Bosch Diesel Fuel Injection

 In 1922, Robert Bosch embarked on a journey to develop accessories required for a diesel engine (fuel injection pumps and nozzles). These pumps had to withstand several hundred atmospheres and nozzles had to have quite fine outlet openings in order to atomize the fuel droplets.

The fuel injection pump should be capable of producing high pressure and also inject small amounts of fuel so that the engine can operate even at low idle speeds. For full load operations, the fuel quantity should be increased by four to five times.

Development of Fuel Injection Pump:

Different pump designs were tried out. Some were spool controlled and some were valve controlled. The fuel quantity to be injected was varied by altering the plunger lift. In March 1925, Bosch came in agreement with Acro AG to utilize their diesel engine system with air chamber and its injection pump and nozzle. 

The Acro pump, designed by Franz Lang was a unique pump consisting of a special valve spool with helix. The spool could be rotated to regulate the quantity of fuel to be delivered. Later on, Lang moved the helix to the pump plunger. After Lang's departure from the company in October 1926, Bosch focused on the development of the Acro pumps which would later be named as In-line fuel injection pumps.

For more information on Inline pumps, click on the link below:

Inline fuel injection pumps

Nozzles and Nozzle Holders:

Initially pintle nozzles were used in pre-combustion chamber engines. Hole type nozzles were added at the start of 1929 with the introduction of Bosch's in-line fuel injection pump in direct injection diesel engines.

Nozzle holders were adapted in terms of the size of nozzles. Engine manufacturers started demanding that nozzles could be screwed into the cylinder head just like a spark plug on a gasoline engine. Bosch started to produce screw-in nozzle holders.

Governor for fuel injection pump:

Diesel engines are not self governing like gasoline engines. It needs a governor to protect against overspeed and self destruction. Engine manufacturers used to develop their own governors. However, Bosch latched on to the idea of a mechanical governor being combined with the fuel injection pump. In 1931, Bosch introduced its first mechanical governor.