Evidence
Hydrogen and HHO gas in engines have been studied by universities and research bodies for more than 50 years. Below is a selection of that published research, including studies that found small or no net savings, with each original source linked so you can read it yourself. These are not tests of the Hydroxi system. Our own field results will be added here as they are recorded.
Hydroxy (HHO) gas in a diesel engine: Çukurova University, Turkey (2010)
A 2010 study at Çukurova University, Turkey, used hydroxy (HHO) gas made by electrolysis as a supplementary fuel in an unmodified four-cylinder diesel engine. The researchers reported better engine performance and lower levels of some exhaust emissions under the test conditions.
Source: Yilmaz, Uludamar & Aydin, International Journal of Hydrogen Energy 35(20):11366–11372 (2010). https://doi.org/10.1016/j.ijhydene.2010.07.040
Hydrogen-oxygen addition and diesel engine efficiency: University of South Australia (2010)
Researchers at the University of South Australia added a hydrogen-oxygen mixture, made by water electrolysis, to a diesel generator engine running at constant speed. They reported higher thermal efficiency and lower diesel use at the loads tested. HC, CO and CO₂ emissions fell, while NOx emissions rose.
Source: Bari & Esmaeil, Fuel 89(2):378–383 (2010). https://doi.org/10.1016/j.fuel.2009.08.030
Hydrogen added to petrol in a production engine: NASA (1977)
A 1977 NASA Lewis Research Center report found that adding hydrogen to petrol let a 7.4-litre production engine run efficiently on a leaner mixture and made the flame burn faster. Emissions fell at the leaner settings.
Source: Cassidy, NASA Technical Note D-8487 (May 1977). https://ntrs.nasa.gov/citations/19770016170
Hydrogen added to natural gas: Lund Institute of Technology, Sweden (2002)
Research at Lund Institute of Technology in 2002 found that adding hydrogen to natural gas made the fuel burn faster and gave more stable running on a leaner mixture in a single-cylinder test engine.
Source: SAE technical paper 2002-01-2686 (2002), “Hydrogen Addition for Improved Lean Burn Capability of Slow and Fast Burning Natural Gas Combustion Chambers”, Lund University. https://doi.org/10.4271/2002-01-2686
On-board hydrogen generator for petrol engines: Jet Propulsion Laboratory, California Institute of Technology (1974)
In the 1970s, engineers at the Jet Propulsion Laboratory built an on-board hydrogen generator for hydrogen-enriched petrol engines. The hydrogen came from partly burning petrol, not from water.
Source: Jet Propulsion Laboratory, California Institute of Technology, 1974 papers on on-board hydrogen generation (Houseman et al.). SAE Technical Paper 740600
Hydrogen-rich gas from exhaust fuel reforming in a diesel engine: University of Birmingham, UK (2003)
A 2003 study at the University of Birmingham, UK, fed a hydrogen-rich gas, made by reforming fuel with exhaust gas, back into a diesel engine running on diesel and biodiesel blends. The researchers reported lower smoke and NOx together under test conditions.
Source: Tsolakis, Megaritis & Wyszynski, Energy & Fuels 17:1464–1473 (2003). https://doi.org/10.1021/ef0300693
HHO gas in a petrol engine: Alexandria University, Egypt (2016)
A peer-reviewed 2016 study at Alexandria University tested HHO gas from a dry cell on a 1.3-litre petrol engine. Under laboratory conditions it reported higher thermal efficiency, lower fuel consumption and lower emissions.
Source: El-Kassaby et al., Alexandria Engineering Journal 55:243–251 (2016), open access. https://doi.org/10.1016/j.aej.2015.10.016
Smoke opacity before and after: one diesel car (workshop test)
In one workshop opacity test on a 2008 Renault Modus, average smoke opacity fell from 1.30 to 0.40 m⁻¹ with the unit switched on (supplier printouts).
Opacity measures visible smoke only. One vehicle, one test.
Source: Supplier opacity report with OFF/ON printouts from a certified opacimeter.
Customer-reported fuel saving on excavators and bulldozers: Italy (2023)
An Italian construction company reported saving 7 to 8 litres of fuel per hour on its excavators and bulldozers in full operation, measured with the machines’ engine data recorders (customer letter, 2023).
Source: Customer letter, Italy, 2023. Company not named for confidentiality. Details available on request.
Customer-reported fuel saving on articulated buses and trucks: Italy (2023)
The same Italian construction company reported a 22% fuel saving on its articulated buses and trucks, measured with the vehicles’ engine data recorders (customer letter, 2023).
Source: Customer letter, Italy, 2023. Company not named for confidentiality. Details available on request.
South African field trial on a FAW truck (2026)
A FAW 500 truck fitted with the system is in a field trial in South Africa. The owner reported about 2.8 km per litre for this truck, against 2.25 to 2.3 km per litre for other trucks in the same fleet. This is an owner comparison, not a controlled test, and the result is still being checked.
Source: Owner field report, South Africa, June 2026. Owner not named.
Manufacturer-reported result: Volvo C70 2.0 diesel car
The manufacturer’s results table lists a 35% fuel saving for a Volvo C70 2.0 diesel car. No test method, dates or conditions are given.
Source: Manufacturer’s results table. No test method, dates or conditions given.
Manufacturer-reported result: DAF 12,600 cc truck
The manufacturer’s results table lists a 30% fuel saving for a DAF truck with a 12,600 cc diesel engine. No test method, dates or conditions are given.
Source: Manufacturer’s results table. No test method, dates or conditions given.
Manufacturer-reported result: Iveco Stralis Cursor 13 truck
The manufacturer’s results table reports fuel economy improving from 1.6–1.8 km per litre to 2.1–2.2 km per litre. No test method, dates or conditions are given.
Source: Manufacturer’s results table. No test method, dates or conditions given.
Manufacturer-reported result: 28 m motor yacht
The manufacturer’s results table reports fuel use on a 28 m yacht with twin 22,000 cc Mercedes engines falling from 340 to 280 litres per hour, with a speed gain of 5.5 knots. No test method, dates or conditions are given.
Source: Manufacturer’s results table. No test method, dates or conditions given.
Manufacturer-reported result: large motor yacht (2024)
The manufacturer reports that after the system was fitted to a large, older motor yacht, fuel use fell by 30 to 45 litres per hour and top speed at full load rose by about 5 knots. Similar results are reported on fishing boats of different sizes. Vessel details and test method were not provided.
Source: Manufacturer report, August 2024. Details available on request.
Manufacturer-reported result: 4.2 V8 supercharged petrol car
The manufacturer’s results table lists a 25% fuel saving for a 4.2-litre V8 supercharged petrol car. No test method, dates or conditions are given.
Source: Manufacturer’s results table. No test method, dates or conditions given.
Manufacturer-reported result: Hitachi 9,000 cc mechanical shovel
The manufacturer’s results table lists a 25% fuel saving. No test method, dates or conditions are given.
Source: Manufacturer’s results table. No test method, dates or conditions given.
Manufacturer-reported result: Iveco 2,800 cc refrigerated van
The manufacturer’s results table lists a fuel saving of 22–25%. No test method, dates or conditions are given.
Source: Manufacturer’s results table. No test method, dates or conditions given.