The Control Unit
The analyser control unit is placed under the bonnet where it is supplied with 12V from the battery and connected to 2 pressure sensors and 4 temperature probes. It transmits data to the mobile phone via Bluetooth every second.
The Mobile Phone app
Is installed on any Android mobile phone running Android 5.0 or higher. It displays the turbocharger/intercooler pressures and temperatures in real time and can record of significant events for later upload and analysis. It can spray water over the outside intercooler body to determine if any benefit can be derived from this cooling, or whether it's all a myth. The mobile phone app communicates with the monitoring unit and is updated with the latest data once every second.
The Turbo/Intercooler System
The output power of a diesel engine may be enhanced by increasing the the density of the induction air. Air of higher density contains more molecules of oxygen which can be used to burn fuel and release thermal energy. To to achieve this purpose a turbocharger is used to compress air drawn in through the air filter and delivers it to the intake manifold. An unwelcome side effect compressing air is that the compressed air heats up, and this heating inhibits the increase of air density. Maximum air density is attained when the compressed charge is at ambient temperature.
To cool the hot, compressed air it is passed through the core of an Intercooler which, in turn is cooled by an ambient airflow induced by the forward motion of the vehicle. An intercooler may be mounted on top of the engine directly below the bonnet-mounted air scoop that diverts part of the slipstream over the bonnet downward through the intercooler's radiator, or alternatively it can be mounted next to the engine coolant radiator where it can benefit from the same ambient airflow that cools the radiator, and the activity of the radiator fan.
A turbocharger will generally try to compress the incoming air to 1000mB, which is 200% of the ambient pressure at sea level, after which the waste gate will bypass further exhaust gas around the turbine. Assuming no increase in temperature this will also double the density in the induction air and potentially provide for a 100% increase in engine power over the normally aspirated equivalent. In practice it is very difficult to cool the compressed charge all the way back to ambient, so the 100% power gain is never fully achieved. This Analyser measures all the relevant temperature and pressure parameters under highway driving conditions, calculates their effect, and displays the result on a mobile phone inside the vehicle.
The two major factors that determine the turbo/intercooler system's effectiveness are therefore firstly the absolute output pressure of the turbocharger and, secondly, how this increase in pressure is converted into air density - and hence engine power - by the cooling capacity of the intercooler. All relevant parameters are displayed on the mobile device, as well as the result of the pressure/temperature computation.
There are two assessments displayed on the mobile's screen, the first is a depiction of the efficiency of the cooling process given as a percentage of perfection. A score of 100% indicates that the induction air is at ambient. A lower score indicates the temperature differential between actual and ambient as a percentage of the ambient temperature in Kelvins, adjusted for the turbo pressure prevailing at that time.
The other display button depicts the power gain that the turbo/intercooler system delivers over and above that which would have been available without any air density elevation taking place. The figure displayed here is derived from the absolute air pressure modified by the degree of cooling that has taken place. It will often show 0% but will rarely, if ever, reach 100%.
(None of the above applies to petrol engines since the boost ratio is far lower and fuel evaporation causes substantial cooling of the intake air.)
Important Temperature Gradients
The job of the intercooler is to cool induction air as near as possible to the temperature of the ambient airflow captured by the bonnet-mounted scoop, or the grille at the front of the vehicle. Heat energy is transferred through the metal intercooler radiator and body to the passing airflow, which is heated in the process.
The contact interface area between induction air and intercooler metal must be large enough to transfer sufficient energy in the time available. Then there must be adequate airflow outside the intercooler body to carry this energy away and keep the metallic components cool enough to accept more energy from the induction charge.
How effective this process is is given by the measured elevation of induction temperature above the ambient air immediately above or ahead of the intercooler radiator. An elevation of more than 30°C is cause for concern and needs to be investigated. Either the heat is not being shifted into the metal body, or the metal body is not passing the heat to the passing airflow. Or a combination of the two.
A useful clue is found in the temperature of the passing airflow measured immediately below (or behind) the intercooler radiator. If this temperature closely matches that of the cooled induction air then the heat transfer has been as good as it's going to get given the existing flow. Increasing the rate of airflow over the outer IC may increase enthalpy and deliver cooler induction ait.
