The system common rail or direct injection with slope common or direct Injection to high pressure is a modern version of the Diesel engine with direct injection. Its characteristic lies in the presence of single led to high pressure, between 300 and 1.400 bars with full load, for the food of fuel in the cylinders. In the preceding engines with direct injection, a pump with low pressure supplied the injectors or of the conduits with high pressure to the valves controlled by a camshaft. The third generation of diesel engines common rail uses piezoelectric injectors which make it possible to very precisely control the quantity of fuel and a pressure which can go to 1.900 bars, even beyond that.
The valves solenoids or piezoelectric allow an electronic control of the duration of the injection as well as the quantity exact of fuel to use, moreover, the high pressure allows a better distribution of the fuel cloud. To reduce the noise of operation of the engine, a negligible quantity of fuel is injected before the principal injection. This solution called pre-injection, makes it possible the fuel to start to burn in a particular point of the combustion chamber, unlike the traditional diesel engines in which one had several not controlled firing points. So the engines equipped with the system common rail are quieter and do not know any more of the peaks of pressure by obtaining a combustion much more regular, and allow a clear reduction in the gas emissions not flarings and consumption from approximately 15% with a rise of the services of 12%. The system of pre-injection gives to the common rail an aspect much more similar to the engines with positive ignition, like the traditional petrol engines. The most sophisticated engines can carry out up to five injections per cycle, they are called Multijet, thus named by their inventor FIAT and Magneti-Marelli.
History of the common rail
Engines with a principle former to the common rail were used, in the past, the engines marine and railway, on certain engines. The engine Cooper-Bessemer GN-8 of 1942, is the typical example of the diesel engine common the hydraulic rail most known.
The principle of the engine Common rail to direct injection was developed by researchers of the Polytechnic school of Zurich as from the Thirties but it forever tried on engines of small-engined car to be installed on motor vehicles before the revolution of the development carried out by the engineers FIAT in 1996. A pump, indépendemment of the mode of rotation of the engine, injects gas oil inside a conduit, the common rail or common collector, and generates a pressure inside this conduit which becomes a hydraulic accumulator, i.e. a fuel tank under pressure ready to be injected in the cylinders of the engine.
The pre-industrialization of the system Common rail began in 1990 in the common laboratories from research and development from the companies Magneti-Marelli, Centro Ricerche FIAT and Elasis. Benefitting from research and preceding experiments from Group FIAT, a license was yielded to the month of April 1994 at the German company Robert Bosch AG for his manufacture and its marketing with large scales.
Group FIAT had presented in 1986, the first car in the world been driven by a diesel engine with a direct injection, FIAT Croma TD i.d.
It is in October 1996 that the permière was introduced conveys in the world equipped with the famous system common rail, the Alfa Romeo 156 JTD.
The engines Common rail of the type MultiJet of 3rd generation currently equip with many models of group FIAT like, for example, FIAT Panda and FIAT Punto, the Alfa Romeo 147, Alfa Romeo 159, Lancia Ypsilon, Musa and Thesis, and well of others.
Practically all the modern engines use technology Common rail, with the only exception of the old engines of the group VAG: Volkswagen, Audi, Seat, Škoda, called TDI, which are still faithful to the system Injector-pump, or PDE, where each injector is equipped with a pump. This system makes it possible to work with pressures of almost 2000 bar, but considering the relatively weak diffusion of this system that no other manufacturer uses, the higher complexity of its adjustments compared to Common Rail, and its high cost of manufacture, its perenniality is compromised simple fact that it underwent his last evolutions to pass from accuracy the course of the standards Euro IV but no new evolution made it possible to make him respect the standards Euro V. VW announced to have to give up this system since 2008 in favor of Common rail Multijet.
A system of direct injection diesel to common slope is made up:
- of an Injecting by cylinder, playing the part of Valve S controlled électrohydrauliquement,
- of a low petrol station Pressure driven by the engine, which aspires the fuel in the tank to bring it to the system of injection,
- of a pump high pressure, it also driven by the engine, which feeds the common slope while carburizing,
- of a Accumulateur hydraulics, called common slope , which constitutes a fuel reserve under high pressure for the injectors,
- of a electromagnetic sluice gate located between the petrol station and high pressure pumps it, which controls the mass fuel rate of flow,
- of a limiting device of pressure to taring mechanical or controlled, which controls the pressure in the common slope,
- of a pressure pick-up in the common slope,
- of a containing hydrocarbon temperature gauge,
- of an electronic computer electronic computer of injection (commonly called ECU for Electronic Control Links English ) controlling the Actionneur S: injectors, the electromagnetic sluice gate of control of the flow and possibly the taring of the limiting device of pressure, starting from the information measured by the sensors.
In practice, it is the calculator of engine control which plays the part of calculator of injection, and for this reason uses the whole of information from the sensors of the engine control: position of the accelerator pedal, pressure in the intake manifold, temperature and air flow to the admission, driving mode and angular position of the camshaft, like possibly the Accélération measured on the block rolls.
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