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Diesel Engines


Diesel Engines

An informative Diesel Engines Article

The diesel engine is a type of internal combustion engine; more specifically, it is a compression ignition engine, in which the fuel is ignited by being suddenly exposed to the high temperature and pressure of a compressed gas, rather than by a separate source of ignition, such as a spark plug, as is the case in the gasoline engine.

This is known as the diesel cycle, after German engineer Rudolf Diesel, who invented it in 1892 based on the hot bulb engine and received the patent on February 23, 1893. Diesel intended the engine to use a variety of fuels including coal dust. He demonstrated it in the 1900 Exposition Universelle (World's Fair) using peanut oil (see biodiesel).

Contents:
1 How diesel engines work
2 Fuel injection in diesel engines
2.1 Mechanical and electronic injection
2.2 Indirect injection
2.3 Direct injection
2.3.1 Distributor pump direct injection
2.3.2 Common rail direct injection
2.3.3 Unit direct injection
3 Types of diesel engines
4 Advantages and disadvantages versus spark-ignition engines
5 Dieseling in spark-ignition engines
6 Fuel and fluid characteristics
7 Diesel applications
7.1 Unusual applications
7.1.1 Aircraft
7.1.2 Automobile racing
8 Current and future developments
9 Modern diesel facts
10 Diesel car history

How diesel engines work

When a gas is compressed, its temperature rises (see the combined gas law); a diesel engine uses this property to ignite the fuel. Air is drawn into the cylinder of a diesel engine and compressed by the rising piston at a much higher compression ratio than for a spark-ignition engine, up to 25:1. The air temperature reaches 700–900 °C, or 1300–1650 °F. At the top of the piston stroke, diesel fuel is injected into the combustion chamber at high pressure, through an atomising nozzle, mixing with the hot, high-pressure air. The resulting mixture ignites and burns very rapidly. This contained combustion causes the gas in the chamber to heat up rapidly, which increases its pressure, which in turn forces the piston downwards. The connecting rod transmits this motion to the crankshaft, which is forced to turn, delivering rotary power at the output end of the crankshaft. Scavenging (pushing the exhausted gas-charge out of the cylinder, and drawing in a fresh draught of air) of the engine is done either by ports or valves. To fully realize the capabilities of a diesel engine, use of a turbocharger to compress the intake air is necessary; use of an aftercooler/intercooler to cool the intake air after compression by the turbocharger further increases efficiency.

In very cold weather, diesel fuel thickens and increases in viscosity and forms wax crystals or a gel. This can make it difficult for the fuel injector to get fuel into the cylinder in an effective manner, making cold weather starts difficult at times, though recent advances in diesel fuel technology have made these difficulties rare. A commonly applied advance is to electrically heat the fuel filter and fuel lines. Other engines utilize small electric heaters called glow plugs inside the cylinder to warm the cylinders prior to starting. A small number use resistive grid heaters in the intake manifold to warm the inlet air until the engine reaches operating temperature. Engine block heaters (electric resistive heaters in the engine block) plugged into the utility grid are often used when an engine is shut down for extended periods (more than an hour) in cold weather to reduce startup time and engine wear.

A vital component of older diesel engine systems was the governor, which limited the speed of the engine by controlling the rate of fuel delivery. Unlike a petrol (gasoline) engine, the incoming air is not throttled, so the engine would overspeed if this was not done. Older injection systems were driven by a gear system from the engine (and thus supplied fuel only linearly with engine speed). Modern electronically-controlled engines apply similar control to petrol engines and limit the maximum RPM through the electronic control module (ECM) or electronic control unit (ECU) - the engine-mounted "computer". The ECM/ECU receives an engine speed signal from a sensor and then using its algorithms and look-up calibration tables stored in the ECM/ECU, it controls the amount of fuel and its timing (the "start of injection") through electric or hydraulic actuators to maintain engine speed.

Controlling the timing of the start of injection of fuel into the cylinder is key to minimising their emissions and maximising the fuel economy (efficiency) of the engine. The exact timing of starting this fuel injection into the cylinder is controlled electronically in most of today's modern engines. The timing is usually measured in units of crank angle of the piston before Top Dead Center (TDC). For example, if the ECM/ECU initiates fuel injection when the piston is 10 degrees before TDC, the start of injection or "timing" is said to be 10 deg BTDC. The optimal timing will depend on both the engine design as well as its speed and load.

