of the up pipe, and went for a drive. On an 80 to 85 deg day I got a WOT temperature of 140 deg, for a 55 to 60 deg approach. That tells me that I need more intercooler. If I can get the temperature down to 100 deg,  the air density in the intake manifold goes up by 7%, so I should flow 7% more air and presumably make 7% more hp. On a 350 hp engine that is 25 hp increase. On a 450 hp engine that's a 30 hp increase. Damn, where's my check book…

Another check is pressure drop. Best way to check it is to find a pressure differential gauge, which has 2 lines instead of the single line a normal pressure gauge has. It checks the difference between the 2 spots it is hooked up to, as opposed to checking the difference in pressure between the spot it is hooked up to and atmospheric pressure, which is how a normal pressure gauge works.

Hook one line of the gauge to the turbo outlet and one to (preferably) the intercooler outlet. The turbo outlet/intercooler inlet pressure is easy, just tee into the actuator supply line off the compressor housing. It would be nice to get the intercooler outlet pressure directly, but there's no convenient spot to hook up to. Hooking into the intake manifold (such as via the line to the boost gauge) is quite convenient, but gives the total pressure drop: intercooler + up pipe + throttle body. That'll give you a pretty good idea though.

Instead of the differential pressure gauge you could use 2 boost gauges, one in each spot, but then you have to worry about whether both gauges are calibrated the same, try to read both at the same time while driving fast, etc and you may spring (i.e., ruin) the gauge on the turbo outlet since when you close the throttle you get a big pressure spike that your normal boost gauge never sees.

If you find more than 4 or 5 psi difference between the intercooler inlet and intake manifold (and I'm just giving an educated guess here, you'd probably want to refer to one of the intercooler manufacturers for a better number) then I would suspect that a larger, lower pressure drop intercooler would offer you some gains.
Comparing competing Intercooler Designs
How to compare competing intercooler designs: Well, ultimately you want the one that will give you the coldest air possible into the intake manifold. This will be the one with highest UA value. When you multiply the heat transfer coefficient by the area (U x A) you get the UA value. This value doesn't really change much with reasonable changes in flow rates or temperatures, so if you could get the data to evaluate the UA for an intercooler in one car then you can use that to extrapolate how it would work in another car.

To evaluate the UA you need enough info to calculate the heat transferred (Q) and the DTlm. Then UA = Q/DTlm. Sounds easy, right? It would be, if the data was available. To properly evaluate an intercooler you would need: the turbo air flow through the intercooler; the pressure and temperature of the air from the turbo; the intercooler outlet temperature and pressure; the outside air temperature; and either the mix temperature of the cooling air as it leaves the intercooler or the flow rate of that air. That's a lot of info, and I'm not going to pretend that a vendor would make all that available to you, or that they would even collect all that data. I'm sure that the majority of the vendors selling bigger intercoolers have a trial and error process that they use to design their offerings rather than putting forth a real engineering effort anyway. But, if they did and they would release the info I would then use that data to figure out the amount of heat transferred (Q) and the DTlm, and then calculate the UA value for the intercooler. I would compare various intercooler's UA values and choose the one with the highest UA since that will give you the highest Q (most heat transferred) and the best DTlm  (closest approach).

TRIAL WITH  AND WITHOUT  INTERCOOLERS

What are they, and why would you want one ?

   First we will try to explain what an intercooler is and what it does.   When the air drawn into the turbo charger is compressed a great deal of heat is added to the air. When the air is heated it becomes less dense and carries less oxygen, therefore packing less of the all important oxygen rich air into the intake manifold. The intercooler is added to cool the air and make it denser so more oxygen rich air can be packed into the intake and from there into the cylinders. When adding an intercooler to a non intercooler car the fuel requirements may increase. Be sure to monitor your fuel delivery after adding an intercooler.
    Most intercoolers are of the air to air variety, which means they transfer heat from the compressed air in the intake plumbing to the cooler outside air. All air to air intercooler work in the same manner, air is pulled in through the air filter to the turbo charger, compressed then routed to the intercooler. Once inside the intercooler it passes through a series of small tubes that have many thin fins attached. The heated compressed air flowing through the intercooler heats up the fins and the tubes, then the cool outside air flowing across the fins pulls heat away from the tubes and fins. This heat transfer occurs constantly while the turbo is working .

