The first time I ever heard of twin charging (using both a turbocharger and a supercharger on the same motor) was probably back in year 2000. At that time I was very interested in doing for the Toyota Celica and simply I also read a lot about its sister cars (that shared some of the same engines) such as the Camry and the Mr2.
One of the most entertaining aftermarket parts I ran across at the time was the Hks turbo kit for the 4Agze powered 1st generation mr2. The 4agze (for those that are not customary with Toyota engines) is a peppy 170 horsepower 1.6 liter machine powered by the Toyota Sc-12 roots type supercharger. On this car Toyota used an electromagnetically clutched supercharger that could be disabled during low power requirements such as cruising, and engaged when the user demands it.
3000 Psi
One of the most foremost parts of the Hks kit is the bypass valve. This valve was used to direct air from the supercharger to the machine at lower rpm/flow points. Once the rpm's rise, and the machine starts to examine more air, and the turbocharger is fully spooled, the valve switches over gently till the turbocharger alone is feeding the machine while the supercharger is thoroughly bypassed. The twin-charged Mr2's were rumored to break the 300hp mark in some cases, depending on the final boost level and the supporting modifications, and this level of power for a 1.6 litre motor at the time was quiet astounding.
The law behind this kind of law is to use a small unavoidable displacement (roots style) supercharger. Supercharger doing efficiency is typically at its top at lower machine and supercharger rpm's (for example from idle to 4000 rpm's). Above 4000 rpm's the supercharger's doing and efficiency starts to drop, the horsepower required to drive it starts to rise exponentially, and the air climatic characteristic coming out of the supercharger starts to rise dramatically limiting performance.
On the other hand, using a generously sized turbocharger will allow us to feed the machine efficiently with cooler air (than that from an overworked supercharger) and speak high rpm performance. The qoute with using a larger turbocharger is that a generously sized turbocharger typically doesn't spool before 3000 to 4000 rpm's giving us a diminutive power band and thus providing no doing boost at lower rpm's.
The idea of twin charging is to use both a supercharger and a turbocharger to have each charger do what it does best, have the supercharger boost the motor for low end torque, and as it runs out of steam, the turbocharger comes online to carry us through to redline.
There are three aspects to these types of systems that make them prohibitive to most tuners:
1. Cost and complexity: Having a perfect supercharger law as well as a perfect turbocharger law on the same car is a lot of money to spend and a lot of parts to deal with and diagnose in case something does go wrong.
2. The bypass valve used to bypass the supercharger (and yet hold in all the air pressure coming from the turbocharger) as well as being able to operate this valve electrically or mechanically requires a institution made one off valve that isn't quite ready off the shelf. Although as I write this it seems potential to find a large sized dual accommodation bypass valve plumbed to operate on the differential pressure between the turbo outlet and the supercharger outlet to switchover once the turbocharger pressure = the supercharger pressure + the tension of the bypass valve occasion mechanism.
3. Since we are using two separate types of chargers with two separate efficiency maps, it can get very complex to figure out how to tune the motor (especially with much simpler fuel injection systems that were used at the time) because the air density can vary dramatically at the same rpm point and pressure level depending on which charger is feeding air to the motor and at what proportion. This is also where the Hks turbo kit for the 4agze was at its weakest, namely at smoothing the transition point fueling between the supercharger to turbocharger switchover.
One of the things that has changed over the last 10 years is the availability (and proliferation of knowledge) about ready alternative fuels or octane boosters. Two such options are:
1- E85 fuel which is comprised of 85% Ethanol which has an octane rating of about 100 to 105 octane vs the typical 87 to 93 octane pump gasoline.
2- Water / methanol injection systems that can be used whether as supplemental fueling law (based on the methanol content which carries an octane rating of 110 octane or higher) or can be used for in cylinder cooling when the water vapor injected with the methanol transforms into steam inside the combustion chamber, thus extracting lots heat out of the combustion chamber, and thus slowing down the speed of travel of the combustion flame front simulating the effects similar to those of a higher octane gasoline.
With the availability of these octane increasing or octane simulating concoctions, it has become more accessible of recent for the doing enthusiast to build a separate type of twin charger law that does not require a bypass valve.
In this type of law the supercharger outlet is routed to feed the turbocharger inlet or vice versa. Rather than whether the supercharger or the turbocharger feeding the machine individually (in parallel operation) and switching between the two, we are now using a two stage compression law where one stage is the premise supercharger, and the 2nd stage is an aftermarket turbocharger system.
The net consequent of the two compressors is a compounding of pressure ratios. For example if the turbocharger waste-gate occasion spring is set to a setting of 7psi of pressure above atmosphere (which is a pressure ratio of 1.5 given that 1 atmosphere is about 14.7 psig); and if the supercharger is mechanically geared to flow 50% more than the machine (for unavoidable displacement roots style superchargers) at any rpm, thus having an same 7psi boost setting or a pressure ratio of 1.5; then the resultant pressure ratio of the law combined is :
Pr total = Pr turbo * Pr supercharger = a pressure ratio of 2.25
A pressure ratio of 2.25 is equivalent to 18.4 psi of boost (not 14psi incredible by adding the two stages together).
So anyway, how does this review to octane requirements ?
