Quote:
Originally Posted by Daox
Why do they vary the fuel pressure?
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It plays a key role in the combustion process. More pressure means better atomization, shorter injection duration, and shorter combustion duration. Higher pressures mean better smoke and better fuel economy, however, NOx increases. If you run too high rail pressures at high loads, the combustion can happen too quickly causing excessive cylinder pressures. Too high rail pressure at low load can overspray the fuel directly onto the piston. So you want different pressures at different speeds & loads.