Author(s): Zeno Intrieri

Abstract: Naturally aspirated engines sacrifice either low-end torque or high-end power when fitted with a fixed-length intake runner, because the pressure-wave tuning that boosts cylinder filling is inherently speed-specific. This research measured the volumetric efficiency and brake torque of a 1.6 L four-cylinder naturally aspirated engine across 1,500 to 6,000 rpm with three fixed runner lengths (220, 310, and 420 mm) and a two-stage variable-geometry intake manifold (VGIM) that switched between the long and short runners at a calibrated engine-speed threshold. Tests were conducted on an eddy-current dynamometer at the National Institute of Vehicle Engineering, Brescia, Italy, between February and September 2024. Each runner length produced a distinct volumetric-efficiency peak: the 420 mm runner peaked at 93.8% near 2,500 rpm, the 310 mm runner at 93.1% near 3,500 rpm, and the 220 mm runner at 93.6% near 4,500 rpm. With any single runner, the efficiency dropped by 14 to 20 percentage points between the peak speed and the opposite end of the speed range. The VGIM, switching from long to short runners at 3,800 rpm, maintained volumetric efficiency above 90.2% from 2,000 to 5,500 rpm a usable bandwidth 2.6 times wider than the best single runner. Brake torque flatness, quantified as the ratio of minimum to maximum torque within the 2,000-5,500 rpm window, improved from 0.72 (best single runner) to 0.89 (VGIM). A one-dimensional gas-dynamics simulation reproduced the measured trends within 2.1% RMS error and confirmed that the VGIM's advantage comes from keeping the dominant first-harmonic pressure-wave resonance aligned with the operating speed throughout the speed range.

DOI: https://www.doi.org/10.22271/27078205.2026.v7.i2a.80

Pages: 12-16 | Views: 177 | Downloads: 72

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