- Bentley W12 Twin-Turbocharged Engine

A brief history of turbocharging

T​urbocharging is widely used in the automotive industry to lower exhaust emissions & to improve the fuel efficiency and power output of the engine

A brief history of the combusion engine

Jean Joseph Lenoir engine

Jean Joseph Lenoir engine

Back in 1860, Belgian inventor called Jean Joseph Lenoir came up with the first working engine. After many attempts he managed to develop a system in which the pistons sliding inside a cylinder connected to a rod mounted on a crankshaft that rotates a flywheel fast enough to provide momentum to power a vehicle.

Nicolaus August Otto four-cycle engine

Nicolaus August Otto four-cycle engine

In 1876, German engineer Nikolaus Otto came up with a four-cycle engine based on the findings of Jean Joseph Lenoir. This engine announced the forthcoming of the modern combustion engines.

In 1885, German engineer Gottieib Daimler and his fellow countryman Wilhelm Maybach invented the carburettor to allow forceful induction of the air and fuel mixture in to the cylinder.

1886 Daimler Motorized Carriage

1886 Daimler Motorized Carriage

In 1900 at the Exposition Universell fair in Paris, Rudolf Diesel demonstrated his engine concept. This engine used an open flame in a tube or a spark inside the cylinder to burn the gasoline and fuel mixture.

This combustion engine developed by Rudolf Diesel is a compression engine and was commonly known as the spark ignition engine. This creation relied on extremely high pressure at the cylinder chamber. It had almost six times the compression ratio of the internal combustion engine developed by Nikolaus Otto, thus allowing the intense heat to ignite the fuel.

Diesel engine

Diesel engine

Most of the engines are falling under the internal combustion category. Internal combustion engines are also known as normally aspirated or naturally aspirated engines. What happens is the engines inhale air when needed to mix with fuel to allow combustion. The air and fuel mixture then enters the engine through carburettors or a fuel injection system at the atmospheric pressure rated at one bar. One bar pressure is equivalent to 14.5 pounds per square inch or 14.5psi at sea level.

S​upercharging and Turbocharging

Turbocharger internal structure. Image credit goes to Terry Wha at creativecommons

Turbocharger internal structure. Image credit goes to Terry Wha at creativecommons

With time, the more powerful engines were required to get certain tasks done. This also meant that more aggressive forced induction engines required engine belts, chains, gears or an engine crankshaft to drive them. Supercharging systems were developed to address the more demanding compression requirements. Over the decades the supercharging system evolved and improved.

In supercharging systems the air density is increased by increasing its pressure before entering the engine cylinder.

The first method to get this done is the use of a mechanical supercharging system in which a separate pump or compressor being driven by the power taken from the engine thus providing compressed air.

The second method is known as turbocharging. In this a compressor and a turbine on a single shaft is used to boost the inlet air/air and fuel mixture density. The kinetic energy available in the engine's exhaust system is then used to drive the turbocharger turbine. This then drives the turbocharger compressor, raising the inlet fluid density before it enters to each cylinder.

An intercooler or an aftercooler system is then used to cool the fluid after compression, before entering the cylinder, can be used to further increase the air/ air and fuel mixture density.

Turbocharging system was invented by a Swiss engineer called Alfred Buchi in 1905 while working for the Gebrüder Sulzer. Rudolf Diesel interned years before going on his own way to develop the Diesel engine. Alfred Buchi came up with a new way to increase the flow of the fuel and air mixture to the cylinders, thus increasing the performance. His patent was described as an exhaust driven turbo supercharger for internal combustion engines or as a pre-compressor for the cylinders through a cooling system of inlet air and fuel mixture.

In 1915 he finished the first prototype. This was suppose to solve the loss of power experienced by aircraft engines due to decreased density of air at high altitudes. However, the system wasn't a success due to reliability issues, and required constant developments and research.

In 1916, French engineer Auguste Rateau applied for a patent for a turbocharging solution that could be applied for Renault engines to use them on French fighter planes.

In 1917, a separate testing done by the American National Advisory Committee for Aeronautics and aviation engineer Sanford Alexander Moss concluded that a turbocharger could enable an engine to avoid any power interruption or loss at an altitude of almost 14,000 ft above sea level. The testing was done at Pikes Peak using a V12 Liberty aircraft engine.

