Boost (automotive engineering) | Wikipedia audio article


A turbocharger, colloquially known as a turbo,
is a turbine-driven forced induction device that increases an internal combustion engine’s
efficiency and power output by forcing extra compressed air into the combustion chamber. This improvement over a naturally aspirated
engine’s power output is due to the fact that the compressor can force more air—and proportionately
more fuel—into the combustion chamber than atmospheric pressure (and for that matter,
ram air intakes) alone. Turbochargers were originally known as turbosuperchargers
when all forced induction devices were classified as superchargers. Today the term “supercharger” is typically
applied only to mechanically driven forced induction devices. The key difference between a turbocharger
and a conventional supercharger is that a supercharger is mechanically driven by the
engine, often through a belt connected to the crankshaft, whereas a turbocharger is
powered by a turbine driven by the engine’s exhaust gas. Compared with a mechanically driven supercharger,
turbochargers tend to be more efficient, but less responsive. Twincharger refers to an engine with both
a supercharger and a turbocharger. Turbochargers are commonly used on truck,
car, train, aircraft, and construction equipment engines. They are most often used with Otto cycle and
Diesel cycle internal combustion engines.==History==
Forced induction dates from the late 19th century, when Gottlieb Daimler patented the
technique of using a gear-driven pump to force air into an internal combustion engine in
1885. The turbocharger was invented by Swiss engineer
Alfred Büchi (1879–1959), the head of diesel engine research at Gebrüder Sulzer (now simply
called Sulzer), engine manufacturing company in Winterthur, who received a patent in 1905
for using a compressor driven by exhaust gases to force air into an internal combustion engine
to increase power output, but it took another 20 years for the idea to come to fruition. The first use of turbocharging technology
based on his design was for large marine engines, when the German Ministry of Transport commissioned
the construction of the “Preussen” and “Hansestadt Danzig” passenger liners in 1923. Both ships featured twin ten-cylinder diesel
engines with output boosted from 1750 to 2500 horsepower by turbochargers designed by Büchi
and built under his supervision by Brown Boveri (BBC) (now ABB). During World War I French engineer Auguste
Rateau fitted turbochargers to Renault engines powering various French fighters with some
success. In 1918, General Electric engineer Sanford
Alexander Moss attached a turbocharger to a V12 Liberty aircraft engine. The engine was tested at Pikes Peak in Colorado
at 14,000 ft (4,300 m) to demonstrate that it could eliminate the power loss usually
experienced in internal combustion engines as a result of reduced air pressure and density
at high altitude.Turbochargers were first used in production aircraft engines such as
the Napier Lioness in the 1920s, although they were less common than engine-driven centrifugal
superchargers. Ships and locomotives equipped with turbocharged
diesel engines began appearing in the 1920s. Turbochargers were also used in aviation,
most widely used by the United States. During World War II, notable examples of U.S.
aircraft with turbochargers—which included mass-produced ones designed by General Electric
for American aviation use—include the B-17 Flying Fortress, B-24 Liberator, P-38 Lightning,
and P-47 Thunderbolt. The technology was also used in experimental
fittings by a number of other manufacturers, notably a variety of experimental inline engine-powered
Focke-Wulf Fw 190 prototype models, with some developments for their design coming from
the DVL, a predecessor of today’s DLR agency, but the need for advanced high-temperature
metals in the turbine, that were not readily available for production purposes during wartime,
kept them out of widespread use. Turbochargers are widely used in car and commercial
vehicles because they allow smaller-capacity engines to have improved fuel economy, reduced
emissions, higher power and considerably higher torque.==Turbocharging versus supercharging==In contrast to turbochargers, superchargers
are mechanically driven by the engine. Belts, chains, shafts, and gears are common
methods of powering a supercharger, placing a mechanical load on the engine. For example, on the single-stage single-speed
supercharged Rolls-Royce Merlin engine, the supercharger uses about 150 horsepower (110
kilowatts). Yet the benefits outweigh the costs; for the
150 hp (110 kW) to drive the supercharger the engine generates an additional 400-horsepower,
a net gain of 250 hp (190 kW). This is where the principal disadvantage of
a supercharger becomes apparent; the engine must withstand the net power output of the
engine plus the power to drive the supercharger. Another disadvantage of some superchargers
is lower adiabatic efficiency when compared with turbochargers (especially Roots-type
superchargers). Adiabatic efficiency is a measure of a compressor’s
ability to compress air without adding excess heat to that air. Even under ideal conditions, the compression
process always results in elevated output temperature; however, more efficient compressors
