Regarding the octane rating of gasoline

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Regarding the octane rating of gasoline, it is a measure of a gasoline’s resistance to detonation under lean mixture conditions. Numerically, it equals the volume percentage of isooctane in the standard fuel that has the same blast resistance as the sample under specified conditions. The determination of octane number is carried out in a specially designed single-cylinder test engine with variable compression ratio. Standard fuel is composed of a mixture of isooctane and n-heptane. Isooctane is used as a standard with excellent anti-knock properties, and its octane rating is set at 100 ； Heptane is used as a standard for poor anti-knock properties, with an octane rating of 0. By mixing these two hydrocarbons in different volume ratios, standard fuels with octane numbers ranging from 0 to 100 can be prepared. By mixing in different volume ratios, standard fuels with an octane rating ranging from 0 to 100 can be prepared. The higher the volume percentage of isooctane in the mixture, the better its anti-knock properties. When determining the octane number of a sample in an octane tester, the compression ratio is increased until standard ignition intensity is achieved; thereafter, with the compression ratio kept constant, a standard fuel with a specific composition is used for testing under the same conditions to induce an ignition intensity equivalent to that obtained. When it is determined that the standard fuel used consists exactly of 70% octane and 30% n-heptane, then the octane number of this test oil can be assessed as 70. Functions and significance of editing this section: 1. The grades of automotive gasoline are determined based on their octane rating. There are equal signs at 66, 70, 76, 80, 85, etc. For example, gasoline rated as No. 70 indicates that its octane rating is not lower than 79. The vehicle gasoline grade can be determined based on the measured octane value ； 　　2. Octane number is an important indicator of the anti-knock performance of fuels for carbureted engines, and it is listed first among the specifications for automotive gasoline. The higher the octane rating of gasoline, the better its resistance to detonation, allowing the engine to use a higher compression ratio. In other words, if the octane rating of the gasoline produced by refineries continues to increase, automobile manufacturers can raise the compression ratio of engines. This not only enhances engine power and increases driving range but also saves fuel, which is of great significance for improving the power efficiency of gasoline ； 　　3. The octane rating of gasoline is closely related to its chemical composition, particularly the molecular structure of the hydrocarbon molecules in gasoline ； 　　4. By measuring the octane rating of gasoline with an anti-knock agent, the effectiveness of the agent can be assessed, and the appropriate amount to add can be determined. Edit this paragraph: Octane rating evaluation method. Hydrocarbons with different chemical structures possess varying resistance to knocking. Isooctane (2,2,4-trimethylpentane) has good anti-knock properties, with an octane rating of 100. Heptane has poor anti-knock properties, assigned a value of 0. The determination of gasoline octane number is carried out using isooctane and n-heptane as reference fuels, under standard conditions, via a comparative method on a standard laboratory single-cylinder gasoline engine. By adjusting the proportions of the components in the standard fuel so that the detonation intensity produced by it is identical to that of the sample, the volume percentage of octane in the standard fuel represents the octane number of the sample. Depending on the testing conditions, there are mainly the following types of octane numbers: 1. Motor Octane Number (MON). The testing conditions are quite stringent: the engine speed is 900 r/min, and the intake air temperature is 149°C. It reflects the resistance of gasoline to detonation when the vehicle is operating at high speeds under heavy load conditions. 　　2. Study of octane number (RON): The measurement conditions are mild, with a rotation speed of 600 r/min and the intake air at room temperature. This octane rating reflects the anti-knock property of gasoline when the car is driving at low speeds in urban areas. For the same type of gasoline, its research octane number is about 0–15 units higher than its motor octane number; the difference between the two is referred to as sensitivity. 　　3. Road octane number, also known as driving octane number, is determined through actual testing with vehicles or by simulating road driving conditions on a full-power test bench. Road octane number can also be calculated using empirical formulas based on motor method and research method octane numbers. The average of the motor octane number and the research octane number is called the anti-knock index, which can approximately represent the road octane number. 4. Octane number by dielectric constant method: The octane number of gasoline is determined based on its dielectric constant. This measurement method employs segmented regression for calibration, and the octane number is read directly using the differential method; it is a simple and fast approach. At present, Changsha Fuland has developed the latest octane rating tester, the FDR-3601. It is calibrated using standard oil samples, and then the tested samples are analyzed with this calibrated device, resulting in high accuracy of the test results. There is also a cetane rating tester model FDR-3621, which measures the cetane index of diesel with high accuracy. Cetane number is an indicator of the auto-ignition property of diesel when it burns in a diesel engine. The cetane number of pure hexadecane is usually set at 100, while that of pure α-methylnaphthalene is set at zero. By mixing them in different proportions, standard fuels with cetane numbers ranging from 0 to 100 and varying levels of anti-knock properties can be obtained, which are then compared with the diesel fuel under test on a single-cylinder testing machine of a specific design.