2-Ethylhexyl nitrate (EHN) is the most widely used and effective diesel cetane number improver globally today. It is not used as a primary component of fuel but rather as a critical additive (typically added at 0.05%–0.3% by volume) to significantly enhance the cetane number of diesel.
Key Functions and Mechanism of Action
Improving Cetane Number:
Significant Effectiveness: A small addition can markedly increase the cetane number of diesel (typically, adding 0.1% by volume of EHN can raise the cetane number by approximately 3–5 units). This is its core function.
Mechanism of Action: Under the high-temperature and high-pressure conditions at the end of the compression stroke in a diesel engine, the O–NO₂ bond in EHN molecules preferentially breaks, generating highly reactive free radicals (e.g., NO₂, RO•). These free radicals act as "ignition seeds," rapidly initiating the oxidation chain reaction of surrounding diesel hydrocarbon molecules. This significantly shortens the ignition delay period, enabling smoother and faster compression ignition of the fuel.
Resulting Engine Benefits:
Reduced Engine Roughness: A shorter ignition delay means smoother combustion, significantly lowering engine noise and vibration (knocking).
Improved Cold Start Performance: Facilitates easier ignition of diesel in low-temperature environments.
Reduced Emissions: Promotes more complete and rapid combustion, helping to reduce white smoke (unburned hydrocarbons) and particulate matter (PM) emissions during cold starts.
Areas of Application
Automotive Diesel: Used to adjust the cetane number of refinery-produced diesel to meet national or regional standards (e.g., China VI and Euro VI diesel require a cetane number ≥ 51).
Diesel Blending Components: Refineries can incorporate a higher proportion of lower-cetane, cost-effective components (such as catalytic cracked diesel) during diesel blending. By adding EHN, they can meet final product specifications, thereby optimizing production costs.
Alternative Fuel Compatibility: Used to enhance the ignition performance of certain alternative fuels with relatively low cetane numbers (e.g., some types of biodiesel).
