See also: Diesel
Fruit of the work undertaken by the German engineer Diesel Rudolf between 1893 and 1897, the diesel engine is an Internal combustion engine whose lighting is not not ordered but spontaneous, by phenomenon of spontaneous combustion. It thus does not need plugs spark. That is possible thanks to a very extremely Ratio compression (volumetric report/ratio) from approximately 18 with 22:1, making it possible to obtain a temperature of 600 °C. Preheating plugs are often used to allow the starting of the cold engine by increasing the temperature of the combustion chamber, but their presence is not systematic.
The diesel engine usually function with the Gazole, the heavy Fuel or the plant oils. They can as well be with two times as with four times. This type of engine athigh compression ratio knew a fast expansion in Automobile starting from the end of the year 1980.
PrincipleLike the thermal engine with gasoline, the diesel engine consists of sliding pistons in cylinders, closed by a cylinder head connecting the cylinders to the intake manifolds and exhaust and provided with valves mechanically operated by a camshaft.
Its operation rests on the spontaneous combustion of the Gazole, heavy fuel or raw plant oil in compressed air with 1:20 of the volume of the cylinder (approximately 35 bar), and whose temperature is carried of 600 °C with 1500 °C approximately. As soon as the fuel injected (pulverized), this one ignites almost instantaneously, without it not being necessary to resort to an ignition spark by candle. While burning, the mixture strongly increases the temperature and the pressure in the cylinder (60 to 100 bars), pushing back the piston which provides a labor force on a rod, which involves the rotation of the crankshaft (or tree crank acting as driving axis). (see Crank-connecting rod system)
The cycle Diesel at four times comprises:
- admission of air by the opening of the Valve of admission and the descent of the Piston;
- compression of the air by increase of the piston, the inlet valve being closed;
- injection - combustion - relaxation : little before the high dead Point one introduces, by a Injecteur, the Carburant which mixes with the compressed air. The fast combustion which follows constitutes driving time, the hot gases push back the piston, releasing part of their energy. This one can be measured by the Courbe of power engine;
- exhaust of gases waste by the opening of the exhaust valve, pushed by the increase of the piston.
Speed and power
The number of revolutions of the diesel engine is very different from an engine to another. Indeed more the engine is large, plus the diameter of the piston is large, and more the engine is slow. Three classes of engines are thus defined:
- low-speed engine: less than 200 tr/min
- driving semi-rapid: between 400 and 1000 driving tr/min
- rapid: 1000 tr/min and more
It should be noted that the setting in overspeed of the engine is likely to lead to shocks Pistons - valves which often result in the buckling of the tails of Soupape S or their stems of order.
Certain slow diesel engines of type at 2 times, reach 100.000 CH. (see the container ships Emma Mærsk) as Wärtsilä RT-flex96C 14 cylinders, engine 2 slow times (92/102 turns/minute). The cylinders have a boring of 960 mm and the piston a race of 2500 Misters. This engine has a height of approximately 13 m and a 26 m length for a weight of 2300 tons.
It is the navy of war which was interested in first in the diesel engines, and before very for the submarines. The French engineer Maxime Laubeuf equipped with it his submarine the Aigrette (1901) because the spark-ignition engines then did not develop enough power and the engines steam released too much smoke. During between two wars, the diesel knows an important progression in the Merchant navy, but heating (coal and fuel oil) remains still dominating. As for the first terrestrial vehicles been driven by diesel engines, it is necessary to await the beginning of the year 1920.
On the other hand, it is seldom used on the motor bikes and the Avion S, in particular for a question of embarked mass. However, the aeronautical use of diesel engines starts to develop: engines specific (SMA) or derived to the car (Centurion on Mercedes basis of the German motor mechanic Thielert); private planes DA-40 and DA-42 of the Diamond Austrian, Ecoflyer of French APEXES aircraft (ex-Dr. 400 of Robin) equipped with the Thielert Centurion 1.7 , planes of construction Dieselis amateur and Gaz' wing 2.
The Gas oil having a Calorific value voluminal more important than the gasoline and profiting from a taxation slightly more favorable in France, the diesel engines seems more economic with the use although more expensive with the purchase.
