HHO gas composition: why flow rate is not gas quality
Short answer: A flow rate states how much gas reached the engine, not what the gas was. Our review of the 2026 Scientific Reports paper found no reported independent analytical characterization of H2 concentration, O2 concentration, H2:O2 ratio or purity for the gas delivered by the HG80.
Last reviewed: August 2026 · Combustion Enhancement technical review
This page is part of our oxyhydrogen evidence cluster. Published figures are attributed to the paper reporting them, manufacturer figures are labelled as manufacturer claims, and our own interpretation is labelled as our technical analysis. See the 2026 Scientific Reports HHO study review.
Terminology used on this page
| Term | Definition |
|---|---|
| H₂ | Hydrogen. |
| O₂ | Oxygen. |
| H₂/O₂ | A hydrogen and oxygen mixture. |
| HHO / oxyhydrogen | Commonly used terminology for an electrolytically generated hydrogen/oxygen mixture delivered to an engine intake. |
| PEM / SPE | Proton exchange membrane / solid polymer electrolyte electrolysis — a solid-membrane, pure-water architecture with no liquid caustic electrolyte. |
| Alkaline KOH electrolysis | Electrolysis using a liquid potassium hydroxide electrolyte. |
| BSFC | Brake specific fuel consumption — fuel consumed per unit of engine work. |
| BTE | Brake thermal efficiency — the share of fuel energy converted to useful engine work. |
What was reported about the gas
The paper reports approximately 1.3 L/min HHO production and approximately 230 W electrical consumption for the generator used in the vehicle experiment.
Our review found no reported independent analytical gas-composition characterization in the publication. That is a statement about the reporting record. It is not a claim that the gas was impure, and we make no such claim.
| Parameter | Reported in the paper? |
|---|---|
| Total HHO flow | Reported (≈ 1.3 L/min) |
| Electrical consumption | Reported (≈ 230 W) |
| H₂ concentration | Not identified in our review |
| O₂ concentration | Not identified in our review |
| H₂:O₂ ratio | Not identified in our review |
| Gas purity / moisture | Not identified in our review |
| Electrolyte carryover | Not identified in our review |
Why composition is part of the treatment
Our technical analysis: in an engine-combustion experiment the composition of the injected gas is part of the experimental treatment, so leaving it uncharacterized limits how far a result can be attributed to HHO as a category.
Two generators delivering the same volumetric flow can deliver different hydrogen mass, different H₂:O₂ ratios and different moisture content. Without composition data, the treatment is defined only by volume.
Questions.
Did the 2026 study report the H2/O2 composition of the gas?
- The published study reports HHO flow and electrical consumption, but we found no reported independent analytical characterization of H2 concentration, O2 concentration, H2:O2 ratio or overall gas purity delivered to the engine.
Why does gas composition matter?
- Gas flow alone does not establish gas composition or purity. H2 concentration, O2 concentration, H2:O2 ratio, moisture and potential electrolyte carryover can all be relevant experimental variables.
Are you claiming the HG80 produced poor-quality gas?
- No. We make no claim about the gas produced by the unit tested. The point is that composition is not established in the published record.
Sources
- Synák, F. (2026). Evaluation of hydrogen and oxygen mixture addition in internal combustion engines under real driving conditions. Scientific Reports.DOI 10.1038/s41598-026-54105-y · also at nature.com
- Read the original 2026 Scientific Reports HHO study on nature.com
- Review the HG80 manufacturer's specificationsManufacturer documentation
- Review the HG80 manufacturer's KOH/electrolysis informationManufacturer documentation
PEM/SPE oxyhydrogen systems
Unlike the HG80 alkaline system tested in the 2026 Scientific Reports experiment, PEM/SPE oxyhydrogen systems such as the HydroHub™ use solid-polymer electrolysis and pure water, with no potassium hydroxide electrolyte.
Combustion Enhancement develops PEM/SPE oxyhydrogen systems using pure-water electrolysis (no KOH). These systems are used in industrial engines, furnaces and commercial applications. Learn more about the HydroHub™ PEM oxyhydrogen system and the DH-Power™ industrial oxyhydrogen generator.
Related evidence pages
- Alkaline HHO versus PEM/SPE oxyhydrogen
How liquid-electrolyte alkaline KOH HHO generators differ from PEM/SPE pure-water oxyhydrogen systems, and why a test of one is not a test of the other.
- How to test PEM oxyhydrogen properly
The measurement set required to evaluate PEM/SPE oxyhydrogen on an engine: gas composition, purity, flow, electrical input, load, fuel consumption, emissions, dosing, repeats and uncertainty.
- HHO dosing: why the HHO-to-fuel ratio matters
Why HHO dosing and the HHO-to-fuel ratio determine what an engine test measures, and why an unoptimized fixed retrofit dose samples one point rather than characterizing the technology.