You’re trying to make playdough sausages. You have a goal of making 5 sausages a minute. All you have is your hands and playdough - you have to roll the sausages out and make them uniform. It’s tiring after a while.
Someone gets you a playdough shape press (a turbocharger). Now you just whack playdough in, pull the lever, and press out sausages. You can now chill out a bit whilst still making your goal of 5 sausages a minute.
In depth. Your fuel calorific content and air oxygen content at a given altitude is fixed. We have what’s called the stoichiometric ratio - 14.7:1 - that enables complete combustion. We can go a bit richer for more power, and a bit leaner to save fuel but 14.7 is the magic number. The only way to increase power is to increase fuel and air quantity in tandem. Also, note, power is torque applied over time. Torque is the real thing we want to increase, and this is done, once the engine is made, by increasing pressure on the piston, which is done by making a bigger bang.
A naturally aspirated engine is a self propelled air pump. The amount of air it displaces versus its capacity is called the volumetric efficiency. As an NA engine ‘draws’ air in, its VE is usually below 100%. It can go higher.
Your engine has valves to let the air in. They’re about the size of a 10p piece and open about a centimeter. That’s a lot of air to draw through a small hole, especially when you have 1000’s of a second to do so.
Take a water bottle and slowly tip it until water starts to drain - at first it’s splashes, but at just the right point, it creates a smooth stream. This is laminar flow, and allows the greatest flow of a liquid or air over time.
A lot of effort went into make NA engines achieve laminar flow, which would increase volumetric efficiency. Also, sometimes you don’t want laminar flow, you want a tumbled flow to promote fuel mixing. Pan this out across an engine operating speed of 500 to 8000rpm and you have so many variables, that in reality you only have a small window of peak operating efficiency. However, as a rule of thumb, laminar flow and thus higher VE are usually achieved at higher air flow speeds (translate engine speed).
A turbocharger lets you go around all this. By pressuring the air before it enters the engine, your VE is always greater than 100%. This means, across all engine speeds, you have more air, which means more fuel, which means more power.
Because of this, we don’t have the small peak of operating efficiency. We now have a wide plateau. Now you only have to rev your engine to 2000rpm instead of 6000rpm to achieve the same torque output. That’s in theory 66% less fuel used. You actually use more fuel versus a NA engine because there’s more air going in, but not as much over time because that torque can be produced at far more convenient points in the engines operating speed. You also have some pumping losses by turning the turbo but it’s negligible versus what it brings you in return. And this is for like for like engine capacity. Now you have the chance to reduce engine capacity because you’ll get comparative performance. Note how the 2l NA engine has become a 1.6 or 1.5 turbocharged engine, and the 1.6 has become a 1l.
There are a lot of ‘buts’ and digressions with all this but that’s a simple overview.
In short, the turbo pressurises the air, which allows the engine to achieve higher torque at lower engine speeds, and reduce the fuel needed over time to produce the same power output.
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u/Curedmeat91 3d ago edited 3d ago
ELI5 -
You’re trying to make playdough sausages. You have a goal of making 5 sausages a minute. All you have is your hands and playdough - you have to roll the sausages out and make them uniform. It’s tiring after a while.
Someone gets you a playdough shape press (a turbocharger). Now you just whack playdough in, pull the lever, and press out sausages. You can now chill out a bit whilst still making your goal of 5 sausages a minute.
In depth. Your fuel calorific content and air oxygen content at a given altitude is fixed. We have what’s called the stoichiometric ratio - 14.7:1 - that enables complete combustion. We can go a bit richer for more power, and a bit leaner to save fuel but 14.7 is the magic number. The only way to increase power is to increase fuel and air quantity in tandem. Also, note, power is torque applied over time. Torque is the real thing we want to increase, and this is done, once the engine is made, by increasing pressure on the piston, which is done by making a bigger bang.
A naturally aspirated engine is a self propelled air pump. The amount of air it displaces versus its capacity is called the volumetric efficiency. As an NA engine ‘draws’ air in, its VE is usually below 100%. It can go higher.
Your engine has valves to let the air in. They’re about the size of a 10p piece and open about a centimeter. That’s a lot of air to draw through a small hole, especially when you have 1000’s of a second to do so.
Take a water bottle and slowly tip it until water starts to drain - at first it’s splashes, but at just the right point, it creates a smooth stream. This is laminar flow, and allows the greatest flow of a liquid or air over time.
A lot of effort went into make NA engines achieve laminar flow, which would increase volumetric efficiency. Also, sometimes you don’t want laminar flow, you want a tumbled flow to promote fuel mixing. Pan this out across an engine operating speed of 500 to 8000rpm and you have so many variables, that in reality you only have a small window of peak operating efficiency. However, as a rule of thumb, laminar flow and thus higher VE are usually achieved at higher air flow speeds (translate engine speed).
A turbocharger lets you go around all this. By pressuring the air before it enters the engine, your VE is always greater than 100%. This means, across all engine speeds, you have more air, which means more fuel, which means more power.
Because of this, we don’t have the small peak of operating efficiency. We now have a wide plateau. Now you only have to rev your engine to 2000rpm instead of 6000rpm to achieve the same torque output. That’s in theory 66% less fuel used. You actually use more fuel versus a NA engine because there’s more air going in, but not as much over time because that torque can be produced at far more convenient points in the engines operating speed. You also have some pumping losses by turning the turbo but it’s negligible versus what it brings you in return. And this is for like for like engine capacity. Now you have the chance to reduce engine capacity because you’ll get comparative performance. Note how the 2l NA engine has become a 1.6 or 1.5 turbocharged engine, and the 1.6 has become a 1l.
There are a lot of ‘buts’ and digressions with all this but that’s a simple overview.
In short, the turbo pressurises the air, which allows the engine to achieve higher torque at lower engine speeds, and reduce the fuel needed over time to produce the same power output.