Hydrotreated vegetable oil (HVO) is becoming a widely accepted renewable drop-in alternative fuel to diesel. However, conventional diesel combustion does not fully exploit HVO’s superior physicochemical parameters. Its high cetane index should significantly improve the performance and emission of next-generation, dual-fuel, reactivity-controlled compression ignition (RCCI) engines. These have a promising future in marine and off-road sectors. This study is the first comprehensive verification of HVO’s benefits towards achieving superior RCCI combustion with natural gas. It used a sophisticated, single-cylinder research engine with a fully controllable air/fuel paths, calibrated in conventional compression ignition mode. The calibration experiments in a corresponding RCCI setpoint covered the cross-sensitivity of high-reactivity fuels (HVO and diesel) to boost pressure, excess air ratio, exhaust gas recirculation and start of injection, investigated at 85 % and 93 % energy-based blending ratios with natural gas. Extensive measurement instrumentation provided combustion and emission characterisation, enabling observations regarding both the phenomenology and applied potential of HVO-activated RCCI. Best performance was observed at the boundary of mixture dilution, restricted by the misfire or combustion variability limits. High reactivity of HVO allows for extending combustion stability limits, enabling increasing both, the local dilution (earlier injection timings) and the global dilution (higher mixture strengths or higher exhaust recirculation ratios). Calibrated along these phenomenological outcomes, HVO and diesel allow achieving efficiency over 2 percentage points superior in RCCI mode, compared to conventional diesel reference. With HVO, RCCI can be calibrated to comfortably meet EPA Tier 4 emission limits in all legislated species, without aftertreatment. Particular merits are in NOX reduction, for which the best case HVO-RCCI tested at 0.7 g/kWh vs 2.8 g/kWh of diesel-RCCI. HVO further cuts down methane slip by more than 45 %, while PM emissions for RCCI are generally measured ultra-low. Corresponding conventional diesel reference exceeds the EPA NOX and PM limits by respectively 1500 % and 400 %.

中文翻译：

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柴油和加氢处理植物油作为反应性控制压缩点火中的高反应性燃料的比较


加氢处理植物油 （HVO） 正在成为一种被广泛接受的可再生即用型柴油替代燃料。然而，传统的柴油燃烧并不能充分利用 HVO 的卓越物理化学参数。其高十六烷指数应该会显着改善下一代双燃料反应性控制压燃式 （RCCI） 发动机的性能和排放。这些产品在船舶和越野领域前景广阔。这项研究首次全面验证了 HVO 在利用天然气实现卓越的 RCCI 燃烧方面的优势。它使用了一个复杂的单缸研究发动机，具有完全可控的空气/燃料路径，在传统的压燃模式下校准。在相应的 RCCI 设定值中进行的校准实验涵盖了高反应性燃料（HVO 和柴油）对增压、过剩空气比、废气再循环和喷射开始的交叉敏感性，以 85 % 和 93 % 的基于能源的天然气混合比进行研究。广泛的测量仪器提供了燃烧和排放特征，能够观察 HVO 激活的 RCCI 的现象学和应用潜力。在混合物稀释的边界处观察到最佳性能，受失火或燃烧可变性极限的限制。HVO 的高反应性允许延长燃烧稳定性极限，从而能够增加局部稀释（更早的喷射时间）和整体稀释（更高的混合强度或更高的废气再循环率）。根据这些现象学结果进行校准，与传统柴油参考相比，HVO 和柴油可以在 RCCI 模式下实现超过 2 个百分点的效率。 借助 HVO，可以校准 RCCI 以轻松满足所有法定物种的 EPA Tier 4 排放限制，而无需后处理。特别优点是减少 NOX，最佳情况 HVO-RCCI 的测试值为 0.7 g/kWh，而柴油-RCCI 为 2.8 g/kWh。HVO 进一步减少了 45% 以上的甲烷逃逸，而 RCCI 的 PM 排放量通常测得超低。相应的传统柴油参考分别比 EPA NOX 和 PM 限值高出 1500 % 和 400 %。