Technical Information

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

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.

A simple Common Rail Injection engine showing the high-pressure pump, the Rail and the hydraulically operated injectors

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.

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)

Pump Duse Nozzle Injection System

Pumpe Duse Diesel Injector Pumpe düse (PD) is a quite rare beast, because in the world of diesel cars, it's only the Volkswagen Group that uses this technology for cars. The name Pumpe Düse is German for Pump Metering. This refers to the PD unit being an all-in-one assembly comprising the high pressure pump (that pressurises fuel to injection pressure) and the injector (which injects the pressurised fuel into the engine cylinder).

There is one complete pump düse assembly (otherwise known as a unit injector) on the cylinder head for each cylinder, and the pump part of the PD is driven by a camshaft in the cylinder head (usually the same camshaft that operates the engine's own cylinder valves), or by a hydraulic oil pressure system.

PD is mechanically more fiddly than common rail, and it needs a specially designed cylinder head, so it's costly too. But its big advantage is that is can generate considerably higher injection pressure than even common rail can, and VW's PD units are good for 2,050 bar (against common rail's typical 1600 to 1800 bar). That's great for producing more torque than would otherwise be possible, and it's also very useful for reducing polluting exhaust emmisions. Like common rail, PD has pilot-injection built into it to hush combustion rattle, and Volkswagen has said that it will soon be possible to build multiple-injection technology (such as that incorporated into the very latest CR systems) to further clean-up emissions and reduce noise.

The Volkswagen Group is unique in adopting this technology, and some say that other's shun it because its scope for further refinement - particularly in terms of the number of multiple injections - is limited. Proponents of the system though, point out that it's safer, in that it doesn't store fuel in a rail at incredibly high pressure, but simply generates that pressure as and when needed. Of course, as with Common Rail, electronic management constantly monitors what the engine and driver are up to, and continually adjusts injection timing and fuel dosage.

The basic components of a common rail system are:

  • A low pressure pump to feed fuel to the individual injectors.
  • Injectors for each cylinder which pressurise the fuel and inject precise amounts combustion chamber as required.
  • A diesel control unit – the ‘brain’ of the system, which precisely controls fuel flow, pressure and timing while continuously monitoring the operating conditions of the engine.

Verteiler (VE) Variable Pressure System

This is an older type of diesel engine used by Audi and Volkswagen, and is still current in some models, although they are being phased out in favour of Common Rail or Pumpe Duse systems.

There is a single fuel pressurisation pump that feeds all cylinders, but it does not have the constantly pressured common rail. As the pump is mechanically controlled by the engine, pumping speed rises directly in line with the engine revolutions. The pressurised fuel is fed to each cylinder in turn from the pump.

VE systems generally use turbos to increase the air compression to increase available power. In terms of operation for driving and tuning, they operate similarly to Common Rail diesel engines, although the sensor control ports are located either on the main pump body or on the ECU.

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