Advancing (injecting when the piston is further away from TDC) the start of injection results in higher in-cylinder pressure, temperature, and higher efficiency but also results in higher emissions of Oxides of Nitrogen (NOx) due to the higher temperatures. At the other extreme, very retarded start of injection or timing causes incomplete combustion. This results in higher Particulate Matter (PM) and unburned hydrocarbon (HC) emissions and more smoke.

Fuel injection in diesel engines

Mechanical and electronic injection

Older engines make use of a mechanical fuel pump and valve assembly which is driven by the engine crankshaft, usually via the timing belt or chain. These engines use simple injectors which are basically very precise spring-loaded valves which will open and close at a specific fuel pressure. The pump assembly consists of a pump which pressurizes the fuel, and a disc-shaped valve which rotates at half crankshaft speed. The valve has a single aperture to the pressurized fuel on one side, and one aperture for each injector on the other. As the engine turns the valve discs will line up and deliver a burst of pressurized fuel to the injector at the cylinder about to enter its power stroke. The injector valve is forced open by the fuel pressure and the diesel is injected until the valve rotates out of alignment and the fuel pressure to that injector is cut off. Engine speed is controlled by a third disc, which rotates only a few degrees and is controlled by the throttle lever. This disc alters the width of the aperture through which the fuel passes, and therefore how long the injectors are held open before the fuel supply is cut, controlling the amount of fuel injected.

Older diesel engines with mechanical injection pumps could be inadvertently run in reverse, albeit very inefficiently as witnessed by massive amounts of soot being ejected from the air intake. This was often a consequence of Bump starting a vehicle using the wrong gear.

This contrasts with the more modern method of having a separate fuel pump (or set of pumps) which supplies fuel constantly at high pressure to each injector. Each injector then has a solenoid which is operated by an electronic control unit, which enables more accurate control of injector opening times depending on other control conditions such as engine speed and loading, resulting in better engine performance and fuel economy. This design is also mechanically simpler than the combined pump and valve design, making it generally more reliable, and less noisy, than its mechanical counterpart.

Both mechanical and electronic injection systems can be used in either direct or indirect injection configurations. (see below)

Indirect injection

An indirect injection diesel engine delivers fuel into a chamber off the combustion chamber, called a prechamber, where combustion begins and then spreads into the main combustion chamber, assisted by turbulence created in the chamber. This system allows smoother, quieter running, and because combustion is assisted by turbulence, injector pressures can be lower, which in the days of mechanical injection systems allowed high-speed running suitable for road vehicles (typically up to speed of around 4,000 rpm). The prechamber had the disadvantage of increasing heat loss to the engine's cooling system and restricting the combustion burn, which reduced the efficiency by between 5-10% in comparison to a direct injection engine, and nearly all require some form of cold-start device such as glow plugs. Indirect injection engines were used widely in small-capacity high-speed diesel engines in automotive, marine and construction uses from the 1950s, until direct-injection technology advanced in the 1980s. Indirect injection engines are cheaper to build and it is easier to produce smooth, quiet running vehicles with a simple mechanical system, so such engines are still often used in applications which carry less stringent emissions controls than road-going vehicles, such as small marine engines, generators, tractors, pumps. With electronic injection systems, indirect injection engines are still used in some road-going vehicles, but most prefer the greater efficiency of direct injection.

Direct injection

Modern diesel engines make use of one of the following direct injection methods:

Distributor pump direct injection

The first incarnations of direct injection diesels used a rotary pump much like indirect injection diesels, however the injectors were mounted in the top of the combustion chamber rather than in a separate pre-combustion chamber. Examples are vehicles such as the Ford Transit and the Austin Rover Maestro and Montego with their Perkins Prima engine. The problem with these vehicles was the harsh noise that they made and particulate (smoke) emissions. This is the reason that in the main this type of engine was limited to commercial vehicles— the notable exceptions being the Maestro, Montego and Fiat Croma passenger cars. Fuel consumption was about fifteen to twenty percent lower than indirect injection diesels, which for some buyers was enough to compensate for the extra noise.