produce less excess heat. Roots superchargers impart significantly more
heat to the air than turbochargers. Thus, for a given volume and pressure of air,
the turbocharged air is cooler, and as a result denser, containing more oxygen molecules,
and therefore more potential power than the supercharged air. In practical application the disparity between
the two can be dramatic, with turbochargers often producing 15% to 30% more power based
solely on the differences in adiabatic efficiency (however, due to heat transfer from the hot
exhaust, considerable heating does occur). By comparison, a turbocharger does not place
a direct mechanical load on the engine, although turbochargers place exhaust back pressure
on engines, increasing pumping losses. This is more efficient because while the increased
back pressure taxes the piston exhaust stroke, much of the energy driving the turbine is
provided by the still-expanding exhaust gas that would otherwise be wasted as heat through
the tailpipe. In contrast to supercharging, the primary
disadvantage of turbocharging is what is referred to as “lag” or “spool time”. This is the time between the demand for an
increase in power (the throttle being opened) and the turbocharger(s) providing increased
intake pressure, and hence increased power. Throttle lag occurs because turbochargers
rely on the buildup of exhaust gas pressure to drive the turbine. In variable output systems such as automobile
engines, exhaust gas pressure at idle, low engine speeds, or low throttle is usually
insufficient to drive the turbine. Only when the engine reaches sufficient speed
does the turbine section start to spool up, or spin fast enough to produce intake pressure
above atmospheric pressure. A combination of an exhaust-driven turbocharger
and an engine-driven supercharger can mitigate the weaknesses of both. This technique is called twincharging. In the case of Electro-Motive Diesel’s two-stroke
engines, the mechanically assisted turbocharger is not specifically a twincharger, as the
engine uses the mechanical assistance to charge air only at lower engine speeds and startup. Once above notch # 5, the engine uses true
turbocharging. This differs from a turbocharger that uses
the compressor section of the turbo-compressor only during starting and, as a two-stroke
engines cannot naturally aspirate, and, according to SAE definitions, a two-stroke engine with
a mechanically assisted compressor during idle and low throttle is considered naturally
aspirated.==Operating principle==In naturally aspirated piston engines, intake
gases are drawn or “pushed” into the engine by atmospheric pressure filling the volumetric
void caused by the downward stroke of the piston (which creates a low-pressure area),
similar to drawing liquid using a syringe. The amount of air actually inspired, compared
with the theoretical amount if the engine could maintain atmospheric pressure, is called
volumetric efficiency. The objective of a turbocharger is to improve
an engine’s volumetric efficiency by increasing density of the intake gas (usually air) allowing
more power per engine cycle. The turbocharger’s compressor draws in ambient
air and compresses it before it enters into the intake manifold at increased pressure. This results in a greater mass of air entering
the cylinders on each intake stroke. The power needed to spin the centrifugal compressor
is derived from the kinetic energy of the engine’s exhaust gases.In automotive applications,
‘boost’ refers to the amount by which intake manifold pressure exceeds atmospheric pressure. This is representative of the extra air pressure
that is achieved over what would be achieved without the forced induction. The level of boost may be shown on a pressure
gauge, usually in bar, psi or possibly kPa. The control of turbocharger boost has changed
dramatically over the 100-plus years of their use. Modern turbochargers can use wastegates, blow-off
valves and variable geometry, as discussed in later sections. In petrol engine turbocharger applications,
boost pressure is limited to keep the entire engine system, including the turbocharger,
inside its thermal and mechanical design operating range. Over-boosting an engine frequently causes
damage to the engine in a variety of ways including pre-ignition, overheating, and over-stressing
the engine’s internal hardware. For example, to avoid engine knocking (also
known as detonation) and the related physical damage to the engine, the intake manifold
pressure must not get too high, thus the pressure at the intake manifold of the engine must
be controlled by some means. Opening the wastegate allows the excess energy
destined for the turbine to bypass it and pass directly to the exhaust pipe, thus reducing
boost pressure. The wastegate can be either controlled manually
(frequently seen in aircraft) or by an actuator (in automotive applications, it is often controlled
by the engine control unit).===Pressure increase (or boost)===
A turbocharger may also be used to increase fuel efficiency without increasing power. This is achieved by diverting exhaust waste
energy, from the combustion process, and feeding it back into the turbo’s “hot” intake side
that spins the turbine. As the hot turbine side is being driven by
the exhaust energy, the cold intake turbine (the other side of the turbo) compresses fresh
