EDITOR’S NOTE: Welcome to our first guest writer, Taylor, our very own in-house car guy. This is a very dense article about turbochargers and intercoolers. We hope for many more from Taylor in the future.

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Turbocharger Illustration

When categorizing car engines there are two groups that describe how the air/fuel mixture is sent into the cylinders. Most common is the naturally-aspirated engine (with no forced induction system). This engine brings air into the cylinder at atmospheric pressure and temperature to be mixed with fuel and combusted (or burned). This would work fine for all engines, but more power can be developed if more air is brought in because more air means more oxygen. At higher pressures, air will be denser and can be mixed with more fuel to deliver more power per stroke of the engine. To create this higher pressure, a forced induction system, such as a turbocharger or supercharger, is added.

A turbocharger (or turbo, for short) system has a compressor that is used to compress the intake air for the engine and a turbine that is used to drive the compressor. The turbine, like a wind turbine, is driven by the exhaust gases leaving the engine, which contain a fair amount of kinetic energy that would otherwise be wasted to the atmosphere. This is like recycling the exhaust energy. As the exhaust passes through the turbine, it spins up and gains rotational inertia, which is transmitted to the compressor through a mechanical linkage. Air from outside the car is sucked into the compressor where it will rise in temperature as well as become denser. This rise in temperature, however, is undesirable. Air at higher temperatures will have lower density than air at atmospheric conditions.

The density through the compressor will still increase a good amount though, but it could be made better if the output temperature were lower. To help this situation an intercooler is introduced. The intercooler is basically a heat exchanger that runs the hot air from the compressor through it. Its main goal is to cool the air before it goes into the engine without losing any of the pressure from the compressor. It is usually placed at the very front of the car so that air coming from the atmosphere flows through the intercooler and cools the hot air from the compressor (which is flowing inside the intercooler in a series of little tubes). These tubes even have little ‘fins’ to increase the surface area of the intercooler so that maximum heat transfer between outside air and the pressurized air can occur.

So air comes from the atmosphere, into the compressor (driven by the exhaust turbine), exits the compressor into the intercooler, then the cooled and pressurized air enters the cylinder where it is ignited with some fuel. It then leaves the cylinder as exhaust where it will spin the turbine for in order to compress more intake air. After passing through the turbine the air leaves the car through the exhaust pipe into the atmosphere.

Turbo System Diagram

A supercharger is similar because its function is to compress the intake air for the engine. It only differs in that its compressor is driven by the engine itself instead of an exhaust turbine. This robs some engine power, but the pressurized air advantage (more oxygen) more than makes up for the power consumed to drive the compressor.

Although still fairly rare, turbocharged cars are making a comeback in recent years due in part to rising fuel costs and demand for technologically advanced engines. Maybe you’ve seen some surviving sport-compact cars from the 1980’s with their prominent ‘TURBO’ stickers still intact. Although stickers are sometimes used to increase visual appeal (think racing stripes), these labels generally indicate that the car is indeed equipped with a turbo. Turbo advantages include decreased fuel consumption because they allow smaller engines to produce the power of much larger ones. They also allow for a lighter engine so they are popular for high-performance cars trying to cut weight everywhere possible. It’s common to see turbocharged engines that are about 2.0 liters (in total piston stroke displacement, which is a unit of engine volume) providing the same power as naturally aspirated engines with almost twice the volume. Some disadvantages are that fuel consumption is increased if the driver always drives the car as hard as possible because more fuel than usual is used when running the engine under ‘boost’, or with a pressurized intake. It also takes higher engine speeds (RPM) to generate enough exhaust to effectively drive the turbine, so a turbo does not provide ample boost until the driver has the car about midway through the engine’s RPM range, this delay is also known as “turbo lag”. Overall though, a turbo is an effective way to give more power to a small engine by simply forcing more oxygen into the cylinder, which yields more power.

Amazing illustration from clfloyddesign.com. Diagram from BTN Turbo.

Categories: In-Depth Articles
Tags: Cars, Intercooler, Turbo, Turbocharger
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