water injection

Jim Steck 72614.557 at CompuServe.COM
Fri Sep 13 06:56:56 GMT 1996


>>I Remember two relevant curves - holding fuel constant, power went up
>>linearly with water on a percent by percent basis.  100% fuel 10% water,
>> + 10% power etc. until a practical limit of about 50% was reached.
>>
>>Holding power constant, each percent of water displaced a percent of
>>fuel until about a 50 50 ratio was reached.

> So if I went out to my car and fed my 455ci engine a 50/50 mix of water/
> fuel I'd get the same power?  I have a hard time believing this at full
throttle
> plus I cant afford that much water :(, but will it work for part throttle, 
> ie cruising, speeds?  I think I can get around the mineral buildups with
> a weekly trip to the track w/ high octane gas.....

If you're remembering Ricardo's curves, you've got the power part right,
but manifold pressure was a variable in his experiment.  The curve plotted
power at the manifold pressure that resulted in the onset of detonation.  
First he increased the amount of excess fuel to the point of maximum 
usefulness, then he started adding water and found that he could reduce 
the amount of excess fuel (beyond stoicometric) roughly equal to the 
amount of water that was added without affecting the results . . . so by 
increasing the amount of water, he was able to increase the manifold 
pressure . . . which increased horsepower.  It is not the injection of 
water that increased horsepower, but the increased resistance to 
detonation which allowed higher manifold pressures to be used.

The full description of his results can be found in the fourth edition of 
Sir Henry Ricardo's "The High Speed Internal Combustion Engine" 
pages 165-171.  (only in the fourth edition)

Jim Steck
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