intake air and drives it into the engine’s intake. By using this otherwise wasted energy to increase
the mass of air, it becomes easier to ensure that all fuel is burned before being vented
at the start of the exhaust stage. The increased temperature from the higher
pressure gives a higher Carnot efficiency. A reduced density of intake air is caused
by the loss of atmospheric density seen with elevated altitudes. Thus, a natural use of the turbocharger is
with aircraft engines. As an aircraft climbs to higher altitudes,
the pressure of the surrounding air quickly falls off. At 18,000 feet (5,500 m), the air is at half
the pressure of sea level, which means that the engine produces less than half-power at
this altitude. In aircraft engines, turbocharging is commonly
used to maintain manifold pressure as altitude increases (i.e. to compensate for lower-density
air at higher altitudes). Since atmospheric pressure reduces as the
aircraft climbs, power drops as a function of altitude in normally aspirated engines. Systems that use a turbocharger to maintain
an engine’s sea-level power output are called turbo-normalized systems. Generally, a turbo-normalized system attempts
to maintain a manifold pressure of 29.5 inches of mercury (100 kPa).===Turbocharger lag===
Turbocharger lag (turbo lag) is the time required to change power output in response to a throttle
change, noticed as a hesitation or slowed throttle response when accelerating as compared
to a naturally aspirated engine. This is due to the time needed for the exhaust
system and turbocharger to generate the required boost which can also be referred to as spooling. Inertia, friction, and compressor load are
the primary contributors to turbocharger lag. Superchargers do not suffer this problem,
because the turbine is eliminated due to the compressor being directly powered by the engine. Turbocharger applications can be categorized
into those that require changes in output power (such as automotive) and those that
do not (such as marine, aircraft, commercial automotive, industrial, engine-generators,
and locomotives). While important to varying degrees, turbocharger
lag is most problematic in applications that require rapid changes in power output. Engine designs reduce lag in a number of ways: Lowering the rotational inertia of the turbocharger
by using lower radius parts and ceramic and other lighter materials
Changing the turbine’s aspect ratio Increasing upper-deck air pressure (compressor
discharge) and improving wastegate response Reducing bearing frictional losses, e.g.,
using a foil bearing rather than a conventional oil bearing
Using variable-nozzle or twin-scroll turbochargers Decreasing the volume of the upper-deck piping
Using multiple turbochargers sequentially or in parallel
Using an antilag system Using a turbocharger spool valve to increase
exhaust gas flow speed to the (twin-scroll) turbineSometimes turbo lag is mistaken for
engine speeds that are below boost threshold. If engine speed is below a turbocharger’s
boost threshold rpm then the time needed for the vehicle to build speed and rpm could be
considerable, maybe even tens of seconds for a heavy vehicle starting at low vehicle speed
in a high gear. This wait for vehicle speed increase is not
turbo lag, it is improper gear selection for boost demand. Once the vehicle reaches sufficient speed
to provide the required rpm to reach boost threshold, there will be a far shorter delay
while the turbo itself builds rotational energy and transitions to positive boost, only this
last part of the delay in achieving positive boost is the turbo lag.===Boost threshold===
The boost threshold of a turbocharger system is the lower bound of the region within which
the compressor operates. Below a certain rate of flow, a compressor
produces insignificant boost. This limits boost at a particular RPM, regardless
of exhaust gas pressure. Newer turbocharger and engine developments
have steadily reduced boost thresholds. Electrical boosting (“E-boosting”) is a new
technology under development. It uses an electric motor to bring the turbocharger
up to operating speed quicker than possible using available exhaust gases. An alternative to e-boosting is to completely
separate the turbine and compressor into a turbine-generator and electric-compressor
as in the hybrid turbocharger. This makes compressor speed independent of
turbine speed. In 1981, a similar system that used a hydraulic
drive system and overspeed clutch arrangement accelerated the turbocharger of the MV Canadian
Pioneer (Doxford 76J4CR engine).Turbochargers start producing boost only when a certain
amount of kinetic energy is present in the exhaust gasses. Without adequate exhaust gas flow to spin
the turbine blades, the turbocharger cannot produce the necessary force needed to compress
the air going into the engine. The boost threshold is determined by the engine
displacement, engine rpm, throttle opening, and the size of the turbocharger. The operating speed (rpm) at which there is
enough exhaust gas momentum to compress the air going into the engine is called the “boost
threshold rpm”. Reducing the “boost threshold rpm” can improve
throttle response.==Key components==
The turbocharger has three main components: The turbine, which is almost always a radial
inflow turbine (but is almost always a single-stage axial inflow turbine in large Diesel engines)
