*Flash point definition: the lowest temperature at which the fuel can form an ignitable mixture in air In the table below we can see some of the main properties of gasoline (petrol) and diesel fuel. Also, the properties of the fuel determines how the combustion is initiated, how the flame is propagated and also the content of the exhaust gas. From this point of view, there are differences between diesel and gasoline (petrol), especially regarding how the air-fuel mixture is created and how the combustion process is triggered. The generation of pollutant exhaust gas emissions also depends on a great extent on the sequence of engine phases (engine cycle). The efficiency and power output of an internal combustion engine depends on a great extent on the pressure characteristic of the engine (p-V diagram), which depends on the engine cycle (4-stroke): induction/intake, compression, power (combustion) and exhaust.
For the same reason, the oxigen may also be insufficient for combustion, which will generate carbon monoxide (CO).ĭue to the limitations of the fuel conversion efficiency, there are unintended outputs of an internal combustion engine.
Also, since the air-fuel mixture is not 100% homogeneous, a part of the fuel will not burn (oxidize), which means that in the exhaust gases we’ll have unburnt hidrocarbons (HC).
Since more than 70 % percent of the air is nitrogen (N 2), a part from it will react with oxygen and form oxides of nitrogen (NO x). In reality the fuel is mixed with air and not pure oxygen (O 2). Image: Methane (CH4) complete combustion process
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