When the first diesel engine was invented, no suitable fuel injection system was available and each engine manufacturer would make their own system. Rudolf Diesel’s first engines ran with an ‘air blast’ system where the fuel was blown into the cylinder by compressed air, which also helped to atomise the fuel and mixing with the air in the cylinder. This type of injection system was common for many years until inline jerk type pumps became available. The metering of the fuel was often carried out at the injector by a cam driven linkage.

The first common rail injection systems were patented by Vickers Ltd. and used in Atlas Imperial engines in about 1914. These systems used a multi-cylinder pump which fed fuel at pressures of around 300 – 400 bar to an accumulator. The individual injectors were connected to the accumulator and fuel injection was controlled by wedges positioned between the cam followers and the push rods which opened and closed the injection nozzles. The injection pressure was lowered at idle to prevent the injection duration from becoming too short. An electrically operated injection valve was patented by Vickers about 1920.

A modification to the common rail system was made by Cooper Bessemer by introducing a rotary valve to time and meter the fuel to the different cylinders giving the industry its first rotary distribution pump.

In 1927, Robert Bosch modified his oil injection pump for use with diesel fuel and introduced the first ‘solid’ injection system which became the standard for many years. The pump was produced in different multi-cylinder forms which had one pumping element per cylinder and injectors which were opened and closed hydraulically. Shortly afterwards, an integral governor was added, initially pneumatically operated, but later flyweight governors were added.

In 1952, Vernon Roosa was granted a patent for a rotary pump which was compact and relatively cost effective and this began to be used on tractors and higher speed engines. A licence for these types of pumps was granted to Lucas (now Delphi) who then produced the DPA pump, initially for the European market.

Due to the ever increasingly stringent emissions legislation and the demand for better driveability, electronic control of injection systems was introduced in the mid 1980s. This gave the engine manufacturer the chance to control both injection quantity and, in certain cases, timing. The mechanical devices which had been added to the fuel pumps to control fuelling based on altitude and manifold pressure disappeared and pumps became smaller, although the total system cost increased due to the addition of sensors, cable harnesses and control units. The first electronically controlled systems had a relatively small number of functions compared to today’s systems which are linked to the control of the total vehicle.

Common rail systems reappeared in 1995 with the introduction of Denso’s ECD-U2 system on Hino trucks. Passenger cars followed and in 1999, Bosch introduced common rail systems on passenger cars. Shortly afterwards, the first piezo actuated common rail injectors were introduced by Siemens (now Continental). Other generations of piezo actuated injection systems have followed from other manufacturers.

In contrast to the early systems where injection pressure was in the order of 300 bar, modern injection systems operate at pressures up to 3000 bar.