The reasons of the success of the diesel engine in the car, beyond of tax advantages which concern policy options and nontechnical, are due primarily to its Rendement, higher than that of the petrol engine. This output can be still improved by the use of a Turbocompresseur (the most recent models are “with variable geometry” (TGV), technology which enables them to be more powerful with low mode) and the Common rail (direct injection with high pressure) invented by FIAT and Magneti-Marelli. NB: There exist two kinds of compressor: the mechanical compressor (pulled by a belt) and the turbocompressor driven by another turbine which turns thanks to the force of rejected exhaust fumes.
- It should be noted that if the direct injection exists since the beginnings of the diesel engine, it was not used in Automobile for technical reasons (fume and noise superiors, gradient of pressure too high obliging a use of very solid and very heavy pistons, which prevented from turning too quickly), but only on the low-speed engines (industrial, weight-heavy and marine).
- With new the injector-pump, crawls common and piezoelectric, the pressure reaches until 2 500 bars (against 900) what ensures a turbulent pulverization of the gas oil, continues, constant and distributed well, essential for a good combustion; this technology bears the name of HDi (in car manufacturer PSA) for High-presses Direct Injection , or DCI ( Direct Common rail Injection ) in other manufacturers. This injection high pressure was invented by the company Elasis S.C.p.A., subsidiary of FIAT, and was used for the first time on the Alfa Romeo 156. This engine took the name of 1.9 JTD (1910 Cm3) and developed 105 horses for 26 mkg of couple.
- overfeeding calls upon a compressor to increase the quantity of air (thus of Oxygène) introduced into the engine, which is particularly appreciable in altitude (and thus in aviation). This principle makes it possible to increase the power without increasing the mode and the cubic capacity of the engine. The compressor charged to compress the air admission is pulled by a turbine (or turbo) which recovers part of the energy of exhaust fumes, approximately 25 % of the energy provided by the fuel. Overfeeding makes it possible to increase the Rendement engine: the power and the couple increase without substantial effect on fuel consumption, which is not the case on a petrol engine.
- to facilitate the cold departure by raising the temperature of the walls of the combustion chamber and the admitted air, the diesel engines (in particular engines theheavy ones) are equipped with systems of pre-heating (sometimes called candles ), of reheating of air, or of a system of overload to the injection pump.
- In the beginning regarded as a “dirty” engine because of its fuel less refined and of the important noise of operation (slappings), the Diesel improved today in terms of atmospheric pollution as well as sound. From the point of view of pollution, the principal advantage of the diesel engines is to produce, at equal power, because of their higher output, less that their equivalents with gasoline, typically 20% less. They produce also less Carbon monoxide (which oxidizes quickly out of carbon dioxide in the atmosphere) and of unburnt hydrocarbons that the petrol engine , in particular before the catalyst of the latter does not go up in temperature. Recent treatment of the problems which had with the emission of fine particles unburnt by the filters particles, as well as the question of nitrogen oxides are discussed in the section disadvantages.
- the content sulfur of the fuels (gas oil, fuel) is gradually decreased in the worldwide, in order to reduce the quantity of sulfur derivatives emitted to the exhaust.
- This engine can, under certain conditions, to burn Plant oil in the place of the Gazole resulting from oil. It is however preferable to use a transformed and refined fuel (Diester), in order to improve of it the characteristics and in particular fluidity (incompatibility of the too viscous fuels with the slopes high pressure).
Certain disadvantages of the first diesel engines, which were heavier, noisier and much less powerful than their counterparts with gasoline, are partly eliminated on the modern vehicles grace, in particular, with the Turbocompresseur with variable Géométrie, with the slopes of admission common or Injector-pump very high pressure. The reduction of the noise level depends much on the management of the injection and of course of the provisions of sound-proofing. These engines are however increasingly heavier from their design, than their counterparts with gasoline.
The principal disadvantages of the diesel engine relate to pollution and their precursors, the polycyclic aromatic hydrocarbons, as well as the emission of oxides of nitrogen, which generate in period of heat wave pollution to the Ozone.
