That to is made for reduction of noise as just one perinjection did not get the noise down enough to compete with the petrols, the side effect of that is it looks like a big pulse width,the 5 preinjections are hardwared in the latest systems these do not vary according to the fuel requirement only the final injection pulse varies,that is if a system is designed with 3 preinjection pulses than it will give 3 pre injections from lowest to the highest rpm [through out the rev range] same is the case with 5 preinjection [the only excemption can be that if the engine temperature is high enough the preinjection can be reduced, but I am not sure about this].5 pre injectionssystems are seen only in really expansive cars [read merc,beemeers,etc] not the cheap common rails, swift,dicors,etc.these make do with put 3 injections.
Also higher number of preinjections means that the cylinder remains hot for longer duration, this help the diesel burn more efficiently.As these are used when the piston is moving towards the TDC, and not at the TDC. |