underdriven Roots blower for throttling loss reduction

[hawk2100n]

Originally Posted by serialk11r

I already shot my own idea down, the only energy recoverable is miniscule in most cases due to the way Roots blowers are built.

I know no work is performed on the throttle body, the point is that there is an energy loss due to free expansion at the throttle body in the typical case. Cylinders drawing air unevenly reduces this slightly. As I wrote, a Roots blower would suffer nearly the same magnitude of loss to free expansion while having additional inefficiencies, thus it's not a good idea. I was mistaken in thinking it would recover significant energy because that energy would come from the pistons pulling a deeper vacuum.

And again, if the Roots blower exit was coupled more or less directly to the intake valves then it would be a different story but that's very difficult to do.

Actually timed pulses from a roots blower is a good idea and wouldn't be too difficult. You would need a blower running at engine speed with n/2 lobes where n is the number of cylinders. And timing isn't complicated because you could put it on a toothed belt like top fuel dragsters and extremely high performance cars do. And timed pulses could keep a more even pressure inside of the manifold.

I would love to be in engine development. Maybe one day...

[Christ]

Originally Posted by hawk2100n

Actually timed pulses from a roots blower is a good idea and wouldn't be too difficult. You would need a blower running at engine speed with n/2 lobes where n is the number of cylinders. And timing isn't complicated because you could put it on a toothed belt like top fuel dragsters and extremely high performance cars do. And timed pulses could keep a more even pressure inside of the manifold.

I would love to be in engine development. Maybe one day...

Roots blowers generally use a helix type rotor design to help smooth the pulses out. Only very old designs use "impulse" style charging, because it creates a pulse frequency that can make proper fueling very difficult.

Thus, there's really no way to "time" the pressure pulses exactly to a specific event, since the design is meant to provide steady pressure, rather than pulsed pressure.

Even if you designed a blower that provided pulses, it would only serve to enhance the effects of helmholtz tuning (frequency-based freeair supercharging), and wouldn't provide much of an efficiency gain over just charging and maintaining pressure in the intake tract.

[hawk2100n]

Originally Posted by Christ

Roots blowers generally use a helix type rotor design to help smooth the pulses out. Only very old designs use "impulse" style charging, because it creates a pulse frequency that can make proper fueling very difficult.

Thus, there's really no way to "time" the pressure pulses exactly to a specific event, since the design is meant to provide steady pressure, rather than pulsed pressure.

Even if you designed a blower that provided pulses, it would only serve to enhance the effects of helmholtz tuning (frequency-based freeair supercharging), and wouldn't provide much of an efficiency gain over just charging and maintaining pressure in the intake tract.

Purely hypothetetical. But yes I would specify a roots blower instead of a screw type. But who knows what it would do. You would only have a slight gain over a similar setup at the resonant frequency. Really none of this applies because superchargers don't improve efficiency but power. The work I have done with engines is in the racing sphere and that is very different than efficiency. Max power has been driven into my head.

[Christ]

Originally Posted by hawk2100n

Purely hypothetetical. But yes I would specify a roots blower instead of a screw type. But who knows what it would do. You would only have a slight gain over a similar setup at the resonant frequency. Really none of this applies because superchargers don't improve efficiency but power. The work I have done with engines is in the racing sphere and that is very different than efficiency. Max power has been driven into my head.

A blower /can/ improve efficiency. They normally aren't used that way. However, to use a blower as a negative to throttle losses only seems to add complexity and cost without remittance of benefit.