One of the first small-capacity, mass-produced direct-injection engines that could be called refined was developed by the Rover Group.[citation needed] The '200Tdi' 2.5-litre 4-cylinder turbodiesel (of 111 horsepower) was used by Land Rover in their vehicles from 1989, and the engine used an aluminium cylinder head, Bosch two-stage injection and multi-phase glow plugs to produce a smooth-running and economical engine while still using mechanical fuel injection.

This type of engine was transformed by electronic control of the injection pump, pioneered by Volkswagen Audi group with the Audi 100 TDI introduced in 1989. The injection pressure was still only around 300 bar, but the injection timing, fuel quantity, exhaust gas recirculation and turbo boost were all electronically controlled. This gave much more precise control of these parameters which made refinement much more acceptable and emissions acceptably low. Fairly quickly the technology trickled down to more mass market vehicles such as the Mark 3 Golf TDI where it proved to be very popular. These cars were both more economical and more powerful than indirect injection competitors of their day.

Common rail direct injection

In older diesel engines, a distributor-type injection pump, regulated by the engine, supplies bursts of fuel to injectors which are simply nozzles through which the diesel is sprayed into the engine's combustion chamber.

In common rail systems, the distributor injection pump is eliminated. Instead an extremely high pressure pump stores a reservoir of fuel at high pressure - up to 1,800 bar (180 MPa, 26,000 psi) - in a "common rail", basically a tube which in turn branches off to computer-controlled injector valves, each of which contains a precision-machined nozzle and a plunger driven by a solenoid.

Most European automakers have common rail diesels in their model lineups, even for commercial vehicles. Some Japanese manufacturers, such as Toyota, Nissan and recently Honda, have also developed common rail diesel engines.

Different car makers refer to their common rail engines by different names, e.g. DaimlerChrysler's CDI, Ford Motor Company's TDCi (most of these engines are manufactured by PSA), Fiat Group's (Fiat, Alfa Romeo and Lancia) JTD, Renault's DCi, GM/Opel's CDTi (most of these engines are manufactured by Fiat, other by Isuzu), Hyundai's CRDi, Mitsubishi's D-ID, PSA Peugeot Citroen's HDi, Toyota's D-4D, Volkswagen's TDi, and so on.

Unit direct injection

This also injects fuel directly into the cylinder of the engine. However, in this system the injector and the pump are combined into one unit positioned over each cylinder. Each cylinder thus has its own pump, feeding its own injector, which prevents pressure fluctuations and allows more consistent injection to be achieved. This type of injection system, also developed by Bosch, is used by Volkswagen AG in cars (where it is called Pumpe Düse - literally "pump nozzle"), Mercedes Benz (PLD) and most major diesel engine manufacturers, in large commercial engines (Cat, Cummins, Detroit Diesel). With recent advancements, the pump pressure has been raised to 2,050 bar (205 MPa), allowing injection parameters similar to common rail systems.

Types of diesel engines

There are two classes of diesel engines: two-stroke and four-stroke. Most diesels generally use the four-stroke cycle, with some larger diesels operating on the two-stroke cycle.

Normally, banks of cylinders are used in multiples of two, although any number of cylinders can be used as long as the load on the crankshaft is counterbalanced to prevent excessive vibration. The inline-6 is the most prolific in medium- to heavy-duty engines, though the V8 and straight-4 are also common.

As a footnote, prior to 1949, Sulzer started experimenting with two-stroke engines with boost pressures as high as 6 atmospheres, in which all of the output power was taken from an exhaust turbine. The two-stroke pistons directly drove air compressor pistons to make a positive displacement gas generator. Opposed pistons were connected by linkages instead of crankshafts. Several of these units could be connected together to provide power gas to one large output turbine. The overall thermal efficiency was roughly twice that of a simple gas turbine. (Source 'Modern High-Speed Oil Engines Volume II' by C. W. Chapman published by 'The Caxton publishing co. ltd.' reprinted in July 1949)

Advantages and disadvantages versus spark-ignition engines

Diesel engines are more efficient than gasoline (petrol) engines of the same power, resulting in lower fuel consumption. A common margin is 40% more miles per gallon for an efficient turbodiesel; for example, the current model Skoda Octavia, using Volkswagen engines, has a combined Euro mpg of 38.2 mpg for the 102 bhp petrol engine and 53.3 mpg for the 105 bhp — and heavier — diesel engine. The higher compression ratio is helpful in raising efficiency, but diesel fuel also contains approximately 10-20% more energy per unit volume than gasoline.