Eventually in 1925, Alfred Buchi successfully implemented turbochargers on several ten-cylinder diesel engines. The diesel engines showed clear increase in power output from 1750hp to 2500hp. This engine was then used by the German Ministry of Transport to power two large passenger ships known as Hansestadt Danzig and Preussen. This is considered as the first ever commercial application of a turbocharger. The design was then licensed to several manufacturers.

Turbocharging systems showed up on large marine diesel engines that powered war ships that were built in between WW1 and WW2. Aircraft manufacturers also adopted the turbocharging system from early on due to the added advantages.

Before WW2, aircraft manufacturers used turbochargers to increase power and also to raise the service ceilings for their engines as the compression recreated the atmospheric air pressure at much lower altitudes.

Turbocharged aircraft engines were widely used in WW2 era piston engine powered fighters and high altitude long range bombers. Even though these early systems required considerable amount of extra plumbing and hardware, the advantages of such system convinced the manufacturers to adopt.

Boeing B-17 Flying Fortress

Boeing B-17 Flying Fortress

The amount of extra plumbing and hardware occupied a considerable amount of space and added considerable amount of weight but its ability to maintain high power output even at 30,000 or even higher altitudes made them necessary for high speed dog fighting and long rage heavy weight bomb raids.

Boeing B-17 Flying Fortress was powered with a turbocharged R-1820-97 Cyclone radial engines packing 1200hp each. Service ceiling was now measured at 35,600 ft. B-17 was equipped with turbochargers made by General Electric.

The Consolidated B-24 Liberator was equipped with four Prat and Whitney R-1830 Twin Wasp turbocharged engines, packing 1200hp each. Service ceiling was 28,000 ft.

1942 Consolidated B-24 Liberator

1942 Consolidated B-24 Liberator

Lockheed P-38H Lightning was equipped with an Allison V-17 10-113 turbocharged V12 engine. The maximum power output was measured at 1600hp and the service ceiling is an impressive 44,000 ft.

Focke-Wulf Fw 190, an experimental aircraft produced by the Germans also used turbocharged aeroplane engines.

First practical application for diesel truck engines.

In 1938, Adolph Saurer A.G developed and unveiled an all new D1 KT turbocharged diesel engines to power commercial trucks. BXD and BZD engines were manufactured with optional turbocharging since 1931. Swiss manufacturers like Sulzer, Saurer and Brown, Boveri and Cie, and ASEA Brown Boveri played a pioneering role in the development of the turbocharged engines.

Turbocharging wasn't much used automobiles due to the added complexity, costs, weight, and various technical issues.

T​urbocharging for motorsport events.

1952 cummins diesel special

1952 cummins diesel special

In 1950, the Cummins Engine manufacturers came up with an aluminium-block JS 600 diesel engines to compete in the Indianapolis 500 event. This inline-six 401 cubic inch engine attached to a gear driven Roots type blower delivered 345 horsepower maximum at 4000rpm, allowing the racer to record a 129.2mph top speed in the qualifying sessions.

As a prototype, the car had to be placed at the back of the thirty six entrants, yet managed to achieve sixteenth overall position by the fifty second lap. A mechanical failure forced the racer to retire. Despite the setback and turbo lag, the advantages of the turbocharging system was evidant and this was just the beginning for the Cummins engineering team.

In 1952, a privateer called Fred Agabashian entered a Cummins diesel engine powered car with a further improved turbocharger system. This turbocharged NHH engine delivered 380 horsepower maximum at 2.1 bar boost pressure.

The NHH engine had an aluminium engine block and cylinder heads. The crankshaft was of magnesium built.

Kurtis Kraft was hired to design and manufacture the body of the racer with hours of wind tunnel testing to improve aerodynamics.

The inline-six engine was then mounted horizontally in the Kurtis Kraft racer body to improve weight distribution and centre of gravity.

The privateer qualified in the wheels of the car with a top speed of 139mph. In the event he ran for seventy one laps before tire debris from an other car got stuck in the low mounted air intake of the turbocharger, resulting in engine overheating and lack of power.

