Thursday, November 3, 2011

CRDI


Common rail

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"HDi" redirects here. For the interactive format, see HDi (interactivity).
"DCi" redirects here. For other uses, see DCI (disambiguation).
"CRDi" redirects here. For other uses, see CRDi (disambiguation).
Common rail direct fuel injection is a modern variant of direct fuel injection system for petrol and diesel engines.
Common rail fuel injector
On diesel engines, it features a high-pressure (over 1,000 bar/15,000 psi) fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding unit injectors (Pumpe/Düse or pump nozzles). Third-generation common rail diesels now feature piezoelectric injectors for increased precision, with fuel pressures up to 1,800 bar/26,000 psi.
In gasoline engines, it is used in gasoline direct injection engine technology.

Contents

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[edit]History

The common rail system prototype was developed in the late 1960s by Robert Huber of Switzerland and the technology further developed by Dr. Marco Ganser at the Swiss Federal Institute of Technology in Zurich, later of Ganser-Hydromag AG (est.1995) in Oberägeri.
The first successful usage in production vehicle began in Japan by the mid-1990s. Dr. Shohei Itoh and Masahiko Miyaki of the Denso Corporation, a Japanese automotive parts manufacturer, developed the common rail fuel system for heavy duty vehicles and turned it into practical use on their ECD-U2 common-rail system mounted on the Hino Rising Ranger truck and sold for general use in 1995.[1] Denso claims the first commercial high pressure common rail system in 1995.[2]
Common rail fuel system close up
Modern common rail systems, whilst working on the same principle, are governed by an engine control unit(ECU) which opens each injector electronically rather than mechanically. This was extensively prototyped in the 1990s with collaboration between Magneti Marelli, Centro Ricerche Fiat and Elasis. After research and development by the Fiat Group, the design was acquired by the German company Robert Bosch GmbH for completion of development and refinement for mass-production. In hindsight the sale appeared to be a tactical error for Fiat as the new technology proved to be highly profitable. The company had little choice but to sell, however, as it was in a poor financial state at the time and lacked the resources to complete development on its own.[3] In 1997 they extended its use for passenger cars. The first passenger car that used the common rail system was the 1997 model Alfa Romeo 156 2.4 JTD,[4] and later on that same year Mercedes-Benz C 220 CDI.
Common rail engines have been used in marine and locomotive applications for some time. The Cooper-Bessemer GN-8 (circa 1942) is an example of a hydraulically operated common rail diesel engine, also known as a modified common rail.
Vickers used common rail systems in submarine engines circa 1916. Doxford Engines Ltd.[5] (opposed piston heavy marine engines) used a common rail system (from 1921 to 1980) whereby a multi-cylinder reciprocating fuel pump generated a pressure of approximately 600bar with the fuel being stored in accumulator bottles. Pressure control was achieved by means of an adjustable pump discharge stroke and a "spill valve". Camshaft operated mechanical timing valves were used to supply the spring-loaded Brice/CAV/Lucas injectors which injected through the side of the cylinder into the chamber formed between the pistons. Early engines had a pair of timing cams, one for ahead running and one for astern. Later engines had two injectors per cylinder and the final series of constant pressure turbocharged engines were fitted with four injectors per cylinder. This system was used for the injection of both diesel oil and heavy fuel oil (600cSt heated to a temperature of approximately 130°C).
The common rail system is suitable for all types of road cars with diesel engines, ranging from city cars such as the Fiat Nuova Panda to executive carssuch as the Audi A6.

[edit]Common rail today

Today the common rail system has brought about a revolution in diesel engine technology. Robert Bosch GmbH, Delphi Automotive Systems, Denso Corporation, and Siemens VDO (now owned by Continental AG) are the main suppliers of modern common rail systems. The car makers refer to their common rail engines by their own brand names:

[edit]Principles

Common Rail Scheme.svg
Solenoid or piezoelectric valves make possible fine electronic control over the fuel injection time and quantity and the higher pressure that the common rail technology makes available provides better fuel atomisation. In order to lower engine noise, the engine's electronic control unit can inject a small amount of diesel just before the main injection event ("pilot" injection), thus reducing its explosiveness and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold starting and so on. Some advanced common rail fuel systems perform as many as five injections per stroke.[6]
Common rail engines require very short (< 1 s) or no heating up time at all[citation needed]and produce lower engine noise and emissions than older systems.
Diesel engines have historically used various forms of fuel injection. Two common types include the unit injection system and the distributor/inline pump systems (See diesel engineand unit injector for more information). While these older systems provided accurate fuel quantity and injection timing control, they were limited by several factors:
  • They were cam driven and injection pressure was proportional to engine speed. This typically meant that the highest injection pressure could only be achieved at the highest engine speed and the maximum achievable injection pressure decreased as engine speed decreased. This relationship is true with all pumps, even those used on common rail systems; with the unit or distributor systems, however, the injection pressure is tied to the instantaneous pressure of a single pumping event with no accumulator and thus the relationship is more prominent and troublesome.
  • They were limited in the number and timing of injection events that could be commanded during a single combustion event. While multiple injection events are possible with these older systems, it is much more difficult and costly to achieve.
  • For the typical distributor/inline system, the start of injection occurred at a pre-determined pressure (often referred to as: pop pressure) and ended at a pre-determined pressure. This characteristic resulted from "dummy" injectors in the cylinder head which opened and closed at pressures determined by the spring preload applied to the plunger in the injector. Once the pressure in the injector reached a pre-determined level, the plunger would lift and injection would start.
In common rail systems, a high pressure pump stores a reservoir of fuel at high pressure — up to and above 2,000 bars (29,000 psi). The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high pressure. This accumulator supplies multiple fuel injectors with high pressure fuel. This simplifies the purpose of the high pressure pump in that it only has to maintain a commanded pressure at a target (either mechanically or electronically controlled). The fuel injectors are typically ECU-controlled. When the fuel injectors are electrically activated, a hydraulic valve (consisting of a nozzle and plunger) is mechanically or hydraulically opened and fuel is sprayed into the cylinders at the desired pressure. Since the fuel pressure energy is stored remotely and the injectors are electrically actuated, the injection pressure at the start and end of injection is very near the pressure in the accumulator (rail), thus producing a square injection rate. If the accumulator, pump and plumbing are sized properly, the injection pressure and rate will be the same for each of the multiple injection events.

[edit]See also

  • Gasoline Direct Injection
  • Unit Injector
  • Unit pump
  • Turbocharged Direct Injection
  • Fuel filter
  • Water sensor
  • Air flow sensor
  • _____________________________________________________________________________________]

  • CRDI Technology In Plain English

    December 22, 2009
    By 
    Advertisement
    Ever since I wrote about the MPFI Technology , I wanted to cover CRDI also. In this article, I have used simple words and terms that help you easily understand how things work with CRDI / CRDe / DICOR / TDI etc. If I have to draw an analogy, I would say CRDI is for Diesel Engine as MPFI is for Gasoline/Petrol Engine.
    CRDI Engine

    Common Rail Direct Injection or CRDI


    CRDI is an intelligent way of controlling a diesel engine with use of modern computer systems. CRDI helps to improve the power, performance and reduce harmful emissions from a diesel engine. Conventional Diesel Engines (non-CRDI engines) are sluggish, noisy and  poor in performance compared to a CRDI engine.
    CRDI or common rail direct injection system is also sometimes referred to by many similar or different names. Some brands use name CRDe / DICOR / Turbojet / DDIS / TDI etc. All these systems work on same principles with slight variations and enhancements here and there.
    CRDI system uses common rail which is like one single rail or fuel channel which contains diesel compresses at high pressure. This is a called a common rail because there is one single pump which compresses the diesel and one single rail which contains that compressed fuel. In conventional diesel engines, there will be as many pumps and fuel rails as there are cylinders.
    As an example, for a conventional 4 cylinder diesel engine there will be 4 fuel-pumps, 4 fuel rails each feeding to one cylinder. In CRDI, there will be one fuel rail for all 4 cylinders so that the fuel for all the cylinders is pressurized at same pressure.
    The fuel is injected into each engine cylinder at a particular time interval based on the position of moving piston inside the cylinder. In a conventional non-CRDI system, this interval and the fuel quantity  was determined by mechanical components, but in a CRDI system this time interval and timing etc are all controlled by a central computer or microprocessor based control system.
    To run a CRDI system, the microprocessor works with input from multiple sensors. Based on the input from these sensors, the microprocessor can calculate the precise amount of the diesel and the timing when the diesel should be injected inside the cylinder. Using these calculations, the CRDI control system delivers the right amount of diesel at the right time to allow best possible output with least emissions and least possible  wastage of fuel.
    The input sensors include Accelerator Pedal Position (APP) sensor, crank position sensor, pressure sensor, lambda sensor etc. The use of sensors and microprocessor to control the engine makes most efficient use of the fuel and also improved the power, fuel-economy and performance of the engine by managing it in a much better way.
    One more major difference between a CRDI and conventional diesel engine is the way the fuel Injectors are controlled. In case of a conventional Engine, the fuel injectors are controlled by mechanical components to operate the fuel injectors. Use of these mechanical components adds additional noise as there are many moving components in the injector mechanism of a conventional diesel engine. In case of a CRDI engine, the fuel injectors are operated using solenoid valves which operate on electric current and do not require complex and noisy mechanical arrangement to operate the fuel Injection into the cylinder. The solenoid valves are operated by the central microprocessor of the CRDI control system based on the inputs from the sensors used in the system.
    So if I summarize it, CRDI works on intelligently controlling the Diesel Engine by using sensors and microprocessors. It replaces some of the mechanical components with intelligent electrical and electronic systems which improves the power, response, efficiency and performance. It also reduces the noise, emissions and vibration levels to a considerable extent.
    I hope I have used simple words so that you don’t get confused in the technical jargons.
     
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    This entry was posted on november 03 2011 at 2:17 pm and is filed under Automobile Technology. You can follow any responses to this entry through the RSS 2.0 feed.
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