2026 Scientific Reports HHO Study: What Was Actually Tested?
A methodological analysis of a real-world HHO retrofit evaluation published in Scientific Reports. The study is useful evidence about the specific commercially available system and test conditions it used. It does not establish how an optimized PEM/SPE oxyhydrogen system with characterized gas quality and controlled dosing would behave, because that was not what was tested.
- Author
- František Synák
- Journal
- Scientific Reports, vol. 16, Art. 23305
- Published
- 22 May 2026
- DOI
- 10.1038/s41598-026-54105-y
Read the primary source in full: Evaluation of hydrogen and oxygen mixture addition in internal combustion engines under real driving conditions (doi.org/10.1038/s41598-026-54105-y).
This page critiques the experimental scope and reporting of the published study. It does not claim that the authors acted improperly, nor does it claim that PEM oxyhydrogen technology is proven effective under every operating condition.
The 2026 Scientific Reports HHO study in facts.
Each row below is attributed to its source: the published paper, or the HG80 manufacturer's own documentation. Nothing here is a measurement taken by us.
| Fact | Finding | Source |
|---|---|---|
| Study | Scientific Reports (Nature Portfolio), 2026 | Published paper |
| Paper | Evaluation of hydrogen and oxygen mixture addition in internal combustion engines under real driving conditions | Published paper |
| DOI | 10.1038/s41598-026-54105-y | Published paper |
| Generator tested | Hydrogen Energy HG80 | Published paper |
| Generator type | Alkaline HHO generator | Manufacturer specification |
| Electrolyte | KOH, approximately 20–25% according to the manufacturer | Manufacturer specification |
| Reported HHO flow | Approximately 1.3 L/min | Published paper |
| Reported electrical consumption | Approximately 230 W | Published paper |
| PEM/SPE technology tested? | No — the HG80 is an alkaline system | Manufacturer specification |
| Independent H₂/O₂ gas-composition analysis reported? | Not identified in the published paper | Our technical analysis |
| HHO dosing optimized? | No — the paper states dosing and the HHO-to-fuel ratio were not optimized | Published paper |
| Primary limitation | The experiment evaluates one commercial retrofit configuration rather than PEM/SPE oxyhydrogen technology generally | Our technical analysis |
This review separates reported experimental observations from manufacturer specifications and from our technical interpretation. Numerical and technical claims are attributed to their original source wherever possible.
Synák, František. “Evaluation of hydrogen and oxygen mixture addition in internal combustion engines under real driving conditions.” Scientific Reports (Nature Portfolio), 2026. DOI: 10.1038/s41598-026-54105-y.
Read the original 2026 Scientific Reports HHO study · Review the HG80 manufacturer's specifications · Review the HG80 manufacturer's KOH/electrolysis information
Definitions 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. |
| KOH alkaline electrolysis | Electrolysis using a liquid alkaline (potassium hydroxide) electrolyte. |
| HG80 | The Hydrogen Energy HG80 onboard HHO generator identified in the 2026 Scientific Reports experiment. |
| HydroHub™ | Our PEM/SPE oxyhydrogen product range, operated by YBG Group International Pty Ltd. |
Two materially different propositions.
Short answer: The 2026 Scientific Reports paper reports a negative result for one commercially available HHO retrofit configuration under real driving conditions. That is not the same proposition as a demonstration that PEM/SPE oxyhydrogen injection cannot improve engine combustion.
A general verdict on HHO
A result for one configuration
The second proposition is what the data supports. The first is a generalization across gas-generation technologies, dosing strategies, engine platforms and duty cycles that a single real-driving retrofit evaluation cannot carry. The distinction is not rhetorical: it determines which variables remain untested.
The study evaluated commercially available retrofit devices without optimization of HHO dosing or control of the HHO-to-fuel ratio.Paraphrase of the paper's own stated scope — Synák (2026)
What was the HG80?
Short answer: The generator identified in the experiment is the Hydrogen Energy HG80. According to the manufacturer, the HG80 is an alkaline electrolyser using an approximately 20–25% KOH electrolyte with stainless-steel 304 electrodes. It is not a PEM/SPE electrolyser.
