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Diesel Tuning Fundamentals: Pilot Injection Events

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Pilot Injection Events


00:00 - With the precise control afforded by modern electronic fuel injection systems, coupled with the incredibly high fuel pressures that current common rail diesel engines operate at, it's common practice to provide multiple injection events per engine cycle.
00:15 Normally this will consist of a number of injection events that occur prior to the main injection event, and in some instances, we may also see post injection events that occur later in the engine cycle, primarily for emissions purposes.
00:30 In modern diesel engines we may see four or more separate injection events occur during each engine cycle.
00:37 The pilot injection pulse serves two purposes.
00:41 Firstly it raises the temperature inside the combustion chamber as a result of the small amount of fuel that's just been combusted.
00:48 In itself this increase in temperature helps to reduce the ignition delay, when the main injection event begins.
00:56 At the same time the pilot injection event also helps to smooth the rising pressure curve inside the combustion chamber and again helps to reduce the audible knock.
01:07 The downside of pilot injection is that it can create exhaust smoke.
01:11 This is why we now see many modern diesel engines fitted with diesel particulate filers or DPFs, which we'll discuss in detail later in the course.
01:22 So the important concept to take away from this module is that modern diesel engines will typically use multiple injection pulses aside from the main injection event, and that pilot injection events can be very effective at reducing the ignition delay and hence the audible knocking sound that's common in diesel engines.