Solutions for the improvement of this engine on the level of the particulate emission and oxides of nitrogen are proposed today.
the reduction of the quantity of emitted particles depends on the quality of the fuel and the design of the engine (improvement of the injection, devices with multiple injections…). For certain not easily combustible particles a Filtre with particles (FAP) very expensive is necessary. This technology will spread as from 2009, during the adoption of the European antipollution standards EURO V. However, the FAP still let pass the finest particles (PM 10) and more carcinogenic;
- the problem of nitrogen oxides (Nox) will undoubtedly be even more difficult to solve because they are generated in the presence of oxygen with the high temperatures, in addition necessary to a good output. The Nox and particulate emissions are a balance between an effective combustion, a weak Nox emission and a level of emitted particles low. The device more the current is the use of the Recirculation of exhaust fumes (EGR: Exhaust Gas Recirculation).
- the way of the Catalyze of Nox seems rather delicate because they are relatively stable and degrade themselves only in four hours under the effect of the Ultraviolet S, to transform itself into Ozone (O3), gas very irritant, poison thus harmful in lower atmosphere although essential in high-altitude. However, Toyota tested itself there with a system of catalysis of Nox on its last engine 2.2 D-4D in its version developing 177 ch.
- But the major disadvantage of the catalytic pot lies in the fact that its effectiveness intervenes only after one more or less long period of heating (according to the external room temperature). This phenomenon makes the motorization diesel unsuited to the urban circulation which is characterized by rather short ways, often insufficient to make it possible the catalytic device to reach the temperature which is the condition of its effectiveness.
- the diesel engines produce on average a ton of CO2 for 250 liters of gas oil. The use of the diesel engines thus makes it possible to reduce the emissions of CO2, with the detriment of the particulate emissions.
- There exist fuels of synthesis (Fischer-Tropsch) stripped of sulfur, which make it possible to reduce the particulate emissions to very low levels. These fuels, the dimethyl ether in particular, can be synthesized starting from hydrocarbons. However, any synthesis (or chemical conversion) induced itself a consumption and an emission of CO2: it is thus necessary to enter the whole of the energy expenditure, and not only what the ultimate consumer is capable to perceive and to conceive.
Here the list of the various names given to the modern diesel engines (injecting pumps or common slope) according to the marks which market them:
- JTD: FIAT, Alfa Romeo, Lancia - inventive of the system Common rail 1st generation,
- MJtd: FIAT, Alfa Romeo, Lancia, Iveco - inventive and distributer of the system Common rail 2nd and 3rd generation,
- HDi: Peugeot, Citroen
- dCi: Renault, Nissan, Dacia
- TDCI: Mercedes, Smart
- CRD: Jeep
- Td (X), TDV (X): Land rover (ex: Td4 or TDV8)
- D: BMW (ex: 530d)
- TDI: Audi, Seat, Skoda, Volkswagen
- D-4D: Toyota
- D: Lexus (ex: IS 220 d)
- CDTI: Opel (the DTI are direct fuel injection engines without common slope)
- VDi: old denomination of Nissan, replaced today by dCi
- DI-D: Mitsubishi
- D: Volvo (ex: 2.4D or D5), Jaguar (ex: 2.7D)
- TDCi: Ford
- MZR-CD: Mazda
- i-CTDi : Honda
- CRDi: Hyundai
- CRDI : Kia
- TCDi, VCDi: Chevrolet
- TID: Saab
At the time of the edition 2007, Peugeot engaged in its turn a vehicle been driven by a diesel engine, the Peugeot 908. It is been driven by an engine V12 HDi developing approximately 700 horses. One of the three Peugeot 908 at the beginning was classified in second position.
Chemical reaction in which the combustion of the fuel (sharp oxidation of hexadecane) by dioxygene present in the air releases from heat more of the residues of combustion: carbon dioxide and water. Perfect equation of the diesel combustion of the gas oil: hexadecane + dioxygene = carbon dioxide + water 2 C16H34 + 49 O2 = 32 CO2 + 34 H2O
In practice it is considered that it is necessary to envisage 30 G of air to burn 1 G of fuel.
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