The onboard generator described in the experiment is the Hydrogen Generator HG80, sold by HYDROGEN ENERGY DOO of Belgrade, Serbia. The specifications below are the manufacturer's published claims, not measurements taken by the study or by us.
| Parameter | Manufacturer claim |
|---|---|
| HHO output | Up to 80 L/hour |
| Current | 10–15 A |
| Voltage | 14 V |
| Power | 140–220 W |
| Water consumption | 20–30 g distilled water/hour |
| Engine range | Approximately 500–2,500 cc |
| Electrodes | Stainless steel 304 |
| Electrolyte | KOH solution, approximately 20–25% |
| Gas delivery | Direct feed into engine intake |
| Storage | No hydrogen storage |
Primary source for the experiment: Read the original 2026 Scientific Reports paper (DOI 10.1038/s41598-026-54105-y). Manufacturer sources: HG80 product page and manufacturer FAQ (manufacturer claims).
Alkaline KOH electrolysis
KOH electrolyte → stainless-steel electrodes → H₂/O₂ gas → intake
PEM/SPE electrolysis
pure water → PEM/SPE membrane cell → controlled oxyhydrogen → intake
HG80 = alkaline KOH electrolysis. HG80 ≠ PEM/SPE electrolysis. This is not an assertion that PEM automatically produces better engine outcomes — that has to be established experimentally. It is an assertion that the two architectures are materially different and must be compared directly rather than assumed equivalent.
What the paper measured about the generator.
Short answer: The paper reports approximately 1.3 L/min HHO production and approximately 230 W electrical consumption for the generator used in the vehicle experiment. Those two figures describe quantity and electrical demand, not gas composition.
The study reports an HHO production rate of approximately 1.3 L/min — about 78 L/hour — at an electrical demand of roughly 230 W. That output is almost exactly the manufacturer's headline 80 L/hour rating, which is consistent with a unit operating as specified.
| Parameter | Scientific Reports (2026) | HG80 manufacturer claim |
|---|---|---|
| Gas output | ~1.3 L/min (~78 L/h) | Up to 80 L/h |
| Electrical power | ~230 W | 140–220 W |
| Electrolyte | Not fully characterized in the paper | KOH ~20–25% |
| Cell technology | Not identified as PEM | Alkaline stainless-steel electrode system |
Study figures: Synák (2026). Manufacturer figures: hhogas.rs.
Flow rate is not gas quality.
Short answer: Our review of the published paper found no reported independent analytical characterization of H2 concentration, O2 concentration, H2:O2 ratio, purity or moisture in the gas delivered to the engine. Flow rate alone does not establish gas composition.
If the dependent variable is engine response to H₂/O₂ addition, then the composition and purity of the injected gas are part of the experimental treatment — not an incidental detail. A volumetric flow rate describes how much gas arrived. It does not describe what that gas was.
We found no reported independent analytical verification in the published paper of the composition or purity of the gas delivered by the HG80. That is a statement about the reporting record, not about the gas. Read the original 2026 Scientific Reports paper.
| Parameter | Reported / verified in study? |
|---|---|
| Total HHO flow rate | Reported |
| Electrical consumption of the generator | Reported |
| H₂ concentration of delivered gas | Not reported |
| O₂ concentration of delivered gas | Not reported |
| H₂:O₂ ratio | Not reported |
| Independent gas-purity analysis | Not reported |
| KOH carryover / electrolyte aerosol | Not reported |
| Water vapour / moisture content | Not reported |
| Gas contamination analysis | Not reported |
| Independent gas-quality certification | Not reported |
| PEM/SPE cell technology | No — the HG80 is an alkaline unit |
None of this establishes that the gas was impure, wet or contaminated. It establishes that the published record does not allow a reader to determine the composition of the treatment, which limits how far the result can be attributed to "HHO addition" as a general category rather than to one device's actual output.
Alkaline KOH versus PEM/SPE.
Short answer: Alkaline HHO generation uses a liquid KOH electrolyte; PEM/SPE electrolysis uses a solid proton-exchange membrane with a pure-water feed. Because the HG80 is an alkaline unit, the 2026 experiment is not a direct test of PEM oxyhydrogen.
The manufacturer's own documentation states the HG80 operates with a potassium hydroxide solution of approximately 20–25% across stainless-steel electrodes. That places it in the alkaline liquid-electrolyte family. PEM/SPE systems use a solid proton-exchange membrane with a pure-water feed.
