Diesel Tuning Fundamentals: Diesel Injector Operation
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Diesel Injector Operation
04.58
| 00:00 | - The fuel injectors used for common rail diesel engines are generally grouped into two methods of operation, piezo, or piezo electric, and inductive or solenoid. |
| 00:09 | As a diesel engine tuner it's not strictly essential to have a deep understanding of the specifics of the injector construction and operation, however it's still useful to understand the basic concepts. |
| 00:22 | In particular it's important to know that the way piezo and inductive injectors are controlled by the ECU are very different. |
| 00:28 | This is more relevant for those of you considering the fitment of a univeral standalone ECU rather than reflashing the factory fitted ECU. |
| 00:38 | An inductive injector is similar in operation to a conventional low pressure gasoline port fuel injector, where a magnetic coil inside the injector is responsible for opening and closing the injector to control fuel flow. |
| 00:52 | In a common rail diesel injector this presents some challenges however as a result of the incredibly high fuel pressures that the injectors are subject to, and the very fast response required from the injector. |
| 01:04 | Part of the solution to this is the very high voltages and currents used to control the injectors. |
| 01:11 | For example it's common for peak voltages to exceed 100 volts and peak current to reach in excess of 10 amps. |
| 01:19 | A piezo injector on the other hand uses a crystal stack inside the injector which is typically made from quartz. |
| 01:26 | The principal of operation is that when voltage is applied to the crystal stack, it expands, albeit only very slightly. |
| 01:34 | It's this movement that is in turn used to actuate and open the injector to start fuel flowing. |
| 01:40 | The original benefit of the piezo injector design was the very fast operation which was up to five times faster than the inductive injectors of the time. |
| 01:50 | Advances however in inductive diesel injector technology have meant that both injector types can now provide similar performance and it's difficult to clearly pick a winner. |
| 02:01 | In the OE world, Bosch and Siemens produce piezo injectors while Delphi favour the inductive method. |
| 02:08 | Denso have their bases covered, developing both technologies. |
| 02:11 | The signals used to drive common rail diesel injectors are far more complex than what we may see for a conventional gasoline port injector, requiring accurate control on the part of the ECU in order to control the current through the injector, through the separate stages of the injector's operation. |
| 02:30 | Again this is more of a concern for those tuners dealing with aftermarket standalone ECUs than those reflashing a stock ECU. |
| 02:38 | Due to the complex operation of the injectors themselves, coupled with the physical fitment to the engine, swapping to larger injectors from a different engine or even aftermarket injectors is difficult or in some cases impossible. |
| 02:52 | This leads to some challenges if we're aiming to increase engine performance by virtue of a significant increase in fuel delivery. |
| 03:01 | Fortunately there is a work around here as the injector is designed as a two part system. |
| 03:07 | We have the injector body which houses the actuation system which we've just discussed, along with a nozzle which is the part of the injector that locates into the combustion chamber and includes a number of tiny holes through which the fuel is physically sprayed into the cylinder. |
| 03:23 | In the aftermarket we often have access to larger or modified nozzles that can supply more fuel for a given injector pulse width. |
| 03:31 | As diesel engine development has advanced and we've seen a drive for improved fuel economy and lower emissions, manufacturers have put more emphasis into the design of their injector nozzles. |
| 03:42 | In particular we've seen the size of the holes in the nozzle shrink and these may be in the region of 0.4 millimetres or thereabouts. |
| 03:51 | These very small holes coupled with increased fuel pressure allow for better atomisation of the fuel. |
| 03:57 | In order to supply sufficient fuel in a given pulse width, more holes are used and this also allows the manufacturer to control how and where the fuel is distributed within the combustion chamber. |
| 04:09 | One of the problems of modern injector production is accurately replicating the size of these holes across every injector in a mass manufacturing situation. |
| 04:19 | It's possible for example to see a variation that may be as great as 20% across a set of production injectors. |
| 04:27 | The result is that there can be significant differences in injector flow from one injector to the next. |
| 04:33 | Obviously this will have a big impact on the fuel delivery to the engine, so in the OE world this is dealt with by an individual code on each injector which describes its flow characteristics. |
| 04:45 | If the injectors are changed then the ECU needs to be coded to the new injectors in order for the ECU to be able to correctly control them. |