Naturally aspirated diesel engines are heavier than gasoline engines of the same power for two reasons; the first is that it takes a larger capacity diesel engine than a gasoline engine to produce the same power. This is essentially because the diesel cannot operate as quickly — the "rev limit" is lower — because getting the correct fuel-air mixture into a diesel engine quickly enough is more difficult than a gasoline engine [1]. The second reason is that a diesel engine must be stronger to withstand the higher combustion pressures needed for ignition, and the shock loading from the detonation of the ignition mixture. As such the reciprocating mass (the piston and connecting rod), and the resultant forces to acclerate and to decelerate these masses, are substantially higher the heavier, the bigger and the stronger the part, and the laws of diminishing returns of component strength, mass of component and intertia - all come into play to create a balance of offsets, of optimal mean power output, weight and durability.

Yet it is this same build quality that has allowed some enthusiasts to acquire significant power increases with turbocharged engines through fairly simple and inexpensive modifications. A gasoline engine of similar size cannot put out a comparable power increase without extensive alterations because the stock components would not be able to withstand the higher stresses placed upon them. Since a diesel engine is already built to withstand higher levels of stress, it makes an ideal candidate for performance tuning with little expense. However it should be said that any modification that raises the amount of fuel and air put through a diesel engine will increase its operating temperature which will reduce its life and increase its service interval requirements. These are issues with newer, lighter, "high performance" diesel engines which aren't "overbuilt" to the degree of older engines and are being pushed to provide greater power in smaller engines.

The addition of a turbocharger or supercharger to the engine (see turbodiesel) greatly assists in increasing fuel economy and power output, mitigating the fuel-air intake speed limit mentioned above for a given engine displacement. Boost pressures can be higher on diesels than gasoline engines, and the higher compression ratio allows a diesel engine to be more efficient than a comparable spark ignition engine. Although the calorific value of the fuel is slightly lower at 45.3 MJ/kg (megajoules per kilogram) to gasoline at 45.8 MJ/kg, diesel fuel is much denser and fuel is sold by volume, so diesel contains more energy per litre or gallon. The increased fuel economy of the diesel over the gasoline engine means that the diesel produces less carbon dioxide (CO2) per unit distance. Recently, advances in production and changes in the political climate have increased the availability and awareness of biodiesel, an alternative to petroleum-derived diesel fuel with a much lower net-sum emission of CO2, due to the absorption of CO2 by plants used to produce the fuel.

The two main factors that held diesel engine back in private vehicles until quite recently were their low power outputs and high noise levels (characterised by knock or clatter, especially at low speeds and when cold). This noise was caused by the sudden ignition of the diesel fuel when injected into the combustion chamber. This noise was a product of the sudden temperature change, hence why it was more pronounced at low engine temperatures. A combination of improved mechanical technology (such as two-stage injectors which fire a short 'pilot charge' of fuel into the cylinder to warm the combustion chamber before delivering the main fuel charge) and electronic control (which can adjust the timing and length of the injection process to optimise it for all speeds and temperatures) have almost totally solved these problems in the latest generation of common-rail designs. Poor power and narrow torque bands have been solved by the use of turbochargers and intercoolers.

Diesel engines produce very little carbon monoxide as they burn the fuel in excess air except at full load, at which point a full stochiometric quantity of fuel is injected per cycle. However, they can produce black soot from their exhaust, consisting of unburned carbon compounds. This is often caused by worn injectors, which do not atomize the fuel sufficiently, or a faulty engine management system which allows more fuel to be injected than can be burned with the available air. Particles of the size normally called PM10 (particles of 10 micrometres or smaller) have been implicated in health problems, especially in cities. Modern diesel engines catch the soot in a particle filter, which when saturated is automatically regenerated by burning the particles. Other problems associated with the exhaust gases (nitrogen oxides, sulfur oxides) can be mitigated with further investment and equipment; some diesel cars now have catalytic converters in the exhaust.