On the other hand if the induction air is considerably hotter (by 20°C or more) than that measured immediately below (or behind if front-mounted) the I/C then heat transfer from the I/C body to the outside air is inadequate and steps should be taken to improve this air flow. Either the bonnet scoop's duct is too small or there is some other impediment such as blocked or bent radiator fins or something underneath interfering with airflow. If the induction air at this point is more than 30°C warmer than ambient a larger intercooler surface area is needed, which normally means a larger intercooler. If the difference is 30°C or less then the system is working as well as can be expected.
When Towing a Trailer
If the towing of a trailer increases the tow vehicle's fuel consumption, (which it invariably does), then it stands to reason that the extra air required to burn the higher fuel quantity must pass through, and be cooled by, the intercooler, and the added load will result in warmer induction air being delivered to the engine. How much hotter this air will be depends on many factors, some of which are hard to predict, so the practical outcome is best measured empirically under real highway operating conditions.
Live testing has shown that a 10% - 20% loss of intercooler efficiency can be expected while towing a medium-sized (1000kg) trailer. On a flat road at highway speed the induction air temperature will rise from about 20 degrees C above ambient to around 60 degrees above. During hard 3rd gear climbs the induction air temperature may reach 100 degrees C above ambient.
The standard Intercooler as designed by the motor manufacturer are generally well capable of fulfilling their intended function, and it is difficult to make a convincing case for enhancing their capacity or performance. This does not apply to towing trailers however where arduous conditions can overload an intercooler and result in a loss of up to 15% of total potential engine power. Increasing intercooler capacity might lead to a recovery of much of this power loss.
Low Speed Climbing
Top-mounted intercoolers rely entirely on forward movement of the vehicle to drive ram air into the bonnet-mounted scoops and down through the intercooler radiator into the engine compartment. At highway speeds this works well, but under arduous low-speed climbs the airflow can easily break down and even reverse, with hot air in the engine compartment flowing upwards through the intercooler's radiator, resulting in very hot air being delivered to the intake manifold. This is where front-mounted intercoolers enjoy a distinct advantage since they benefit from cooling airflow forced by the engine's fan even under the lowest forward speeds.
Intercoolers and Engine Temperature
There is a commonly held belief that the intercooler assists in lowering engine temperature. This is entirely incorrect. At least 74% (27MJ/L) of the heat released when diesel fuel is burned is discharged through the exhaust pipe, the oil cooler, or the radiator. An efficient intercooler delivers denser air which allows more fuel to be burned per engine revolution. Since more fuel is burned in the denser intake air, more heat energy is released in a given time and the excess must be dissipated through these channels. Therefore a more efficient intercooler will tend to make the engine run hotter and not cooler, if the extra available power is used.
What the Analyser Does
It measures and reports the partial vacuum that exists between the air filter and the turbocharger. Over 100 litres of air is sucked through the air filter every second when the engine is developing full power and any resistance offered by the air filter will cause a pressure drop of up to 100hPa (0,1 Bar) in this section of the system.
It measures and reports the output pressure of the turbocharger. At cruise speed this may be as high a 1000hPa depending on throttle opening, but at other times it can be a lot lower.
It measures and reports the air temperature between the turbocharger and the intercooler up to the probe's limit of 127 degrees C. The actual temperature of this compressed charge could be as high as 120 degrees C above ambient, but this value is of passing interest only as it had no direct bearing on engine performance.
It measures and reports the temperature of the air coming out of the intercooler. This is of vital interest as it is a mojor component of determining intercooler efficiency.
It measures and reports the temperature of the ambient airflow above (or before) the intercooler. This is the target temperature that the intercooler is attempting to reach and determines its efficiency.
It measures and reports the temperature of the air below (or behind) the intercooler.
It calculates and reports total power enhancement provided by the turbo/intercooler system.
It has a flashlight for working in the dark.
It can squirt water onto the intercooler on command from the mobile phone app.
What Benefits You Can Expect.
Any standard factory fitted intercooler will deliver between 80% and 90% efficiency under highway cruise conditions, which means the induction air will be cooled to within between 30 and 60 degrees centigrade of ambient. Since this represents a loss of potential engine power of only 5 - 10% it is difficult to justify an expensive after-market intercooler, which itself will never be more than 90% efficient since heat transfer slows markedly as the temperature gradient across the intercooler reduces - the last 30 degrees of heat is the most difficult to dissipate.
However what will be interesting to learn is:
- How much power enhancement does the turbo/intercooler system deliver?
- How much vacuum is developed between the air filter and the intake of the turbocharger?
- How readily does the turbocharger deliver maximum pressure as RPM and throttle-opening increase?
- How well does the bonnet-mounted scoop work at highway speeds?
