Diesel engine

A diesel engine is an internal combustion engine in which ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is called a compression-ignition engine. This contrasts with engines using spark plug-ignition of the air-fuel mixture, such as a petrol engine or a gas engine. The diesel engine is named after its inventor, German engineer Rudolf Diesel.

Introduction

Diesel engines work by compressing only air, or air combined with residual combustion gases from the exhaust. Air is inducted into the chamber during the intake stroke, and compressed during the compression stroke. This increases air temperature inside the cylinder so that atomised diesel fuel injected into the combustion chamber ignites. The torque a diesel engine produces is controlled by manipulating the air-fuel ratio ; instead of throttling the intake air, the diesel engine relies on altering the amount of fuel that is injected, and thus the air-fuel ratio is usually high.
The diesel engine has the highest thermal efficiency of any practical internal or external combustion engine due to its very high expansion ratio and inherent lean burn, which enables heat dissipation by excess air. A small efficiency loss is also avoided compared with non-direct-injection gasoline engines, as unburned fuel is not present during valve overlap, and therefore no fuel goes directly from the intake/injection to the exhaust. Low-speed diesel engines can reach effective efficiencies of up to 55%. The combined cycle gas turbine is a combustion engine that is more efficient than a diesel engine, but due to its mass and dimensions, is unsuitable for many vehicles, including watercraft and some aircraft. The world's largest diesel engines put in service are 14-cylinder, two-stroke marine diesel engines; they produce a peak power of almost 100 MW each.
Diesel engines may be designed with either two-stroke or four-stroke [|combustion cycles]. They were originally used as a more efficient replacement for stationary steam engines. Since the 1910s, they have been used in submarines and ships. Use in locomotives, buses, trucks, heavy equipment, agricultural equipment and electricity generation plants followed later. In the 1930s, they slowly began to be used in some automobiles. Since the 1970s energy crisis, demand for higher fuel efficiency has resulted in most major automakers, at some point, offering diesel-powered models, even in very small cars. According to Konrad Reif, the EU average for diesel cars at the time accounted for half of newly registered cars. However, air pollution and overall emissions are more difficult to control in diesel engines compared to gasoline engines, so the use of diesel engines in the US is now largely relegated to larger on-road and off-road vehicles.
Though aviation has traditionally avoided using diesel engines, aircraft diesel engines have become increasingly available in the 21st century. Since the late 1990s, for various reasons—including diesel's inherent advantages over gasoline engines, but also for recent issues peculiar to aviation—development and production of diesel engines for aircraft has surged, with over 5,000 such engines delivered worldwide between 2002 and 2018, particularly for light airplanes and unmanned aerial vehicles.

History

Diesel's idea

In 1878, Rudolf Diesel, who was a student at the "Polytechnikum" in Munich, attended the lectures of Carl von Linde. Linde explained that steam engines are capable of converting just 6–10% of the heat energy into work, but that the Carnot cycle allows conversion of much more of the heat energy into work by means of isothermal change in condition. According to Diesel, this ignited the idea of creating a highly efficient engine that could work on the Carnot cycle. Diesel was also introduced to a fire piston, a traditional fire starter using rapid adiabatic compression principles which Linde had acquired from Southeast Asia. After several years of working on his ideas, Diesel published them in 1893 in the essay Theory and Construction of a Rational Heat Motor.

Constant temperature

Diesel was heavily criticised for his essay, but only a few found the mistake that he made; his rational heat motor was supposed to utilise a constant temperature cycle that would require a much higher level of compression than that needed for compression ignition. Diesel's idea was to compress the air so tightly that the temperature of the air would exceed that of combustion. However, such an engine could never perform any usable work. In his 1892 US patent #542846, Diesel describes the compression required for his cycle:

Constant pressure

By June 1893, Diesel had realised his original cycle would not work, and he adopted the constant pressure cycle. Diesel describes the cycle in his 1895 patent application. Notice that there is no longer a mention of compression temperatures exceeding the temperature of combustion. Now it is simply stated that the compression must be sufficient to trigger ignition.
In 1892, Diesel received patents in Germany, Switzerland, the United Kingdom, and the United States for "Method of and Apparatus for Converting Heat into Work". In 1894 and 1895, he filed patents and addenda in various countries for his engine; the first patents were issued in Spain, France and Belgium in December 1894, and in Germany in 1895 and the United States in 1898.
Diesel was attacked and criticised over several years. Critics claimed that Diesel never invented a new motor and that the invention of the diesel engine is fraud. Otto Köhler and were two of the most prominent critics of Diesel's time. Köhler had published an essay in 1887, in which he describes an engine similar to the engine Diesel describes in his 1893 essay. Köhler figured that such an engine could not perform any work. Emil Capitaine had built a petroleum engine with glow-tube ignition in the early 1890s; he claimed against his own better judgement that his glow-tube ignition engine worked the same way Diesel's engine did. His claims were unfounded and he lost a patent lawsuit against Diesel. Other engines, such as the Akroyd engine and the Brayton engine, also use an operating cycle that is different from the diesel engine cycle. Friedrich Sass says that the diesel engine is Diesel's "very own work" and that any "Diesel myth" is "falsification of history".