Liquid-electrolyte architecture
- · Liquid KOH electrolyte
- · Conventional electrode/electrolyte cell design
- · Potential for electrolyte carryover must be managed
- · Gas quality depends on cell design, separation, water management and gas handling
Membrane architecture
- · Solid proton-exchange membrane
- · Pure-water feed, no caustic electrolyte
- · Membrane-based electrochemical separation
- · Different electrode/catalyst architecture and gas-management characteristics
We do not claim PEM is inherently superior in every respect; each architecture has engineering trade-offs. The narrow point stands on its own: the fact that the 2026 study used an alkaline HHO generator is sufficient to prevent the study from being treated as a direct test of PEM/SPE oxyhydrogen injection. Read the original 2026 Scientific Reports paper · HG80 manufacturer specification
Dosing was not optimized.
Short answer: The paper states that the commercially available retrofit devices were evaluated without optimization of dosing or control of the HHO-to-fuel ratio. Published engine research reports that the response to hydrogen or H2/O2 addition is conditional on load, speed and dose.
“In this study, HHO systems are evaluated specifically as commercially available retrofit devices, without optimization of dosing or control of the HHO-to-fuel ratio, in order to reflect their real-world application conditions.”
Source: Synák, “Evaluation of hydrogen and oxygen mixture addition in internal combustion engines under real driving conditions”, Scientific Reports, 2026 — Read the original 2026 Scientific Reports paper
DOI: 10.1038/s41598-026-54105-y
Location in paper: Introduction (verified in the published HTML article text).
Why this matters
Engine response to hydrogen/oxygen enrichment depends on the amount of gas supplied relative to engine load and fuel flow. The paper's own statement that dosing and the HHO-to-fuel ratio were not optimized means the experiment does not establish whether a different dosing strategy would have produced a different result.
The lack of optimization is a limitation when attempting to generalize the result to other HHO or oxyhydrogen systems.
- · Generator tested: Hydrogen Energy HG80.
- · Generator technology: alkaline KOH electrolysis, according to the manufacturer's documentation.
- · Reported HHO flow: approximately 1.3 L/min.
- · Reported electrical consumption: approximately 230 W.
- · PEM/SPE system tested: No.
- · HHO dosing optimization: The paper states that commercially available retrofit devices were evaluated without optimization of dosing or control of the HHO-to-fuel ratio.
- · Independent gas-quality characterization: No such characterization is identified in the published paper.
| The study establishes | The study does not establish |
|---|---|
| Results obtained with the tested commercial HHO retrofit configuration | That all HHO systems produce the same result |
| Performance under the tested vehicle and operating conditions | Performance of an optimized PEM/SPE oxyhydrogen system |
| Approximately 1.3 L/min HHO was used/reported in the experiment | That the gas had a particular independently verified H₂/O₂ composition unless such analysis is explicitly reported |
| The observed effect under the experimental conditions | That the observed effect would be identical at different HHO-to-fuel ratios |
| Real-world retrofit performance of the tested system | Universal effectiveness or ineffectiveness of oxyhydrogen combustion enhancement |
Items in the right-hand column are outside the experimental scope of the published study. Their absence does not imply the opposite result; it means those propositions cannot be inferred from this experiment.
This matters because the published literature is close to unanimous that the engine response to hydrogen or H₂/O₂ addition is conditional rather than fixed. Reported outcomes depend on engine speed, engine load, air-fuel ratio, hydrogen fraction, HHO flow, fuel-injection strategy, combustion timing, intake conditions, exhaust after-treatment and electrical parasitic load. A fixed retrofit dose samples one region of that space.
The reviews are equally clear that results are mixed and that NOₓ frequently rises with hydrogen addition even where particulates, CO and smoke fall — see the 2016 Renewable and Sustainable Energy Reviews review of hydrogen addition to compression-ignition engines and the 2023 Fuel review covering diesel and biodiesel operation. Neither supports a universal benefit claim, and neither supports a universal null result.
The energy penalty is part of the answer.
Short answer: An onboard generator drawing approximately 230 W takes that energy from the alternator, and ultimately from fuel. Any net efficiency claim has to clear that electrical penalty, which is why full electrical accounting belongs in the measurement set.
At roughly 230 W for roughly 1.3 L/min, an onboard generator draws its electrical energy from the vehicle's alternator, which in turn draws mechanical energy from the engine, which consumes fuel. The study itself discusses the energy demand of onboard HHO production.
Did the HHO improve combustion?
Did the benefit exceed the net energy penalty?
