View Single Post
Old 03-11-2006, 06:39 AM   #1
Richard L
Scooby Newbie
 
Member#: 85153
Join Date: Apr 2005
Location: Sussex England
Vehicle:
2004 Citroen Picasso
Silver

Default There are failsafe, failsafe and failsafes...

I think we have discussed most of the systems available and their capabilties. It is a good moment to see what failsafe mechanisms are available from the simpest to the most complex. I will update the list when more contributions are posted, if any.

Direct detection:

1. Fluid tank level sensor :
Advance warning but only good for early warning but little use for system power failure or blocked nozzle.

2. Loss of system power:
If power is interrupted to the WIA system, it will de-engergise a relay and performs "Plan B", will not detect blocked jet or cut pipe or no fluid flow.

3. Inline pressure gauge:
This is very cost effective but require user paying attention.

4. Inline single pressure switch:
If the system looses fliud pressure during activation, an inline preset pressure switch can action a boost drop etc.

5. Two inline pressure switches:
Detects blocked nozzle (over pressure) and "lost of fluid pressure" (under pressure). This method is quite cost effective and within DIY capability.

6. Flow switch:
In inline flow switch, comprised of spring-load magnetic plunger inside a tube where the water flows through. The rate of spring determines the promixity of a reed switch again the magnetic pluger deflection. Output: on/off. - cost: low

7. Turbine flow sensor:
Good for progressive system but requires complex electronics circuitry to report a differnce between the "actual" and "planned" flow in real time.


More..?

In-direct detection:

1. Knock detection:
This a by far the simplest, comes free with your car. It will only work up to certain power upgrade. Beyond a few PSI from stock, the ECU's ability to wind back ignition would be heavily taxed and may not dial in enough retard to cope with heavy knock. Don't forget, retarding igntion will also drastically increase your combustion temperature - not good.

2. AFR tracking:
If your ECU is capable of regulating the afr at WOT, it will be very effective. Unfortunately factory lambda is not of the "wide band" type so without equipping yourself with a wide-band lambda probe system, it will not work very well. The reliability on this method may lie on the accuracy of you wide-band interfacing mechanism. Method is effective but no good for mix other than high concentration of alcohol.

3. EGT tracking:
This method is rarely considered. Reading EGT has many benifits, it can indirectly estimate your afr, you ignition timing and more importly, when is your pistons are about to melt. It is a pity that not many EGY gauge gives you an analogue output so that you can use it for "Plan B" if the EGT exceeds certain preset value. I believe the SPA digital gauges has a "hi/lo" detection circuit inbuilt and an output capable of switching a relay. Need some research.

3. PWM vs pump cycle-rate tracking:
This method can only be incorporated by the manufacturer of the water/alcohol injection systems. It looks at the duty cycle of the WI system (PWM type only) against the predicted flow relative to the pump speed. If it is out of the predicted envelope, it outputs a "fault signal" to switch a relay. Difficult to incorporate into a rotary pump due to the lag time caused by the rotating mass of the motor.

3. PWM vs flow sensor tracking:
Self-contain system that reads the actual flow against the WIA valve's PWN or a fixed flow system. Very reliable but require some electronic processing.

4. Inlet temperature tracking:
If two temperature probes are placed "before" and "after" the water jet, any temperature differential will indicate the presence of "latent heat" at work.

I leave it as it is until the this topic attracts more interest. It is important to know what how "safe" is a "failsafe" . If anyone and suggest more method, please post here and I will update this database of this failsafes.

Richard
* Registered users of the site do not see these ads.

Last edited by Richard L; 03-16-2006 at 03:54 AM. Reason: update
Richard L is offline   Reply With Quote