Water injection used on internal combustion reciprocating (piston) engines has a long and interesting history. Some WWII military aircraft used water injection to boost horsepower and increase performance. Water injection is still used today on some aircraft and high-performance automotive engines for the same purpose.
It seems counter-intuitive for an engine to produce more power when water is sprayed into the intake. The key is that the water doesn't actually increase the engine power directly. It works two ways: delaying detonation onset, and cooling the intake charge.
These days water injection seems to be most popular in forced-induction engines. Forced-induction (FI), as opposed to normally aspirated engines use some sort of pump, such as a turbocharger or supercharger, to compress air into the engine. Added air means more fuel can be injected, and more power can be produced. The problem is that detonation is more of a problem on a FI engine, and limits how much boost can be used without causing damage. This is due not only to the added compression caused by the pressurized air, but also the act of compressing the air causes it to heat up. The hotter air makes detonation more likely. Using water injection on a FI car not only takes advantage of waters' anti-detonation properties, but also cools the compressed air by a considerable amount. Cooling the air decreases the tendency to detonate and increases the air density, allowing more air to be packed into the cylinders. Some engines use intercoolers to do this instead of water injection.
Water injection is used to a lesser extent on normally aspirated engines to control detonation in hot weather, under heavy loads (such as towing or drag racing), and when high compression and/or advanced spark timing are used. Most modern fuel-injected engines use ping sensors and continually tune the engine to get peak performance. This is usually done by retarding the spark timing when detonation is sensed, which helps reduce or eliminate the pinging but robs power from the engine. When water injection is used on a modern engine, since the pinging doesn't occur, the ping sensor doesn't signal the computer, and the computer keeps the full spark advance applied, running the engine at peak power. The amount of power increase this causes is highly dependent on a number of factors such as air temperature, engine load, fuel octane, altitude, etc. There is considerable debate as to whether or not the power gains on normally aspirated stock engines are worth the bother and expense of water injection.
russ wrote: »
When handled correctly hydrogen is perfectly safe - but as with any combustible material if it is handled in an unsafe manner you can have a disaster.
mike90045 wrote: »
When we run out of heilum, then we'll see Hydrogen blimps again.
Hydrogen fires are notable for being less destructive to immediate surroundings than gasoline explosions because of the buoyancy of H2, which causes heat of combustion to be released upwards more than circumferentially as the leaked mass ascends in the atmosphere; hydrogen fires are more survivable than fires of gasoline and of wood. The hydrogen in the Hindenburg burned out within about 90 seconds.
russ wrote: »
Correct - there has to be an explosive mix - If you can maintain the local atmosphere O2 content at below 3% then no problem. I don't remember the other end of the envelope.