We make no claim that the HG80's efficiency was poor. The published study does not provide enough generator characterization to establish its comparative energy efficiency against a modern PEM/SPE system, which is exactly why that comparison remains an open experimental question rather than a settled one. Read the original 2026 Scientific Reports paper.
Heterogeneous, conditional, and worth reading carefully.
Short answer: The wider peer-reviewed literature on hydrogen and H2/O2 addition reports gains under some controlled operating conditions, null results under others, and frequent NOx trade-offs. Neither a universal benefit nor a universal null result is supported.
The broader literature contains a large body of hydrogen-enrichment and H₂/O₂ engine research reporting improvements under particular operating conditions, including studies reporting double-digit reductions in specific fuel consumption or improvements in thermal efficiency at selected hydrogen or H₂/O₂ dosing levels. It also contains null results and clear NOₓ trade-offs. Both halves are part of the record.
The wider literature contains heterogeneous results, including controlled experiments reporting improvements under particular hydrogen/H₂-O₂ dosing and operating conditions. These results cannot be generalized universally either.
| Study | Engine | Fuel | H₂ / H₂-O₂ addition | Operating condition | Reported result | Qualification |
|---|---|---|---|---|---|---|
| Fuel (2012), H₂/O₂ addition | Heavy-duty diesel | Diesel | 50, 60 and 70 L/min H₂/O₂ | Controlled engine test, selected operating points | BTE reported rising from 31.1% to 39.9% at 70 L/min; BSFC reductions of ~3.2%, ~9.9% and ~10.5% at 50, 60 and 70 L/min | A controlled test at particular operating conditions with very high gas flow — not proof of a universal 10%+ fuel saving in service |
| Renew. Sustain. Energy Rev. (2016) review | Compression ignition, multiple | Diesel | Varied hydrogen fractions | Survey across published tests | Efficiency and smoke improvements reported under some conditions; outcomes vary widely | NOₓ increase frequently reported; results condition-dependent |
| Fuel (2023) review | Compression ignition, multiple | Diesel / biodiesel | Varied hydrogen fractions | Survey across published tests | Mixed outcomes; benefits concentrated at particular loads | Emissions trade-offs and load dependence emphasised |
| Scientific Reports (2026) | Passenger vehicles, real driving | Conventional fuel | ~1.3 L/min HHO, alkaline HG80 | Unoptimized commercial retrofit, real driving conditions | Little measurable benefit reported | No reported gas-composition characterization; dosing not optimized; alkaline, not PEM |
The purpose of this table is to show that the literature is heterogeneous — not that every study supports large savings. We publish no headline savings percentage for our own equipment; see field results and our general evidence review.
Why the 2026 study does not test HydroHub™ PEM.
Commercial alkaline HHO retrofit
- · KOH liquid electrolyte (HG80, manufacturer-stated)
- · ~78 L/h at ~230 W as reported
- · Fixed real-world retrofit application
- · No reported independent gas-quality characterization
- · No optimized HHO-to-fuel control
- · Specific passenger-vehicle application
PEM/SPE oxyhydrogen
- · PEM/SPE membrane technology, pure-water electrolysis
- · No caustic electrolyte
- · Engine-sized system selection by displacement
- · Published gas production and system specifications
- · Continuous-duty fleet, genset, marine and heavy-equipment applications
- · Designed specifically for combustion-enhancement duty
This is not a claim that HydroHub performs better. The two systems are different technologies. The 2026 experiment therefore cannot be treated as a direct validation or invalidation of HydroHub PEM technology.
The most important scientific question.
Short answer: Because the published record does not characterize the injected gas or optimize dosing, the 2026 findings cannot be generalized to PEM/SPE oxyhydrogen. The question of how an optimized, characterized PEM system behaves remains experimentally open.
Was the HHO generator itself sufficiently characterized to make a negative result attributable to HHO technology as a category?
Based on the information reported in the paper, that question remains unresolved.
The experiment demonstrated the result obtained with the selected commercial generator under the selected conditions. It did not independently establish gas composition, gas purity, H₂:O₂ ratio, electrolyte carryover, generator efficiency relative to alternatives, optimized dosing, optimized engine calibration, or whether a PEM/SPE system would behave differently.
A plausible alternative explanation is that the particular HHO generator, its gas characteristics, its energy efficiency, its dosing rate, or the absence of optimized control limited the measurable effect. The published experiment does not provide enough generator characterization to rule this possibility out — and equally, does not establish it. It is an untested explanation, not a demonstrated cause.