The compressor, which is almost always a centrifugal compressor
The center housing/hub rotating assemblyMany turbocharger installations use additional
technologies, such as wastegates, intercooling and blow-off valves.===Turbine===Energy provided for the turbine work is converted
from the enthalpy and kinetic energy of the gas. The turbine housings direct the gas flow through
the turbine as it spins at up to 250,000 rpm. The size and shape can dictate some performance
characteristics of the overall turbocharger. Often the same basic turbocharger assembly
is available from the manufacturer with multiple housing choices for the turbine, and sometimes
the compressor cover as well. This lets the balance between performance,
response, and efficiency be tailored to the application. The turbine and impeller wheel sizes also
dictate the amount of air or exhaust that can flow through the system, and the relative
efficiency at which they operate. In general, the larger the turbine wheel and
compressor wheel the larger the flow capacity. Measurements and shapes can vary, as well
as curvature and number of blades on the wheels. A turbocharger’s performance is closely tied
to its size. Large turbochargers take more heat and pressure
to spin the turbine, creating lag at low speed. Small turbochargers spin quickly, but may
not have the same performance at high acceleration. To efficiently combine the benefits of large
and small wheels, advanced schemes are used such as twin-turbochargers, twin-scroll turbochargers,
or variable-geometry turbochargers.====Twin-turbo====Twin-turbo or bi-turbo designs have two separate
turbochargers operating in either a sequence or in parallel. In a parallel configuration, both turbochargers
are fed one-half of the engine’s exhaust. In a sequential setup one turbocharger runs
at low speeds and the second turns on at a predetermined engine speed or load. Sequential turbochargers further reduce turbo
lag, but require an intricate set of pipes to properly feed both turbochargers. Two-stage variable twin-turbos employ a small
turbocharger at low speeds and a large one at higher speeds. They are connected in a series so that boost
pressure from one turbocharger is multiplied by another, hence the name “2-stage.” The distribution of exhaust gas is continuously
variable, so the transition from using the small turbocharger to the large one can be
done incrementally. Twin turbochargers are primarily used in Diesel
engines. For example, in Opel bi-turbo Diesel, only
the smaller turbocharger works at low speed, providing high torque at 1,500–1,700 rpm. Both turbochargers operate together in mid
range, with the larger one pre-compressing the air, which the smaller one further compresses. A bypass valve regulates the exhaust flow
to each turbocharger. At higher speed (2,500 to 3,000 RPM) only
the larger turbocharger runs.Smaller turbochargers have less turbo lag than larger ones, so often
two small turbochargers are used instead of one large one. This configuration is popular in engines over
2,500 CCs and in V-shape or boxer engines.====Twin-scroll====
Twin-scroll or divided turbochargers have two exhaust gas inlets and two nozzles, a
smaller sharper angled one for quick response and a larger less angled one for peak performance. With high-performance camshaft timing, exhaust
valves in different cylinders can be open at the same time, overlapping at the end of
the power stroke in one cylinder and the end of exhaust stroke in another. In twin-scroll designs, the exhaust manifold
physically separates the channels for cylinders that can interfere with each other, so that
the pulsating exhaust gasses flow through separate spirals (scrolls). With common firing order 1–3–4–2, two
scrolls of unequal length pair cylinders 1 and 4, and 3 and 2. This lets the engine efficiently use exhaust
scavenging techniques, which decreases exhaust gas temperatures and NO x emissions, improves
turbine efficiency, and reduces turbo lag evident at low engine speeds.====Variable-geometry====Variable-geometry or variable-nozzle turbochargers
use moveable vanes to adjust the air-flow to the turbine, imitating a turbocharger of
the optimal size throughout the power curve. The vanes are placed just in front of the
turbine like a set of slightly overlapping walls. Their angle is adjusted by an actuator to
block or increase air flow to the turbine. This variability maintains a comparable exhaust
velocity and back pressure throughout the engine’s rev range. The result is that the turbocharger improves
fuel efficiency without a noticeable level of turbocharger lag.===Compressor===
The compressor increases the mass of intake air entering the combustion chamber. The compressor is made up of an impeller,
a diffuser and a volute housing. The operating range of a compressor is described
by the “compressor map”. Ported shroud The flow range of a turbocharger compressor
can be increased by allowing air to bleed from a ring of holes or a circular groove
around the compressor at a point slightly downstream of the compressor inlet (but far
nearer to the inlet than to the outlet). The ported shroud is a performance enhancement
that allows the compressor to operate at significantly lower flows. It achieves this by forcing a simulation of
impeller stall to occur continuously. Allowing some air to escape at this location