T​urbocharging in production cars

1962 Oldsmobile Jetfire

1962 Oldsmobile Jetfire

In 1962, GM unveiled the Oldsmobile Jetfire and Chevrolet Corvair Monza Spyder with Garrett Ai Research turbochargers. However, the engines soon turned out to be unreliable and expensive to maintain, forcing GM to retire the turbocharged Oldsmobile Jetfire in 1963 and turbocharged Chevrolet Corvair Monza in 1966. Despite their short lifespan these cars are considered as the first ever mass produced turbocharged road legal cars.

Chevrolet Corvair Monza convertible 1964

Chevrolet Corvair Monza convertible 1964

In 1973, BMW 2002 Turbo models made a sudden appearance and achieved a massive success in terms of both commercial and mechanical terms. Despite the reliability, and its effectiveness, the excessive turbo lag was still a issue.

1974 BMW 2002 Turbo

1974 BMW 2002 Turbo

The turbo lag is the delay that occurs during acceleration as exhaust pressure builds up enough to spin the turbo charger producing more horsepower. However, the turbo lag not only hurts in terms of speed, it also posed a risk to safety and overall drivability.

The main reason for this was the too much exhaust pressure that builds up when over speeding the turbocharger turbine and generating higher cylinder pressure levels. To address this issue, the engineers had to develop a bypass valve system or a wastegate as it is mostly known. This is usually built into the turbocharger casing and consists of a spring operated valve acting according to the inlet manifold pressure on a controlling diaphragm.

When the wastegate is open, a portion of the exhaust gas flows through the turbine and generates power while the remainder is passed directly into the exhaust system by passing the turbine.

According to the engineers, the exhaust temperatures of a typical engine can reach upto 1050-degrees Celsius or 1900-degrees Fahrenheit when it has a heavy load. Under similar conditions the turbocharger turbine can spin as fast as 150,000rpm.

To improve engine reliability and performance, intercooling systems were developed. Since it is impossible to compress air without heating unless the compressor is cooled, it is best to cool the air after delivery to the compressor and before the intake to the cylinders. This allows more fuel to be burnt since the charge density increases with aftercooling or intercooling. This also results in higher power output.

1974 BMW 2002 Turbo rear

1974 BMW 2002 Turbo rear

With the 1973 OPEC fuel embargo on Western countries resulted in massive economical and cultural downfall, reducing the demand for high performance vehicles due to the ever rising fuel charges and state enforced rationing system. Following the lack of demand, BMW withdrew the BMW 2002 Turbo cars at the end of the 1974 model year.

However, despite these setbacks Porsche unveiled their Porsche 911 Turbo after several years of absolute dominance of the World Championship events. Porsche 911 Turbo proved to be economical and reliable than most of the competitors, soon earning a reputation as highly capable racing machines.

Following the 1973 global oil crisis and 1977 Clean Air Act amendments, automobile manufacturers began to focus more on the implementation of turbocharged engines in automobiles due to the advantages such as reduced fuel consumption and exhaust emissions.

Turbocharger applications can be categorized into two main groups: those that require changes in power output such as automobiles, and those that do not such as aeroplanes, marine, engine powered industrial generators and locomotives.

Benefits of Turbocharging

renault RS01 the first turbocharged formula one car

renault RS01 the first turbocharged formula one car

A well engineered turbocharging system can deliver more power and torque than the naturally aspirated engines with identical engine displacement. More torque allows the car to accelerate faster.

Torque is a measure of the displacement of an engine to do work, while power is a measurement of the rate at the work is done.

Horsepower is a unit of measurement and one horsepower is equal to 550 pounds pressure per foot in a time span of just one second. Brake horsepower or bhp is the power output at the shaft of an engine or a motor.

When an engine is supercharged or turbocharged, it pressures the air and fuel mixture to the cylinder, resulting in an increased intensity of the spark ignited explosion. This results in more horsepower and more pressure on the piston connected to a rotating crankshaft. Since the crankshaft is receiving more pressure, it attributes more twisting energy or torque.

Even though the power and torque has a clear relationship, they do not happen in parallel . Engineers use computer based software algorithms and expensive sensors and equipment to calculate and observe the torque and power curves. They then do changes to make them meet and produce the targeted torque and horsepower to achieve precise fuel economy, emissions, and performance.

This sort of work requires an unprecedented amount of discipline and commitment. This is where Porsche outshines its competitors.

