How to test PEM oxyhydrogen properly
Short answer: 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, with repeated runs and stated statistical uncertainty.
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. |
The measurement set
Our technical analysis: the measurement set below is written as an objective standard that applies to any supplier, including us.
Each parameter exists to remove an alternative explanation for an observed change. Omitting one does not invalidate a test, but it does limit what the result can be attributed to.
- —Gas side: H₂ concentration, O₂ concentration, H₂:O₂ ratio, purity, moisture, flow
- —Electrical side: electrolyser input power and alternator parasitic load
- —Engine side: load, speed, fuel consumption, combustion parameters
- —Emissions: CO, CO₂, HC, NOx, particulate or smoke
- —Design: repeated runs, multiple loads, stated uncertainty, dosing recorded per condition
Why each element is there
According to the published literature, hydrogen addition effects vary with load and dose and commonly trade particulates against NOx, so single-condition testing without emissions coverage cannot describe the outcome.
Reviews of compression-ignition testing report both benefits and null results depending on operating condition, which is why repeats across loads matter more than a single headline figure.
Our industrial oxyhydrogen work
Our technical analysis: Combustion Enhancement supplies PEM/SPE oxyhydrogen systems that electrolyse purified water across a solid proton-exchange membrane. There is no potassium hydroxide electrolyte in the cell and no onboard hydrogen storage — gas is generated on demand while the equipment runs. Systems are applied to internal combustion engines (fleet, mining, marine, generator sets, agriculture) and to industrial combustion equipment.
Our audited results: an installation at a Coca-Cola bottling operation in India was evaluated with third-party audit of the specific fuel ratio before and after installation; audit scope and measurement method are provided on request. Our field observations: furnace, burner and engine trials are described in general terms only, and we do not publish figures where a documented measurement method is not available.
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.
Read our industrial oxyhydrogen case studies and field observationsQuestions.
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.
Why measure electrical input?
- The electrolyser draws power from the alternator, which draws mechanical energy from the engine. Any net efficiency result has to clear that penalty.
How many runs are enough?
- Enough repeated runs at each tested condition to state a statistical uncertainty alongside the mean; a single pass cannot separate an effect from normal variation.
Sources
- Hydrogen addition to compression-ignition engines — review, Renewable and Sustainable Energy Reviews (2016)
- Hydrogen addition with diesel and biodiesel fuelled engines — review, Fuel (2023)
- 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
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
- 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.
- 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.