For commercial uses requiring towing, load carrying and other tractive tasks, diesel engines tend to have more desirable torque characterstics. Diesel engines tend to have their torque peak quite low in their speed range (usually between 1600-2000 rpm for a small-capacity unit, lower for a larger engine used in a lorry or truck). This provides smoother control over heavy loads when starting from rest, and crucially allows the diesel engine to be given higher loads at low speeds than a petrol/gasoline engine, which makes them much more economical for these applications. This characteristic is not so desirable in private cars, so most modern diesels used in such vehicles use electronic control, variable geometery turbochargers and shorter piston strokes to achieve a wider spread of torque over the engine's speed range, typically peaking at around 2,500-3000 rpm.

The lack of an electrical ignition system greatly improves the reliability. The high durability of a diesel engine is also due to its overbuilt nature (see above) as well as the diesel's combustion cycle, which creates less-violent changes in pressure when compared to a spark-ignition engine, a benefit that is magnified by the lower rotating speeds in diesels. Diesel fuel is a better lubricant than gasoline so is less harmful to the oil film on piston rings and cylinder bores; it is routine for diesel engines to cover 250,000 miles or more without a rebuild.

Unfortunately, due to the greater compression force required and the increased weight of the stronger components, starting a diesel engine is a harder task. More torque is required to push the engine through compression.

Either an electrical starter or an air start system is used to start the engine turning. On large engines, pre-lubrication and slow turning of an engine, as well as heating, are required to minimize the amount of engine damage during initial start-up and running. Some smaller military diesels can be started with an explosive cartridge that provides the extra power required to get the machine turning. In the past, Caterpillar and John Deere used a small gasoline "pony" motor in their tractors to start the primary diesel motor. The pony motor heated the diesel to aid in ignition and utilized a small clutch and transmission to actually spin up the diesel engine. Even more unusual was an International Harvester design in which the diesel motor had its own carburetor and ignition system, and started on gasoline. Once warmed up, the operator moved two levers to switch the motor to diesel operation, and work could begin. These engines had very complex cylinder heads (with their own gasoline combustion chambers) and in general were vulnerable to expensive damage if special care was not taken (especially in letting the engine cool before turning it off).

As mentioned above, diesel engines tend to have more torque at lower engine speeds than gasoline engines. However, diesel engines tend to have a narrower power band than gasoline engines. Naturally-aspirated diesels tend to lack power and torque at the top of their speed range. This narrow band is a reason why a vehicle such as a truck may have a gearbox with as many as 16 or more gears, to allow the engine's power to be used effectively at all speeds. Turbochargers tend to improve power at high engine speeds, and if an intercooler is added, torque tends to improve at lower speeds.

Dieseling in spark-ignition engines

A gasoline (spark ignition) engine can sometimes act as a compression ignition engine under abnormal circumstances, a phenomenon typically described as "pinging" or "pinking" (during normal running) or "dieseling" (when the engine continues to run after the electrical ignition system is shut off). This is usually caused by hot carbon deposits within the combustion chamber that act as would a "glow plug" within a diesel or model aircraft engine. Excessive heat can also be caused by improper ignition timing and/or fuel/air ratio which in turn overheats the exposed portions of the spark plug within the combustion chamber.

Fuel and fluid characteristics

Diesel engines can operate on a variety of different fuels, depending on configuration, though the eponymous diesel fuel derived from crude oil is most common. Good-quality diesel fuel can be synthesised from vegetable oil and alcohol. Biodiesel is growing in popularity since it can frequently be used in unmodified engines, though production remains limited. Petroleum-derived diesel is often called "petrodiesel" if there is need to distinguish the source of the fuel.

The engines can work with the full spectrum of crude oil distilates, from compressed natural gas, alcohols, gasolene, to the "fuel oils" from diesel oil to residual fuels. The type of fuel used is a combination of service requirements, and fuel costs.

"Residual fuels" are the "dregs" of the distilation process and are a thicker, heavier oil, or oil with higher viscosity, which are so thick that they are not readily pumpable unless heated. Residual fuel oils are cheaper than clean, refined diesel oil, although they are dirtier. Their main considerations are for use in ships and very large generation sets, due to the cost of the large volume of fuel consumed, frequently amounting to many tonnes per hour. The poorly refined biofuels straight vegetable oil (SVO) and waste vegetable oil (WVO) can fall into this category. Moving beyond that, use of low-grade fuels can lead to serious maintenance problems. Most diesel engines that power ships like supertankers are built so that the engine can safely use low grade fuels.

