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Electric buses have been used widely as cities' short-range commuter vehicles, because of their excellent power, fuel economy and emission characteristics. However, the lack of a noise masking effect for the traditional internal combustion engine, the high-frequency noise becomes more prominent for the powertrain system. The high-frequency noise gives people an unpleasant feeling on psychological and physiological. To control electric vehicle powertrain noise, the identification of the main noise source of the powertrain is well needed. In this paper, Empirical Mode decomposition (EMD) combined with Independent component Analysis (ICA) and continuous Wavelet transform (CWT) was used to identify the main noise source of the electric bus powertrain. The contribution of each noise source to the overall noise level was calculated and compared.

Spray-wall impingement is an unavoidable physical process in homogeneous charge compression ignition (HCCI) diesel engines using early injection strategy which is the main source for the hydrogen carbon (HC) and monoxide (CO) emissions. Dimethyl ether (DME) is a potential fuel additive to decrease HC and CO emissions due to its higher oxygen content. However, issues relating to structural design and early injection timing mean spray-wall impingement still occurs when using the diesel-DME blended fuels, which directly affect the fuel-air mixture formation in the near wall region and further influence the emission characteristics. The better understanding for the effects of spray-wall impingement parameters on fuel-air mixture formation in near wall region for diesel-DME blended fuels is helpful for the improvement of HC and CO emissions for HCCI diesel engines.

Because of the advantages of excellent power, fuel economy and zero-emission characteristics, electric buses have been used widely as cities’ short-range commuter vehicles. However, the high-frequency noise becomes more prominent for the powertrain system of the electric bus due to the lack of noise masking effect for the traditional internal combustion engine. To improve the noise characteristic of electric bus powertrain, the identification of the main noise source of the powertrain is well needed. In this paper, the effects of the motor and transmission on the noise level of the electric bus powertrain have been studied using lead packaging method. The variations of acoustical power level of the powertrain according to different rotation speed and torque under the conditions of only motor covered and only transmission covered have been discussed.

A low-speed and heavy-duty electric powertrain was selected as the research object, the influence of electric powertrain characteristics on whole vehicle noise under accelerating condition (Speed range 800 r∙min−1~2200 r∙min−1; Torque range 500 N∙m~960 N∙m) was studied. Considering the traveling characteristics around the city, the interior and powertrain noise were recorded as the accelerating working range (10 km/h~50 km/h).