Diesel and Bi-Fuel Probe Vehicles Noise Emission Assessment as a Function of Speed, Gear and RPM

Nowadays, road traffic noise pollution still represents a considerable problem in Europe despite the efforts gathered by the scientific community, local authorities, and policymakers to tackle this issue. Research mostly focused on the development of Road Traffic Noise Models (RTNMs) and Noise Emission Models (NEMs) to forecast respectively traffic noise levels in terms of equivalent continuous sound levels and single-vehicle noise emissions in terms of sound power level. However, although the validity of such models was demonstrated in the literature, most of them are not able to deeply characterize the source in terms of motorization, engaged gear, and in idling conditions (i.e., a vehicle stopped in neutral gear with the engine running). Therefore, in this paper, an approach (based on standards and regulations) to obtain noise emission curves as a function of speed, motorization, and engaged gear, and a mathematical relationship between the sound pressure level (measured at the exhaust tube pipe) and the engine Revolution Per Minute (RPM) will be presented. Both methods are based on regressions (non-linear and linear, respectively). Two probe vehicles with different motorization (one diesel and one bi-fuel) were adopted to this end. Results showed that there exists a variability among the noise emission curves based on motorization information and engaged gear (at low speeds for manual transmission vehicles). Moreover, exhaust noise emissions, which are a function of motorization, linearly depend on RPM. All the obtained regressions are characterized by high determination coefficients (above 0.9) confirming the goodness of the presented approaches.