Normal diesel fuel is more difficult to ignite than gasoline because of its higher flash point, but once burning, a diesel fire can be fierce.

Diesel applications

The vast majority of modern heavy road vehicles (trucks), ships, large-scale portable power generators, most farm and mining vehicles, and many long-distance locomotives have diesel engines.

Besides their use in merchant ships and boats, there is also a naval advantage in the relative safety of diesel fuel, additional to improved range over a gasoline engine. The German "pocket battleships" were the largest diesel warships, but the German torpedo-boat called "Schnellboot" of the Second World War was also a diesel craft. Conventional submarines have used them since before the First World War. It was an advantage of American diesel-electric submarines that they operated a two-stroke cycle as opposed to the four-stroke cycle that other navies used.

Mercedes-Benz, cooperating with Robert Bosch GmbH, has a successful run of diesel-powered passenger cars since 1936, sold in many parts of the World, with other manufacturers joining in the 1970s and 1980s. The second car manufacturer was Peugeot, prior to 1960.

In the U.S., probably due to some hastily offered cars in the 1980s, Diesel is not as popular in passenger vehicles as in Europe. Such cars have been traditionally perceived as heavier, noisier, having performance characteristics which make them slower to accelerate, and of being more expensive than equivalent gasoline vehicles. This image certainly does not reflect recent designs, especially where the very high low-rev torque of modern Diesels is concerned -- which have characteristics similar to the big V8 gasoline engines popular in the US. General Motor's Oldsmobile division produced a variation of its gasoline-powered V8 engine which is the main reason for this reputation. Light and heavy trucks, in the U.S., have been diesel-optioned for years.

European governments tend to favor diesel engines in taxation policy because of diesel's superior fuel efficiency. In addition, diesel fuel used in North America still has higher sulphur content than the fuel used in Europe, effectively limiting diesel use to industrial vehicles, before the introduction of 15 parts per million Ultra low Sulfur Diesel, which will start at 15 October 2006 in the U.S. (1 June 2006 in Canada). Ultra Low Sulfur Diesel is not mandatory until 2010 in the US.

In Europe, where tax rates in many countries make diesel fuel much cheaper than gasoline, diesel vehicles are very popular and newer designs have significantly narrowed differences between petrol and diesel vehicles in the areas mentioned. Often, among comparably designated models, the Turbo-Diesels outperform their naturally aspirated petrol-powered sister cars. One anecdote tells of Formula One driver Jenson Button, who was arrested while driving a diesel-powered BMW 330cd Coupé at 230 km/h (about 140 mph) in France, where he was too young to have a gasoline-engined car hired to him. Button dryly observed in subsequent interviews that he had actually done BMW a public relations service, as nobody had believed a diesel could be driven that fast. Yet, BMW had already won the 24 Hours Nürburgring overall in 1998 with a 3-series diesel. The BMW diesel lab in Steyr, Austria is led by Ferenc Anisits and develops innovative diesel engines.

Mercedes-Benz, offering diesel-powered passenger cars since 1936, has put the emphasis on high performance diesel cars in its newer ranges, as does Volkswagen with its brands. Citroën sells more cars with diesel engines than gasoline engines, as the French brands (also Peugeot) pioneered smoke-less HDI designs with filters. Even the Italian marque Alfa Romeo, known for design and successful history in racing, focuses on Diesel that are also raced.

A few motorcycles have been built using diesel engines, but the weight and cost disadvantages generally outweigh the efficiency gains in this application.

High-speed
High-speed (approximately 1200 rpm and greater) engines are used to power trucks (lorries), buses, tractors, cars, yachts, compressors, pumps and small generators.

Medium-speed
Large electrical generators are driven by medium speed engines, (approximately 300 to 1200 rpm) optimised to run at a set speed and provide a rapid response to load changes.

