ニュース

A turbocharger is a type of forced induction system that significantly increases an engine's power output and efficiency by compressing the air entering the engine.

In simple terms, an engine makes power by burning a mixture of air and fuel. A naturally aspirated (non-turbo) engine can only draw in a limited amount of air (and thus burn a limited amount of fuel) based on its displacement. A turbocharger acts as an air pump that forces significantly more air into the engine's cylinders, allowing more fuel to be added and resulting in a much larger, more powerful combustion event.

A turbocharger is a brilliant piece of engineering that uses energy that would otherwise be wasted to create more power. It is composed of two main sections connected by a single shaft: the turbine and the compressor.

1. The Turbine Side (The Power Source)

The turbine section is mounted on the engine's exhaust manifold.

• Exhaust Gas Flow: Hot exhaust gases, which are the byproducts of combustion, exit the engine's cylinders and are channeled into the turbine housing.

• Spinning the Wheel: This high-velocity exhaust gas strikes the blades of the turbine wheel, causing it to spin at extremely high speeds, often exceeding 200,000 revolutions per minute (RPM).

• Waste Recycling: The energy from the exhaust gas, which is normally expelled uselessly into the atmosphere, is effectively recycled to power the entire system.

2. The Compressor Side (The Power Maker)

The compressor section is connected to the engine's air intake.

• Shared Shaft: The turbine wheel is physically connected to the compressor wheel by a forged steel shaft. As the turbine spins, the compressor spins with it.

• Air Intake and Compression: The rapidly spinning compressor wheel draws in ambient air and violently flings it outward, compressing the air and forcing it into the engine's intake manifold. This compressed air is known as boost.

• Intercooler: When air is compressed, it heats up. Hot air is less dense and contains fewer oxygen molecules. To counter this, the compressed air is routed through an intercooler (a heat exchanger similar to a radiator) to cool it down, making it denser and packing more oxygen into the cylinder for maximum power.

The net effect is that the engine's cylinder receives a pressurized, dense charge of air, enabling it to burn much more fuel and generate significantly more horsepower and torque than a non-turbocharged engine of the same size.

The Benefits of Turbocharging

Turbochargers have become common on everything from sports cars to family sedans due to two primary advantages:

1. Enhanced Power and Performance (Power Density)

A turbocharged engine can produce the power of a much larger engine. For example, a modern $2.0$-liter turbocharged four-cylinder engine can easily generate the same horsepower as a naturally aspirated $3.5$-liter V6. This allows manufacturers to:

• Downsize Engines: Use a smaller, lighter engine block, which improves overall vehicle handling and packaging.

• Increase Power Density: Get more horsepower per unit of engine displacement.

2. Improved Fuel Efficiency and Emissions

During normal, light driving conditions (low engine load), the turbocharger is not producing significant boost, allowing the engine to operate efficiently as a smaller engine.

• "Right-Sizing": The small engine provides excellent fuel economy during cruising, and the turbo provides the extra power only when the driver demands it (like accelerating or passing).

• Reduced Emissions: The more complete and efficient burning of fuel, aided by the forced oxygen, helps reduce harmful exhaust emissions.

The Trade-offs: Turbo Lag

The main disadvantage of a turbocharger is a phenomenon called turbo lag. Since the turbo is powered by exhaust gas, it takes a moment for enough gas flow to build up and spin the turbine wheel fast enough to create meaningful boost pressure.

When you press the accelerator pedal:

1. The engine starts producing more exhaust gas.

2. The exhaust gas takes time to spin the heavy turbine up to its operating speed (lag).

3. Once the target speed is reached, the boost is suddenly delivered, and the car rapidly accelerates.

Modern turbochargers, particularly those with smaller turbine wheels (to decrease inertia) or twin-scroll designs, have significantly minimized this lag.