Fuel Additives

Basics

• This page goes over all the various additives that can be added to (liquid) fuels such as Gasoline , Diesel , Kerosene / Jet Fuel etc

Additives

General

• Antioxidants to slow fuel “aging”
• Metal Deactivators / Corrosion Inhibiter Compounds to Prevent Tank Rust and also potential Catalytic Degradation of Fuel
• ”Oxygenate Additives” which help reduce Carbon Monoxide and Hydrocarbon Emissions via allowing the fuel to burn more cleanly (An analogy would be why racing engines use Nitromethane or Nitrous Oxide )

Common In Spark Ignition Engine Fuels (Gasoline)

Antiknock Additive

• Also known as Antiknock Agents or Octane Boosters
• A substance with a high Octane Rating added to a fuel to decrease the fuel’s reactivity which allows for more compression (re: Compression Ratio ) to be used before the eventual ignition of the fuel by a Spark Plug
  • Resisting ‘’’preignition’’’ which is called Engine Knock hence the name
• One of the most common was Tetraethyl Lead, but due to the widespread lead exposure caused by this, as well as the more mundane fact that it oead to Catalyst Poisoning of Catalytic Converters it was phased out (Outside of most Avgas ; 100LL Avgas is still common)
• Ethanol has largely taken up the role in most gasoline
  • For Boat Engines, Generators, or Long Term Storage, Ethanol Free Gasoline (typically from Hydrocracked Fractions) is sold
• In engines designed for the lead accumulation in terms of Valve Seats and Valve Seat Wear , Ferrocene or Methylcyclopentadienyl manganese tricarbonyl (Often Abbreviated to MMT ) may be used
  • Issues of Catalyst Poisoning , and how well the iron or manganese compare to lead in protective+sealing functionality needs to be investigated
  • Health issues seem to be much less, if even extant (although being less harmful than Lead is a VERY low bar)

Scavenging Agents for Organometallic Complex Based Antiknock Additives

• These are mostly irrelevant in modern formulations, and also ‘’’debated’’’ (and as per modern engines that have never seen a drop of leaded fuel yet work fine), the Lead in Tetraethyl Lead is Liberated during combustion
  • This gradually builds up not just in the local area, but also on certain parts of the engine, most noticeably on the Spark Plug, the Exhaust Valve, and most importantly the Valve Seat
• For things like the spark plug it could lead to wear or short circuiting
• For the valve seat however it was a self healing soft layer of sorts
• In order to reduce these deposits though, various additives can be used
• The main non-historical application would be ‘’’IF’’’ Iron or Manganese deposits form in a similar manner, although this would need to be investigated, and also different chemistries may be involved

Common in Compression Ignition Engine Fuels (Diesel)

• Supposedly Hydrodesulfurization for making Ultra-Low Sulfur Diesel (which as of this edit is now ALL DIESEL including Off-Road Diesel ) removes various compounds that would otherwise aid in lubricity, conductivity (and thus ESD ignition risk)
• Thus additives are needed
• Mainly:
  • Fuel Lubricity Additives (especially with more novel CI fuels such as DME )
    • 2% Blending of a Fatty Acid Methyl Ester (aka Transesterification Biodiesel Biodiesel ) can get most fuels up to spec supposedly
      • Almost akin to how Ethanol is now the standard anti-knock additive post TEL being phased out, thus all non-premium/specialized gas having 10% Ethanol (ie E-10 Fuel )
    • Other additives do exist though, hunting for SDS ‘s currently as most pages ramble on without giving away the krabby patty secret formula so to speak
• Gel Point Depressors are also added (Especially in the Winter Months, this also relates to Diesel Grade Numbers if i remember correctly (citation needed))
• Depending on the Feedstocks/Refineries used Additives may be needed to raise the Cetane Rating of the fuel to the required standards

Common in Aerospace/Military

• Anti-Icing Additives
• Look into JP-5 and JP-8 etc Fuel Specifications

External Links

• A Cadence Petroleum Page on Fuel Additives
• A MSP . Energy Page from 2023 Titled “ A Fuel Supplier’s Perspective On Gasoline Fuel Additives”
• A Royal Society of Chemistry Book’s Page Titled “ Chapter 12: Green Anti-knock Agents for Enhancement of Gasoline Performance”
• A Fleet Maintenance Magazine Maintenance Magazine Article from 20202’Tutled “Diesel Fuel Additive Considerations”