AIR SUSPENSION

LAYOUT OF AIR SUSPENSION

                        A rigid six wheel truck equipped with pairs of air springs per axle is shown in Fig. 3.1.  The front suspension has an air spring mounted between the underside of each chassis side-member and the transverse axle beam, and the rear tandem suspension has the air springs mounted between each trailing arm and the underside of the chassis.

                        Air from the engine compressor passes through both the unloader valve and the pressure regulator valve to the reservoir tank.  Air is also delivered to the brake system reservoir (not shown).  Once the compressed air has reached some pre-determined upper pressure limit, usually between 8 and 8.25 bar, the unloader valve exhausts any further air delivery from the pump directly to the atmosphere, thereby permitting the compressor to ‘run light’.  Immediately the air supply to the reservoir has dropped to a lower limit of 7.25 bar, the unloader valve will automatically close its exhaust valve so that air is now transferred straight to the reservoir to replenish the air consumed.  Because the level of air pressure demanded by the brakes is greater than that for the suspension system, a pressure regulator valve is incorporated between the unloader valve and suspension reservoir valve, its function being to reduce the delivery pressure for the suspension to approximately 5.5 bar.

                        Air now flows from the suspension reservoir through a filter and junction towards both the front and rear suspensions by way of a single central levelling valve at the front (Fig. 3.2) and a pair of levelling valves on each side of the first tandem axle.  These levelling valves are bolted to the chassis, but they are actuated by an arm and link rod attached to the axles.  It is the levelling valves’ function to sense any change in the chassis to axle height and to increase or decrease the pair pressure supply passing to the air springs, thereby raising or reducing the chassis height respectively.  The air pressure actually reaching the springs may vary from 5.5 bar fully laden down to 2.5 bar when the vehicle is empty.

                        To improve the quality of ride, extra volume tanks can be installed in conjunction with the air springs to increase the volume of air in the system.  This minimises changes in overall pressure and reduces the spring rate (spring stiffness), thus enabling the air springs to provide their optimum frequency of spring bounce.

                        An additional feature at the front end of the suspension is an isolating valve which acts both as a junction to split the air delivery to the left and right hand air springs and to permit air to pass immediately to both air springs if there is a demand for more compressed air.  This valve also slows down the transfer of air from the outer spring to the inner spring when the body rolls while the vehicle is cornering.

4.       MAIN COMPONENTS OF AIR SUSPENSION SYSTEM

4.1.      Levelling Valve (Fig. 4.1(a) and (b))

                        A pre-determined time delay before air is allowed to flow to or from the air spring is built into the valve unit.  This ensures that the valves are not operated by axle bump or rebound movement as the vehicle rides over road surfaces, or by increased loads caused by the roll of the body on prolonged bends or on highly cambered roads.

                        The valve unit consists of two parts; a hydraulic damper and the air control valve (Fig. 3.2).  Both the damper and the valves are actuated by the horizontal operating lever attached to the axle via a vertical link rod.  The operating lever pivots on a cam spindle mounted in the top of the valve assembly housing.  The swing movement of the operating lever is relayed to the actuating arm through a pair of parallel positioned leaf springs fixed rigidly against the top and bottom faces of the flat cam, which forms an integral part of the spindle.

                        When the operating lever is raised or lowered, the parallel leaf springs attached to the lever casing pivot about the dam spindle.  This caused both leaf springs to deflect outwards and at the same time applies a twisting movement to the cam spindle.  It therefore tends to tilt the attached actuating arm and accordingly the dashpot piston will move either to the right or left against the fluid resistance.  There will be a small time delay before the fluid has had time escape from the compressed fluid side of the piston to the opposite side via the clearance between the piston and cylinder wall, after which the piston will move over progressively.  A delay of 8 to 12 seconds on the adjustment of air pressure has been found suitable, making the levelling valve inoperative under normal road surface driving conditions.

a)         Vehicle Being Loaded (Fig. 4.1 (a))

                        If the operating lever is swung upward, due to an increase in laden weight, the piston will move to the right, causing the tubular extension of the piston to close the exhaust valve and the exhaust valve stem to push open the inlet valve.  Air will then flow past the non-return valve through the centre of the inlet valve to the respective air springs.  Delivery of air will continue until the predetermined chassis-to-axle height is reached, at which point the lever arm will have swung down to move the piston to the left sufficiently to close the inlet valve.  In this phase, the spring weight receive or lose air.  It is therefore the normal operating position for the levelling valve and springs.

b)         Vehicle Being Unloaded (Fig. 4.1 (b))

                        If the vehicle is partially unloaded, the chassis will rise relative to the axle, causing the operating arm to swing downward.  Consequently, the piston will move the left so that the exhaust valve will now reach the end of the cylinder.  Further piston movement to the left will pull the tubular extension of the piston away from its rubber seat thus opening the exhaust valve.  Excessive air will now escape through correct vehicle height has been established.  At this point the operating lever will begin to move the piston in the opposite direction, closing the exhaust valve.  This cycle of events will be repeated as the vehicle’s laden weight changes.  A non-return valve is incorporated on the inlet side to prevent air loss from the spring until under maximum loading or if the air supply from the reservoir should fail.

