Pintle-regulated Venturi Air/Fuel Induction for Fuel Economy and Performance

REDUCED THROTTLE LOSS IMPROVES FUEL EFFICIENCY

PRV improves the volumetric efficiency by reducing the engine pumping losses, defined as the non-recoverable work exerted by the piston to pull the charge into the engine and push the exhaust gases out of the engine. A conventional throttle plate regulates airflow to the engine by suffocation, whereas the PRV manifold controls airflow by sonic velocity.

The cylinder pressure of a PRV induction system is entirely different for three reasons. First, the PRV manifold pressure is always ambient (or turbocharger discharge) pressure. Second, when the cylinder intake valve closes, air from the manifold can flow around the pintle, equalizing the Venturi discharge pressure with the manifold. Third, as the piston accelerates downward, at some point the air flow through the Venturi approaches sonic velocity and the airflow becomes regulated. Note that flow control only occurs near the bottom of the piston travel -- when sonic velocity is approached at the Venturi throat. Consequently, PRV induction causes a pulsating airflow with the typical cylinder pressure profile shown in Figures 1 and 2.

The cooler charge increases the effective compression of the engine, causing a faster burn rate. The faster burn rate near the top dead center of the piston travel increases the engine’s thermal efficiency.

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, C. F. (1985). The internal combustion engine in theory and practice. Cambridge MA: MIT press. PRV data from prototype pressure sensor.