Basic depiction of the heat transfer principle of an intercooler

   The following graphs give you an idea of the type of temperature drops achieved with an intercooler.
Equipment

• 1988 Dodge Shelly Shadow CSX-T
• 2.2 l Turbo I
• 5-speed
• Turbocharged (stock unit)
• (3) KO-type thermocouples
•   One installed in air box
•   One installed before the throttle body
•   One to measure ambient temperature
• Campbell Data logger (Program to run logger written by Fadi Kanafani)
• Data sample rate set at 0.5 seconds

Before Data

Taken during a full throttle run. 1st through 4th gear, with shifts at 6000 rpm in every gear. Boost pressure was at 10 psi (stock levels)

Conclusions
In the graph you will notice that the air temperature inside the air box would actually increase during the shift. We believe this is because the throttle blade is closed causing all the heat to build up inside the box because of no air flow. The maximum temperature found in front of the throttle body was 147.1 (F). At the same moment our lowest temperature was recorded inside the air box, which was 86.7 (F). The average ambient temperature was 79.34 (F) during the testing. This testing shows that as the air comes into the air box at 86.7(F), after going through the Turbocharged and then heading towards the throttle body, it will actually increase 61.03 (F). Towards the end of the graph, you'll notice that the air box temperature increase quite quickly. What had happened was I did a full lift off of the throttle, the air box didn't have any air flow and the temperature inside started to heat up quickly.

After Data

After installing the Conquest Intercooler, finally got the Campbell Data acquisition system hooked up on the CSX-T. The Campbell was setup to collect the Ambient Air Temperature, Air temp before the intercooler, Air temp after the intercooler, Air box temperature, and Temperature right before the throttle body.
The engine was warmed up before all data was taken. Data was taken during a full throttle run from 1st through 4th gear, while shifting at 6000 rpm in ever gear. The boost level was registering 9psi on the DRBII unit. The Campbell was setup to take data at a sample rate of 0.5 seconds.

The above data shows that the average ambient temperature during the run was 88.31 F. During this time, the temperature before the intercooler rose to 195.7 F. After the air went across the intercooler the temperature decreased a maximum of 72.6 F, by the time it went into the Intake manifold. The maximum temperature found at the throttle body was 122.3 F. This is colder then before the intercooler was installed (maximum temperature, before intercooler installed, was 147.1 F).
   The above graphs give you an idea of the temperature drops that can be achieved with an intercooler. There are various types of intercoolers that can be installed in a non intercooler car. They vary from after market intercoolers from such companies as HKS and GReddy and Spearco to factory installed intercoolers.
  The most cost effective way to intercool a car is to get a factory installed intercooler. Intercoolers are readily available from your neighborhood auto recycler or from individuals that have upgraded to an after market intercooler. There are many types of cars that came from the factory with intercoolers installed, such as the late 80s Dodge turbo cars, Volvo turbo cars and the Eagle and Mitsubishi cars.
   Once you decide to add an intercooler you will need to decide where you are going to place the intercooler. It will need to be put in a location where it will get maximum air flowing through it. The better the air flow through the intercooler, the better it will be able to cool the compressed intake air. When an appropriate location is found you will have to consider where the plumbing will be routed. You must take into consideration the plumbing from the turbo outlet to the intercooler as well as the plumbing from the intercooler to the intake manifold. Try to keep the length of the plumbing as well as the number of sharp bends to a minimum.
   Most people will use a combination of metal tubing and rubber or silicone hose. It is important to use the rubber or silicone hose to allow some flex in the plumbing. The flex is important because the intercooler will be fixed in position and the engine will be moving during acceleration. If flex is not built into the setup then the plumbing will pull apart and cause leakage.
   When choosing what type of hose to use you must consider the heat that the hose will be exposed to. This consideration is what makes silicone hose such as good choice.

