This could be extra of a generic query however my buddies and I bought right into a dialogue about increase and one among them stated that extra increase will all the time make extra energy as a result of you have got extra strain pushing extra air and gas into the cylinder. This didn’t sound correct. Are you able to clarify what’s occurring right here?
It is a difficult, nuanced topic that we’ll attempt to condense right into a (comparatively) concise reply.
The straightforward reply for any supercharger or turbocharger, is that it’s designed to run inside a sure vary of optimized operation. This space contains shaft velocity, how a lot air the supercharger or turbocharger is shifting, and the way a lot increase these energy adders produce.
That is the rationale why there are such a lot of completely different sizes of superchargers, centrifugal superchargers, and turbochargers. There are actually tons of of various sizes and configurations. But for a selected utility, there can be pretty slim vary of supreme candidates.
Unsure of the excellence between compelled induction strategies? Learn this: What’s the Distinction Between a Turbocharger & Supercharger
Now let’s get extra particular.
Let’s simply say that we now have a supercharger designed to maneuver a set quantity of air and produce 20 psi of increase. Increase is the strain and is most frequently expressed in kilos per sq. inch (psi) however may also be given in inches of mercury (“Hg). In lots of instances a supercharger is merely shifting extra air than the engine can settle for, in order that this strain builds up contained in the consumption manifold.
If the supercharger is then requested to spin sooner by altering the pulley ratio, for instance, then it’ll transfer extra air than it did earlier than. However it’ll even be making extra warmth as a result of we at the moment are spinning it sooner than the designer meant. This extra warmth is added to the traditional warmth created when strain is added to a closed container. When a store air compressor runs, in case you put your hand on the big tank, it’ll really feel heat. That’s as a result of as strain is added to the tank, the air naturally heats up as a result of the air molecules are compelled to be nearer collectively, creating warmth.
This improve in inlet air temperature (warmth) is dangerous as a result of a fundamental working premise is that, to make energy, the air must be cooler—and due to this fact extra dense. However as temperature will increase, this lowers air density. So whereas strain (increase) will increase contained in the engine’s consumption manifold, so does the warmth. This extra warmth lowers the precise density of the air.
Air density could be described a number of methods. Most frequently it’s used to judge the precise quantity of oxygen in a given quantity of air. Let’s say we now have a one cubic foot container of air at normal temperature and strain. This normal is 14.7 psi atmospheric strain at 68 levels F with zero humidity or zero vapor strain. Now let’s evaluate that to the identical container of air that has been heated to 150 levels F however on the similar atmospheric strain.
The air within the second container will characteristic far fewer oxygen molecules as a result of the molecules have expanded so they’re farther aside. Conversely we now have one other one cubic foot container with air that’s solely 40 levels F. The air on this container can be denser with extra oxygen molecules.
The identical factor happens after we add strain. Positive, we squeeze the molecules collectively so they’re denser, however this added increase comes at the price of further warmth—which is an inevitable consequence of compressing the air. This has the direct have an effect on of decreasing the air’s density.
So with any supercharger or turbocharger, there’s a level the place the unit works most effectively. That is the place it creates a given quantity of increase whereas including the least quantity of further warmth.
If we spin the blower sooner, this creates extra increase strain however can also improve the quantity of warmth put into the air. This lowers the air density in order that the web results of extra increase (past its supreme degree) turns into counter-productive to rising energy as a result of the air is hotter and due to this fact much less dense—even with the added increase.
That’s why, for a given supercharger or turbocharger, including extra increase sooner or later will lead to much less energy as a result of the air is much less dense. Positive, it has extra increase, however the temperature acquire (and subsequent discount in density) will negate any improve in energy.
Plus, the opposite variable is that this greater increase requires extra horsepower to spin the supercharger sooner, which solely leads to even much less flywheel horsepower.
If further airflow and increase is critical, this can require a bigger supercharger or turbocharger that strikes extra air per revolution. This bigger unit will work extra effectively at greater airflow numbers. After all, this implies it won’t be as environment friendly at decrease engine speeds—however that’s the compromise that should be made to make the elevated energy at these greater engine speeds.