Differences Between Petrol And Diesel

Both petrol (gasoline) and diesel are extracted from petroleum or crude oil. Crude oil is a mixture of aliphatic hydrocarbons of different lengths having different properties. Hydrocarbons are a chain of carbon and hydrogen linked together having certain properties. Petrol and diesel are also hydrocarbons present in the crude oil having different properties.

Each hydrocarbon has a different boiling point. Therefore, petrol and diesel can be extracted from crude oil based on their boiling points. Crude oil is boiled in oil refineries and later petrol and diesel or any other hydrocarbon chain can be separated at different temperatures. This method is called fractional distillation.

Let's look at some of the differences between petrol and diesel properties.

PETROL	DIESEL
Chemical Formula: Commonly used petrol has a chemical formula of C8H18.	Chemical Formula: Diesel has an average chemical composition of C12H23.
Density: Density of gasoline is around 737 kg/m3 at 600 F.	Density: Density of diesel is around 832 kg/m3 at 150 C.
Calorific Value: The net calorific value of gasoline is approximately 44.4 MJ/kg.	Calorific Value: The net calorific value of diesel is approximately 43.4 MJ/kg.
Auto-ignition temperature: The auto-ignition temperature of petrol is 2460 C.	Auto-ignition temperature: The auto-ignition temperature of diesel is 2100 C.
Method of ignition: Spark plugs are used in petrol engines to burn gasoline.	Method of ignition: Diesel is injected at the end of compression stroke in diesel engine. It burns automatically due to the intense pressure and temperature inside the cylinder.
Energy Content: Petrol has a lower energy content of approximately 33.7 MJ/kg.	Energy Content: Diesel has higher energy content of approximately 36.7 MJ/kg.
Boiling point: Boiling point of petrol is between 350 C to 2000 C	Boiling point: Boiling point of diesel is between 1800 C and 3600 C
Flash Point: Flash point is the lowest temperature at which enough fuel in the evaporated state is available for ignition. Flash point of gasoline is -430 C	Flash point: Flash point of diesel varies from 520 C to 950 C
Fire point: Fire point is the temperature at which enough vapours of fuel is available to burn for at least 5 seconds. Fire point of petrol is at least 10 degree higher than the flash point around -330 C	Fire point: Fire point is at least 10 degree higher than flash point around 620 C.
Combustion reaction: The combustion reaction in gasoline engine is as follows: 2 C8H18 + 25 O2 → 16 CO2 + 18  H2O	Combustion reaction: The combustion reaction in diesel engine is as follows: 4 C12H23 + 71 O2 → 48 CO2 + 46  H2O
Octane Rating: Petrol is rated by octane number. In certain cases, petrol and air mixture may auto-ignite due to the heat and pressure inside the cylinder rather than ignite from the spark plug at the specific time. This causes detonation or knocking resulting in rapid pressure rise causing damage to the engine. Octane rating expresses the level of resistance a gasoline fuel has to auto-ignition or knocking. Octane number or rating is defined as the percentage by volume of iso-octane (2,2,4- trimethylpentane) in a combustible mixture of the mixture of iso-octane  and n-heptane which have the same anti-knocking capacity as the fuel under test. Research Octane Number (RON) is used to measure the octane rating of gasoline. A standard unleaded gasoline has a octane rating of 95 RON. Gasoline of higher quality has 98 RON. A high performance gasoline engine uses gasoline of 102 RON.	Cetane Number: Cetane number is the converse of octane number. It indicates the combustion speed of diesel fuel. The higher the cetane number, the easier it is to ignite the diesel fuel. Cetane number is defined as the percentage by volume of cetane (Hexadecane) in a combustible mixture of cetane and 1-methylnapthalene which have the same ignition characteristics as that of the fuel tested. A standard diesel engine requires diesel fuel with a minimum cetane rating of 51.