inhibits the onset of surge and widens the operating range. While peak efficiencies may decrease, high
efficiency may be achieved over a greater range of engine speeds. Increases in compressor efficiency result
in slightly cooler (more dense) intake air, which improves power. This is a passive structure that is constantly
open (in contrast to compressor exhaust blow off valves, which are mechanically or electronically
controlled). The ability of the compressor to provide high
boost at low rpm may also be increased marginally (because near choke conditions the compressor
draws air inward through the bleed path). Ported shrouds are used by many turbocharger
manufacturers.===Center housing/hub rotating assembly===
The center hub rotating assembly (CHRA) houses the shaft that connects the compressor impeller
and turbine. It also must contain a bearing system to suspend
the shaft, allowing it to rotate at very high speed with minimal friction. For instance, in automotive applications the
CHRA typically uses a thrust bearing or ball bearing lubricated by a constant supply of
pressurized engine oil. The CHRA may also be considered “water-cooled”
by having an entry and exit point for engine coolant. Water-cooled models use engine coolant to
keep lubricating oil cooler, avoiding possible oil coking (destructive distillation of engine
oil) from the extreme heat in the turbine. The development of air-foil bearings removed
this risk. Ball bearings designed to support high speeds
and temperatures are sometimes used instead of fluid bearings to support the turbine shaft. This helps the turbocharger accelerate more
quickly and reduces turbo lag. Some variable nozzle turbochargers use a rotary
electric actuator, which uses a direct stepper motor to open and close the vanes, rather
than pneumatic controllers that operate based on air pressure.==Additional technologies commonly used in
turbocharger installations=====
Intercooling===When the pressure of the engine’s intake air
is increased, its temperature also increases. This occurrence can be explained through Gay-Lussac’s
law, stating that the pressure of a given amount of gas held at constant volume is directly
proportional to the Kelvin temperature. With more pressure being added to the engine
through the turbocharger, overall temperatures of the engine will also rise. In addition, heat soak from the hot exhaust
gases spinning the turbine will also heat the intake air. The warmer the intake air, the less dense,
and the less oxygen available for the combustion event, which reduces volumetric efficiency. Not only does excessive intake-air temperature
reduce efficiency, it also leads to engine knock, or detonation, which is destructive
to engines. To compensate for the increase in temperature,
turbocharger units often make use of an intercooler between successive stages of boost to cool
down the intake air. A charge air cooler is an air cooler between
the boost stage(s) and the appliance that consumes the boosted air.===Top-mount (TMIC) vs. front-mount intercoolers
(FMIC)===There are two areas on which intercoolers
are commonly mounted. It can be either mounted on top, parallel
to the engine, or mounted near the lower front of the vehicle. Top-mount intercoolers setups will result
in a decrease in turbo lag, due in part by the location of the intercooler being much
closer to the turbocharger outlet and throttle body. This closer proximity reduces the time it
takes for air to travel through the system, producing power sooner, compared to that of
a front-mount intercooler which has more distance for the air to travel to reach the outlet
and throttle.Front-mount intercoolers can have the potential to give better cooling
compared to that of a top-mount. The area in which a top-mounted intercooler
is located, is near one of the hottest areas of a car, right above the engine. This is why most manufacturers include large
hood scoops to help feed air to the intercooler while the car is moving, but while idle, the
hood scoop provides little to no benefit. Even while moving, when the atmospheric temperatures
begin to rise, top-mount intercoolers tend to underperform compared to front-mount intercoolers. With more distance to travel, the air circulated
through a front-mount intercooler may have more time to cool.===Water injection===An alternative to intercooling is injecting
water into the intake air to reduce the temperature. This method has been used in automotive and
aircraft applications.===Methanol Injection===
Methanol/water injection has been around since the 1920s but was not utilized until World
War II. Adding the mixture to intake of the turbocharged
engines decreased operating temperatures and increased horse power. Turbocharged engines today run high boost
and high engine temperatures to match. When injecting the mixture into the intake
stream, the air is cooled as the liquids evaporate. Inside the combustion chamber it slows the
flame, acting similar to higher octane fuel. Methanol/water mixture allows for higher compression
because of the less detonation-prone and, thus, safer combustion inside the engine.===Fuel-air mixture ratio===In addition to the use of intercoolers, it
is common practice to add extra fuel to the intake air (known as “running an engine rich”)
for the sole purpose of cooling. The amount of extra fuel varies, but typically