4.2       Isolating Valve (Fig. 4.2 (a) and (b))

                        An isolating valve is necessary when cornering to prevent air being pumped from the spring under compression to that under expansion, which could considerably reduce body roll resistance.

                        The valve consists of a T-piece pipe air supply junction with a central cylinder and plunger valve. 

                        When the air springs are being charged, compressed air enters the inlet part of the valve from the levelling valve and pushes the shuttle valve towards the end of its stroke against the spring situated between the plunger and cylinder blank end.  Air will pass through the centre of the valve and come out radially where the annular groove around the valve aligns with the left and right hand output ports which are connected by pipe to the air springs.

                        Once the levelling valve has shut off the air supply to the air springs, the shuttle valve springs are free to force the shuttle valve some way back towards the inlet port.  In this position the shuttle skirt seals both left and right hand outlet ports preventing the highly pressurised outer spring from transferring its air charge to the expanded inner spring (which is subjected to much lower pressure under body roll conditions).

                        The shuttle valve is a loose fit in its cylinder to permit a slow leakage of air from one spring to the other should one spring be inflated more rapidly than the other, due possibly to uneven loading of the vehicle.

4.3       Air Spring Bags (Fig. 4.3 (a) (b))

                        Air spring bags may be of the two or three convoluted bellows (Fig. 4.3 (a)) or rolling lobe (diaphragm) type (Fig. 4.3 (b)), each having distinct characteristics.  In general, the bellows air spring (Fig. 4.3 (a)) is a compact flexible air container which may be loaded to relatively high load pressures.  Its effective cross-sectional area changes with spring height – reducing with increase in static height and increasing with a reduction in static height.  This is due to the squeezing together of the convolutes so that they spread further out.  For large changes in static spring height, the three convolute bellows type is necessary, but for moderate suspension deflection the twin convolute bellow is capable of coping with the degree of expansion and contraction demanded.

                        With the rolling diaphragm or lobe spring (Fig. 4.3 (b)) a relatively higher installation space must be allowed at lower static pressures.  Progressive spring stiffening can be achieved by tapering the skirt of the base member so that the effective working cross-sectional area of the rolling lobe increases as the spring approaches it maximum bump position.

                        The normal range of natural spring frequency for a simply supported mass when fully laden and acting in the direct mode is 90-150 cycles per minute (cpm) for the bellows spring and for the rolling lobe type 60 – 90 cpm.  The higher natural frequency for the bellow spring compared to the rolling lobe type is due mainly to the more rigid construction of the convolute spring walls, as opposed to the easily collapsible rolling lobe.

                        As a precaution against the failure of the supply of air pressure for the springs, a rubber limit stop of the progressive type is assembled inside each air spring, and compression of the rubber begins when about 50 mm bump travel of the suspension occurs.

                        The springs are made from tough, nylon-reinforced Neoprene rubber for low and normal operating temperature conditions but Butyl rubber is sometimes preferred for high operating temperature environments.

                        An air spring bag is composed of a flexible cylindrical wall made from reinforced rubber enclosed by rigid metal end-members.  The external wall profile of the air spring bags normally consists of two or more layers of rubber coated rayon or nylon cord laid in a cross-ply fashion with an outside layer of abrasion-resistant rubber and sometimes an additional internal layer of impermeable rubber to minimise the loss of air.

                        In the case of the bellow type springs, the air bags (Fig. 4.3 (a)) are located by an upper and lower clamp ring which wedges their rubber moulded edges against the clamp plate tapered spigots.  The rolling lobe bag (Fig. 4.3 (b)) relies only upon the necks of the spring fitting tightly over the tapered and recessed rigid end members. Both types of spring bags have flat annular upper and lower regions which, when exposed to the compressed air, force the pliable rubber against the end-members, thereby producing a self-sealing action.

4.4       Anti-roll Rubber Blocks (Fig. 4.4)

                        A conventional anti-roll bar can be incorporated between the trailing arms to increase the body roll stiffness of the suspension or alternatively built-in anti-roll rubber blocks can be adopted.  During equal bump or rebound travel of each wheel the trailing arms swing about their front pivots.  However, when the vehicle is cornering, roll causes one arm to rise and the other to fall relative to the chassis frame.  Articulation will occur at the rear end of the training arm where it is pivoted to the lower spring base and axle member.  Under these conditions, the trailing arm assembly adjacent to the outer wheel puts the rubber blocks into compression, whereas in the other trailing arm, a tensile load is applied to the bolt beneath the rubber block.  As a result, the total roll stiffness will be increased.  The stiffness of these rubber blocks can be varied by adjusting the initial rubber compressive perload.

