Reducing NVH Caused by Diesel Combustion Mode Switching, 03-R9656

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Principal Investigator
Thomas E. Reinhart

Inclusive Dates:  10/1/06 – Current

Background - As diesel engine emissions standards become more stringent, engines will use multiple combustion modes over the operating range. In addition, the regeneration of aftertreatment devices may require step changes in parameters such as air-to-fuel ratio and exhaust gas recirculation (EGR) flow. Step changes in combustion modes or operating parameters can have a large effect on the noise level of an engine, as well as the sound quality. Because consumers will object to unexpected changes in engine noise, transitions in engine operating modes must be developed in such a way as to make the transitions driver-transparent.

Approach - A prototype Tier 2, bin 5 diesel engine has been selected for the project. First, the engine was operated over a range of combustion modes, and the most subjectively objectionable transitions were selected for further study. The engine operating parameters, noise levels, and sound-quality metrics were measured for the transitions of interest. Using a combination of engine operating data and noise data, the root causes of the NVH issues have been identified. Next, modifications to the calibration were developed in an effort to minimize the noise change and turn any step change into a more gradual change. The next step will be to develop engine control algorithms that will allow more precise control of combustion noise related parameters such as timing, fueling, EGR flow, air-to-fuel ratio, etc., during combustion mode transitions. The goal is to develop and demonstrate techniques for reducing or eliminating NVH issues due to combustion mode transitions.

Accomplishments - Combustion mode transitions that create a subjective NVH issue have been identified. The transitions have been carefully studied to determine how control parameters such as timing, fueling, EGR flow, and air-to-fuel ratio determine the level and sound quality of combustion noise. Calibration modifications have been developed and demonstrated that significantly improve the NVH of the engine during the transitions of interest. Further development of control algorithms will be required to achieve driver-transparent transitions. The development of improved engine control algorithms is the next project task.

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