Classification of domestic unleaded gasoline brands and octane numbers
Gasoline-graded by research octane number, such as: No.90 gasoline, that is, the research octane number is not less than (equal to) 90. If we master the classification method, we can solve some problems. For example, GB 17930- 1999 "Unleaded Gasoline for Vehicles" only has the standards of No.90, No.93 and No.95, but we can deduce from the definition that the octane number of No.97 gasoline should not be lower than 97. Octane number Octane number is an agreed value, which is used to represent the antiknock performance of ignition engine fuel (antiknock refers to the performance that gasoline will not knock when burning). It is determined by comparing it with the standard fuel in the standard engine test under specific conditions. It is expressed by the volume percentage of isooctane (2,2,4-trimethylpentane) in the standard fuel with the same antiknock performance as the test fuel. Octane number is the most important quality index of motor gasoline, and it is a comprehensive reflection of a country's refining industry level and vehicle design level. An experimental single cylinder testing machine with variable compression ratio is usually used to evaluate the octane number of gasoline, which is called octane number machine. To determine the octane number of gasoline by octane number machine, the standard fuel must be blended first. The standard fuel is made of two alkanes with different antiknock properties. One is isooctane (2,2,4-trimethylpentane) with excellent antiknock performance, and its octane number is set to100; The other is n-heptane with poor antiknock performance, and its octane number is set to 0; Various standard fuels with octane number from 0 to 100 can be obtained by blending with different volume ratios. (1) Engine octane number Engine octane number refers to the antiknock performance of gasoline when the engine is running at 900 rpm. The measurement is carried out at a higher temperature of the mixed gas (generally heated to 65438 049℃). The octane number measured by motor method represents the antiknock performance of gasoline when the automobile is driving at high speed or long distance under heavy load. (2) Research octane number Research octane number refers to the antiknock performance of gasoline when the engine is running at 600 rpm. The testing machine used to determine the octane number of the research method is basically the same as the motor method, and the test is carried out at a lower temperature of the mixed gas (generally without heating). The octane number measured by the research method represents the antiknock performance of gasoline at low speed under the condition of frequent acceleration. This research method is widely used in the United States and western European countries. The octane number of high-quality gasoline is generally 96 ~ 100, and that of ordinary gasoline is 90 ~ 95. When the automobile uses low-grade automobile gasoline, the antiknock performance of automobile gasoline is not enough, which leads to insufficient combustion of gasoline, easy to knock the engine (commonly known as knocking on the cylinder), reduce power and increase fuel consumption. Users using low-grade gasoline on high compression ratio engines will also increase carbon deposition in engine cylinders and fuel injectors, and increase the failure rate and maintenance times of automobiles. Due to the insufficient combustion of engine oil, the exhaust emission is deteriorated and the pollution to the atmospheric environment is aggravated.
Additives that can improve the antiknock performance of gasoline are called antiknock agents, and alkyl lead is often used as antiknock agents, such as tetraethyl lead and tetramethyl lead. Because tetraethyl lead is highly toxic, the harm of automobile exhaust to the environment is becoming more and more serious. Now it has been restricted to add lead to gasoline to achieve lead-free. At present, most domestic gasoline octane number testers use ASTM-CFR testing machine.