4.5       Air Filter

                        It is incorporated between auxiliary reservoir and levelling valve.  Sintered bronze filters are fitted in the ports to protect the internal mechanism from damage by foreign matter which may be carried back from the interior of the spring.

4.6       Pressure Regulator

                        As the level of air pressure demanded by the brakes is greater than that of the suspension system, a pressure regulator valve is incorporated between the unloader valve and suspension reservoir valve, its function is to reduce the delivery pressure for suspension to approximately 5.5 bar.

4.7       Drier

                        Any moisture in the air in air-spring will corrode the interior of the spring.  Hence, drier is fitted in suspension air circuit.  It contains silica gel which absorbs moisture from air.  Exhaust air from air spring is used as a re-generative agent to remove moisture from silica gel and make it fresh.

5.       AIR SPRING CHARACTERISTICS

                        The bounce frequency of a spring decreases as the sprung weight increases and increases as this weight is reduced.  This factor plays an important part in the quality of ride which can be obtained on a heavy goods or passenger vehicle where there could be a fully laden to unladen weight ratio of up to 5 : 1.

                        An inherent disadvantage of leaf, coil and solid rubber springs is that the bounce frequency of vibration increases considerably as the sprung spring mass is reduced (Fig. 5.1).  Therefore, if a heavy goods vehicles is designed to give the best ride frequency, say 60 cycles per minute fully laden then as this load is removed, the suspension’s bounce frequency could rise to something like 300 cycles per minute when steel or solid rubber springs are used, which would produce a very harsh, uncomfortable ride.  Air springs, on the other hand, can operate over a very narrow bounce frequency range with considerable changes in vehicle laden weight, say 60 – 110 cycles per minute for a rolling lobe air spring (Fig. 5.1).  Consequently the quality of ride with air springs is maintained over a wide range of operating conditions.

                        Steel springs provide a direct rise in vertical deflection as the spring mass increases, that is, they have a constant spring rate (stiffness) whereas air springs have a rising spring stiffness with increasing load due to their effective working area enlarging as the spring deflects (Fig. 5.2).  This stiffening characteristic matches far better the increased resistance necessary to oppose the spring deflection as it approaches the maximum bump position.

                        To support and maintain the spring mass at constant spring height, the internal spring air pressure must be increased directly with any rise in laden weight.  These characteristics are shown in Fig. 5.3 for three different set optimum spring heights.

                        The spring vibrating frequency will be changed by varying the total volume of air in both extra tank and spring bag (Fig. 5.4).  The extra air tank capacity, if installed, is chosen to provide the optimum ride frequency for the vehicle when operating between the unladen and fully laden conditions.

 

 

6.       VOLVO OPTIMISED AIR SUSPENSION (VOAS) SYSTEM

                        The Volvo optimised air suspension (VOAS) system is a modified version of the previous air suspension on rear axles of Volvo GM heavy duty trucks (Figure 6.1).  A number of modifications in the VOAS system provide improved ride, reduced unspring weight, increased durability, and better alignment ability.  The VOAS system is available on all Volvo GM on-highway tractors.  The operation of the VOAS system is similar to the operation of other air suspension systems explained previously.

                        The spring brackets in the VOAS system are manufactured from ductile iron, and these brackets have closed sections and cutouts to reduce the weight of each bracket by 4 lb (2 kg) (Fig. 6.2).

                        As in previous models, a polyethylene wear pad provides a very smooth surface for the end of the spring to contact (Fig. 6.3).  This type of wear pad eliminates noise caused by contact between the spring and metal wear pad in other suspension systems. The wear pad in the VOAS 50 % is lighter compared with the wear pad in previous suspension systems.  A single fastener retains the wear pad to the spring bracket legs.

                        The Z-spring is redesigned with a larger clamping surface at the axle seat and improved alignment with other suspension components (Fig. 6.4).  The Z-spring is also redesigned to provide more clearance between this spring and the lower shock absorber mounting bracket.

                        The rear of the radius spring is mounted between the axle seat and the Z-spring.  The front end of each radius spring contains a bushing that is bolted to openings in the lower end of the spring bracket.  In the VOAS system each radius spring has an improved bushing for increased durability.  Each radius spring has a locating pin for accurate positioned of the radius spring, Z-spring, and axle seat.  This design provides improved axle alignment.