The first diesel engine

Diesel sought out firms and factories that would build his engine. With the help of Moritz Schröter and, he succeeded in convincing both Krupp in Essen and the Maschinenfabrik Augsburg. Contracts were signed in April 1893, and in early summer 1893, Diesel's first prototype engine was built in Augsburg. On 10 August 1893, the first ignition took place, the fuel used was petrol. In winter 1893/1894, Diesel redesigned the existing engine, and by 18 January 1894, his mechanics had converted it into the second prototype. During January that year, an air-blast injection system was added to the engine's cylinder head and tested. Friedrich Sass argues that, it can be presumed that Diesel copied the concept of air-blast injection from George B. Brayton, albeit that Diesel substantially improved the system. On 17 February 1894, the redesigned engine ran for 88 revolutions – one minute; with this news, Maschinenfabrik Augsburg's stock rose by 30%, indicative of the tremendous anticipated demands for a more efficient engine. On 26 June 1895, the engine achieved an effective efficiency of 16.6% and had a fuel consumption of 519 g·kW⁻¹·h⁻¹.
However, despite proving the concept, the engine caused problems, and Diesel could not achieve any substantial progress. Therefore, Krupp considered rescinding the contract they had made with Diesel. Diesel was forced to improve the design of his engine and rushed to construct a third prototype engine. Between 8 November and 20 December 1895, the second prototype had successfully covered over 111 hours on the test bench. In the January 1896 report, this was considered a success.
In February 1896, Diesel considered supercharging the third prototype. Imanuel Lauster, who was ordered to draw the third prototype "Motor 250/400", had finished the drawings by 30 April 1896. During summer that year the engine was built, it was completed on 6 October 1896. Tests were conducted until early 1897. First public tests began on 1 February 1897. Moritz Schröter's test on 17 February 1897 was the main test of Diesel's engine. The engine was rated 13.1 kW with a specific fuel consumption of 324 g·kW⁻¹·h⁻¹, resulting in an effective efficiency of 26.2%. By 1898, Diesel had become a millionaire.

Timeline

1890s

1893: Rudolf Diesel's essay titled Theory and Construction of a Rational Heat Motor appears.
1893: February 21, Diesel and the Maschinenfabrik Augsburg sign a contract that allows Diesel to build a prototype engine.
1893: February 23, Diesel obtains a patent titled "Arbeitsverfahren und Ausführungsart für Verbrennungsmaschinen".
1893: April 10, Diesel and Krupp sign a contract that allows Diesel to build a prototype engine.
1893: April 24, both Krupp and the Maschinenfabrik Augsburg decide to collaborate and build just a single prototype in Augsburg.
1893: July, the first prototype is completed.
1893: August 10, Diesel injects fuel for the first time, resulting in combustion, destroying the indicator.
1893: November 30, Diesel applies for a patent for a modified combustion process. He obtains it on 12 July 1895.
1894: January 18, after the first prototype was modified to become the second prototype, testing with the second prototype begins.
1894: February 17, The second prototype runs for the first time.
1895: March 30, Diesel applies for a patent for a starting process with compressed air.
1895: June 26, the second prototype passes brake testing for the first time.
1895: Diesel applies for a second patent US Patent # 608845
1895: November 8 – December 20, a series of tests with the second prototype is conducted. In total, 111 operating hours are recorded.
1896: April 30, Imanuel Lauster completes the third and final prototype's drawings.
1896: October 6, the third and final prototype engine is completed.
1897: February 1, Diesel's prototype engine is running and finally ready for efficiency testing and production.
1897: October 9, Adolphus Busch licenses rights to the diesel engine for the US and Canada.
1897: 29 October, Rudolf Diesel obtains a patent on supercharging the diesel engine.
1898: February 1, the Diesel Motoren-Fabrik Actien-Gesellschaft is registered.
1898: March, the first commercial diesel engine, rated 2×30 PS, is installed in the Kempten plant of the Vereinigte Zündholzfabriken A.G.
1898: September 17, the Allgemeine Gesellschaft für Dieselmotoren A.-G. is founded.
1899: The first two-stroke diesel engine, invented by Hugo Güldner, is built.