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Over the past two decades, significant work has been accomplished in the development and commercial applications of powertrains fueled by alternate fuels like compressed natural gas, hydrogen, liquefied petroleum gas, and alcohol, etc. These fuels have been proven to be very promising in terms of fuel economy and clean emissions. However, almost no work has been done or reported in terms of the noise and vibration aspects of powertrains being powered by these fuels. In this paper, an attempt has been made to elaborate the noise and vibration behavior of powertrains fueled by various alternate fuels. Some distinct powertrain NVH features due to alternate fuel combustion have been portrayed in detail.*

Powertrain noise is broadly classified into two main categories - Mechanical Noise and Combustion Noise. Mechanical noise, because of its periodicity in time scale, can be easily characterized using customary spectral analysis methods. However, combustion noise which is controlled by the cylinder pressure profile has more periodicity in crank angle scale. Hence, the standard spectral analysis is often not sufficient for combustion NVH assessment. Combustion noise can be better characterized with time-frequency analysis. In this paper, results obtained with the time-frequency analysis are presented. Also a brief portrayal of advanced signal processing tools for combustion noise analysis has been provided.

New techniques like Nearfield Acoustic Holography (NAH) and Spatial Transformation of Sound Field (STSF) possess all the potential to become widely-accepted tools for powertrain noise analysis in near future. These techniques demonstrate versatility, rapidity and inexpensiveness, which are very important features for faster and cost-competitive NVH development of the powertrain. Yet, there are certain limitations, for example, high-frequency cut-off depending on how small the microphone-grid resolution is, etc. This paper includes a concise discussion of problems and promises of NAH application for powertrain systems. Portrayals are given of the detailed application of acoustic holography techniques for complete powertrain system noise analysis. An insight into a few algorithms to circumvent the high-frequency cut-off limitations is provided.