REDUCED THROTTLE LOSS IMPROVES FUEL EFFICIENCY

The throttle control of the conventional throttle plate is accomplished by non-recoverable frictional loss of the butterfly valve. Consequently, the piston is pulling against full vacuum for the entire down stroke, resulting in substantially higher pumping losses than PRV induction. PRV induction does not use a throttle plate. Consequently, when the intake valve closes on any of the four Venturis, that entire Venturi -- intake, throat and discharge relaxed ambient (or turbocharger) pressure.

The intake pressure from PRV induction pulsates to reduce pumping losses whereas a conventional manifold operates at a steady, but low, pressure (Figures 1 and 2). The streamlined convergent-divergent Venturi nozzle accelerates airflow as the throat is approached and decelerates airflow in the divergent section. Concurrently, as the air slows down, the pressure increases. The pressure recovery process is governed by the conservation of energy as described by Bernoulli’s principal. The pressure recovery attribute of PRV improves the piston-pressure history and, consequently, reduces pumping loss.

Figure 3 compares the in-cylinder pressure of a conventional manifold to a PRV induction system. When the intake valve opens on a conventional manifold, the cylinder pulls air from a plenum under vacuum. In contrast, the PRV plenum is constantly at ambient pressure. The bottom-dead-center cylinder pressures are identical for both intake systems because the engine torque is dependent on the amount of mixture at the end of the intake cycle. Since the pressure trace is much higher for PRV induction, there is a cumulative saving of work by the piston. The work saving is reflected in the fuel economy improvement demonstrated by early PRV prototypes.

Figure 3: cylinder pressure of a conventional manifold versus individual throttle plates and PRV induction; normally aspirated engine (conventional manifold data from Taylor, 1985, p. 345, PRV data from prototype measurement).