 

TYPES OF INTERCOOLER

                         

 

The relelationship between pressure ratio and air charge density ratio if the air temperature is held constant at three different temperatures is shown in fig.(  ). The graphs show that as the air density ratio increases , the air density ratio increases likewise, however , the more air is intercooled and its temperature reduced, the greater will be the rise in air charge density. Thus if the air temperature is maintained at 30°c, the density at a pressure ratio of 2.2:1 will be about 2.1:1, whereas if the air temperature is kept constant at 90°c the air density ratio only rises to 1.64:1 Well designed intercoolers can hold the compressed air temperature to about 60°c.

The broken curve shows how the air density ratio increases if there is no intercooling.

Here , it can be seen that as the boost pressure ratio increases beyond about 1.6:1 there is very little useful increase in the air density ratio for a considerable further increase in the pressure ratio.

    

When including the compressor efficiency it can be shown , on a number of constant

efficiency curves, that is the pressure ratio increases, the useful charge density as a percentage  increases, but the increase is greatly influenced by the efficiency of the compressor. Thus, for a 50%efficiency compressor at a pressure ratio of 2.2:1 the increases in air density amounts to about 24%, whereas for an 80% efficient compressor the density rise is as much as 55% for the same ratio  increases.

The effects of boost pressure ratio on the ‘Brake mean effective pressure’ developed in the cylinder are clearly illustrated . The lower curve shows that if there is no intercooling , so that the compressed air temperature is allowed to rise uncontrolled then, as the boost pressure ratio increases from the naturally aspirated condition to 2.2:1, the b.m.e.p. also increases from 7.6 bar to 10.6 bar resp.Note the intercooler has very little effect on the b.m.e.p. below a pressure ratio of around 1.4:1

However, if the air charge is intercooled by an air to liquid intercooler, so that temperature is maintained is about 80°c, there is marked  increase in b.m.e.p. for a boost pressure ratio of 1.4:1 to2.2:1 which raises the b.m.e.p. from 9bar to 12.6 bar. Even better results can be obtained if an air –air intercooler is used, where compressed air is cooled down to 30°c, as the graph shows. Here, with a1.4:1 pressure ratio the b.m.e.p. reaches to 11.0 bar, and as the pressure ratio 2.2:1 theb.m.e.p. will be as high as 14.4 bar

A very convincing case for the employment of an intercooler as one of the stages of improving engine performance.

Intercooler effectiveness

The cooling of the delivery charge after it has been compressed contributes considerably to the recovery of the charge’s density ratio. The benefit of an intercooler to reduce charge’s temperature and there raises it’s density ratio . However, the ability to   increase the density of the compressed charge for a given pressure ratio by cooling the heated charge is dependant upon effectiveness of the intercooler. Intercooler effectiveness is defined as follows :

Intercooler effectiveness= Actual heat transfer

                                           Maximum possible heat transfer

 

 

 

 

 

 

 

FABRICATION OF AN INTERCOOLER

This article details the fabrication of a complete intercooler assembly using commercially available cores. Intercoolers are heat exchangers placed between the turbocharger compressor and engine intake manifold to drop the temperature of the compressed air and increase its density. The higher the charge density, the higher the power will be at a given boost pressure. The higher the boost pressure the more you need an intercooler.
Core Selection
We recommend using Spearco cores. They use a highly efficient pierced fin design on both the inside and outside of the tubes. This design offers high charge cooling efficiency and low pressure drop. Spearco offers a very wide range of cores and has an excellent catalog with detailed data comparing airflow rates vs. efficiency at various forward speeds. In dealing with Spearco for over 15 years, we have always had excellent service and their pricing is fair for the performance that their cores offer. If you are tempted to use OE intercoolers for a serious performance project, expect to be disappointed. Most OE cores are inefficient and have high pressure drops. You get what you pay for in this business.