The study's negative result should be distinguished from the broader proposition that HHO or oxyhydrogen technology is inherently ineffective. The experiment evaluated a particular commercial retrofit configuration under particular operating conditions; it did not constitute a controlled comparison of different electrolysis technologies.
This is our analytical distinction about experimental scope, not a conclusion drawn by the paper itself. Read the original 2026 Scientific Reports paper.
A negative result from one retrofit configuration should not automatically be generalized to every H₂/O₂ generation technology.
What would a properly characterized PEM comparison measure?
Short answer: A rigorous evaluation of PEM oxyhydrogen should measure gas composition, gas purity, flow, electrical input, engine load, fuel consumption, emissions and HHO dosing across controlled engine operating conditions, with repeated runs and stated uncertainty.
Set out as an objective experimental standard, applicable to any supplier including us. A rigorous comparison should measure and report:
- 01 H₂ concentration
- 02 O₂ concentration
- 03 H₂:O₂ ratio
- 04 Total gas flow
- 05 Gas purity
- 06 Moisture content
- 07 Electrolyte carryover (where applicable)
- 08 Electrolyser electrical input
- 09 Alternator / engine parasitic load
- 10 Engine fuel consumption
- 11 Engine load
- 12 Engine speed
- 13 Combustion parameters
- 14 CO
- 15 CO₂
- 16 HC
- 17 NOₓ
- 18 Particulate / smoke
- 19 Repeated runs
- 20 Statistical uncertainty
- 21 Multiple engine loads
- 22 Dosing optimization
This is the level of characterization required to distinguish the effect of the gas-generation technology from the effect of simply adding an unspecified quantity of commercially generated HHO.
Read the paper for what it is.
Short answer: The study is valid evidence about one commercial alkaline HHO retrofit configuration under the conditions tested. It is not a controlled comparison of alkaline versus PEM/SPE electrolysis, and it should not be read as one.
The 2026 Scientific Reports study should be read for what it is: a real-world evaluation of a particular commercially available HHO retrofit configuration.
It is valuable evidence.
But it is not a controlled comparison of alkaline versus PEM/SPE electrolysis, nor does it independently characterize the gas quality delivered by the HG80, nor does it optimize HHO dosing against engine operating conditions.
Its negative findings therefore cannot reasonably be generalized into the proposition that PEM/SPE oxyhydrogen injection does not work.
The appropriate scientific response is not to dismiss the paper, but to identify the variables it did not control and test those variables directly.
- · We are not disputing the experimental result.
- · We are questioning the extent to which that result can be generalized.
- · The study tested a particular commercial HHO retrofit configuration.
- · The HG80 is an alkaline KOH system, not PEM/SPE.
- · The paper does not provide the same type of direct experimental comparison that would be required to evaluate PEM/SPE oxyhydrogen.
- · The paper states that HHO dosing / HHO-to-fuel ratio was not optimized.
- · The published paper does not identify independent gas-quality characterization sufficient to establish the detailed composition and purity of the gas delivered to the engine.
- · Therefore, the study should not be presented as a definitive test of PEM/SPE oxyhydrogen technology.
Read the original 2026 Scientific Reports paper · DOI 10.1038/s41598-026-54105-y
HydroHub™ takes that engineering question further: PEM/SPE oxyhydrogen, pure-water electrolysis, defined system specifications, controlled gas production and application-specific sizing.
Where this analysis connects.
- · PEM electrolysis technology used in HydroHub™ systems
- · PEM versus alkaline electrolysis compared for engine retrofits
- · Evidence review: does hydrogen fuel enhancement work?
- · Attributed field results and measurement method
- · Engine applications for hydrogen combustion enhancement
- · Run a controlled fleet trial on your own equipment
- · Contact our technical team about a measured evaluation
Sources.
- 1. Synák, F. (2026). Evaluation of hydrogen and oxygen mixture addition in internal combustion engines under real driving conditions. Scientific Reports, 16, Article 23305. DOI: 10.1038/s41598-026-54105-y · nature.com
- 2. HYDROGEN ENERGY DOO, Belgrade, Serbia — Hydrogen Generator HG80 product specifications (manufacturer claim): hhogas.rs
- 3. HYDROGEN ENERGY DOO — frequently asked questions (manufacturer claim): hhogas.rs FAQ
- 4. Effect of regulated harmful matters from a heavy-duty diesel engine by H₂/O₂ addition to the combustion chamber. Fuel (2012): sciencedirect.com
- 5. Hydrogen addition to compression-ignition engines — review. Renewable and Sustainable Energy Reviews (2016): sciencedirect.com
- 6. Hydrogen addition with diesel and biodiesel fuelled engines — review. Fuel (2023): sciencedirect.com
No projected, typical or expected fuel-saving figure is published. Actual results vary materially with engine condition, duty cycle, load profile, fuel quality, installation and operating conditions. A controlled field evaluation on your own equipment, with baseline data captured before installation, is required before any commercial projection.