                        The crossbeam in the VOAS system is manufactured from thinner, high-strength steel with cutouts.  Each crossbeam is 12 lb (5 kg) lighter than previous models.

7.      ELECTRONICALLY CONTROLLED AIR SUSPENSION SYSTEMS

                        Electronically controlled air suspension systems are not widely used as standard equipment at present.  This type of suspension system is in the experimental and developmental stage.  However, with the ever-expanding use of electronics in the trucking industry, electronically controlled air suspension systems may be standard equipment on new tractors in the near future.  Because electronically controlled air suspension systems are not standard equipment at present, the discussion is brief.

                        An electronic control unit (ECU) in the suspension system received voltage input signals from various sensors including two rear axle and one front axle height sensor, air pressure sensor, accelerator position sensor, and steering angle sensor.  The steering angle sensor is mounted on the steering column shaft and senses the amount and speed of steering wheel rotation.  Other ECU inputs may include the brake light switch, ignition switch, vehicle speed, and engine speed.  Solenoids mounted in a solenoid valve block are operated electronically by the ECU (Fig. 7.1).  Air pressure is supplied from the air brake system to these solenoids.  If the left rear axle height sensor indicates the left rear frame height is less than specified, the ECU energises the appropriate solenoid.  This action opens the solenoid, and supplies air pressure to the left rear air spring to restore the frame height to specifications.  When the left rear height sensor signal to the ECU indicates the left rear frame height is within specifications, the ECU de-energises the solenoid.  Under this condition the solenoid closes and maintains the air pressure in the solenoid.

                        When a height sensor signal indicates to the ECU that the frame height is above specifications, the ECU energises the appropriate solenoid so it is in the vent mode.  Under this condition air pressure is released from the air spring to restore the frame height to specifications.  The ECU can switch the air suspension very quickly to a firm or hard mode by rotating valves in the shock absorbers (dampers).  During the soft shock absorber mode the shock absorber valves are positioned so they offer less restriction to the flow of oil.  If the ECU enters the firm mode and rotates the shock absorber valves, these valves move to a position that provides more restriction to oil movement.  This firm mode may be entered by the ECU and shock absorbers during fast avoidance manoeuvres, fast cornering, hard braking, rapid traction changes, continued road irregularities, cross winds, and high static load.  The capability of the electronically controlled suspension system to switch quickly to the firm mode provides improved vehicle stability and safety.

8.       ADVANTAGES OF AIR SUSPENSION SYSTEM

1.                  The improved ride quality provided by an air suspension system reduces driver fatigue.

2.                  An air suspension system provides improved tire-to-road contact, and this improves braking capability.

3.                  An air suspension system provides low frequency and viscous damping of the suspension, and this action reduces wheel hop while braking.

4.                  The improved roll resistance of an air suspension system provides better vehicle stability.

5.                  An air suspension provides pneumatic equalising between the forward and rearmost rear axles for improved weight distribution between these axles.  This helps to reduce overloading of one axle and one set of tires.

6.                  Because the vehicle attitude is also constant, changes in headlamp alignment due to varying loads are avoided.

7.                  The spring rate varies much less between the laden and unladen conditions, as compared with that of conventional steel springs.  This reduces the dynamic loading.

8.                  The improved standard of ride comfort and noise reduction attained with air springs reduces both driver and passenger fatigue.

9.       COMPARISON OF AIR SUSPENSION SYSTEM AND CONVENTIONAL SUSPENSION SYSTEM

Sr. No.	Parameter	Air Suspension	Conventional Suspension
1.	Load Carrying Capacity	Higher	Lower
2.	Ability to absorb shocks and vibrations	Better	Good
3.	Car height control	Better	No
4.	Cost	Costly	Cheaper
5.	Maintenance	More	Less
6.	Passenger Comfort	Excellent	Not satisfactory
7.	Electronic control	Possible	Not possible
8.	Life	More	less
9.	Noise level	Less	Higher

10.     CONCLUSION

                        The air springs in air suspension system take the place of the leaf springs in a conventional suspension system.  An air suspension system eliminates the interleaf friction encountered in a leaf-spring suspension system.  Compared with a leaf-spring suspension system, an air suspension system minimises road shock transferred from the suspension to the truck frame, driver, and cargo.  An air suspension adjusts automatically to different load conditions, and provide a softer suspension system with light loads and a firmer suspension system with heavier loads.  An air suspension system provides a constant frame height under various load conditions.  Compared with a leaf-spring suspension system, an air suspension system provides a considerable unsprung weight saving.

                        From all above points it is clear that air suspension system makes significant overall improvement to vehicle ride and comfort.  It is clear from the seminar that air suspension system provides a better alternative for conventional suspension system.

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