Ambient air flows through this surface
If you can afford it and you want maximum performance, always try to fit the largest core possible. Remember to allow for the size of the tanks and the piping required to hook up to your turbo and throttle body. Tanks will add roughly 4.5 to 5 inches to the size of the core in the dimension that the air flows through the tubes. The higher the number of tubes, the lower the flow restriction will be. The longer the tubes, the lower the charge temperature will be. As a rough rule of thumb for matching cores when the peak hp is known, figure 1.5 X HP = airflow in CFM. A 300 hp engine would be flowing about 450 CFM. For street applications, its nice to see pressure drops of less than 1.5 psi at peak flow and efficiencies of at least 75% at 50 mph. For race applications pressure drops should be under .75 psi and efficiencies should be over 90%. Generally speaking, increased core volume (height X length X depth) will give lower charge temperatures and lower pressure drops. Many people worry about getting lag with an intercooler setup. This is usually not a factor on a well designed system. Remember that our 300 hp engine was flowing 450 CFM or 7.5 cubic feet /second. Even with a huge core having a tube volume of .5 cubic feet, the core would be completely aspirated in less than 1/10 of a second at peak rpm/full power.

Compressed turbo air flows through this surface
Low speed applications require larger surface areas to be effective while high speed applications can use lower surface areas. Ducting can substantially increase airflow rates through the cores and is often overlooked. Just because the airflow it hitting the front of the core, does not mean that there is much air flowing through it. Airflow is dependent on the pressure differential between the front and the rear of the core. Air exiting the core should ideally dump into a low pressure zone and the core face should be in a clean, high pressure zone.

ADVANTAGES OF TURBO INTERCOOLING:

Turbocharger intercoolers provide a means of reducing the charge inlet air or air-fuel mixture temperature between the compressor outlet and the engines inlet  ports .This achieves several objectives.

Ø  It  keeps the cylinder head temperature low even  under heavy  load conditions ,thus reducing thermal stresses ,and therefore it prolongs the life of the engines components.

Ø  It increases the mass of charge that can be crammed into each cylinder during each induction stroke thereby increasing the power.

Ø  It reduces the oxides of nitrogen (Nox)emission  due to the lower combustion temperature.

Ø  It reduces diesel engine black smoke emission at low engine speeds and high loads due to the reduction in the charge temperature.

Ø  It  raises the knock limit for  petrol engines and therefore permits a higher mean effective pressure.

LIMITATIONS OF TURBOINTERCOOLING:

Test results have shown that for every 10°C reduction in the compressed charge temperature there is an increase in power output of roughly 3 %. It has,however, been found that turbointercooling  can only be justified if the charge can be cooled by a minimum of 20°C, corresponding to a power increase of around 6%.

  

CONCLUSION:

Intercoolers is a must for every turbo car! The intake charge temperature is crucial to the performance of your turbo vehicle and the engine temps intercooler are crucial to prevent compressor surge and killing your turbo !  Intercoolers improve both the efficiency and power of any turbocharged application by rapidly reducing inherent heat levels of the compressed intake air charge before entering the engine. By utilizing a special tube and fin design, the intercooler acts as a large heat exchanger that dissipates the heat generated by the compression of the intake charge without creating reductions in boost pressure or response. As the pressurized air is channeled through the thin tubes of the intercooler core, that are filled with internal radiating fins, cool ambient air rushes through the front of the core, where the external radiating fins of the tubes draw out the heat. This heat transfer decreases the likelihood of detonation by reducing the inlet temperatures and maximizes power output by increasing the density of the air inlet charge, therefore increasing overall horsepower levels as the intake charge is now cooler and denser. Boost response and airflow is also often improved from the intercooler upgrades’ larger flow capacity and cooling efficiency. Intercooler plays a vital role in any turbo system because they not only improve the performance of your vehicle but they also increase the longevity of the turbocharger as well.