- How does low forward speed affect scoop performance?
- How much efficiency, and hence power, is lost when towing a trailer?
- How much, or how little, benefit could potentially be derived from an enlarged after-market intercooler?
An average-sized turbocharged engine at full power sucks upwards of 100 litres of air every second. All of that air must pass through minute holes in a paper screen, holes that may not be larger than 5 microns in diameter. Any clogging of those holes will impede airflow and cause a partial vacuum between the filter and the turbocharger. With a clean air filter that pressure drop will vary between 10 and 20hPa and never exceed 30hPa. It is common practice for workshops to simply blow out air filter elements with compressed air, thereby clearing large particles of dust and debris from the paper folds, but this does not extend the life of the air filter in any way. Once the element has changed colour from from the original white or yellow to a dull grey it has become so contaminated that it will resist the free-flow of air to the extent that it causes a pressure drop of up to 100hPa in the intake tract, which will definitely affect engine power. An air filter element should be replaced as soon as it looks dirty.
Turbochargers require large volumes of exhaust gas to drive the turbine of a turbocharger hard enough to develop 1000hPa of boost pressure. This volume of gas cannot be generated unless the engine is working at large throttle openings under load.- which requires highway driving conditions. Excessive boost is prevented by an exhaust gas waste gate opening as the turbocharger approaches maximum boost. The operation of the waste gate can only be tested under full load conditions.
Under highway driving conditions the air pressure under the bonnet will be very close to ambient. At 120Km/h the ram effect at the intake of the scoop above the intercooler will be 555 Pascal or 5,5hPa above ambient, which is sufficient pressure differential to send a strong airflow through the intercooler's vanes. During an arduous climb at 60km/h with the engine's cooling fan working hard, this pressure differential can be much reduced, slowing this airflow considerably - even reversing it at times, when hot air from the radiator flows upwards through the intercooler elevating induction air temperatures to as high as 150 degrees Centigrade and rendering the intercooler totally ineffective.
Collectively these conditions can rob the engine of a considerable portion of its potential power, and they can be comparatively inexpensive to remedy.
The Water Sprayer
Popular myth has it that spraying water onto an intercooler's core will bring magical benefits.
When water undergoes a phase change from liquid to gas it absorbs 2256 Joules per millilitre without changing temperature. This principal can be useful to remove heat energy from the surface of which water is being evaporated. For water to evaporate it needs to be in contact with air the is not already saturated with water vapour, this is to say it's relative humidity must be less than 100%. When air at any given temperature absorbs water vapour its relative humidity increases, and when this figure reaches 100% no more water vapour can be absorbed. Increasing the temperature of the air will also increase its capacity to hold water, so heating the air reduces its relative humidity. The layer of air that is closest to the wet surface will be the part that reaches saturation first. Therefore air needs to keep moving for evaporation to proceed. New, dry, air must replace that which has reached saturation point.
Airflow that is carrying sprayed water very likely has had its humidity increased to at, or close to, 100% of relative humidity and is not available to accept much more vapour from the IC's core. Therefore the spray should not be continuous but be delivered in blasts that thoroughly wet the IC's core and then stop, to allow dry air to evaporate the water layer coating the IC and thereby augment cooling. As soon as the core is substantially dry another blast of water should be applied.
Since most of the sprayed water can be expected to pass through the core without wetting anything, and the water that does hit the core will form a very thin coating that will tend to be blown in the direction for the airflow, it would be unduly optimistic to expect significantly improved cooling from this process.
The controller can deliver 12V output power, through a relay controlled from the mobile phone app, to an external water spray pump, to simulate the effects of improved intercooler efficiency. The spray pump is typically an after-market window-washer pump that must be separately installed.
The Forward-facing Snorkel
It is easy to imagine vast amounts of air being forced down the throat of a forward-facing snorkel and greatly augmenting the engine's output power. In fact the laws of physics tell us the dynamic (ram) pressure at the mouth of the snorkel would be only 5.5hPa at 120Km/h, and that only if no air was flowing into the mouth of the snorkel. With the snorkel drawing in air at 120 litres per second the dynamic pressure drops to about 2.5hPa, depending on the cross-sectional area of the mouth. Compare this to the partial vacuum of up ten times that figure that may exist between the air filter and the turbocharger if the filter is even slightly dirty, to put this in perspective. A forward-facing snorkel will make no significant improvement to an engine's output power, though it may confer other important benefits such as dust and splashed water avoidance.