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• Enhancing the ignition energy has little influence on ignition with the static condition. • The multi-strike is superior to the continuous discharge at the lean limit of static condition. • Enhancing the ignition energy improves the ignition performance with the turbulent condition. • The discharge duration is more critical on ignition than the discharge power under the strong flow field. • The continuous discharge is better than the multi-strike for ignition under the strong flow field. Diluted combustion can promote thermal efficiency and decrease NO x emissions for natural gas engines, but also presents high cycle-by-cycle variations. Enhancing the in-cylinder flow field is beneficial for the combustion stability, but brings challenges for the stable ignition. Therefore, advanced ignition strategies are critical for extending the diluted limit. In this work, by using the constant volume combustion vessel, rapid compression and expansion machine, and multi-cylinder natural gas engine, the lean methane/air or natural gas/air mixtures under the static and turbulent conditions are established to compare various discharge strategies. The comparisons include: (1) different discharge energies, (2) power and duration enhancements with similar discharge energies, (3) the continuous discharge and multi-strike. For the static condition, once the flame kernel can be successfully established, enhancing discharge power or duration has few effects on ignition. The continuous discharge and multi-strike show no clear differences. At the lean limit, the multi-strike shows better performance than the continuous discharge. For the turbulent condition, increasing discharge energy can promote the initial flame propagation. When the flow velocity around the spark plug increases to some extent, enhancing the discharge duration shows better performance than enhancing the discharge power. Moreover, the continuous discharge is better for the ignition processes than the multi-strike. For the multi-cylinder engine tests, compared to the single strike of one coil, the continuous discharge and multi-strike extend the lean limit from the excess air ratio of 1.51 to 1.61. The multi-strike is more beneficial for the combustion phase stability than the continuous discharge. [ABSTRACT FROM AUTHOR]

• The start of vegetation growing season (SOS) dynamics were analyzed over Xinjiang. • Regional scaling of SOS shifted from advancing to delaying before and after 2005. • Temperature was important for driving SOS, whereas more precipitation delayed SOS. Understanding the response of vegetation spring phenology to climatic factors in arid regions is crucial for projecting the land-climate interactions of arid ecosystems under climate change. The Xinjiang region, an important part of northern China with complex climatic features, was selected as a case study. We investigated the impact of temperature, precipitation, and solar radiation on the start of the vegetation growing season (SOS) using a long-term series of the normalized difference vegetation index, climate data from 1982 to 2014, and the partial least squares regression (PLS) method. The primary findings were following: (1) the regional scaling of the mean SOS ranged from 95 to 113 day of year (DOY) and showed distinct spatial heterogeneity for different vegetation types. The relative percentage of the area that exhibited advanced SOS (65.80%) was larger than that of the area that exhibited delayed SOS (34.20%), with a regional advancing tendency of 0.19 days per year during the study period. Different vegetation types showed an advancing SOS, which shifted to delaying after 2005. (2) Temperature significantly affected the SOS for various vegetation types. Generally, the warming spring temperatures led to advanced SOS, whereas reduced warming in spring after 2005 reversed the SOS trends. The higher solar radiation occurring from late winter to spring also contributed to the advance in the SOS. Conversely, the increasing precipitation during this period caused a delay in the SOS. These results can provide a useful reference for improving the vegetation phenology models of arid regions. [ABSTRACT FROM AUTHOR]