The average ambient temperature during the run was 88.31F .During  this time ,the temperature  before the intercooler rose to 195.7F.After the air went across the intercooler the temperature decreased a maximum of 72.6F,by the time it went into the intake manifold .The maximum temperature found at the throttle body was 122.3F.This is colder than before the intercooler was installed .This Increases the power output and efficiency of the engine.

BIOLIOGRAPHY

Heinz Heisler,” Advanced engine technology”, Edward Arnold  Publishers Limited 1994

Auto India, ”Turbo intercooler”-June 2003

www.msn .com

www.howstuffworks.com

CFD

CFD

A Trend in Automobile Aerodynamics Technology

Abstract :

Aerodynamics in automobile plays a crucial role, how will they behave on road & how efficient they performs the task they are designed for. For all vehicles ranging from small passenger vehicles to

commercial busses & trucks, reducing air drag is one of the most efficient ways of improving fuel economy.

Optimum aerodynamic design has to produce the best balance between drag that allows the car to

be stable & drivable at high speed. In this paper we study the optimum aerodynamics design & basic steps

to be followed during the design using Computational Fluid Dynamics.

Computational Fluid Dynamics (CFD) gives you a means of visualization and understanding

your design as it is a tool for predicting what will happen under the given set of circumstances before

physical prototyping.

CFD helps you to design better and faster, it provides numerical approximations to the equations

that govern the fluid motions. In CFD, governing equations are solved with the help of computer software.

What Is CFD?

Computational fluid dynamics (CFD) is the computational science of simulating

fluid flows by using computers. CFD is the simulation of fluids engineering systems

using modeling (mathematical physical problem formulation) and numerical methods

(discretization methods, solvers, numerical parameters, and grid generations, etc.) CFD

made possible by the advent of digital computer and advancing with improvements of

computer resources. CFD provides numerical approximation to the equations that govern

fluid motion.

Application of the CFD to analyze a fluid problem. First, the mathematical

equations describing the fluid flow are written. These are usually a set of partial

differential equations. These equations are then discretized to produce a numerical

analogue of the equations. The domain is then divided into small grids or elements.

Finally, the initial conditions and the boundary conditions of the specific problem are

used to solve these equations. The solution method can be direct or iterative. In addition,

certain control parameters are used to control the convergence, stability, and accuracy of

the method.

Why To Use CFD?

Basically, the compelling reasons to use CFD are these three:

1. Insight

There are many devices and systems that are very difficult to prototype. Often,CFD analysis shows you parts of the system or phenomena happening within the system that would not otherwise be visible through any other means. CFD gives you a means of visualizing and enhanced understanding of your designs.

2. Foresight

Because CFD is a tool for predicting what will happen under a given set of circumstances, it can answer many ‘what if?’ questions very quickly. You give it variables. It gives you outcomes. In a short time, you can predict how your design will perform, and test many variations until you arrive at an optimal result. All of this is done before physical prototyping and testing. The foresight you gain from CFD helps you to

design better and faster.

3. Efficiency

Better and faster design or analysis leads to shorter design cycles. Time and money are saved. Products get to market faster. Equipment improvements are built and installed with minimal downtime. CFD is a tool for compressing the design and development cycle.

A Case Study On Opel Astra:

Optimum Design Procedure:

CFD flow simulation can thus be used to readily make statements about flow circulation around a car to the point where models or prototypes are not available.Offering comprehensive information to designers about the entire flow field can therefore accelerate the process of aerodynamic design. The flow field around a vehicle is physically very complex.

The efficiency of an aerodynamic CFD simulation depends on the time span required to achieve the first set of results, as well as the accuracy of the simulated flow quantities. The turn around time and confidence level in the predictions is two major criteria for success that compete with one another. Creation of the model geometry,discretization of the physical domain, and choice of a suitable numerical computing scheme are significant factors that can determine the level of success of such an effort.

