[Diy_efi] water injection

Mike niche
Thu Sep 6 03:28:58 UTC 2007

At 08:55 AM 9/6/07, you wrote:
> Some pulling tractors use water injection and multiple turbos at 250PSI plus boost, and LOADS of diesel fuel; they are getting 2000 HP (intermittent) from an engine that was originally made to put out 200 HP.

Yes very true, they run whats called a "Wet Manifold" which huge amounts of water and its often
chilled as well. I have a Power point file with some pictures of a tractor engine modified for the
pulling competition which split the block horizontally - ie Not at the head but horizontally through
the outside of the block, pretty amazing set of pics, I'll see if I can upload it to my web area if I
can find room, I recall the pics were taken as it happened !

By the way, it might appear that a diesel operates from compression ignition, and that is often
confused with knock. But what actually happens is, the compression heats the air so its above
the ignition temperature of the fuel so that as soon as the injection pump and injector manifolding
starts to spray fuel into the top of the combustion area it immediately burns (smoothly) as soon
is the injection event proceeds. It is helpful to have a stronger engine geometry as it is more
stressful on the pistons and big ends due to to higher compression ratio but it is not at all a
knock condition. The sound a diesel makes might also be interpreted as knock but it isnt.

So for a n/a diesel engine the only useful thing that water injection (WI) can do is:-

a. Over a period of time it cleans off carbon deposits pretty effectively if there is enough water
    and its in the form of a mist/droplets and not a vapour when it gets into the chamber
b. If as a result of excessive carbon buildup or engine problems there is knock, then WI is a
   useful and cheap knock suppressant and over time by scouring off carbon deposits which
   might have caused propensity to knock then WI can lengthen the life of the engine.
   Incidentally, as a result of this it might well increase fuelk economy a little but only if there
   is some knocking happening without WI

The trick is to have enough water and at the right mist/droplet size, you dont want vapour
by any means as all it will do is displace the air and reduce efficiency.

For a turbo, yes good amounts of water will be effective to reduce chance of knock and even
better if the water is chilled and perhaps with the addition of a little methanol so it wont ice
up as easily at the nozzle if its chilled and the engine is getting WI some time below max boost.

A good type of water injection system is one in which chilled water is constantly circulated
through the piping at above manifold pressure much like the fuel return system in a gasoline
EFI engine. ie Have the spray solenoid off a 'T' junction close to the atomiser so the system
has minimal delay to spray as soon as a preset level of boost is present etc...

PWM of the water pump might be ok but you really need to develop enough pressure at the
nozzle early on to ensure you get consistent droplet size regardless of flowrate, it would be
ideal if there were a PWM solenoid atomiser with a 'T' feed for all the reasons described,

Regards from

Mike Massen
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>----- Original Message ----- From: <bearbvd at mindspring.com>
>To: <diy_efi at diy-efi.org>
>Sent: Wednesday, September 05, 2007 6:46 PM
>Subject: RE: [Diy_efi] water injection
>>Original Message:
>>From: Klaus Allmendinger klaus at Innovate-tech.com
>>Date: Wed, 5 Sep 2007 15:02:35 -0700
>>To: diy_efi at diy-efi.org
>>Subject: RE: [Diy_efi] water injection
>>Water injection on a gasoline engine is mainly there for knock
>>supression. A diesel operates on "knock". It lives by compression
>>ignition, which in a spark ignited engine is the reason for knock. The
>>only reason I can think of for using port WI on a diesel is for slight
>>NOx reduction. In a diesel with port WI this results in an increase in
>>CO and HC emissions and a slight increase in fuel consumption from all
>>the research papers I read.
>>First of all, a diesel does NOT operate on 'KNOCK' !!! Detonation will
>>destroy a diesel absolutely as fast as it will destroy a spark ignition
>>(Otto cycle) engine.
>>The burn in a diesel happens as fast as the fuel is EVAPORATED (after
>>atomization). This is NOT an 'explosive' process, as knock is. This is
>>PRECISELY why a diesel will destroy itself if fed a fuel which is harder to
>>ignite (to low a cetane rating) , such as gasoline !!!
>>WI in the ports of a diesel isn't worth much, but it CAN be EVERY bit as
>>effective as an intercooler if injected immediately post compressor !!
>>WI , done properly, as an 'internal coolant' IS an effective knock
>>suppressant, but it does a LOT more than that. GO READ THE ARCHIVES !!!!!
>>- Klaus
>>-----Original Message-----
>>From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
>>On Behalf Of ian
>>Sent: Wednesday, September 05, 2007 2:42 PM
>>To: diy_efi at diy-efi.org
>>Subject: [Diy_efi] water injection
>>Hi guys.
>>Im considering adding water injection to my little 1.0 turbo diesel
>>has anyone done something similar and has advice?
>>Im intending to use a washer pump and agricultural (metal) spray nozzle,
>>with a PWM controller that increases the pump duty cycle based on boost
>>pressure in the plenum. I was intending to spray directly into the
>>plenum, so as not to have water interfering with the turbo.
>>thoughts ?

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