1.1 本试验方法包括计算十六烷指数公式，该公式代表了直接 估计 根据API比重和中沸点计算的馏出燃料的ASTM十六烷值。根据公式计算的指标值称为计算十六烷指数。 2. 1.2 计算十六烷指数不是表示ASTM十六烷值的可选方法。在适当考虑其局限性的情况下，它是估算十六烷值的补充工具。 1.3 计算十六烷指数公式特别适用于直馏燃料、催化裂化原料和两者的混合物。 注1: 该试验方法暂时保留，因为向美国环保局提出的通过40计算十六烷指数最小值控制柴油燃料芳烃浓度的建议是基于试验方法之间的相关性 第976页 以及芳烃浓度。试验方法 D4737年 是十六烷值估算的首选方法。 1.4 本标准并不旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践，并确定监管限制的适用性。 1.5 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《国际标准、指南和建议制定原则决定》中确立的国际公认标准化原则制定的。 =====意义和用途====== 4.1 计算十六烷指数是一种用于估算ASTM十六烷值的工具，如果测试引擎无法确定该特性。当样本量对于发动机额定值而言太小时，可采用该方法近似十六烷值。 如果一种燃料的十六烷值已初步确定，则该指数可用作对该燃料后续样品进行十六烷值检查，前提是其来源和制造模式保持不变。 4.2 试验方法 D4737年 也可用于近似柴油的ASTM十六烷值。 4.2.1 试验方法程序A D4737年 由于试验方法之间的偏差较大 第976页 十六烷指数和试验方法的结果 D613型 在整个相关范围内。通常，已发现使用测试方法 D4737年 与使用试验方法相比，偏移量更小 第976页 ，但在某些特定情况下，这是不正确的。 4.2.2 试验方法程序A D4737年 建议估算硫含量高于500 ppm或1号-D柴油的十六烷值。 4.2.3 试验方法步骤B D4737年 建议用于估算No。 硫含量等于或低于500 ppm的2-D柴油。 4.3 试验方法中所述的计算十六烷指数 第976页 –80，是美国环保局认可的一种替代方法，可满足含硫量低于500 ppm的柴油燃料的美国联邦柴油芳烃限值。试验方法中十六烷指数的计算公式 第976页 –80，在此版本中( 第976页 –06）相同。

1.1 This test method covers the Calculated Cetane Index formula, which represents a means for directly estimating the ASTM cetane number of distillate fuels from API gravity and mid-boiling point. The index value, as computed from the formula, is termed the Calculated Cetane Index. 2 1.2 The Calculated Cetane Index is not an optional method for expressing ASTM cetane number. It is a supplementary tool to estimate cetane number when used with due regard for its limitations. 1.3 The Calculated Cetane Index formula is particularly applicable to straight-run fuels, catalytically cracked stocks, and blends of the two. Note 1: This test method is temporarily retained because the proposal to the U.S. EPA to control diesel fuel aromatics concentrations via a 40 Calculated Cetane Index minimum is based on the correlation between Test Method D976 and aromatics concentration. Test Method D4737 is the preferred method as estimator of cetane number. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 4.1 The Calculated Cetane Index is one tool available for estimating ASTM cetane number where a test engine is not available for determining this property. It may be employed for approximating cetane number where the quantity of sample is too small for an engine rating. In cases where the cetane number of a fuel has been initially established, the index is useful as a cetane number check on subsequent samples of that fuel, provided its source and mode of manufacture remain unchanged. 4.2 Test Method D4737 may also be used to approximate the ASTM cetane number of diesel fuels. 4.2.1 Procedure A of Test Method D4737 was developed as a result of a larger degree of offset between Test Method D976 Cetane Index and the results of Test Method D613 over the entire range of the correlation. Generally, it has been found that use of Test Method D4737 results in less offset than use of Test Method D976 , but there can be specific cases where this is not true. 4.2.2 Procedure A of Test Method D4737 is recommended to estimate the cetane number of diesel fuels with sulfur contents above 500 ppm or No. 1–D diesel fuels. 4.2.3 Procedure B of Test Method D4737 is recommended to estimate the cetane number of No. 2–D diesel fuels with sulfur contents at or below 500 ppm. 4.3 Calculated Cetane Index, as described in Test Method D976 –80, is recognized by the United States EPA as an alternative method to meet the U.S. Federal Diesel aromatics limit for diesel fuels containing less than 500 ppm sulfur. The equation for Calculated Cetane Index in Test Method D976 –80 and in this version ( D976 –06) of the test method are the same.