[Diy_efi] water injection

Thu Sep 6 14:57:11 UTC 2007

Hi,

I did not want to imply that diesels "knock". They work by compression
ignition, with a steady burn. Knock of course applies to gas engines. 
BUT: Diesels can also "knock", but that is hard to do. In a diesel the
spray evaporates, creating a local charge with very much varying lambda
within the spray cone. After injection the droplets evaporate and, after
a delay dependent on the local lambda in the charge, start to ignite at
the most favourable lambda location. The flame-front proceeds from
there.
With higher inert dilution, like from water or EGR, the ignition delay
increases.
Yes, WI can cool the intake charge. In a highly modified engine, like a
tractor puller, where emissions and fuel consumption do not matter, it
can be effective. But they don't just spray water in and go. The
injection timing is adjusted to the amount of water injection. Diesel
injection timing has a large influence on output power. Just like
ignition timing in a gas engine.
Read the SAE papers on WI or diesel/water emulsion injection in diesels.
There has been a lot of research done on that. For an otherwise
unmodified small diesel engine it would be more effective to just
increase the size and effectiveness of the intercooler than use WI as
intercooler replacement IMHO. One of the reasons tractor pullers use WI
as intercooler replacement also is that they are running basically as
stationary engines. It's very hard to get effective intercooler
operation if you don't have much airflow over it. That's different in a
car.

- Klaus

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
On Behalf Of bearbvd at mindspring.com
Sent: Wednesday, September 05, 2007 4:47 PM
To: diy_efi at diy-efi.org
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

Why?

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.

BZZZZZZZTTT !!!

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
!!!!!

Greg

- 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
charade.

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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