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Technical Information

Details of the various diesel engine systems we supply tuning boxes for and how they work.

Common Rail System Pump Duse System Variable Pressure System


Common Rail Direct Fuel Injection (CRD) System

Diesel engines were first developed by Rudolph Diesel around 1893. While there were refinements in the design, the next major advance in diesel engine technology was the common rail direct fuel injection system. The common rail system prototype was developed in the late 1960s by Robert Huber of Switzerland, Dr. Ganser at the Swiss Federal Institute of Technology in Zurich and Dr. Shohei Itoh and Masahiko Miyaki, of the Denso Corporation, a Japanese automotive parts manufacturer. Firstly used for large enginces for trains and ships, The Denso Corporation were the first to develop a Common Rail Fuel System for trucks, first using it on the Hino Rising Ranger truck sold in 1995.

Development on the smaller engines required for cars took a little longer, and the invention of modern electronic engine control units (ECU) allowed each injector to be controlled 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 Bosch for completion of development and making suitable for mass-production.

The first passenger cars to use the common rail system were the 1997 Alfa Romeo 156 1.9 JTD and the 1997 Mercedes-Benz E 320 CDI.

The most significant change since 1997 has been the move away from simple electrical solenoid motors to control the valves to more accurate piezoelectric control (similar to those used in ink jet printers). to give even finer levels of control.

Common rail diesel engine
A simple Common Rail Injection engine showing the high-pressure pump, the Rail and the hydraulically operated injectors
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Pressure Comparison diagram for the three main types of engines
Blue = Common Rail, Red = Pump Duse, Green = Variable Pressure

In conventional diesel engines injection pressure is generated for each injector individually. A direct injection engine based on the common rail principle first stores the fuel under high pressure in a central container ("common rail") and delivers it to the individual injection valves (injectors) only on demand. This way an injection pressure of up to 1,800 bar is available at all times, even at low engine speeds. The high pressure produces a very fine atomisation of the fuel leading to better and cleaner combustion. As the rail is pressured all the time, the fuel supply is not dependent on the engine revolutions but can be optimised independently. The time and duration of fuel injection is not fixed as it is controlled by the ECU and not mechanically and can be controlled precisely to optimise combustion and emissions. In modern common rail systems injection is usually split into several individual injections: pre-injection, main injection and post-injection.

Four basic components of a common rail system are:

  • A high pressure pump with pressure regulator and inlet metering valve.
  • A rail which contains a pressurised reserve of fuel.
  • Injectors which inject precise amounts of fuel into the combustion chamber as required.
  • A diesel control unit – the ‘brain’ of the system, which precisely controls injector flow and timing as well as rail pressure while continuously monitoring the operating conditions of the engine.

Benefits of the common rail principle compared to conventional diesel engines are lower engine noise levels, much shorter 'pre-warning' time, stronger performance and greater combustion efficiency leading to lower emissions and enhanced fuel economy.

BMW 2 litre Diesel Engine Diagram Example specifications for a Common Rail Diesel Engine from a 2009 BMW 335D

  • In-line 6-cylinder-diesel engine with aluminium crankcase
  • Third generation common rail direct injection with Variable Twin Turbo
  • Capacity: 2,993 cc
  • max. power: 210 kW/286 bhp at 4,400 rpm
  • max. torque: 580 Nm at 1,750-2,250 rpm
  • acceleration [0-100 km/h]: 6.0 seconds
  • top speed: 250 km/h
  • average fuel consumption: 35 MPG (6.7 litres/100 kilometres)
  • CO2 emissions: 177 g/km (178 g/km)