Water injection in engines: what’s known
This page explains water injection, an old and well-documented engine technique. It matters because outside writers and the Embry-Riddle thesis both point to water vapor as one likely reason for the Thunderstorm Generator’s modest measured gains.
Plain definition
What water injection is
Water injection sprays water into the air going into an engine, or straight into the combustion chamber. It is also called anti-detonant injection (ADI).
The water does not burn. It soaks up heat, which cools hot spots that can make fuel ignite too early. That early ignition is called knock, or detonation.
Plain definition
Where it has been used
World War II–era aircraft engines, such as the BMW 801 and the Pratt & Whitney R-2800, used water-alcohol mixes for short bursts of extra power. Early jet airliners, including early Boeing 707s, used it for extra takeoff thrust.
In cars, Saab used it on the 1978 Saab 99 Turbo S, and BMW used it on the BMW M4 GTS, introduced in 2015. Bosch, which developed a system with BMW, sells one called WaterBoost.
Plain definition
What it is known to do
Because it reduces knock, water injection lets an engine use a higher compression ratio or more boost. Wikipedia’s summary says that, depending on the engine, power and fuel efficiency can also improve from water alone, and it may reduce nitrogen oxides (NOx) or carbon monoxide (CO).
Results depend on the engine. A gain on one design is not a promise for another.
Seller claim
A maker’s own figures
Bosch claims up to 5% more engine performance, up to 4% less carbon dioxide (CO₂), and up to 13% better fuel economy from its system, as summarized by Wikipedia. These are the maker’s “up to” figures, not independent measurements.
Outside commentary
How this connects to the Thunderstorm Generator
Brian Dunning (Skeptoid, Dec 16, 2025) argues the device is an exhaust heat riser plus water injection, and that small gains are “probably true” if they stay small.
The Embry-Riddle thesis says water injection has shown benefits in independent research, and it ties its measured gain to heat recovery and water vapor rather than to water acting as a fuel.
Measured
What the test measured
The Embry-Riddle test found about 9–10% lower fuel use (small generator; 9.67%) and about 34% less carbon monoxide (CO) in an idle test. Carbon dioxide (CO₂), oxygen and hydrocarbons did not change significantly; the one-vehicle road test was about 8.7%.
Inventor claim
The inventor’s view is different
Malcolm Bendall describes his device as using plasmoids to let “water be used as an atomic fuel.” That is the inventor’s model. Water injection, by contrast, treats water only as a coolant, and the thesis did not test the inventor’s explanation.
Sources
Pages we opened and read for this explainer. The label in parentheses says which side each one speaks for.
- Wikipedia — Water injection (engine) (reference; history, Bosch figures) (opens in a new tab)
- Hall, W. (2026), Embry-Riddle Aeronautical University master’s thesis (measured) (opens in a new tab)
- Skeptoid #1019, “Testing the Thunderstorm Generator,” Brian Dunning, Dec 16, 2025 (outside commentary) (opens in a new tab)
Get new explainers by email
About one short email when a new explainer or correction goes up. No ads, no selling your address. Unsubscribe anytime with the link in every email.