What physical and chemical phenomena are the basis of removing carbon deposits with hydrogen-oxygen gas (HHO)?
The basis of removing the carbon deposits in a combustion engine by HHO gas is the chemical reaction between Carbon and Hydrogen and Oxygen, at elevated pressure and temperature, facilitated by the presence of traces of Nickel and Cobalt.
Context
HHO carbon-cleaning is the process of removing carbon deposits from the internals of the combustion engine and the exhaust tract – DPF, EGR valve, Catalytic Converter, etc. – by means of adding a mixture of gaseous Hydrogen and Oxygen (HHO gas) into the engine air-intake manifold.
The goal of HHO carbon-cleaning is to reduce the negative impact of carbon deposits formation in the engine, in order to reduce harmful exhaust emissions, lower maintenance costs, and improve fuel efficiency.
The process of removing carbon deposits
The basis of removing the carbon deposits in a combustion engine by HHO gas, such treatment being primarily applied to the diesel engines, is the chemical reaction between Carbon and Hydrogen and Oxygen, at elevated pressure and temperature, facilitated by the presence of traces of Nickel and Cobalt, found in combustion engine block components, as catalysts.
From R. F. Baddour and J. M. Iwasyk:

The reaction of Carbon with Hydrogen and Oxygen
The chemical reactions between Carbon (C) in solid form, and Hydrogen (H2) and Oxygen (O2) in active gaseous forms, are:
C + 2H2 → CH4
C + O2 → CO2 (for Carbon valency +4)
2C + O2 → 2CO (for Carbon valency +2)
Simultaneously, in the presence of CO2 and CO, the Sabatier reaction takes place:
CO2 + 4H2 → CH4 + 2H2O
CO + 3H2 → CH4 + H2O
From Stefan Rönsch and Jens Schneider:


Finally, the resulting Methane is combusted together with the fuel, and the resulting CO2 and the water vapour are mixed with the exhaust gases of the combustion engine:
CH4 + 2O2 → CO2 + 2H2O
The equipment required for an efficient carbon-cleaning operation could be the high-performance C-600 hydrogen machine, or similar.
The effectiveness of removing carbon deposits
The effectiveness of the carbon-cleaning process can be verified by measuring two types of parameters:
- Short-term parameters – measured immediately after the procedure;
- Long-term parameters – measured during weeks or months after the procedure;
Some of the short-term parameters, related to the level of effectiveness of the process of HHO carbon-cleaning:
- The opacity of the exhaust gases ‘Before’ and ‘After’ the process, measured by a standard opacimeter, in 1/m units;
- DPF back-pressure ‘Before’ and ‘After’ the process, measured via an OBD-II diagnostic tool, in Mpa units;
- Airflow through DPF ‘Before’ and ‘After’ the process, measured via an OBD-II diagnostic tool, in g/sec units;
- Soot accumulation in DPF ‘Before’ and ‘After’ the process, measured via an OBD-II diagnostic tool, in grams;
- Visual inspection of engine and exhaust components ‘Before’ and ‘After’ the process;
Some of the long-term parameters, related to the level of effectiveness of the process of HHO carbon-cleaning:
- Lower fuel consumption, measured over the same period ‘Before’ and ‘After’ the HHO carbon-cleaning;
- Lower maintenance cost, linked to a reduced number of issues with DPF, EGR valve, etc.
The equipment required for efficient verification of the effectiveness of the carbon-cleaning operation could be the ultra-portable MP-0.1 Diesel Smoke Meter, or similar.
Further reading
The reaction of Carbon with Hydrogen at High Pressure. JD Blackwood.
https://doi.org/10.1071/CH9590014
The reaction between carbon and the products of hydrogen, oxygen and water microwave discharges. F.J Vastola, P.L Walker Jr., J.P Wightman.
https://doi.org/10.1016/0008-6223(63)90004-6
Reaction of Hydrogen Atoms with Solid Carbon. G. M. HARRIS, A. W. TICKNER.
https://doi.org/10.1038/160871a0
Sabatier reaction
https://en.wikipedia.org/wiki/Sabatier_reaction
Review on methanation – From fundamentals to current projects. Stefan Rönsch, Jens Schneider, et al.