1.1 通过四变量方程计算的十六烷指数提供了估算ASTM十六烷值的方法（试验方法 D613 )通过密度和蒸馏回收温度测量得到的馏出燃料。根据该方程计算的值被称为四变量方程计算的十六烷指数。 1.2 通过四变量方程计算的十六烷指数不是表示ASTM十六烷值的可选方法。当通过试验方法得出结果时，它是估算十六烷值的补充工具 D613 不可用，如果未使用十六烷值改进剂。作为补充工具，必须使用四变量方程计算的十六烷指数，并适当考虑其局限性。 1.3 程序A将用于规范 D975 ，等级1–D S15、1–D S500、1–D S5000、2–D S15、2–D S5000和4–D。这种估算十六烷值的方法由雪佛龙研究公司开发。 2. 程序A基于数据集，包括相对较少的1-D号燃料。试验方法 D4737 程序A可能不太适用于No。 1–D S15、1–D S500和1–D S5000比2–D级S5000或4–D燃料高。 1.3.1 已验证程序A适用于2-D级S15柴油。 3. 1.4 程序B将用于规范 D975 ，等级2–D S500。 1.5 “通过四变量方程计算十六烷指数”的试验方法特别适用于含有直馏和裂化原料的1–D S5000级、1–D S500级、2–D S5000级和2–D S500级柴油及其混合物。它也可以用于90%的较重燃油 % 恢复点小于382 °C以及含有油砂和油页岩衍生物的燃料。 注1: Sxx是该等级规定的最大含硫量的名称。例如，S500等级是指最大硫限量为500的等级 ppm（μg/g）。 1. 6. 生物柴油混合物不包括在本试验方法中，因为它们不是用于制定程序A或B的数据集的一部分。 1.7 以国际单位制表示的数值应视为标准值。本标准不包括其他计量单位。 1.8 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.9 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《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 当试验发动机无法直接确定十六烷值以及未使用十六烷值改进剂时，通过四变量方程计算的十六烷值指数有助于估计ASTM十六烷值。当可用样本量对于发动机额定值来说太小时，可以方便地使用它来估计十六烷值。在先前已确定燃料的ASTM十六烷值的情况下，通过四变量方程计算的十六烷指数可用作该燃料后续批次的十六烷值检查，前提是燃料的来源和制造模式保持不变。 注2: 试验方法 D6890 和 D7170 当样本量对于发动机测试而言太小时，可用于获得衍生十六烷值（DCN）。这些方法确实测量了十六烷值改进剂的效果。 5.2 在32.5至56.5十六烷值的范围内，通过四变量方程预测计算十六烷指数的程序A的预期误差将小于±2十六烷值65 % 评估的馏出燃料。对于性能不在推荐应用范围内的燃料，误差可能更大。

1.1 The calculated Cetane Index by Four Variable Equation provides a means for estimating the ASTM cetane number (Test Method D613 ) of distillate fuels from density and distillation recovery temperature measurements. The value computed from the equation is termed the Calculated Cetane Index by Four Variable Equation. 1.2 The Calculated Cetane Index by Four Variable Equation is not an optional method for expressing ASTM cetane number. It is a supplementary tool for estimating cetane number when a result by Test Method D613 is not available and if cetane improver is not used. As a supplementary tool, the Calculated Cetane Index by Four Variable equation must be used with due regard for its limitations. 1.3 Procedure A is to be used for Specification D975 , Grades No. 1–D S15, No. 1–D S500, No. 1–D S5000, No. 2–D S15, No. 2–D S5000, and No. 4–D. This method for estimating cetane number was developed by Chevron Research Co. 2 Procedure A is based on a data set including a relatively small number of No. 1–D fuels. Test Method D4737 Procedure A may be less applicable to No. 1–D S15, No. 1–D S500, and No. 1–D S5000 than to No. 2–D grade S5000 or to No. 4–D fuels. 1.3.1 Procedure A has been verified as applicable to Grade No. 2–D S15 diesel fuels. 3 1.4 Procedure B is to be used for Specification D975 , Grade No. 2–D S500. 1.5 The test method “Calculated Cetane Index by Four Variable Equation” is particularly applicable to Grade 1–D S5000, Grade No. 1–D S500, Grade No. 2–D S5000 and Grade No. 2–D S500 diesel fuel oils containing straight-run and cracked stocks, and their blends. It can also be used for heavier fuels with 90 % recovery points less than 382 °C and for fuels containing derivatives from oil sands and oil shale. Note 1: Sxx is the designation for maximum sulfur level specified for the grade. For example, S500 grades are those with a maximum sulfur limit of 500 ppm (μg/g). 1.6 Biodiesel blends are excluded from this test method, because they were not part of the datasets use to develop either Procedure A or B. 1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.8 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. 1.9 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 ====== 5.1 The Calculated Cetane Index by Four Variable Equation is useful for estimating ASTM cetane number when a test engine is not available for determining this property directly and when cetane improver is not used. It may be conveniently employed for estimating cetane number when the quantity of sample available is too small for an engine rating. In cases where the ASTM cetane number of a fuel has been previously established, the Calculated Cetane Index by Four Variable Equation is useful as a cetane number check on subsequent batches of that fuel, provided the fuel's source and mode of manufacture remain unchanged. Note 2: Test Methods D6890 and D7170 may be used to obtain a Derived Cetane Number (DCN) when the quantity of sample is too small for an engine test. These methods do measure the effect of cetane improver. 5.2 Within the range from 32.5 to 56.5 cetane number, the expected error of prediction of Procedure A of the Calculated Cetane Index by Four Variable Equation will be less than ±2 cetane numbers for 65 % of the distillate fuels evaluated. Errors may be greater for fuels whose properties fall outside the recommended range of application.