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Inverse Numerical Acoustics (INA) is the process by which the measurements of the sound pressure near a vibrating object, such as an engine, can be used to reconstruct the surface velocities of the object. This is required when it is difficult to conduct measurement on the structure or when the full structural FE model is not available. In such scenarios, the INA technique allows to back calculate the operational vibrations based on operational near field pressure measurements. When the surface velocities of a vibrating object are known which are independent of the boundary conditions, then the object can be used as a source in any application to compute the sound pressure levels in the surrounding (far field). This paper describes an experimental procedure that relies on INA to characterize an engine noise source in this manner. To this end, a robotic manipulator first measured sound pressures at multiple points in the near acoustic field.

At the onset of soak, air and surface temperatures in an engine bay enclosure are elevated since temperature of heat sources are high while convective cooling is sharply reduced as a result of airflow being shut off from the inlet grilles of the vehicle leading to temperature spikes. Accurate simulation of this important thermal and flow regime that is natural convection driven, highly transient and complex is therefore very important. In this investigation, we simulate flow in the engine bay at the onset of soak with fixed thermal boundary conditions where the geometries representing the engine bay and components are simplified. Good agreement was observed with detailed experimental data available in references for both velocities and temperatures.

The accumulation of ash in a Diesel Particulate Filter (DPF) eventually results in an increase in the pressure drop across the exhaust system component. This situation translates into a reduced capacity for soot, and requires an increased frequency of active regenerations to eliminate this soot. For heavy duty diesel applications, the lifetime of the DPF is long enough to expect that cleaning of the ash from the DPF will be required. The physico-chemical characteristics of the ash as a function of temperature and time will have an impact on the effectiveness of this cleaning. To develop a deeper understanding of this subject, four different samples of ash were characterized in this study that were collected under active or passive regeneration from exhaust systems of engines running on different fuels: ultra low sulfur diesel (ULSD), and biodiesel fuels B20 and B100. The lubricant, an API CJ-4 oil, was used for each engine test.