In the first part of The Diesel Injection Evolution I wrote about how the pressure changes had made smaller fuel droplets possible so that the fuel burning became more efficient and less polluting with the advantage of a more flexible power range.

The higher Common rail pressures of 25000 psi and greater are only part of the solution. The older mechanical injectors would not have been able to utilise them as no adjustments could have been made during the operational cycle over many different loadings, temperature range and fuel grade types found all over the world. The solution was electronic computer control and operation.

There are two main types of electronic injectors. A solenoid operated system and a piezo crystal system. Both of these can control the amount of injector firing valve lift and duration in time that they are lifted. The injectors are controlled by the engine computer and can be fired in rapid succession several times during the injection cycle. With this precise control over injector firings, smaller, staggered quantities of fuel delivery (5 or more) can be timed over the course of the power stroke to promote complete and accurate combustion. In the heavy duty truck systems a Smart injector is now being used which can calculate its and the engine wear and allow for keeping optimum fuelling constantly over its working life time.

Main correction factors the computer looks at include engine temperature, air temperature, oil temperature, engine speed/demand, throttle position, cam shaft position, air flow, boost pressure and other manufactures extra sensors. All of these send data to the ECU which uses this from a minus 20 cold start up to the sweltering desserts the ECU constantly alters the engine fuel requirements to achieve to ensure the best performance and environmental consideration operation of the engine.

The next blog will be on the post engine clean up systems like the DPF and EGR valve.

Thank you for your kind comments regarding these posts and if you would like me to write about a particular diesel fuel injection area old or new please email me: [email protected]

About the author
Graham Williams is the Thomas Injection Workshop Manager and has worked with diesel injection systems and auto electrical systems for over 45 years. He is a Bosch System Technician and a CAV diesel master repairer.