The very first time I ever listened to of twin charging (making use of each a turbocharger and a supercharger on the exact same motor) was most likely again in 12 months 2000. At that time I was quite interested in performance for the Toyota Celica and naturally I also go through a large amount about its sister automobiles (that shared some of the exact same engines) such as the Camry and the MR2.
Just one of the most intriguing aftermarket parts I ran throughout at the time was the HKS turbo package for the 4AGZE powered 1st generation mr2. The 4agze (for individuals that are not common with Toyota engines) is a peppy one hundred seventy horsepower 1.6 liter engine powered by the Toyota SC-twelve roots type supercharger. On this motor vehicle Toyota made use of an electromagnetically clutched supercharger that could be disabled in the course of low electric power prerequisites such as cruising, and engaged when the person demands it.
Just one of the most crucial parts of the HKS package is the bypass valve. This valve was made use of to direct air from the supercharger to the engine at lower rpm/flow factors. Once the rpm’s rise, and the engine begins to demand a lot more air, and the turbocharger is entirely spooled, the valve switches above little by little till the turbocharger alone is feeding the engine though the supercharger is totally bypassed. The twin-charged MR2’s were rumored to break the 300hp mark in some instances, relying on the final enhance stage and the supporting modifications, and this stage of electric power for a 1.6 litre motor at the time was peaceful astounding.
The idea powering this sort of technique is to use a little favourable displacement (roots design) supercharger. Supercharger performance efficiency is commonly at its greatest at lower engine and supercharger rpm’s (for instance from idle to 4000 rpm’s). Earlier mentioned 4000 rpm’s the supercharger’s performance and efficiency begins to fall, the horsepower necessary to travel it begins to rise exponentially, and the air temperature coming out of the supercharger begins to rise considerably limiting performance.
On the other hand, making use of a generously sized turbocharger will enable us to feed the engine proficiently with cooler air (than that from an overworked supercharger) and retain superior rpm performance. The trouble with making use of a greater turbocharger is that a generously sized turbocharger commonly would not spool prior to 3000 to 4000 rpm’s supplying us a restricted electric power band and therefore providing no performance enhance at lower rpm’s.
The idea of twin charging is to use each a supercharger and a turbocharger to have each individual charger do what it does very best, have the supercharger enhance the motor for low close torque, and as it operates out of steam, the turbocharger comes on line to carry us by way of to redline.
There are three areas to these varieties of methods that make them prohibitive to most tuners:
1.Price and complexity: Having a full supercharger technique as perfectly as a full turbocharger technique on the exact same motor vehicle is a large amount of funds to shell out and a large amount of parts to offer with and diagnose in situation some thing does go incorrect.
2.The bypass valve made use of to bypass the supercharger (and yet hold in all the air pressure coming from the turbocharger) as perfectly as staying equipped to handle this valve electrically or mechanically calls for a custom manufactured one particular off valve that isn’t really rather available off the shelf. Even though as I produce this it appears to be possible to find a big sized dual chamber bypass valve plumbed to function on the differential pressure amongst the turbo outlet and the supercharger outlet to switchover the moment the turbocharger pressure = the supercharger pressure + the rigidity of the bypass valve opening mechanism.
3.Considering the fact that we are making use of two unique varieties of chargers with two unique efficiency maps, it can get quite sophisticated to figure out how to tune the motor (especially with considerably less difficult gas injection methods that were made use of at the time) because the air density can fluctuate considerably at the exact same rpm place and pressure stage relying on which charger is feeding air to the motor and at what proportion. This is also the place the HKS turbo package for the 4agze was at its weakest, namely at smoothing the transition place fueling amongst the supercharger to turbocharger switchover.
Just one of the issues that has changed above the final ten decades is the availability (and proliferation of understanding) about available alternate fuels or octane boosters. Two such options are:
1-E85 gas which is comprised of eighty five% Ethanol which has an octane rating of about a hundred to a hundred and five octane vs the regular 87 to ninety three octane pump gasoline.
2-Drinking water / methanol injection methods that can be made use of both as supplemental fueling technique (centered on the methanol articles which carries an octane rating of 110 octane or higher) or can be made use of for in cylinder cooling when the drinking water vapor injected with the methanol transforms into steam inside the combustion chamber, therefore extracting a lot warmth out of the combustion chamber, and therefore slowing down the speed of travel of the combustion flame front simulating the results equivalent to individuals of a higher octane gasoline.
With the availability of these octane expanding or octane simulating concoctions, it has become a lot more available of new for the performance enthusiast to construct a unique type of twin charger technique that does not have to have a bypass valve.
In this type of technique the supercharger outlet is routed to feed the turbocharger inlet or vice versa. Fairly than both the supercharger or the turbocharger feeding the engine separately (in parallel operation) and switching amongst the two, we are now making use of a two stage compression technique the place one particular stage is the factory supercharger, and the 2nd stage is an aftermarket turbocharger technique.
The web result of the two compressors is a compounding of pressure ratios. For instance if the turbocharger waste-gate opening spring is established to a location of 7psi of pressure above atmosphere (which is a pressure ratio of 1.5 provided that 1 atmosphere is about fourteen.7 psig) and if the supercharger is mechanically geared to flow fifty% a lot more than the engine (for favourable displacement roots design superchargers) at any rpm, therefore having an identical 7psi enhance location or a pressure ratio of 1.5 then the resultant pressure ratio of the technique mixed is :
PR total = PR turbo * PR supercharger = a pressure ratio of 2.25
A pressure ratio of 2.25 is equal to eighteen.4 psi of enhance (not 14psi predicted by adding the two phases together).
