Variable intake manifold geometry influence on volumetric efficiency enhancement at gaseous engine starting speeds

This paper studied the effect of variable intake length manifold on filling and volumetric efficiency at starting engine speeds using numerical and experimental process. The investigation is based on acoustic supercharging phenomenon. For this purpose, 1-D engine gas-flow model was developed and optimum intake lengths for several low engine speeds were determined using acoustic theory based-resolution. Using the method of characteristics, pressure waves were predicted at the end of intake line length (intake valve level) in order to test the dynamic inertial supercharging phenomena. The quarter-wave resonator technique was taken into consideration to explore the inlet pressure pulsations. Simulations of pressure wave propagation were achieved during intake stroke and intake valve closed phase. Simulation predictions confirmed the analytically calculated optimum intake length. Numerical investigations were carried out on five in-cylinder flow moving through intake system; air, air-gasoline, air-LPG, air-H-2 and air-LPG-H-2 blend. The percentages of supplied hydrogen with LPG were 0%, 5%, 10%, 15% and 20% in volume. To experimentally validate the analytical founded lengths, an instrumented cold-flow four cylinder Ford SI engine test bench was prepared. Flow through variable intake length manifold was analyzed. Geometry variation was performed on the plenum length. Three engine low speeds are tested; 500 rpm, 750 rpm and 1000 rpm. The experiment results showed an in-cylinder velocity increase by about 60%, 58% and 48% using the optimal intake length at 500 rpm, 750 rpm and 1000 rpm respectively. Furthermore, the collected data proves that varying intake pipe length continuously with the engine speed leads to an average of 39.7% improvement in volumetric efficiency from the original engine configuration at 1000 rpm.