Additives for Automotive Fuels
Anti-Icings
Freezing out the moisture in the air by reducing the temperature by vapourising the petrol. Can be prevented by two kinds of additives. Either Pour point depressants or surface-active materials are added (adhesive force between KW and water increase, and therefore the adhesive forces between the metal and water reduce)
Detergent
Preventing and reducing deposits in the carburettor and intake system. As bonds with a hydrocarbon section and a polar functional group are used as active agents.
Anti-oxidants
Were made necessary only with the introduction of crack petrol, since it contains components that are easily oxidable and thus contribute to the building of knock-producing peroxides and resinous residues (gum). Max. gum content in petrol: Evaporation residue 5mg/10ml. Oxidation through auto-oxidation is aided by metals (Cu, Fe, Ni, Mn, Co). Just 10 mg Cu/l fuel are sufficient to begin the oxidation process.
Corrosion protection additives
Water in petrol (or below the petrol) and/or detergent additives can have a corrosive effect. Long-chained, high-molecular org. acids, esters or amines with surface-active properties are used as corrosion-protection additives. Often, the amines are used with carburettor additives.
| Additive | Effect | Comment |
| 2 Methyl-2-Propanol (tert. Butylalkohol) TBA | anti-knock material | |
| 2 Methyl-1-propanol (Isobutyl alcohol) IBA | anti-knock material | |
| 2-Propanol (Isopropanol) | anti-knock material | |
| N-Methyl-anilin | anti-knock material | Very effective (more effective than MTBE, MeOH etc.) Usage is criticised since it leads to build-up of nitrosomines. |
| MTBE | anti-knock material | Must be added in large quantities (5–15%) |
| Methanol | anti-knock material | Is or was examined in Germany as an alternative to MTBE Recommended concentration: 15% |
| Methylcyclopentadienyl-Mangan-tricarbonyl (MMT), Ferrocen | anti-knock material | MMT has negative influence on emissions MMT is highly volatile |
| Methanol | Carburettor frosting is prevented | Pour point depressants. Not very effective |
| Alcohols | Carburettor frosting is prevented | Pour point depressants |
| Ethanol | Carburettor frosting is prevented | Pour point depressants |
| Isopropanol | Carburettor frosting is prevented | Pour point depressants; hardly used since very expensive |
| Dimethylforamide | Carburettor frosting is prevented | Pour point depressants. Very effective |
| Dimethylacetamide | Carburettor frosting is prevented | Pour point depressants Very effective |
| Dipropylenglycol | Carburettor frosting is prevented | Pour point depressants Very effective |
| Glycols | Carburettor frosting is prevented | Pour point depressants |
| Ketone | Carburettor frosting is prevented | Pour point depressants |
| Heterocyclic bonds (with nitrogen or oxygen) | Carburettor frosting is prevented | Pour point depressants |
| Org. nitrogen bonds | Carburettor frosting is prevented | Surface-active (conc. 50–100g/kg) |
| Org. phosphorous bonds | Carburettor frosting is prevented | Surface-active (conc. 50–100g/kg) |
| Amino salts phosphoric acid di-esters | Carburettor frosting is prevented | Surface-active (conc. 50–100g/kg) |
| Glycerine ester of fatty acids (fats) | Carburettor frosting is prevented | Surface-active (conc. 50–100g/kg) |
| Glycerine ester of fatty acids | Carburettor frosting is prevented | Surface-active (conc. 50–100g/kg) Depending on the size of the fatty acid, it is water soluble or not soluble Are also used as emulgators |
| Formamide (R-CONH2) | Carburettor frosting is prevented | Surface-active (conc. 50–100g/kg) |
| Imidazoline | Carburettor frosting is prevented | Surface-active (conc. 50–100g/kg) |
| Imidazoline | Detergent additive | Only prevents deposits |
| Alkyl-substituted succinimide or succinamide | Detergent additive | Only prevents deposits |
| Alkyl substituted carbamide | Detergent additive | Only prevents deposits |
| Poly-isobuten-amine/polyamine | Detergent additive | Prevents deposits AND removes old deposits e.g. R-NH-(CH2)3-N(CH3)2 or R-NH-CH2-CH2-NH2 R=wear polyisobutene |
| Various amines | Detergent additive | e.g. Polyetheramine, Polyalkylamine, Polyalkylsuccinimide |
| Phenol derivates | Anti-oxidants | e.g. 2.6 di tert. Butyl-phenol or 4-Diisopropyle-amino-anilin etc. |
| Napthalin derivates | Anti-oxidants | |
| Phenylendiamine derivates | Anti-oxidants | |
| 1.3-to-(2-hydroxy-benzylide amino).propane | Anti-oxidants | Effective, because it takes effect as metal deactivator (e.g. against Cu) |
| Mixture of 43% (2-ethyl-hexyl)-(3-methyl-butyl)-phosphate + 39% of a C14-16 Amine | Corrosion inhibitor | 10–20mg/kg |
| 2-(2-(2-ethyl-hexyl)-phenoxyl)-1,1,2,2-teraethoxy-ethanol | Corrosion inhibitor | 10–20mg/kg |
| Ethylendiamine-dinonylnaphthalinsulphonate | Corrosion inhibitor | 10–20mg/kg |
| 86% polymerised linol acid + 6% polymerised methyl-linol acid + 8% org. Phosphorous bond(s) as 50% mixed in kerosene | Corrosion inhibitor | 10–20mg/kg |
| Polyetheramine | Remove residues in the combustion chamber | approx. 3g/kg |
| Polyether Pyrolidon (C4H7NO-) | Remove residues in the combustion chamber | approx. 3g/kg |
| Polyisobutylene amines | 100–600mg/kg Primary to tert. amines, phenolic groups can also be used Polyisobutylene (not the amine) are oily to rubbery substances and are used in lubricant greases (low molecular, for improving viscosity) |
Determination options
FTIR
Ronald L. Fausnight identified additives through FTIR images of petrol inspissated at 40°C through comparison spectrums (4000–600cm-1).
Compiled by Sandor Brandenberger
Literature
1): Volker Hoenig, Tests of the mechanisms of the action of additives for heavy fuel oil, VDI, 84, 1991