reduces the air-fuel ratio to between 11 and 13, instead of the stoichiometric 14.7 (in
petrol engines). The extra fuel is not burned (as there is
insufficient oxygen to complete the chemical reaction), instead it undergoes a phase change
from atomized (liquid) to gas. This phase change absorbs heat, and the added
mass of the extra fuel reduces the average thermal energy of the charge and exhaust gas. Even when a catalytic converter is used, the
practice of running an engine rich increases exhaust emissions.===Wastegate===A wastegate regulates the exhaust gas flow
that enters the exhaust-side driving turbine and therefore the air intake into the manifold
and the degree of boosting. It can be controlled by a boost pressure assisted,
generally vacuum hose attachment point diaphragm (for vacuum and positive pressure to return
commonly oil contaminated waste to the emissions system) to force the spring-loaded diaphragm
to stay closed until the overboost point is sensed by the ecu or a solenoid operated by
the engine’s electronic control unit or a boost controller, but most production vehicles
use a single vacuum hose attachment point spring-loaded diaphragm that can alone be
pushed open, thus limiting overboost ability due to exhaust gas pressure forcing open the
wastegate.===Anti-surge/dump/blow off valves===Turbocharged engines operating at wide open
throttle and high rpm require a large volume of air to flow between the turbocharger and
the inlet of the engine. When the throttle is closed, compressed air
flows to the throttle valve without an exit (i.e., the air has nowhere to go). In this situation, the surge can raise the
pressure of the air to a level that can cause damage. This is because if the pressure rises high
enough, a compressor stall occurs—stored pressurized air decompresses backward across
the impeller and out the inlet. The reverse flow back across the turbocharger
makes the turbine shaft reduce in speed more quickly than it would naturally, possibly
damaging the turbocharger. To prevent this from happening, a valve is
fitted between the turbocharger and inlet, which vents off the excess air pressure. These are known as an anti-surge, diverter,
bypass, turbo-relief valve, blow-off valve (BOV), or dump valve. It is a pressure relief valve, and is normally
operated by the vacuum from the intake manifold. The primary use of this valve is to maintain
the spinning of the turbocharger at a high speed. The air is usually recycled back into the
turbocharger inlet (diverter or bypass valves), but can also be vented to the atmosphere (blow
off valve). Recycling back into the turbocharger inlet
is required on an engine that uses a mass-airflow fuel injection system, because dumping the
excessive air overboard downstream of the mass airflow sensor causes an excessively
rich fuel mixture—because the mass-airflow sensor has already accounted for the extra
air that is no longer being used. Valves that recycle the air also shorten the
time needed to re-spool the turbocharger after sudden engine deceleration, since load on
the turbocharger when the valve is active is much lower than if the air charge vents
to atmosphere.===Free floating===
A free floating turbocharger is the simplest type of turbocharger. This configuration has no wastegate and cannot
control its own boost levels. They are typically designed to attain maximum
boost at full throttle. Free floating turbochargers produce more horsepower
because they have less backpressure, but are not driveable in performance applications
without an external wastegate.==Applications=====Petrol-powered cars===The first turbocharged passenger car was the
Oldsmobile Jetfire option on the 1962–1963 F85/Cutlass, which used a turbocharger mounted
to a 215 cu in (3.52 L) all aluminum V8. Also in 1962, Chevrolet introduced a special
run of turbocharged Corvairs, initially called the Monza Spyder (1962–1964) and later renamed
the Corsa (1965–1966), which mounted a turbocharger to its air cooled flat six cylinder engine. This model popularized the turbocharger in
North America—and set the stage for later turbocharged models from Porsche on
the 1975-up 911/930, Saab on the 1978–1984 Saab 99 Turbo, and the very popular 1978–1987
Buick Regal/T Type/Grand National. Today, turbocharging is common on both diesel
and gasoline-powered cars. Turbocharging can increase power output for
a given capacity or increase fuel efficiency by allowing a smaller displacement engine. The ‘Engine of the year 2011’ is an engine
used in a Fiat 500 equipped with an MHI turbocharger. This engine lost 10% weight, saving up to
30% in fuel consumption while delivering the same HP (105) as a 1.4 litre engine.===Diesel-powered cars===The first production turbocharger diesel passenger
car was the Garrett-turbocharged Mercedes 300SD introduced in 1978. Today, most automotive diesels are turbocharged,
since the use of turbocharging improved efficiency, driveability and performance of diesel engines,
greatly increasing their popularity. The Audi R10 with a diesel engine even won
the 24 hours race of Le Mans in 2006, 2007 and 2008.===Motorcycles===The first example of a turbocharged bike is
the 1978 Kawasaki Z1R TC. Several Japanese companies produced turbocharged
high-performance motorcycles in the early 1980s, such as the CX500 Turbo from Honda-