Questions.
What HHO generator was used in the 2026 Scientific Reports study?
- The study used the Hydrogen Energy HG80 HHO generator. The paper reports approximately 1.3 L/min HHO production during the vehicle experiment.
Is the HG80 PEM or alkaline?
- No. The manufacturer's documentation identifies the HG80 as an alkaline electrolyser using approximately 20–25% KOH electrolyte and stainless-steel electrodes.
Did the Scientific Reports paper independently verify the H2/O2 composition of the HG80 gas?
- The published study reports HHO flow and electrical consumption, but we found no reported independent analytical characterization of the actual H2 concentration, O2 concentration, H2:O2 ratio or overall gas purity delivered to the engine.
Was HHO dosing optimized in the 2026 Scientific Reports study?
- No. The published paper states that the commercially available retrofit devices were evaluated without optimization of dosing or control of the HHO-to-fuel ratio. This is an important methodological limitation when attempting to generalize the result to other HHO or oxyhydrogen systems.
Does the 2026 study test PEM oxyhydrogen?
- No. The identified HG80 generator is an alkaline KOH electrolysis system rather than a PEM/SPE electrolyser. The experiment therefore should not be treated as a direct test of PEM/SPE oxyhydrogen technology.
Does the study prove that HHO technology is ineffective?
- No. The study reports the result obtained using the particular commercial retrofit configuration and operating conditions that were tested. It does not establish that every HHO or PEM/SPE oxyhydrogen system will produce the same result.
Why does gas quality matter?
- Gas flow alone does not establish gas composition or purity. For an engine-combustion experiment, H2 concentration, O2 concentration, H2:O2 ratio, moisture and potential electrolyte carryover can be relevant experimental variables.
What would be required to properly evaluate PEM oxyhydrogen?
- A rigorous evaluation should measure gas composition, gas purity, flow, electrical input, engine load, fuel consumption, emissions and HHO dosing across controlled engine operating conditions.
Related evidence reviews.
Each page below is source-bounded: published figures are attributed to the paper reporting them, manufacturer figures are labelled as manufacturer claims, and our interpretation is labelled as our technical analysis.
- 2012 Fuel study: H₂/O₂ addition to a heavy-duty diesel engine
Source-bounded review of the 2012 Fuel study on hydrogen and oxygen addition to a heavy-duty diesel engine: reported gas flows, BTE and BSFC figures, operating conditions and the limits of generalization.
- 2016 review: hydrogen addition to compression-ignition engines
What the 2016 Renewable and Sustainable Energy Reviews survey of hydrogen addition to compression-ignition engines reports: conditional efficiency gains, mixed results and the NOx trade-off.
- 2023 Fuel review: hydrogen with diesel and biodiesel engines
Source-bounded summary of the 2023 Fuel review of hydrogen addition to diesel and biodiesel engines: what is consistently reported, where results diverge and what remains untested.
- 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.
- HHO gas composition: why flow rate is not gas quality
H2 concentration, O2 concentration, H2:O2 ratio, moisture and electrolyte carryover are experimental variables in an engine test. Why a reported flow rate alone does not characterize the gas.
- 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.
- Industrial oxyhydrogen case studies and field observations
Our industrial PEM/SPE oxyhydrogen work: pure-water electrolysis systems, engine and furnace applications, an audited beverage-plant trial, and how we label audited results against field observations.
- HHO and hydrogen engine literature: an overview
An overview of the peer-reviewed literature on HHO and hydrogen addition to internal combustion engines: what is consistently reported, where results diverge, and which variables drive the difference.
- Does HHO work? A source-bounded technical analysis
A source-bounded answer to whether HHO improves engine fuel economy: what published testing supports, what it does not, and which variables decide the outcome in any given installation.
PEM/SPE oxyhydrogen systems
Unlike the HG80 alkaline system tested in the 2026 study, 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.