Unlike many other manufacturers, Porsche engineers do not attempt to just outperform their competition. What they do is constantly developing and improving the car to perform better than the previous generation car and by making that happen, their cars become more reliable and practical than the likes of Lamborghini and Ferrari.

Porsche do not create cars that other people want to drive. They create cars that they want to drive because they are enthusiasts and who knows the heart of a fellow enthusiasts than another enthusiast.

Turbo Lag in details

Turbo lag is the delay or time it takes to change power output in response to a throttle input. This can be noticed as a slowed throttle response when accelerating when compared to a naturally aspirated engine.

In variable output systems such as automobile engines exhaust pressure at idle, or low engine speeds, or low throttle is usually insufficient to operate the turbine. When the engine reaches sufficient speed, the turbine starts to spool up or spin fast enough to make intake pressure higher above atmospheric pressure.

The reason for turbo-lag is due to the time it takes for the exhaust system and turbocharger to generate the required boost which is also known as spooling. Turbo lag is caused mainly due to the friction, inertia, and compressor load.

Superchargers do not suffer this problem as it is being directly powered by the engine.

To address the turbo lag, engineers implement various engine designs such as lowering the rotational inertia of the turbocharger by the use of lower radius parts and other lightweight materials, increasing compressor discharge and improving wastegate response, reducing bearing friction, changing the turbocharger turbines aspect ratio, the use of variable-nozzle or twin-scroll turbochargers, using an anti-lag system, using a spool valve to increase exhaust gas flow speed to the twin-scroll turbine, and using multiple turbochargers sequentially or in parallel.

Turbocharging versus Supercharging

Inline Six Turbocharged 1980. C @ Hugo-90 creative commons

Inline Six Turbocharged 1980. C @ Hugo-90 creative commons

When the turbochargers were initially introduced, they were known as turbosuperchargers because all forced-induction devices are commonly categorized as supercharger.

In technical view point, all turbochargers are superchargers. But nowadays, supercharger is a word usually applied specifically to mechanically driven forced-induction devices.

The main difference between turbocharger and a conventional supercharger is as follows. The supercharger is driven mechanically by the engine, most of the time through a belt connected to the crankshaft. The turbocharger is powered by a turbine rotated and driven by the exhaust gases of the engine.

Turbochargers are inheritably less responsive than the mechanically driven supercharger.

Belts, chains, gears, and shafts are the most common methods of powering a supercharger, placing a mechanical load on the engine. The engine must withstand the net power output of the engine and the power to drive the supercharger, which is considered as the primary disadvantage of the supercharger.

A turbocharger does not cause direct mechanical load on the engine, but the turbochargers cause exhaust back pressure on the engines, which can cause increased pumping losses. This system is more efficient, because when the increased back pressure charges against the exhaust stroke, most of the energy driving the turbocharger turbine is provided by the yet expanding exhaust gas that would have otherwise be wasted as heat through the pipeline. The main disadvantage of the turbochargers is the turbo-lag, the time it required for an increase in power as the throttle being opened and the turbocharger provides increased intake pressure to the engine and therefore increases the power output.

Lancia Rally 037 supercharged engine

Lancia Rally 037 supercharged engine

Superchargers also has lower adiabatic efficiency (compressor's ability to compress air without adding extra heat to that air) when compared with the turbocharging systems. Even in ideal engine conditions, the compression process results in higher temperature levels, but with more efficient compressors produce less excess heat.

Mustang GT, GT350, Mustang V6, Mustang Cobra, Boss 302, Mach 1 were available with supercharged engines. .

To address the disadvantages of mechanically driven supercharging and exhaust-driven turbocharging, automotive manufacturers use twin-charging.

Twin charging

Lancia Delta S4 twin-charged engine

Lancia Delta S4 twin-charged engine

Twin charging is an engine that was supercharged and turbocharged to reduce turbo lad at low rev speeds. This not commonly applies in automotive industry due to the added complexity and maintenance costs. Twin charging is still applied to maximize the power output efficiency of the high-performance engines powering supercars, high-end factory racers etc.

Examples: Lancia Delta S4 Stradale was powered with a 1.8-liter inline-four twin-charged engine. The maximum power output was officially rated at 483hp. Lancia engineers tested this engine under extreme conditions and the engine developed a 1000hp at 72.52 psi of boost pressure at one point. This was a development of the Rally 037 engine that generated 325hp with a supercharger only.

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