Research On The Influencing Factors And Characteristic Identification Of Dual Fuel Engine Knock

In order to limit marine engine emissions,the International Maritime Organization has issued a series of stringent emission regulations on marine engine emissions.Natural gas has become an ideal alternative fuel for engines due to its excellent properties.At present,diesel/natural gas dual-fuel engines have many advantages over traditional engines,but still have many problems,such as engine knocking when the engine is under high load conditions.This paper uses a combination of experiment and simulation to explore the four parameters of natural gas replacement rate,pilot diesel pre-injection timing,pilot diesel pre-injection ratio and pilot diesel main injection timing through the three-dimensional simulation software CONVERGE.The i MPact of engine knocking and combustion,and at the same time,the knock feature extraction algorithm is co MPared and analyzed by using the collected body vibration signals to provide a theoretical basis for subsequent engine knock determination and control.First,the simulation method is used to study the influence of the above four parameters on the engine knocking combustion process,and it is found that an appropriate increase in the pre-injection ratio can reduce local pressure fluctuations in the cylinder,thereby reducing the engine knock intensity index;local band pass in the cylinder The filtered pressure oscillation amplitude first increases and then decreases with the advancement of the main injection timing.Therefore,the knock intensity index KI first increases and then decreases with the advancement of the main injection timing;in addition,with the advancement of the main injection timing,With the advancement of the pre-injection timing and the increase of the natural gas replacement rate,the amplitude of local pressure fluctuations in the cylinder decreases.In order to further explore the coupling effects of the four parameters on the engine knock combustion process,this paper selects the pairwise coupling between the parameters on the basis of the above research,and explores their interactive effects on the engine knock combustion characteristics.The results show that under the coupling effect of the pre-injection ratio and the main injection timing,the i MPact of the engine knock intensity index KI by the pilot diesel pre-injection ratio will gradually become significant with the advance of the main injection timing;Under the coupling effect of diesel pre-injection ratio,when the natural gas replacement rate is 91.19%,the local pressure peak in the cylinder increases with the increase of the pilot diesel pre-injection ratio;under the coupling effect of diesel pre-injection timing and natural gas replacement rate,explosion The shock intensity is affected by the pre-injection timing under different natural gas substitution rates.The results are different;under the coupling effect of the diesel main injection timing and the pre-injection timing,the pre-injection timing has less influence on the engine knock intensity by the main injection timing.Under different pre-injection timings,the pre-knock intensity index KI of the main injection timing shows an opposite trend.Through the analysis of the test data,the study found that traditional knock detection methods such as direct filtering can extract knock information under strong knock conditions,but the ability to recognize minor knocks is insufficient.Use the camshaft signal to select the knock calculation window,perform discrete wavelet transformation on the data in the window,select the db2 wavelet of Daubechies wavelet,and analyze the detailed component signal to extract the knock feature.Experiments show that this method can effectively extract the vibration signal from the body The slight knock signal is extracted to provide theoretical guidance for the subsequent classification and determination of knock intensity.