Low-speed
The largest diesel engines are used to power ships. These monstrous engines have power outputs over 80MW, turn at about 60 to 100 rpm, and are up to 15 m tall. They often run on cheap low-grade fuel, which require extra heat treatment in the ship for tanking and before injection due to their low volatility. Companies such as Burmeister & Wain and Wärtsilä (e.g., Sulzer diesels) design such large low speed engines. They are unusually narrow and tall due to the addition of a crosshead bearing. Today (2006), the 12 cylinder MAN B&W Diesel K98MC turbocharged two-stroke diesel engine build by MAN B&W Diesel licencee Hyundai Heavy Industries in Korea is the most powerful diesel engine put into service, with a cylinder bore of 980 mm delivering 74.8 MW (101,640 bhp). When put into service in 2007, the 14 cylinder Wärtsilä-Sulzer RTA96-C will become the most powerful diesel engine with 80 MW (110,000 hp).

Unusual diesel applications

Aircraft

The zeppelins Graf Zeppelin II and Hindenburg were propelled by reversible diesel engines. The direction of operation was changed by shifting gears on the camshaft. From full power forward, the diesel engines could be brought to a stop, changed over, and brought to full power in reverse in less than 60 seconds.

Diesel engines were first tried in aircraft in the 1930s. A number of manufacturers built diesel engines, the best known probably being the Junkers Jumo 205, which was moderately successful, but proved unsuitable for combat use in WWII. Postwar, another interesting proposal was the complex Napier Nomad. In general, though, the lower power-to-weight ratio of diesels, particularly compared to kerosene-powered turboprop engines, has precluded their use in this application.

The very high cost of avgas in Europe, and the advances in automotive diesel technology, have seen renewed interest in the concept. New, certified diesel-powered light planes are already available, and a number of other companies are also developing new engine and aircraft designs for the purpose. Many of these run on the readily-available jet fuel, or can run on both jet fuel or conventional automotive diesel.

Automobile racing

Although the weight and lower output of a diesel engine tend to keep them away from automotive racing applications, there are many diesels being raced in classes that call for them, mainly in truck racing and tractor pulling, as well in types of racing where these drawbacks are less severe, such as land speed record racing or endurance racing. Even Diesel engined dragsters exist, despite the diesel's drawbacks being central to performance in this sport.

1931 - Clessie Cummins installs his Diesel in a race car. It runs at 162 km/h in Daytona, and 138 km/h in Indianapolis where it places 12th. [2]

In 1933, A 1925 Bentley with a Gardner 4LW engine was the first diesel-engined car to take part in the Monte Carlo Rally when it was driven by Lord Howard de Clifford. It was the leading British car and finished fifth overall. [3]

In 1952, Cummins Diesel won the pole at the Indianapolis 500 race with a supercharged 3 liter diesel car, relying on torque and fuel efficiency to overcome weight and low peak power, and led most of the race until the badly situated air intake of the car swallowed enough debris from the track to disable the car.

With turbocharged Diesel-cars getting stronger in the 1990s, they were also entered in touring car racing, and BMW even won the 24 Hours Nürburgring in 1998 with a 320d, against other factory-entered Diesel-competition of Volkswagen and about 200 regular powered cars. Alfa Romeo even organized a racing series with their Alfa Romeo 147 1.9 JTD models.

The VW Dakar Rally entrants for 2005 and 2006 are powered by their own line of TDI engines in order to challenge for the first overall diesel win there. Meanwhile, the five time 24 Hours of Le Mans winner Audi R8 race car was replaced by the Audi R10 in 2006, which is powered by a 650 hp (485 kW) and 1100 Nm (810 lb·ft) V12 TDI Common Rail diesel engine, mated to a 5-Speed gearbox, instead of the 6 used in the R8, to handle the extra torque produced. The gearbox is considered the main problem, as earlier attempts by others failed due to the lack of suitable transmissons that could stand the torque long enough.

After winning the 12 Hours of Sebring in 2006 with their Diesel-powered R10, Audi has good chances for the overall win at the 24 Hours of Le Mans, too. This is the first time a sports car can compete for overall victories with Diesel-fuel against cars powered with regular fuel or methanol and bio-ethanol. However, the significance of this is slightly lessened by the fact that the ALMS race rules encourage the use of alternate fuels like Diesel.

Current and future developments

Already, many common rail and unit injection systems employ new injectors using stacked piezoelectric crystals in lieu of a solenoid, which gives finer control of the injection event.