If the turbocharger is feeding the supercharger for example, and the turbocharger is ingesting fresh air at ambient air temperatures (T1), then:
1- The air exiting the turbocharger will be at a climatic characteristic T2, higher than the ambient air climatic characteristic (T1) by about 60-80*C depending on the exact turbocharger, and where we are on the turbocharger compressor and efficiency map.
2- The air entering the supercharger will enter at a climatic characteristic T2 ~=T1+60 and exit at a climatic characteristic T3 which is higher than T2 by about an additional one 60-80*C depending on the exact specifications of the supercharger.
3- If we had an intercooler after the supercharger, then the air entering the intercooler will be at 120 to 160*C above ambient temperatures which is a lot of heat for the intercooler to exertion to shed in the short number of time that the air passes through the intercooler core.
4- If we have no post supercharger intercooler (which is base on cars where the supercharger is packaged into the intake complicated of the car), then the air entering the machine will be at some 120 to 160*C above ambient.
5- This excessively heated air not only reduces power output (By about 1 horsepower for every 13*C) but it also increases the probability of the air fuel compound automatically igniting in the motor pre-maturely before the spark plug has fired, and if this pre-mature ignition occurs early adequate to catch the piston significantly far away from top dead center, then the battling flame front pushing the piston downwards, and the inertia of the law (and force of other firing cylinders rotating this piston via the crankshaft) pushing the piston upwards will cause very high pressures and a climatic characteristic rise on the outside of the piston finally damaging it and perhaps damaging other parts of the motor as well.
For these reasons (pressure compounding, and combined climatic characteristic rise) sequential charging has seen very diminutive application in the past. The use of a higher octane fuel by definition means that the air fuel compound is more resilient to auto-ignition and detonation. Furthermore, in the event of a pre-mature ignition, the higher octane fuel creates a slower traveling flame front which gives the piston more time to travel upwards in the cylinder bore (Closer to top dead center) before meeting the flame front and this reduces the time that the piston outside is improperly pressurized and overheated reducing the possibility of catastrophic failure. Last but not least, the use a water / methanol injection mix includes two phase-change events:
1- The injected methanol changes from a liquid state to a vapor state at its boiling point of 65*C, i.e. As soon as it hits the compressed air compound coming from the supercharger outlet. This phase turn absorbs a lot of the heat out of the air and methanol compound reducing inlet air temperatures even before the compound reaches the combustion accommodation and starts to get compressed. This climatic characteristic reduction goes a long way towards eliminating or very reducing the possibility of detonation.
2- The injected water, changes from a liquid state to a vapor state at its boiling point of 100*C which depending on the availability of an intercooler in the system, my occur in the intake plumbing before reaching the combustion chamber, or may not occur until the compound is ignited. whether way, when the climatic characteristic is high enough, the water mist injected in the air stream will flash vaporize into steam also entertaining a kind number of the heat created in the combustion.
The availability of these two octane boosters makes it now potential for aftermarket doing part manufacturers to deliver safe and trustworthy sequential charging kits to the mass market.
One such kit which I ran across in an description from hot rod magazine was industrialized by hellion doing (http://www.hellionpowersystems.com) for the premise supercharged Gt-500 mustang.
The kit supposedly produce up to 1000 horsepower at a boost level of 24 psi using two 61mm Turbonetics turbochargers.
To perform 1000 hp requires nearby 1500 cfm of airflow at 24psi or 1500cfm at a pressure ratio of 2.63, or 750cfm @ 2.63pr per turbocharger.
Since most compressor maps for this size of turbocharger (61mm) peak out at nearby 600cfm @ 2.63 pr @ nearby 50% efficiency which is an extreme point on the map (i.e. The turbocharger is maxed out at this point). I'm going to say that I am unavoidable that the kit is capable of supporting 800hp with a typical pair 61mm turbocharger, any way 1000hp although dyno-proven, does not agree with what is published on most 61mm turbochargers. I'm not doubting the kit, I am stating that I don't have a good reference for the specific turbocharger used in the kit.
Furthermore, feeding 1000hp from 8 injectors requires eight 750cc/min injectors by my estimate and this agrees with what is mentioned on Hot Rod magazine's description of needing 75lbs/hour injectors (each lb/hour is approximately equivalent to 10.5cc/min) at a minimum or a total fuel deliver requirement of 900 liters per hour of fuel at a the fuel rail pressure which is typically nearby 45psi.
Looking at the flow capacity of the Gs342 fuel pump supplied with the kit, which is 255lph @ 30psi, then using 3 fuel pumps gives us the capacity for 765lph which is about 2125 hp worth of fuel, so in that regard the kit is capable of supporting the power figure.
As you can see, it is potential to organize such a complex law if the information (Turbocharger compressor map, turbocharger climatic characteristic map, supercharger compressor map, supercharger climatic characteristic map ...etc) information were ready before hand. What remains a difficulty and an art of trial and failure, is how over-engineered is your engine, how much torque can it produce and still continue to survive, and how long can it continue to survive at elevated power levels. That is altogether a more entertaining examine to answer.
Twin-Charging - understanding and Example Application
Recommend : rockwell tools blog reviews psp2 go Reviews Automobuy Store
