arghx7
Well-Known Member
If you ever look through a very high resolution crank angle resolved rail pressure trace you can see the pressure drops as injector fires, and you can see some oscillations in the rail pressure. From the perspective of engine performance, the pressure pulsation in a mass production OEM fuel system is a big "yeah, there's some pulsation. So what." It's more related to noise and durability of the rail and hard lines.
The limiting factor is the ability for the pump to maintain rail pressure when the delivery angle is maxed out, meaning the whole stroke of the lobe is commanded to deliver fuel. The number of lobes and the stroke of the lobes sets that. Also, brake specific fuel consumption is a big factor. If the engine isn't breathing well up top due to restriction at the turbo, you end up needing to dump more fuel in, and then your fuel system becomes the limitation.
So yeah the injectors also become a limit, depending how far you are willing to stretch the injection window in terms of crank angle degrees (rather than duty cycle or pulsewidth). As the start of injection gets earlier or end of injection gets later, you can start washing down the cylinder liner and piston top.
The limiting factor is the ability for the pump to maintain rail pressure when the delivery angle is maxed out, meaning the whole stroke of the lobe is commanded to deliver fuel. The number of lobes and the stroke of the lobes sets that. Also, brake specific fuel consumption is a big factor. If the engine isn't breathing well up top due to restriction at the turbo, you end up needing to dump more fuel in, and then your fuel system becomes the limitation.
So yeah the injectors also become a limit, depending how far you are willing to stretch the injection window in terms of crank angle degrees (rather than duty cycle or pulsewidth). As the start of injection gets earlier or end of injection gets later, you can start washing down the cylinder liner and piston top.
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