Differences in the anti-knock properties of diesel and gasoline
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While reading today, I suddenly noticed a problem: diesel engines require n-alkanes with a high cetane number to prevent detonation, whereas gasoline engines need isomeric alkanes with a high octane number for the same purpose. N-alkanes have a high cetane number but a low octane number, while isomeric alkanes have a high octane number but a low cetane number. Since both are used to prevent detonation, why are alkanes with opposite properties required? It turns out that diesel engine knock occurs during the pre-ignition delay period. Diesel engines are compression-ignition engines, and diesel is ignited by self-ignition. Normal alkanes have a low auto-ignition temperature, a short delay period, and good anti-knock properties. Gas engine knock occurs during the later stages of combustion, while diesel engines rely on ignition. Normal alkanes have a low auto-ignition point; they burn unevenly and are prone to spontaneous ignition, resulting in knock. It’s all for knocking; the principles are different, and the oils required are also different.
Due to the different working principles of gasoline engines and diesel engines, gasoline engines rely on ignition. The reason for this need for ignition is that gasoline has a high auto-ignition temperature; compression of the fuel-air mixture alone is not sufficient to cause it to ignite. Additionally, gasoline has a low boiling point as well as a low flash point (or ignition point), which means it ignites easily； Diesel engines, on the other hand, are compression-ignition engines that rely on the self-ignition caused by high-pressure gas and oil to drive the piston and generate power. The original poster has confused two concepts in the question: the anti-knock properties of gasoline and diesel are not the same, and the mechanisms of knocking in gasoline and diesel engines differ as well. For example, in gasoline engines, knocking occurs because, under high temperature and pressure conditions, the n-paraffin components in the fuel-air mixture ignite spontaneously, leading to uncontrolled combustion in the combustion chamber. This phenomenon is mainly caused by the formation of excessive peroxides due to the oxidation of the fuel ； Knocking in diesel engines is mainly caused by poor ignition properties; that is, an insufficient concentration of peroxides leads to a prolonged ignition delay. This results in the accumulation of large amounts of peroxides during the rapid combustion phase, and combustion at this stage causes a sharp increase in temperature and pressure, which in turn exerts force on the piston head and induces knocking.
I’m not confused; I’m just explaining the differences in the anti-knock principles of gasoline and diesel engines
Thanks for sharing, just passing by to learn~ I’m a newbie!
I’m a beginner too; there are many experts here. I’ve come to learn**
Excuse me, to find information on atmospheric and vacuum distillation units, in which section can I look for it? Questions about the device!