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Standards Development
This document specifies a method for the determination of cetane number of diesel fuels by air flow regulation in a standard test engine. This document is applicable to various types of diesel fuels, including vehicle diesel, bio-diesel, synthetic diesel, and similar unconventional products. The cetane number measurement range is from 0 CN to 100 CN, whereas a typical cetane number range of 25 CN to 70 CN. However, the precision for synthetic and unconventional diesel has not been established.
The proposal provides a method of the determination of cetane number of diesel fuels by air flow
regulation in a standard test engine with constant compression ratio.
This method uses a fixed "ignition delay period" (the time interval between the start of fuel injection and
the start of combustion) to determine the cetane number of diesel fuel. The volumes of the combustion
chamber and working chamber are constant, and compression ratio is fixed. By adjusting the intake air
quantity into the cylinder, the ignition temperature in the combustion chamber at the end of the
compression stroke is regulated. A higher intake air quantity results in a higher ignition temperature at
the end of the compression stroke, leading to a lower measured cetane number. Conversely, a lower
intake air quantity results in a lower ignition temperature, leading to a higher measured cetane number
for the diesel sample. Two reference fuels with a difference of no more than 5 cetane number units are
chosen. Using the same method to achieve the same ignition delay period, the ignition quality of the
sample are compared with those of the reference fuels with known cetane numbers to obtain the
cetane number. The principle of air flow regulation method is closer to the actual working conditions of
diesel engines, providing more method options for determining the cetane number of diesel fuels.
This method utilizes a single-cylinder, four-stroke diesel engine. The engine speed, injector fuel
pressure, fuel injection quantity, cylinder coolant temperature, intake air temperature, and crankcase
lubricating oil temperature are set. Reference fuels are prepared, and the cetane number of the sample
falls between the cetane numbers of the reference fuels. After preheating the engine to a stable
condition, the injection advance and ignition delay are adjusted to the specified values. The
measurements are conducted in the sequence of sample-reference fuel 1-reference fuel 2. The air flow
values are recorded, and the cetane number is calculated using the interpolation method.
This method has the following advantages:
1. Unlike existing methods that only allow one-way compression, this method controls the cylinder
compression pressure by adjusting the air flow. The air flow can be freely adjusted in both directions,
making the operation simple and the measurement faster.
2. The air flow regulation in this method uses a linear control mode, providing a wide linear range and
good result stability.
3. The air flow regulation operates based on the fuel-air ratio mass mode, which is not affected by
altitude, thus improving the reliability and precision of the method.
4. This method has a self-purging carbon deposition function. As fuel burns in the cylinder, carbon
deposits are inevitably formed. By adjusting the air flow entering the cylinder, the exhaust air velocity is
increased, facilitating the removal of carbon deposits. This means that carbon deposition can be
cleaned without disassembling the cylinder, reducing cylinder maintenance frequency and extending
the operating cycle.
5. This method requires only 200 mL of reference fuel or sample, which saves fuel, reduces operating
costs, and lowers carbon emissions, leading to social benefits.
6. The apparatus can be enclosed in this method, effectively reducing engine noise and minimizing
harm to human health, ensuring the safety of operators.
The National Standard of the People's Republic of China GB/T 33298-2016 titled as “Standard test
method for determining cetane number of diesel fuels-Airflow regulation” was published and
implemented. It has been widely applied in SINOPEC, CNPC, Algeria Algiers Refinery, and Bangladesh Eastern Refinery.
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