The underlying simulation process is divided into the following steps: CAD

surface preparation, mesh generation, CFD solution of the fluid flow, mesh adaption, and

visualization of the results. The software packages used for these steps include,

UNIGRAPHICS (CAD), ANSA (CAD/mesh generation), TGRID and GAMBIT

(additional mesh generation), and FLUENT (solver and post processing). An elapsed

processing time of between 5 and 11 days, without CAD modeling, is usually required for

the base case simulation of a complete model, comprised of about 3 million cells. This

time scale depends on the complexity of the model. Once the base case has been built,

individual modifications can be realized in a fraction of this time span 

CAD-Model:

To begin the process, the CAD body shell data for the ASTRA is downloaded

from a common CAE database at OPEL, from which all of the vehicle parts and

components can be accessed. For initial concept studies, the vehicle exterior data is made

available by the design department. Underbody data can also be downloaded from the

database. For early theme studies there is usually a simplified generic underbody model

available, which has already been integrated and meshed. For subsequent aerodynamic

studies, individual engine parts are not modeled. In this study, the air cooling vents and

the engine space above the sub frame are closed.

Using this finished base case, numerous types of vehicles can be generated on the

same template for simulation in a short time period. A half model with a centerline

symmetry plane is sufficient for initial design studies, but the ASTRA in this study is

constructed as a full model with an asymmetric geometry (where the asymmetries are

mostly confined to the underbody). This is done to enable detailed predictions of the flow

field around and under the vehicle. The wind tunnel geometry around the model is a

rectangular enclosure. It is of such a dimension that the adverse pressure effects between

the vehicle and the wall are minimized. The three CAD components, namely the outer

body of the vehicle, the underbody with tires, and the wind tunnel together constitutes the

CFD model

Surface Grid:

The integration, preparation and clean up of the CAD components described

above was done with the program ANSA .To do this, the CAD data was exported in

IGES format and read into ANSA, where production of a closed topology of CAD areas

and definition of macro areas was performed. Additionally, auxiliary surfaces were

generated, so that separately meshed fluid zones could later be linked or delinked from

one another. These areas and surfaces were then used to generate the surface grid. The

following description of the task of grid creation is limited to the styling surfaces, since

the wind tunnel and the underbody have already been meshed.

The vehicle body is meshed with triangles having a side length of about 20 mm,

in as uniform a manner A possible. A minimum side length of about 5 mm used in the

areas of the side mirror and the A-pillar. The window frames are covered with regular

quadrilateral elements so as to close the stage of the window later using separately

inserted prism blocks. Experience shows that generation of a fine and uniform grid on the

vehicle body is necessary to obtain realistic values for drag and lift coefficients. Fig

shows the shaded surface mesh of the ASTRA.

Generating The 3d Hybrid Mesh:

A hybrid mesh comprised of tetrahedral and prismatic elements was chosen for

the CFD model of the ASTRA. This was done so as to ensure that an extensive automatic

grid generation of the complex geometry could occur. The volumetric grid was built in

TGRID, using the surface grid that was generated by ANSA. It was then exported in a

FLUENT format. On the one hand, this means that a high quality resolution of the

surface mesh is necessary to create a good volume grid. On the other hand, any

modifications must only be performed in the two-dimensional “space” that is the surface

mesh.This therefore simplifies and accelerates the task of grid generation by taking into

account the possibility of further simulations of various base vehicle variants. To improve

the resolution of the oncoming flow boundary layer, the styling surfaces of the vehicle

and the floor of the wind tunnel were made up of multiple prism layers. In this instance,

avoiding three-dimensional corners or steps in the surface to form a grid with prisms was

effective. This help’s generate cells of good quality. The set-in side windows of the

ASTRA model along with their corresponding rectangular windowsills are not well

suited for direct coverage by prism layers, because distorted prismatic elements would be

created. The same is true for geometric steps in the areas of the cowl and A-pillar, and

also for inserts and steps in the front and rear of the vehicle. In ANSA, these areas are

closed in advance, using the auxiliary surfaces mentioned above. The limiting areas are

filled with either tetrahedral or, as in the case of the side windows, regular hexahedral

blocks generated in GAMBIT.