So anyway, how does this relate to octane prerequisites ?
If the turbocharger is feeding the supercharger for instance, and the turbocharger is ingesting fresh new air at ambient air temperatures (T1), then:
1-The air exiting the turbocharger will be at a temperature T2, higher than the ambient air temperature (T1) by about 60-80*C relying on the precise turbocharger, and the place we are on the turbocharger compressor and efficiency map.
2-The air coming into the supercharger will enter at a temperature T2 ~=T1+60 and exit at a temperature T3 which is higher than T2 by about a different 60-80*C relying on the precise technical specs of the supercharger.
3-If we had an intercooler right after the supercharger, then the air coming into the intercooler will be at one hundred twenty to 160*C above ambient temperatures which is a large amount of warmth for the intercooler to try to drop in the limited sum of time that the air passes by way of the intercooler main.
4-If we have no write-up supercharger intercooler (which is prevalent on automobiles the place the supercharger is packaged into the intake manifold of the motor vehicle), then the air coming into the engine will be at some one hundred twenty to 160*C above ambient.
5-This excessively heated air not only minimizes electric power output (By about 1 horsepower for every 13*C) but it also increases the probability of the air gas mixture routinely igniting in the motor pre-maturely prior to the spark plug has fired, and if this pre-mature ignition takes place early plenty of to capture the piston considerably much absent from top rated dead middle, then the battling flame front pushing the piston downwards, and the inertia of the technique (and pressure of other firing cylinders rotating this piston by using the crankshaft) pushing the piston upwards will induce really superior pressures and a temperature rise on the floor of the piston eventually detrimental it and potentially detrimental other parts of the motor as perfectly.
For these factors (pressure compounding, and mixed temperature rise) sequential charging has witnessed quite minor software in the past. The use of a higher octane gas by definition implies that the air gas mixture is a lot more resilient to car-ignition and detonation. Furthermore, in the event of a pre-mature ignition, the higher octane gas makes a slower traveling flame front which offers the piston a lot more time to travel upwards in the cylinder bore (Closer to top rated dead middle) prior to conference the flame front and this minimizes the time that the piston floor is improperly pressurized and overheated cutting down the chance of catastrophic failure. Past but not the very least, the use a drinking water / methanol injection blend consists of two phase-modify events:
1-The injected methanol adjustments from a liquid state to a vapor state at its boiling place of sixty five*C, i.e. as before long as it hits the compressed air mixture coming from the supercharger outlet. This phase modify absorbs a large amount of the warmth out of the air and methanol mixture cutting down inlet air temperatures even prior to the mixture reaches the combustion chamber and begins to get compressed. This temperature reduction goes a prolonged way in direction of reducing or really cutting down the chance of detonation.
2-The injected drinking water, adjustments from a liquid state to a vapor state at its boiling place of a hundred*C which relying on the availability of an intercooler in the technique, my happen in the intake plumbing prior to achieving the combustion chamber, or could not happen till the mixture is ignited. Either way, when the temperature is superior plenty of, the drinking water mist injected in the air stream will flash vaporize into steam also absorbing a generous sum of the warmth made in the combustion.
The availability of these two octane boosters can make it now possible for aftermarket performance component manufacturers to provide safe and trusted sequential charging kits to the mass market place.
Just one such package which I ran throughout in an article from scorching rod journal was produced by hellion performance (http://www.hellionpowersystems.com) for the factory supercharged GT-five hundred mustang.
The package supposedly develop up to 1000 horsepower at a enhance stage of 24 psi making use of two 61mm Turbonetics turbochargers.
To realize 1000 hp calls for close to 1500 cfm of airflow at 24psi or 1500cfm at a pressure ratio of 2.sixty three, or 750cfm @ 2.63pr for every turbocharger.
Considering the fact that most compressor maps for this size of turbocharger (61mm) peak out at close to 600cfm @ 2.sixty three pr @ close to fifty% efficiency which is an extraordinary place on the map (i.e. the turbocharger is maxed out at this place). I am going to say that I am self-confident that the package is capable of supporting 800hp with a regular pair 61mm turbocharger, on the other hand 1000hp though dyno-established, does not concur with what is released on most 61mm turbochargers. I am not doubting the package, I am stating that I will not have a greater reference for the certain turbocharger made use of in the package.
Furthermore, feeding 1000hp from 8 injectors calls for 8 750cc/min injectors by my estimate and this agrees with what is outlined on Scorching Rod magazine’s article of needing 75lbs/hour injectors (each individual lb/hour is roughly equal to ten.5cc/min) at a minimum amount or a total gas provide necessity of 900 liters for every hour of gas at a the gas rail pressure which is commonly close to 45psi.
Searching at the flow capacity of the GS342 gas pump supplied with the package, which is 255lph @ 30psi, then making use of 3 gas pumps offers us the capacity for 765lph which is about 2125 hp truly worth of gas, so in that regard the package is capable of supporting the electric power figure.
As you can see, it is possible to structure such a complex technique if the facts (Turbocharger compressor map, turbocharger temperature map, supercharger compressor map, supercharger temperature map …and so on) facts were available prior to hand. What stays a secret and an art of demo and failure, is how above-engineered is your engine, how considerably torque can it develop and nonetheless keep on to endure, and how prolonged can it keep on to endure at elevated electric power stages. That is altogether a a lot more interesting problem to reply.