Tuesday, January 2, 2018

Turbocharger vs. Supercharger

When you are browsing the Internet for cars you plan to buy in the future or after you save money for a few more decades, you’ll come across two common automotive terminologies: turbocharger and supercharger, unless you plan to purchase an electric car in which case what you read will only be charger. Just by the names alone, it is easy tell that a car with either supercharger or turbocharger is going to be a lot faster than the same exact model without the additional component. Even in everyday conversation which has nothing to do with automotive engineering, the words turbo and super indicate something superior. Superhero is more fictional than just hero, superman is an alien, supercars are more expensive than cars, and even Super Mario sounds a lot better than Mario. The same thing applies to turbo with turbojet, turbofan, turbo-generator, and so on.

Cars, beside for the purpose of taking people from point A to B, are also excellent for showing-off. This is one of the main reasons that car manufacturers want to produce something faster than ever before and sell it to people who can also afford personal drivers. They can also brag about the fact that their cars are supercharged, turbocharged, or maybe both even when they don’t know exactly how the components work; the not-so rich ones should be content as long as their small slow green electric vehicles are simply charged.

Turbocharger vs Supercharger
Some cars are turbocharged or supercharged, or both; that one is just charged
To understand what turbocharger and supercharger are, let us first take a peek into how combustion engine works. There are pistons inside an engine; they move back and forth to create vacuum, and therefore introduce air (oxygen) into enclosed chambers along with fuel. A mixture of oxygen and fuel creates a highly combustible formula. Movements of the pistons constantly compress the mixture to make the combustion more intense. Fortunately the ratio between air and fuel is quite constant, so an engine that sucks more air can also burn more fuel. Stepping on the throttle pedal deeper only increases the supply of fuel but not air, except when the car is equipped with a turbocharger, supercharger, or both.

Even a typical combustion engine without those components is already fast enough for most people. In real world circumstances and city roads, you don’t actually need any turbocharger or supercharger to get a speeding ticket or arrive on time at a costume party. However, having a ridiculous amount of power at your disposal at any given moment is almost as exciting as actually using it. Everybody loves redundancy – or more precisely things they never use – and it is exactly the same thing with an abundance of horsepower in a car.

Forced Induction System

Both turbocharger and supercharger are forced-induction systems. They compress air and force it to enter the engine. By compressing air before it actually mixes with fuel, the engine does not need to make larger space for more incoming oxygen. Typical forced-induction system can deliver 50% more air. A small engine with either turbocharger or supercharger can match or even surpass the power level of its normal counterpart. It also means more power without sacrificing fuel efficiency. Although those components have the same purpose, they deliver the extra air and power through different methods.

A turbocharger works thanks to the expanding gas inside the engine’s exhaust. It has two turbines: one is connected into the exhaust, and another into the air intake port. As the engine develops power, the exhaust spins one turbine. When this turbine spins, another follows suit and increases engine air intake. Such mechanism gives double advantages. First, there is no direct mechanical load to the engine. Turbocharger is powered solely by the still-expanding gas in the exhaust; it does not require or consume power from the engine at all. Second, it improves efficiency since the power that spins its turbines is basically residue to be wasted as heat through the tailpipe anyway. Turbocharger transforms an otherwise unused heat into more power.

Key disadvantage is something called turbo-lag. Since turbocharger requires wasted energy, you need to produce more of it to get more intense air intake. In other words, you need higher RPM for the action to happen. At low RPM, the amount of backpressure in the exhaust offsets the advantage of air intake increase.

On the other hand, a supercharger is driven by the engine. It is connected to the engine with a belt, gear, chain, shaft, and anything else except supernatural powers. A supercharger spins its turbines because it gets power from the engine as well. However, the increased air intake gives much more power boost than the energy required to spin the turbines. This means a supercharger kicks-in even at low RPM. It does introduce mechanical load to the engine, but there is turbo-lag issue.

To eliminate the disadvantages, some cars are both supercharged and turbocharged at the same time, hence twin-charger. At low RPM, supercharger does the job to deliver more air into the engine, but the task is soon taken over by turbocharger as the engine develops enough RPM to offset the backpressure in the exhaust. Also immediately the supercharger is decoupled and bypassed to eliminate mechanical load. Some examples of cars that come with twin-charger from factory are Volvo T6 and T8 models lineup, Volkswagen 1.4 TSI, Nissan Super Turbo, Lancia Delta S4, and Zenvo ST1.

There is also another variant called electric turbocharger, which takes advantage of both wasted energy in the exhaust and electric compressor developed by Audi. As the name says, it is basically a typical turbocharger but with the addition of energy recovery system to help spin the turbines.

More Air is Better

The real mechanism of turbocharger and supercharger are pretty complicated, but the point is that they deliver more air into fuel combustion chambers. Increased volume of oxygen in the chambers allows the engine to burn an increased amount of fuel and turns it into more horsepower. Think of these chargers as superheroes suits that transform Bruce Wayne into Batman or Tony Stark into Iron Man. Well, Batman does not actually fit to the description because the man behind the bat-suit is already combat-ready anyway; Iron Man does fit nicely, though.