# BMW using Bosch Water Boost to enhance performance



## 559056 (Oct 8, 2016)

*Anecdotes about water injection.*

History:
WW II aircraft, particularly fighters, would carry water (sometimes mixed with methanol), to be injected directly into each cylinder, when they needed to suck every HP available out of their engines. As you noted, when that water tank went dry, back to stock power, which might not be enough to get away from that Zero or Folkwulf 190.
1) Water essentially displaces available combustion chamber volume, raising the effective compression ratio of the engine. That increase thermal efficiency. Because the heat of vaporization is about 580 cal/gram, that also acted as a detonation/knock suppressor, by cooling the flame front, during combustion.
2) There are very few liquids that convert to gas, with such volumetric efficiency as water. So not only did the engine benefit from the push of the fuel/air flame front, it also benefitted from the sudden expansion of gas volume in the cylinder, exactly like steam locomotives.
3) It tends to clean the cylinder of carbon deposits, that might lead to hot spots and further pre detonation of the fuel/air mixture.

Fast forward to the 1970's:
1) Everyone was looking for the quickest, cheapest, technology to improve fuel economy. Especially when the gov't was mandating stupid engine design compromises as a means of controlling emissions. Such as, lower compression to burn lower octane fuel, w/o knock. Plus, lower combustion temperatures to reduce the formation of NOx compounds.
2) A bunch of dumb add on kits were produced, that squirted tap water into the throat of carburetors, to allegedly take advantage of the historical discoveries above. It didn't work, because the water introduced upstream from the combustion chamber, vaporized, adding humidity to the incoming charge. Humidity reduces the density of air. Ergo, such equipped automobiles behaved as if they were operating a high altitude; just the opposite of the desired effect.
3) Any thing short of pure distilled water, contains minerals/compounds that will be pulled from solution and deposited on surfaces, when the water is vaporized. Those precipitates act like sandpaper inside the cylinders.
4) And as previously suggested in a post, those tanks would run dry very quickly, long between gas stops.

What now:
1) A separate injector, must be machined directly into the combustion chamber, for this to work. Liquid water must be introduced, exactly as the fuel/air mixture enters the cylinder, so the effective compression ratio is raised, after the charge is in place. Then volumetric efficiency can be exploited, plus the rapid expansion of water vapor as steam. Such machining is expensive. I doubt any manufacturer is going to take that risk, without extensive testing/trials. 
2) Plus, there are no controls over the consumer. What is going to stop them from just using tap water out of ignorance? The mfgr would be foolish to assume liability for warranty repairs, with that huge unknown.
3) Water weighs 8lbs/gal. That means the user must fill a very large tank, during each fill up, to keep the system from going dry. That is extra weight being carried/propelled around. On the highway, with momentum stored up while droning down the interstate, that is not such a penalty. But in stop and go traffic, that most people find themselves in, that is a liability.


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## Raryel (Aug 10, 2015)

Thank you for that well written explanation. 

Your points are well-taken. Water injection is something that a consumer can screw up, so it would be understandable if we only find it in race cars maintained by professional teams.

How about this idea: Suppose I bought a 2018 BMW 5-series car and let's suppose that BMW offered the water injection option. Could BMW compensate for my being an idiot driver by signing me up for an in house water supply? That is, every X amount of time I receive Y number of jugs containing a distilled water/alcohol mix or whatever BMW has decided is appropriate. The dealer tells me to add this jug to my water tank at X interval and I am told, and the sticker on the car says "USE BMW WATER INJECTION FLUID ONLY."

And the car's warranty would say "Warranty is void if you put any other fluid in the water tank..." Would that work?

How much extra should I pay for said option? Should it be part of the Technology Package and add $750 to the price of the car?


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## Autoputzer (Mar 16, 2014)

Here's a Bosch diagram. The water injection occurs in the intake port, not the combustion chamber. Bosch claims up to 13% improvement in fuel economy and up to 5% improvement in power output. Bosch also claims that a 5 liter (~1.3 gallons) tank of water would last 3000 km (1800 miles).

http://www.roadandtrack.com/new-cars/car-technology/news/a30600/bosch-water-injected-engine-tech/

http://www.bosch-mobility-solutions.com/en/powertrain-electrified-mobility/water-injection/

Maybe they could throw a little bit of Techron in there and keep the intake valves clean.


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## Autoputzer (Mar 16, 2014)

Raryel said:


> Thank you for that well written explanation.
> 
> Your points are well-taken. Water injection is something that a consumer can screw up, so it would be understandable if we only find it in race cars maintained by professional teams.
> 
> ...


BMW would call it "dihydrogen monoxide" and charge $20/gallon for it. Whoopie!


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## 559056 (Oct 8, 2016)

*BMW supplied DiHydrogenMonoxide.*

If there are some BMW marketing types reading this thread, I'm certain you have given them something to think about. 
Consider the average vehicle owner, even BMW, who does not subscribe to this forum. Could they resist the temptation to say; "Gee, I can get this fluid right out of my kitchen tap. Why should I pay BMW all that money?". Alas, how could BMW enforce such a warranty? Then, if/when they lose in some class action suit, the liabilities would be enormous. Ergo, I don't see that happening.


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