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Diesel


Diesel
As you know, one of the main indicators for evaluating the work of anyone, including the thermal engine is its efficiency. The greater the energy released during the combustion of the fuel is converted into useful work, the smaller it is lost during the various transformations, the better. All existing heat engines, these losses are very large, so that more than two-thirds of the released energy in them is wasted in vain. What is the cause? Whether this is due to poor design or heat engine, in principle, can not have a high efficiency by its very nature? For the first time on this issue reflected a French engineer Carnot, who published in 1824 a classic work "Reflections on the motive power of fire." Carnot set out to find out how the process should take place in an ideal heat engine, to its efficiency was the highest possible. By calculations, he finally brought the concept of a circular process in all heat engines (called "Carnot cycle"), in which between two temperatures T1 and T2 of the engine body (the working body - is the gas that moves the piston; they can be steam in a steam engine or explosive gas mixture in the engine) can be as much useful work, and consequently the highest efficiency. The operation of this hypothetical high-efficiency engine as proved Carnot, should consist of four cycles. In the first cycle the working fluid is supplied to the heat from the upper level Q1 at a constant temperature T1 at this level (i.e., in this cycle the working fluid to be expanded, while maintaining a constant temperature, which is achieved by heating the body). During the second cycle extension of the working fluid occurs, but without the supply of heat, as long as its temperature falls to a low level T2. In the third cycle, the working fluid is compressed at a constant temperature T2 (for this purpose it was necessary to continuously remove heat Q2). The fourth step was compressed working fluid without heat removal as long as the temperature does not rise again until T1. In the case of compliance with all of these conditions, it is estimated Carnot engine efficiency was determined by the formula 100 • (1 - T2 / T1) and reached about 70-80%.

Throughout the XIX century calculations Carnot excited the creative thinking of inventors, who tried to find the answer to the question: how the work of real heat engines closer to the work of the "Carnot cycle" and obtain the highest possible efficiency. But all attempts to build such an engine were unsuccessful. For example, the efficiency of the steam engine with a power of 100 hp does not exceed 13%, and in low-power motors it was less than 10%. The efficiency of gasoline and natural gas engines obtained slightly higher, but still did not exceed 22-24%.

Such was the situation when, in the early 90s for the creation of a "perfect engine" took the young German engineer Rudolf Diesel. While still a student, he set a goal to develop such an engine, which indicators would be close to the "Carnot cycle", and the engine was superior to conventional gasoline as a power, and on the economy.

After several years of hard work of the engine project was developed. The idea Diesel was as follows. The first stage piston compresses air in the cylinder to a high pressure, whereby the temperature in the cylinder rises to the ignition temperature of the fuel (this corresponds to the fourth Carnot cycle - compression without heat removal). Thus, in the cylinder reaches about 90 atm pressure and temperature of about 900 degrees. Fuel is fed to the cylinder at the end of the cycle and due to the high compression temperature of a combusted contact with it without any external ignition. The injection of fuel performed uniformly, so that part of the return movement of the piston and the expansion gases occur at constant temperature (in accordance with the first "Carnot cycle"). Further, the piston has moved under the influence of a high pressure fuel without burning (the second "Carnot cycle"). Third cycle correspond to the exhaust and fresh air intake portion. Then all the cycles were repeated. Thanks to this device Diesel thought to increase the efficiency of your engine to unprecedented quantities - 73%. At first, as a fuel it is expected to apply ammonia fumes, but then opted for the coal powder. In 1892, Diesel received a patent on the described principle of operation of the engine, and in 1893 published a booklet, "The theory and rational heat engine design" with a description of the engine and its mathematical calculations.

The brochure has attracted a lot of attention. However, most engineers considered the idea of ​​Diesel pipe. The largest specialist in gas engines at the time Koehler warned that to get such a high level of efficiency is not possible, since diesel engines are very high power loss in the compressed air to the ignition temperature, and with the work of the "Carnot cycle" all useful work will only be spent on maintaining its own movement. Nevertheless, Diesel has become strongly suggest its model of various German companies. At first, he met rejection everywhere. Do not despair, he continued to correspond, argued, argued and finally succeeded: the Krupp firm in Essen agreed to finance the costs, and the management of the Augsburg plant - to produce a test sample.

Already in July 1893 he was made the first single-cylinder diesel engine. In accordance with the original design, the compression in the cylinder it should have been as high as 90 atm, and the temperature before the intake of fuel - 900 degrees. Since the temperature should not greatly exceed that limit, no cooling system for the motor is not provided. The compressor is also planned - carbon powder intended to blow pump.