Variable geometry turbochargers have flexible vanes, which move and let more air into the engine depending on load. This technology increases both performance and fuel economy. Boost lag is reduced as turbo impeller inertia is compensated for.

A technique called accelerometer pilot control (APC) uses a sensor called an accelerometer to provide feedback on the engine's level of noise and vibration and thus instruct the ECU to inject the minimum amount of fuel that will produce quiet combustion and still provide the required power (especially while idling.)

The next generation of common rail diesels are expected to use variable injection geometry, which allows the amount of fuel injected to be varied over a wider range, and variable valve timing similar to that on gasoline engines.

Particularly in the United States, coming tougher emissions regulations present a considerable challenge to diesel engine manufacturers. Other methods to achieve even more efficient combustion, such as HCCI (homogeneous charge compression ignition), are being studied.

Modern diesel facts

(Source: Robert Bosch GmbH)

Fuel passes through the injector jets at speeds of nearly 1500 miles per hour (2400 km/h) – as fast as the top speed of a jet plane.

Fuel is injected into the combustion chamber in less than 1.5 ms – about as long as a camera flash.

The smallest quantity of fuel injected is one cubic millimetre – about the same volume as the head of a pin. The largest injection quantity at the moment for automobile diesel engines is around 70 cubic millimetres.

If the camshaft of a six-cylinder engine is turning at 4500 rpm, the injection system has to control and deliver 225 injection cycles per second.

On a demonstration drive, a Volkswagen 1-liter diesel-powered car used only 0.89 liter of fuel in covering 100 kilometers (264MPG) – making it probably the most fuel-efficient car in the world. Bosch’s high-pressure fuel injection system was one of the main factors behind the prototype’s extremely low fuel consumption. Production record-breakers in fuel economy include the Volkswagen Lupo 3L TDI and the Audi A2 3 L 1.2 TDI with standard consumption figures of 3 liters of fuel per 100 kilometers (78MPG). Their high-pressure diesel injection systems are also supplied by Bosch.

In 2001, nearly 36% of newly registered cars in Western Europe had diesel engines. By way of comparison: in 1996, diesel-powered cars made up only 15% of the new car registrations in Germany. Austria leads the league table of registrations of diesel-powered cars with 66%, followed by Belgium with 63% and Luxembourg with 58%. Germany, with 34.6% in 2001, was in the middle of the league table. Sweden is lagging behind, in 2004 only 8% of the new cars had diesel engine.

Diesel car history

The first production diesel cars were the Mercedes-Benz 260D and the Hanomag Rekord, both introduced in 1936. The Citroën Rosalie was also produced between 1935 and 1937 with an extremely rare diesel engine option (the 1766 cc 11UD engine) only in the Familiale (estate or station wagon) version. [4]

Following the 1970s oil crisis, turbo diesels were tested, e. g. by the Mercedes-Benz C111 experimental and record-setting vehicles. The first production turbo diesel car was, in 1978, the 3.0 5-cyl 115 PS Mercedes 300 SD, available only in North America. In Europe, the Peugeot 604 with a 2.3 litre turbo diesel was introduced in 1979, and then the Mercedes 300 TD turbo.

Many Audi enthusiasts claim that the Audi 100 TDI was the first turbo charged direct injection diesel sold in 1989, but actually it isn't true, as the Fiat Croma, and also the Austin Rover Montego were sold with turbo direct injection in 1988.

What was pioneering about the Audi 100 however was the use of electronic control of the engine, as the Fiat and Austin had purely mechanically controlled injection. The electronic control of direct injection really made a difference in terms of emissions, refinement and power.

It's interesting to see that the big players in the diesel car market are the same ones who pioneered various developments (Mercedes, BMW, Peugeot/Citroën, Fiat, Alfa Romeo, VW/Audi/SEAT/Skoda), with the sad exception of Austin Rover.

In 1998, for the very first time in the history of racing, in the legendary 24 Hours Nürburgring race, a diesel-powered car was the overall winner: the BMW works team 320d, a BMW E36 fitted with modern high-pressure diesel injection technology from Robert Bosch GmbH. The low fuel consumption and long range, allowing 4 hours of racing at once, made it a winner, as comparable petrol-powered cars spent more time refuelling.

This article is licensed under the GNU Free Documentation License.


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