Wherever such auxiliary surfaces could not be used to separate areas of complex

geometry from the surrounding prism layers, the so-called no conformal interfaces option

was used. In the case of the ASTRA, the external mirrors, the entire underbody, and the

wheels are covered using tetrahedral. This means that the prism layers which were

generated on the styling surfaces and on the ground, end at the body sill and at predefined

areas around the external mirror and wheels. A so-called prism side is generated at the

edge of the prism layers. This is a circumscribing zone, which displays quadrilateral

surfaces. To couple the quadrilateral surfaces with the tetrahedral mesh of the wind

tunnel that is yet to be generated, these are copied and triangulated automatically in

TGRID, in correspondence to the distribution of the edge nodes. The triangles that are so

created can be manually modified if necessary. Both areas are later handled as internal

interfaces. This allows the solver to interpolate the flow data between the different types

of elements.

TGRID was used to generate prism layers on the vehicle body shell and ground

plane. The height of each prism element is controlled by entering the aspect ratio of the

first cell and a geometric growth rate. To do this, meshing parameters were chosen to

target a good initial y+ distribution and a smooth transition to the tetrahedral grid in the

external fluid region. The planar sidewalls of the wind tunnel were automatically split

into zones with quad or triangular surface elements, depending upon where the prism

layers join. There they were retriangulated. The regions that had not been made into a

grid using prisms were grouped together to form their own domain. The remaining

volumetric grid generation was completed using TGRID, resulting in a hybrid mesh of

approximately 3 million cells. The maximum skewness was less than 0.8 .

Numerical Solution Of Flow Equations And Grid Adaption :

A 3D steady state, incompressible solution of the Navier-Stokes equations was

performed using FLUENT 5. Turbulence modeling was done with the realizable k model

using non-equilibrium wall functions. The free stream velocity was set to be 140 km/h.

For about the first 300 iterations, a first order upwind discretization scheme was used to

accelerate the convergence.

Thereafter, a second order upwind scheme was used. For simulations of this type,

a total of 5 combined grid adaptions are usually carried out during the solution process, to

satisfy the y+ criteria. Statistical pressure gradient adaption is also executed, acting on

about 1 to 2% of the total cell count. Hanging node adaption is typically used, which

allows for subsequent coarsening of the grid if the need arises later in the solution process.

After each adaption, about 150 iterations are usually required to converge the solution to

the previous residual values. For scaled residuals, the convergence criterion is satisfied if

the residuals fall below a value of 10-3. A more accurate measure is when fluctuations in

the lift and drag coefficients lie within the range of ± 0.001. In this particular case, a total

of 1600 iterations on an eight processor SGI Origin 2000 were performed.

Post-Processing (Flow Visualization):

In a normal wind tunnel test, flow visualization is either too restrictive or too

expensive. In contrast, the CFD simulation process readily generates data for the entire

flow field. This can be combined and presented in the manner the user requires. Flow

field visualization (surface pressure distribution, for example) assisted by path lines can

provide the aerodynamic development engineer with significant insight into the basic

flow features. It also indicates areas for further optimization. In addition, general

statements may be made about the aero-acoustics and contamination of the vehicle. It can

be used to analyze turbulence energy distribution or the progression of wall surface

streamlines in the A-Pillar region and at the side glass. Figure shows examples of flow

field visualization.

CFD flow simulation is a useful tool for providing predictions of pressure

distribution and forces exerted on the vehicle components.

References:

1. www.flowfluent.com/solutions/automobile/aero.html

2. www.cd-adapco.com/apps/automotives.html

3. Tao Xing & Fred Stern,” Introduction to CFD” IIHR-hydro science & Engg., University of Iowa,2002.

4. Ing. Andreas Kleber “ JA123-Simulation Of Air Flow Around Opel Astra Vehicle With Fluent”,2001

5. GRIEBEL M.,DORNSEIFER T. AND NEUNHOEFFER T.”Numerical Simulation in Fluid Dynamics:

A Practical Introduction”. SIAM Monographs on Mathematical Modeling and Computation. SIAM 1998.