View Single Post
  #13  
Old 29-09-2004, 09:37 AM
Richard L Richard L is offline
Manufacturer sponsor
 
Join Date: Oct 2003
Location: England
Posts: 4,936
Default

Just like to iterate the above with more details:

1) lean mixture retards effective-ignition
2) rich mixture retard e-ignition
3) injection of water e-retards ignition


All above conditions will encourage detonation due to the slowing down of the frame front and the end gas has a greater opportunity to detonate. This effect is more apparent at low engine speed due to longer duration of the burnt. This is to assume the frame speed is pretty constant under boost.


1) lean mixture retards e-ignition

A/f ratio between 15-16+:1 Under these condition, detonation in almost imminent due to slow burn and reduced latent heat absorption from injected liquid. The frame-front temperature is also at its higest due to excess oxygen available to fuel the burnt, this will help igniting the end gas that causes detonation.


2) rich mixture retard e-ignition

A/f ratio of 10-11.9:1 Onset of detonation is partially suppressed by temperature reduction of excess fuel, the end-flame is cooled, but still exhibit the same threat of detonation tendencies.

Also like to add that the this method of suppressing detonation will lean to power loss due to some of the oxgen is used to produce Carbon monoxide (10% or more exiting the exhaust pipe) - full power conversion is not fully harvested inside the combustion chamber. Wasterful exercise, as far as I am concerned.

3) injection of water e-retards ignition
A/f ratio 12-15:1 At this region, the burnt rate is at its highest and power conversion is at maximum but at the same time promotes highest cylinder pressure and temperature. Detonation is again highly likely due to the other side of the burnt rate scale, fast burn effectively advances the set ignition timing. By adding water at this point would off set the early ignition and suppress the onset of detonation by ignition retard (niot as much as extent to excess fuel) and quench any abnormal burnt due to non-uniform distribution of a a/f fuel mixture.

The point I am try to make is- it may not be necessary to touch the ignition timing at all if you are running the ideal a/f ratio for your particular combustion design. Some expenses can be spared on paying out high-end third party "piggy-back" or "full-blown" ECUs to tune your water injection equipped engine. Tuning by water is less complicated than protraited on many SAE papers.

Most of my conclusion is based on some factual statement mentioned on this thread. I hope the discussion will continue and really analyse the myths and mysteries that surrounded the water injection concept for years.
__________________
Richard L
aquamist technical support
Reply With Quote