M
Metals
The content of metals in crude oil, vanadium, and nickel, provides an indication of the content of these metals in the heavier products obtained from refining. This is important because, for example, metals in vacuum gas oil are poisons for catalytic cracking and hydrocracking catalysts. A high vanadium content in fuel oil can cause problems with the breaking of furnace and boiler tubes because it forms corrosive products during combustion.
N
Cetane Number
It measures the ease with which spontaneous ignition of diesel oil occurs using a standardized engine and a reference fuel. The cetane number is determined by comparing the ignition time of a cetane (C16) and heptamethylnonane (C15) mixture, which has the same ignition delay time as the fuel under examination. The measured cetane number is the percentage of the cetane compound in the cetane/heptamethylnonane mixture.
C16 has a cetane number of 100 (an easily ignitable paraffin), while C15 has a cetane number of 0 (a slow-burning aromatic).
A high cetane number represents a high ignition quality or a short delay between fuel injection and combustion initiation.
The diesel engine uses high compression to achieve spontaneous ignition of diesel fuel, instead of a spark, as in the case of internal combustion engines. The temperature of the compressed air in the diesel engine is high enough to ignite the diesel fuel.
Linear paraffins have a high cetane number and, therefore, burn well. In contrast, aromatics have a low cetane number and burn poorly, producing carbon deposits and black smoke. For this reason, high-quality diesel fuel must have an aromatic content that is compatible with the specified cetane number.
The cetane number can be calculated from the volatility (corresponding to the 50% distilled temperature) and the density of diesel fuel, and is called the Calculated Cetane Number. The reason for using the formula is the high cost of the cetane engine.
Octane Number (nor)
Reid Vapor Pressure (RVP) and Research Octane Number (RON) are the most important parameters for gasoline quality. RON measures gasoline's resistance to premature ignition or detonation under engine operating conditions.
Premature ignition is characterized by knocking or pinging when gasoline self-ignites, detonating before the cylinder compresses the entire gasoline-air mixture, resulting in a loss of power. Detonation produces sound waves that are detected using special microphones.
The octane number is measured by comparing the detonation noise made by a reference fuel mixture in a standardized engine with that made by the fuel under examination. The reference fuels are iso-octane (2,2,4-trimethylpentane), with an octane number of 100 (high resistance to knocking), and n-heptane, which has an octane number of zero (very low resistance). The determined octane number is the volume percentage of iso-octane in the iso-octane/heptane mixture.
High-octane fuels with a number have greater resistance to premature detonation than those with lower octane numbers. Additionally, fuels with higher octane can be used in engines with higher compression ratios, which are more efficient.
There are two types of engines for determining the octane number in gasoline. One is used in the Research method, and the other is used in the Motor method.
The Research method represents the behavior of an engine in city driving at medium and low speeds. The Motor method represents situations with strong accelerations, such as climbing hills or passing other vehicles.
There is another way to express the octane rating of gasoline, called Road Octane. Road Octane is expressed as the sum of Research Octane plus Motor Octane, divided by 2. Road Octane is used in the United States, while the research method is used in Chile.