The center hub rotating assembly (CHRA) houses the shaft that connects the turbine to the compressor.
Ported shroud designs can have greater resistance to compressor surge and can improve the efficiency of the compressor wheel. Some turbochargers use a "ported shroud", whereby a ring of holes or circular grooves allows air to bleed around the compressor blades. The operating characteristics of a compressor is described by the compressor map. The compressor section of the turbocharger consists of an impeller, a diffuser and a volute housing. The compressor draws in outside air through the engine's intake system, pressurises it, then feeds it into the combustion chambers (via the inlet manifold). This differs from an electric supercharger, which solely use an electric motor to power the compressor.Ĭompressor section with the cover removed The benefit of variable-geometry turbochargers is that the optimum aspect ratio at low engine speeds is very different from that at high engine speeds.Įlectrically-assisted turbochargers Īn electrically-assisted turbocharger combines a traditional exhaust-powered turbine with an electric motor, in order to reduce turbo lag. Because of this, variable-geometry turbochargers often have reduced lag, a lower boost threshold, and greater efficiency at higher engine speeds. By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. If the turbine's aspect ratio is too large, the turbo will fail to create boost at low speeds if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. Some variable-geometry turbochargers use a rotary electric actuator to open and close the vanes, while others use a pneumatic actuator. This is done with the use of adjustable vanes located inside the turbine housing between the inlet and turbine, these vanes affect flow of gases towards the turbine. Variable-geometry turbochargers (also known as variable-nozzle turbochargers) are used to alter the effective aspect ratio of the turbocharger as operating conditions change. Ĭutaway view of a variable-geometry turbocharger Īnother common feature of twin-scroll turbochargers is that the two nozzles are different sizes: the smaller nozzle is installed at a steeper angle and is used for low-rpm response, while the larger nozzle is less angled and optimised for times when high outputs are required.
The scavenging effect of these gas pulses recovers more energy from the exhaust gases, minimizes parasitic back losses and improves responsiveness at low engine speeds. The exhaust manifold keeps these two groups of cylinders separated, then they travel through two separate spiral chambers ("scrolls") before entering the turbine housing via two separate nozzles. For a twin-scroll turbocharger, the cylinders are split into two groups in order to maximise the pulses. In a standard (single-scroll) turbocharger, the exhaust gas from all cylinders are combined and enter the turbocharger via a single intake, which causes the gas pulses from each cylinder to interfere with each other. Twin-scroll Ī twin-scroll turbocharger uses two separate exhaust gas inlets, to make use of the pulses in the flow of the exhaust gasses from each cylinder. Large diesel engines often use a single-stage axial inflow turbine instead of a radial turbine. Various technologies, as described in the following sections, are often aimed at combining the benefits of both small turbines and large turbines. Small turbines can produce boost quickly and at lower flow rates, but can be a limiting factor in the peak power produced by the engine. Large turbines typically require higher exhaust gas flow rates, therefore increasing turbo lag and increasing the boost threshold. Some turbocharger designs are available with multiple turbine housing options, allowing a housing to be selected to best suit the engine's characteristics and the performance requirements.Ī turbocharger's performance is closely tied to its size, and the relative sizes of the turbine wheel and the compressor wheel. The turbine housings direct the gas flow through the turbine section, and the turbine itself can spin at speeds of up to 250,000 rpm.
#Air compressor parts series#
The turbine uses a series of blades to convert kinetic energy from the flow of exhaust gases to mechanical energy of a rotating shaft (which is used to power the compressor section). After the exhaust has spun the turbine it continues into the exhaust and out of the vehicle. The turbine section (also called the "hot side" or "exhaust side" of the turbo) is where the rotational force is produced, in order to power the compressor (via a rotating shaft through the center of a turbo.