But even at the assembly stage, Diesel, checking his calculations, was convinced that Koehler is right - the engine power at the cost of compressed air up to 90 atmospheres proved to be too high and "eat" the entire gain in efficiency due to work on the "Carnot cycle". I had to go directly to alter our plans. To reduce the power losses in compression Diesel decided to reduce the pressure in the cylinder more than doubled - 35-40 atm. In this connection, instead of the compressed air temperature of 900 degrees it should be as low as 600. It was very small - in the formula, the temperature difference is too small Carnot provided for high efficiency. To improve business and increase the capacity of the motor, the diesel had to abandon the second important moment of its design - the expansion of the working fluid at a constant temperature. He calculated that the temperature of the combustion of fuel should increase up to 1500 degrees. This, in turn, required that firstly the most intense cooling of the motor, and secondly, a caloric fuel. Coal dust could not give such a high temperature, so Diesel has been forced to turn to liquid fuel. But at the first attempt to inject gasoline into the cylinder, an explosion occurred nearly claimed the life of the inventor and his assistants.

Thus ended the first test. It had a twofold result. Diesel had step by step quite retreat from the original scheme of his "perfect engine". But, on the other hand, some of the fundamental aspects of its calculations confirmed - strong compression of the working mixture led to an increase in efficiency and in addition (explosion proved it), it turned out that the fuel can really ignite by compression, without resorting to expensive ignition system. Therefore, the firm that financed the project, were generally satisfied with the progress made, and Diesel was able to continue his experiments.

In June 1894 a second engine for which Diesel invented the injector controls the injection of kerosene was built. In this model, the pressure in the cylinder was adjusted to 35-40 bar, and compression end temperature - 500-600 degrees. The motor could not only run but also make work for idle at up to 80 revolutions per minute. It was a great success - Diesel idea was viable. In 1895, the third engine was built, which could already be working with a small load. For the injection of kerosene here compressor was first provided. Furthermore, it was necessary to develop an intensive cooling system to prevent jamming of the cylinder. Only after that in 1896 the launch of a new prototype was successful. When tested with a load motor efficiency proved to be 36% and the flow of kerosene was about 200 grams per horsepower hour. While the numbers were very far from the parameters of the "ideal engine", they are still impressive: the efficiency of the new engine proved to be 10-12% higher than that of gasoline engines at the time, and in its economy, he surpassed them almost doubled. Let Diesel was unable to fulfill his dream, yet he made was of great significance - thanks to his persistence fundamentally new internal combustion engine design has been developed, which has been and remains the best for a hundred years past.

He worked as a new engine in the following way. At the first stroke of the piston at the expense live flywheel power stored during the previous operation of the machine, the air is sucked into the cylinder. During the second course, also perpetrated by the living forces of the flywheel, the air locked in the cylinder is compressed to 35 atmospheres. At the same time the heat generated during compression, bringing it to the ignition temperature of the fuel. At the beginning of the third stroke of the pump by means of kerosene was injected. This injection lasted only a minor part of the course. During the course of the rest of the mass of the gas expands and the piston communicated labor force, which was transmitted through the crank shaft of the engine. In the fourth course of combustion erupted through the exhaust pipe into the atmosphere.

The engine was equipped with a compressor, which in a special tank thickening air at a pressure slightly higher than the highest pressure in the cylinder. This air reservoir through a very small diameter tube directed into a small nozzle chamber, that is fed to the apparatus for spraying the fuel, which was supplied simultaneously kerosene. This chamber communicates with the interior of the cylinder by means of a small hole, lockable needle when this needle is lifted, kerosene is forced into the cylinder due to excess pressure in the chamber. The combustion in the cylinder regulated, depending on the strength of which was to develop the engine, or a change in the fuel intake duration, or a change in pressure in the compressor. The same compressed air was used for the initial engine start-up from cold. At the top of the engine camshaft placed with five cams one control valves, intake air, and the other - a valve to let kerosene, three - valve It produced products of combustion. The last two cam operated valves, through which compressed air is admitted into the cylinder during the initial engine start-up.

The first official tests of the new engine produced a sensation among engineers. Since that time, the triumphal march of "diesel" around the world. Many companies that had previously not responded to the offer of Diesel, hurry to buy from it the right to build his invention of motors, and this right is now costing them dearly (for example, Immanuel Nobel, wanting to set up production of diesel engines in Russia, Diesel paid about 500 thousand dollars). Already in 1898, Diesel, quite unexpectedly, became a millionaire. However, the first engines fired into production, proved to be unsatisfactory, capricious and often broke down. The release of such a complex and high-tech machine was not under force many plants with obsolete equipment. As at the time Watt, Diesel had to spend a lot of effort on it, to perfect the manufacturing process of the manufacture of diesel engines - to develop new tools, to find suitable alloys, to prepare specialists. Within a few years he wandered through Europe and America, visiting factories, which went on production of its engines. By the beginning of XX century the main difficulties have been overcome, and diesel engines gradually began to win more and more new applications in industry and transport. In 1900 at the World Exhibition in Paris Diesel engines have received the Grand Prix. Especially raised the prestige of the new engines the news that the Nobel plant in Russia started manufacturing quite good engines operating on crude oil.

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