adminTURBOCHARGER
A turbocharger is a forced induction device bolted to an engine that uses energy from exhaust gases to spin a turbine, which in turn drives a compressor to force more air into the engine cylinder. The more compressed air allows more fuel to burn producing significantly more power without increasing engine size.
There are several types of turbochargers and they are; single/fixed geometry, twin-scroll , variable geometry (VGT/VNT), parallel twin, sequential twin, compound/series two stage, electric (e-turbo) and Ball bearing turbochargers.
Single/fixed geometry turbo charger is the most fundamental and common turbocharger. The turbine and compressor housing have fixed non-adjustable geometry. They are simple, affordable, easy to diagnose, repair and replace. They are highly durable under normal conditions and are excellent for high RPM power.
Twin-scroll turbocharger is a single turbocharger with a turbine housing divided into two separate scroll passages (volutes), each receiving exhaust pulses from alternating cylinder groups. They are noticeably faster spool-up than single scroll. They have better exhaust gas scavenging with improved volumetric efficiency. They also have a broader, flatter torque curve, higher thermal efficiency, reduced turbo lag with no significant increase in weight or size compared with single scroll turbochargers.
Variable geometry turbocharger (VGT/VNT) is turbochargers with moveable aerodynamic vanes inside the turbine housing that continuously adjust to control exhaust gas flow angle and velocity, thus effectively changing the turbochargers characteristics on the fly. They have near zero turbo lag across entire RPM range. They have outstanding efficiency at all load points. Variable geometry turbochargers eliminate the need for a waste gate; have superior fuel economy, exceptional low-end torque, and precise software controlled boost management.
Parallel twin-turbo has two identical turbochargers working simultaneously, one for each cylinder bank on a V-configuration engine. They are characterized by massive power output capability with redundancy as one turbo can still function if the other fails or has minor issues.
Sequential twin turbochargers are two different sized turbochargers that operate in sequence as a small turbo at low RPM, large turbo at high RPM, thus providing excellent response throughout the entire RPM range. They have the best throttle response of any twin turbo configuration. They have a wide, flat torque curve from low to high RPM. They combine small turbo’s responsiveness and large turbo’s peak power. They have no significant lag at any RPM.
Compound/series two stage turbochargers are two turbochargers arranged in series, the first (high pressure) turbo compresses air which is then fed into the second (low pressure) turbo for a second stage of compression. They deliver and possess extreme torque and power for heavy loads, better efficiency than a single large turbo at equivalent boosts. Each individual turbo unit is smaller and lighter and they allow very high boost in large displacement diesel engines.
Electric turbochargers (e-turbo) is a turbocharger with an integrated electric motor on the shaft between the turbine and compressor wheels. The motor can spin the compressor instantly using electrical power independent of exhaust flow. It has absolute zero turbo lag with instant boost from any RPM. It recovers energy during deceleration, maintains boost during gear changes enables aggressive engine downsizing and seamlessly integrates with mild/full hybrid systems.
Ball bearing turbocharger is a turbocharger using ceramic or steel ball bearings instead of the traditional oil-film floating journal bearings to support the shaft. It has 40-60% faster spool-up versus journal bearing turbo’s. It has less friction, hence better thermal efficiency, longer service life, better cold start performance and reduced oil consumption.
The advantages of turbocharges in automobiles are; turbocharged engines produces significantly more power than the same engine without a turbocharger (say about 30-50% more). Turbocharged engines have better fuel efficiency than non-turbocharged engines. Their ability to recover waste exhaust energy, improves the overall system efficiency. Turbocharged engines compensate for lost power at high altitudes, thereby maintain power output. Turbocharged engines produce high torque at low RPM, thus a small turbo charged engine occupies less space and weighs less than a lrger natural aspirated engine of equivalent power. Turbocharged engines generally have lower emissions. Turbochargers work exceptionally well alongside mild hybrids and full hybrid systems.
The disadvantages of turbochargers in automobiles are; turbochargers exhibit a turbo lag, that is a delay in response between pressing the accelerator and boost building up. Turbochargers results in extreme heat generation thereby inducing thermal stresses on surrounding engine components and may result in unexpected failure. The use of turbochargers requires significant oil lubrication, repair and maintenance cost, higher octane fuel, intercooler heat sink and other additional components thereby increasing the complexity and failure points.
Turbochargers find application in the following; passenger cars, performance and sports cars, luxury sedans and SUVs, pickup trucks and light commercial vehicles, heavy duty trucks, military and special vehicles where engine performance, torque and higher power delivery is a prime consideration.
The future of turbochargers is based on the advances and development of the following technologies; turbocharged engines will increasingly serve as range extenders in PHEV and series hybrids, generator engines in hydrogen fuel cell range extenders and the combustion components in parallel hybrid power trains. Currently hydrogen internal combustion engines (H2-ICE) with turbocharger are being developed by automobile companies to withstand future challenges. 3D-printed turbine and compressor wheels in titanium and nickel super alloy are already in production to obtain complex aerodynamic blade geometries impossible with traditional casting. Future turbochargers control system will use AI and ML to predict driver demand before throttle is fully pressed. There is also need for more research into expensive heat resistance materials to withstand the excessive heat generated by turbochargers such as Inconel, titanium etc. and the use of high of advanced high temperature materials such as ceramic matrix components etc..
SOURCES:
- Maximum boost: Designing, testing and installing turbocharger systems by Corkey Bell.
- Turbocharging the internal combustion engine by N. Waston and M.S Janota.
- Turbo: Real world high performance turbocharger systems by Jay K. Miller.
- Turbocharging performance handbook by Jeff Hartman.
- Turbochargers by Hugh MacInnes.
