Bio-degradation of engine carbon deposits

Engine deposits are not soot alone: they are lacquers built from heavy fuel fractions and partially burnt engine oil, oxidised and nitrated in the flame zones and crevices, polymerised into insoluble films on pistons, injectors and intake valves. “Bio-degradation” of these deposits is market shorthand; the honest question is where, anywhere in an engine, a biological molecule could act at all.

What the deposit is

Deposit formation starts as a liquid film: fuel and oil survive combustion incompletely, their heavy aromatics oxidise to carbonyl and nitro compounds, oligomerise, and bake onto hot metal. Once carbonised at combustion-chamber temperatures — many hundreds of degrees — the residue is effectively graphitic and soluble in nothing. Ethanol-blended petrol adds a failure mode of its own, pulling water and leaving gum. The deposits an additive can actually reach are therefore the cool-side ones: fuel lines, filters, intake valves below roughly 200 °C — not piston crowns. Water, acids and microbes in stored fuel are a separate and genuinely biological problem, but that is tank hygiene, not deposit removal.

Where a protein can and cannot act

Proteins denature within minutes above 100 °C; flame temperatures exceed 2,000 °C. No enzyme touches the combustion chamber, so all biochemical action must happen in the liquid fuel — tank, lines, filters. There the credible mechanisms are interfacial: an enzyme needs a hydration shell, fuel carries dissolved and emulsified water, and at those water-oil surfaces the plausible work is dispersing oxidised gum precursors, holding water as a fine microemulsion (finer spray, cleaner burn) and keeping asphaltenes suspended. What is not chemically credible is bulk cleavage of saturated hydrocarbon chains at fuel temperature over tank residence times — catalysis that slow, on a substrate that insoluble, cannot rate-affect a fill-up. The extreme dilution ratios these products are dosed at, one part in several thousand, are themselves evidence of a catalytic or surface-active mode: grams per thousand litres cannot be stoichiometric digestion.

Where the mechanism tops out

The ceiling follows. A class acting only upstream of combustion can lower the rate of new deposit formation and clean cool-side surfaces; it cannot dissolve the carbonised layer on a piston — that is the job of mechanical decarbonising or strong solvent chemistry. Verification repeats the same asymmetry: bulk marine dosing carries laboratory fuel analysis and engine-maker letters of no objection, while retail bottles lean on user experience. That asymmetry is not fraud — it reflects the mechanism’s own limits: real, interfacial, statistical, and confined entirely to the fuel phase.