a transversely mounted, liquid cooled V-Twin also available in naturally aspirated form. Since then, few turbocharged motorcycles have
been produced. This is partially due to an abundance of larger
displacement, naturally aspirated engines being available that offer the torque and
power benefits of a smaller displacement engine with turbocharger, but do return more linear
power characteristics. The Dutch manufacturer EVA motorcycles builds
a small series of turbocharged diesel motorcycle with an 800cc smart CDI engine.===Trucks===
The first turbocharged diesel truck was produced by Schweizer Maschinenfabrik Saurer (Swiss
Machine Works Saurer) in 1938.===Aircraft===
A natural use of the turbocharger—and its
earliest known use for any internal combustion engine, starting with experimental installations
in the 1920s—is with aircraft engines. As an aircraft climbs to higher altitudes
the pressure of the surrounding air quickly falls off. At 5,486 m (18,000 ft), the air is at half
the pressure of sea level and the airframe experiences only half the aerodynamic drag. However, since the charge in the cylinders
is pushed in by this air pressure, the engine normally produces only half-power at full
throttle at this altitude. Pilots would like to take advantage of the
low drag at high altitudes to go faster, but a naturally aspirated engine does not produce
enough power at the same altitude to do so. The table below is used to demonstrate the
wide range of conditions experienced. As seen in the table below, there is significant
scope for forced induction to compensate for lower density environments. A turbocharger remedies this problem by compressing
the air back to sea-level pressures (turbo-normalizing), or even much higher (turbo-charging), in order
to produce rated power at high altitude. Since the size of the turbocharger is chosen
to produce a given amount of pressure at high altitude, the turbocharger is oversized for
low altitude. The speed of the turbocharger is controlled
by a wastegate. Early systems used a fixed wastegate, resulting
in a turbocharger that functioned much like a supercharger. Later systems utilized an adjustable wastegate,
controlled either manually by the pilot or by an automatic hydraulic or electric system. When the aircraft is at low altitude the wastegate
is usually fully open, venting all the exhaust gases overboard. As the aircraft climbs and the air density
drops, the wastegate must continuously close in small increments to maintain full power. The altitude at which the wastegate fully
closes and the engine still produces full power is the critical altitude. When the aircraft climbs above the critical
altitude, engine power output decreases as altitude increases, just as it would in a
naturally aspirated engine. With older supercharged aircraft without Automatic
Boost Control, the pilot must continually adjust the throttle to maintain the required
manifold pressure during ascent or descent. The pilot must also take care to avoid over-boosting
the engine and causing damage. In contrast, modern turbocharger systems use
an automatic wastegate, which controls the manifold pressure within parameters preset
by the manufacturer. For these systems, as long as the control
system is working properly and the pilot’s control commands are smooth and deliberate,
a turbocharger cannot over-boost the engine and damage it. Yet the majority of World War II engines used
superchargers, because they maintained three significant manufacturing advantages over
turbochargers, which were larger, involved extra piping, and required exotic high-temperature
materials in the turbine and pre-turbine section of the exhaust system. The size of the piping alone is a serious
issue; American fighters Vought F4U and Republic P-47 used the same engine, but the huge barrel-like
fuselage of the latter was, in part, needed to hold the piping to and from the turbocharger
in the rear of the plane. Turbocharged piston engines are also subject
to many of the same operating restrictions as gas turbine engines. Pilots must make smooth, slow throttle adjustments
to avoid overshooting their target manifold pressure. The fuel/air mixture must often be adjusted
far on the rich side of stoichiometric combustion needs to avoid pre-ignition or detonation
in the engine when running at high power settings. In systems using a manually operated wastegate,
the pilot must be careful not to exceed the turbocharger’s maximum rpm. The additional systems and piping increase
an aircraft engine’s size, weight, complexity and cost. A turbocharged aircraft engine costs more
to maintain than a comparable normally aspirated engine. The great majority of World War II American
heavy bombers used by the USAAF, particularly the Wright R-1820 Cyclone-9 powered B-17 Flying
Fortress, and Pratt & Whitney R-1830 Twin Wasp powered Consolidated B-24 Liberator four-engine
bombers both used similar models of General Electric-designed turbochargers in service,
as did the twin Allison V-1710-engined Lockheed P-38 Lightning American heavy fighter during
the war years. All of the above WWII aircraft engines had
mechanically driven centrifugal superchargers as-designed from the start, and the turbosuperchargers
(with intercoolers) were added, effectively as twincharger systems, to achieve desired
