Octane number and Cetane number are used to characterize the combustion phenomena in petrol and diesel fuels respectively. However, they can be extended to other petroleum fuels also. How these numbers relate to various petroleum fuels?
Good question.
As you know, octane number is a quantity which pertains to gasoline rating in combustion performance with gasoline being basically a blend of hydrocarbons (HCs) which contains essentially C5-C12 HCs with alkanes being the major components. The standard reference for measuring the octane number of a given gasoline is a mixture of isooctane "2,2,4-trimethylpentane" getting 100 & n-heptane getting zero.
On the other hand, cetane number is a quantity indicating the ignition performance of diesel relative to cetane as a standard. Diesel is also a blend of HCs, in essence, which contains C10-C16.
While the highly branched isooctane is super alone as gasoline, the straight chain unbranched cetane is super alone as a diesel. In other words, octane number & cetane number cannot be interchanged in evaluating gasoline & diesel. Add to it, the principle of the work of an engine in a vehicle run on gasoline differs from the principle of the engine in a vehicle run on diesel.
The two numbers cannot be extended to other petroleum derivatives & there have been measurements of "fuel values" for the sake of comparison between the various light or heavy fractions including those with < C5 & ≥ C16 .
For example: Biodiesel (blended with diesel, a petroleum deivative) has cetane number.
You said rightly (blended with diesel) & this rendered it to be evaluated by cetane number. Same applies to methanol or ethanol (when blended with gasoline in the fuel that is called GASOHOL) since octane numbers were assigned to these alcohols. The alcohols have shortcomings & this is a different story.
But you will not find octane numbers for, e.g. ethylene or propylene "the derivatives of petroleum which emerge in the overhead line of the rectification tower of crude oil" and you will not find cetane number for, e.g. wax or asphalt "the derivatives of petroleum which pass in the bottoms residuals line of that tower".
Thank you Nizar Matar for your very useful answer and thank you Mala Babagana Gutti for following
The more the octane number of gasoline or petrol the good fuel it is for running petrol engine. For diesel engine, high cetane number for diesel is required for good combustion and hence this becomes good fuel.
Octane number is used for petrol fuels, higher the octane number, the better burning of fuel and efficient. Cetane number is used for diesel, Higher the cetane number, less will be detonation and efficient burning of fuel.
The more the octane and cetane number, gives an indication of a good petrol and diesel fuels respectively. This also indicates to have a proper and good combustion.
Octane number and Cetane number designates the fuel quality for smooth combustion. Higher numbers gives fuel to be good in combustion for petrol and Diesel fuels respectively.
The high octane rating for petrol engine or high cetane rating of diesel engine gives lies for proper burning of fuel with low emissions. This also indicates that fuel is good in nature.
Octane number and Cetane numbers gives the rating of fuel for petrol and Diesel engines respectively. Hence, higher Octane number and higher Cetane number gives proper and good combustion of fuel.
Yes octane and cetane ratings are indicators of the combustion of petrol and Diesel fuels. the quality of the fuel can be understood based on this rating.
Octane rating and Cetane rating gives the combustion characteristics of petrol and Diesel fuel leading to proper combustion. Higher rating gives the way for effective and complete combustion of fuel.
Higher Octane number of petrol and higher Cetane number of Diesel gives the good burning ability of fuel to have a good combustion of fuel. The pollution as well as knocking or detonation characteristics can be reduced.
Cetane number of a diesel engine fuel is indicative of its ignition characteristics. Higher the cetane number better it is in its ignition properties. Cetane number affects a number of engine performance parameters like combustion, stability, drivability, white smoke, noise and emissions of CO and HC. For more details PLZ take a look on pending PDF:
High Octane number of petrol as well as high Cetane number of Diesel gives an indication of proper combustion of fuel with less emissions and thereby increasing thermal efficiency of the engine.
Octane number and Cetane number gives good burning capability of fuel. The more the number, the good the petrol and Diesel fuels. Having high numbers also indicates reduction of knocking and detonation of fuels in combustion chamber.
Octane number and Cetane number has greater influence on petroleum fuels since this tells the good combustion of petrol and Diesel fuels respectively. The high number S indicate less emissions and good characteristics of the fuel.
Octane number shows the ability of a fuel to resist knock (pre-ignition of the fuel) in the Gasoline Engine that needs high compression ratios.
the Cetane number is measures of ignition delay. Higher the cetane number of fuel the shorter the ignition delay, the least time it take to burn. Thus fuel with high cetane no. (but lower octane no.) is ideal for diesel Engines.
ON resistance to otto ignition ranges from (0-100). reflects the tendency to knock
CN fuel ability to ignition. Higher CN means shorter delay period. ranges from 40-65
Octane number can be examined for gasoline sample as Petroleum Fuels in order to measure the knock resistance characteristics of gasoline engines.
Cetane number can be examined for diesel samples as Petroleum fuels in order to measure the ignition delay of diesel engined.
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