Denso claims the first commercial high pressure common rail system in 1995. Centro Bosch common rail system pdf Fiat and Elasis. In hindsight, the sale appeared to be a strategic error for Fiat, as the new technology proved to be highly profitable.
The company had little choice but to sell Bosch a licence, as it was in a poor financial state at the time and lacked the resources to complete development on its own. In 1997 they extended its use for passenger cars. 90 degrees of rotation to keep the fuel pressure adequately constant in the rail. Fuel delivery to individual cylinders could be shut off via valves in the injector lines. Pressure control was achieved by means of an adjustable pump discharge stroke and a “spill valve”.
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. Some advanced common rail fuel systems perform as many as five injections per stroke. Common rail engines require a very short to no heating-up time, depending on the ambient temperature, and produce lower engine noise and emissions than older systems.
Diesel engines have historically used various forms of fuel injection. They are cam driven, and injection pressure is proportional to engine speed. This typically means that the highest injection pressure can only be achieved at the highest engine speed and the maximum achievable injection pressure decreases as engine speed decreases. This relationship is true with all pumps, even those used on common rail systems. With unit or distributor systems, 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 are limited in the number and timing of injection events that can 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.