altitude performance. Today, most general aviation piston engine
powered aircraft are naturally aspirated. Modern aviation piston engines designed to
run at high altitudes typically include a turbocharger (either high pressure or turbonormalized)
rather than a supercharger. The change in thinking is largely due to economics. Aviation gasoline was once plentiful and cheap,
favoring the simple, but fuel-hungry, supercharger. As the cost of fuel has increased, the supercharger
has fallen out of favor. Turbocharged aircraft often occupy a performance
range between that of normally aspirated piston-powered aircraft and turbine-powered aircraft. Despite the negative points, turbocharged
aircraft fly higher for greater efficiency. High cruise flight also allows more time to
evaluate issues before a forced landing must be made. As the turbocharged aircraft climbs, however,
the pilot (or automated system) can close the wastegate, forcing more exhaust gas through
the turbocharger turbine, thereby maintaining manifold pressure during the climb, at least
until the critical pressure altitude is reached (when the wastegate is fully closed), after
which manifold pressure falls. With such systems, modern high-performance
piston engine aircraft can cruise at altitudes up to 25,000 feet (above which, RVSM certification
would be required), where low air density results in lower drag and higher true airspeeds. This allows flying “above the weather”. In manually controlled wastegate systems,
the pilot must take care not to overboost the engine, which causes detonation, leading
to engine damage.===Marine and land-based diesel turbochargers
===Turbocharging, which is common on diesel engines
in automobiles, trucks, tractors, and boats is also common in heavy machinery such as
locomotives, ships, and auxiliary power generation. Turbocharging can dramatically improve an
engine’s specific power and power-to-weight ratio, performance characteristics that are
normally poor in non-turbocharged diesel engines. diesel engines have no detonation because
diesel fuel is injected at or towards the end of the compression stroke and is ignited
solely by the heat of compression of the charge air. Because of this, diesel engines can use a
much higher boost pressure than spark ignition engines, limited only by the engine’s ability
to withstand the additional heat and pressure.Turbochargers are also employed in certain two-stroke cycle
diesel engines, which would normally require a Roots blower for aspiration. In this specific application, mainly Electro-Motive
Diesel (EMD) 567, 645, and 710 Series engines, the turbocharger is initially driven by the
engine’s crankshaft through a gear train and an overrunning clutch, thereby providing aspiration
for combustion. After combustion has been achieved, and after
the exhaust gases have reached sufficient heat energy, the overrunning clutch is automatically
disengaged, and the turbo-compressor is thereafter driven exclusively by the exhaust gases. In the EMD application, the turbocharger acts
as a compressor for normal aspiration during starting and low power output settings and
is used for true turbocharging during medium and high power output settings. This is particularly beneficial at high altitudes,
as are often encountered on western U.S. railroads. It is possible for the turbocharger to revert
to compressor mode momentarily during commands for large increases in engine power.==Business and adoption==
Honeywell Turbo Technologies, Borg Warner and Mitsubishi Turbocharger are the largest
manufacturers in Europe and the United States. Several factors are expected to contribute
to more widespread consumer adoption of turbochargers, especially in the US:
New government fuel economy and emissions targets. Increasing oil prices and a consumer focus
on fuel efficiency. Only 10 percent of light vehicles sold in
the United States are equipped with turbochargers, making the United States an emerging market,
compared with 50 percent of vehicles in Europe that are turbocharged diesel and 27 percent
that are gasoline boosted. Higher temperature tolerances for gasoline
engines, ball bearings in the turbine shaft and variable geometry have reduced driveability
concerns.In 2014, 21 percent of vehicles sold in North America were turbocharged, which
is expected to grow to 38 percent by 2019. In Europe 67 percent of all vehicles were
turbocharged in 2014, which is expected to grow to 69 percent by 2019. Historically, more than 90 percent of turbochargers
were diesel, however, adoption in gasoline engines is increasing.The U.S. Coalition for
Advanced Diesel Cars is pushing for a technology neutral policy for government subsidies of
environmentally friendly automotive technology. If successful, government subsidies would
be based on the Corporate Average Fuel Economy (CAFE) standards rather than supporting specific
technologies like electric cars. Political shifts could drastically change
adoption projections. Turbocharger sales in the United States increased
when the federal government boosted corporate average fuel economy targets to 35.5 mpg by
2016.==Safety==
Turbocharger failures and resultant high exhaust temperatures are among the causes of car fires.==See also==
Boost gauge Engine downsizing
Exhaust pulse pressure charging Hybrid turbocharger
Twin-turbo Twincharger
Variable-geometry turbocharger