[Digestion] Biogas fueling a diesel

Tue May 13 01:24:32 CDT 2008

Hi Everybody,

Pilot Fueling

I must hasten to point out that the 1% pilot fuelling is based on
natural gas (>98% methane) and not on biogas, AND is used on MWe scale
engines where there is space to fit the pilot injectors. I understand
that MAN are offering these machines. In this regard, I was more looking
at the principle rather than the absolute value. Clearly if we add
straight biogas at a volumetric ratio of 2/3 methane, 1/3 CO2 (rough
numbers), the CO2 dilution becomes an issue requiring more diesel to
achieve ignition. Consequently, the observations of 95% replacement with
straight biogas are equivalent to 1% on nearly pure methane. I just
hasten to add that fuel control in this end of the operating environment
is paramount from an engine protection point of view.

Compression

Gerry, I have only ever seen diesel type compressions being used. That
puts it in the 18:1 category. I understand that this is not the maximum
compression - maybe someone else can answer this one.

Prakash

I have been told by a very reliable source to avoid these engines as the
build quality is appalling "some of the worst machining I have seen in
my life!" to quote. So, be aware of that.

Conversion of a Diesel Engine

Gerry, if you are looking to convert a diesel engine, you could
seriously consider using a low speed Listeroid engine. They last forever
at the 300 to 500 rpms that they operate at. 

"Sweet" vs "Straight" Biogas 

Shelby Tyner introduced me to these terms: "sweet" biogas has had
some/all of the CO2 removed. Shelby's experience is that spark ignition
engines work better with sweet biogas whereas diesel engines seem to
work better with straight biogas. This could well be due to the
difference in compression ratios though how the chemical mechanism works
I have no idea.

Hope this helps

Rex

________________________________

From: gp baron [mailto:gpbaron4091 at yahoo.com] 
Sent: 12 May 2008 11:44 AM
To: Michael Barnett; Zietsman, Rex; digestion at listserv.repp.org
Cc: Shelby
Subject: Re: [Digestion] Biogas fueling a diesel

Mike,

Thanks for the link. It looks like a whole book read that should prove
interesting for my rusty engineer's brain.

A few years ago, I thrust a 3/4" water hose delivering biogas into the
air filter of a 25 kVA genset with a naturally aspirated 4 cylinder
Nissan Diesel engine. Biogas delivery pressure would have been the
combined digester output pressure & engine suction. Flow (or quantity),
is what the engine sucked plus some air. The latter didn't matter since
it was supposed to be free.

At 30-40% genset load, diesel consumption was 5-6 liters/hr. With biogas
added, diesel consumption dropped to 3-4 liter/hr. At experiment time,
electricity cost P8/kwhr and diesel cost P30/liter. The approximately
8kw produced was worth P64 while fuel used cost P60. The "savings" was
too small at that time to choose running the genset continuously.

Now that diesel is more expensive & if biogas can decrease diesel
consumption by greater than 50% (with "simple?" improvements in the way
biogas is added), I need to conduct the experiment again. Any ideas &
comments to make the experiment better would be appreciated & I shall
keep you posted on my findings.

Gerry Baron
Philippines   

----- Original Message ----
From: Michael Barnett <dreadlox at cwjamaica.com>
To: gp baron <gpbaron4091 at yahoo.com>; "Zietsman, Rex"
<Rex at Process.co.za>; digestion at listserv.repp.org
Cc: Shelby <shelby at biogaspower.co.za>
Sent: Saturday, May 10, 2008 1:01:27 AM
Subject: Re: [Digestion] Biogas fueling a diesel

Here is a resource online... in case you haven't seen it before.
http://www.gate-international.org/documents/publications/webdocs/pdfs/g3
6ene.pdf

Mike
JAMAICA

----- Original Message ----- 
From: "gp baron" <gpbaron4091 at yahoo.com>
To: "Zietsman, Rex" <Rex at Process.co.za>; <digestion at listserv.repp.org>
Cc: "Shelby" <shelby at biogaspower.co.za>
Sent: Friday, May 09, 2008 5:55 AM
Subject: Re: [Digestion] Biogas fueling a diesel

> Still on the "How long is this piece of string"" question, I looked at

> Diesel to Natural Gas engine conversions (for buses & some smaller 
> vehicles) & found that the major work done involved:
> * pulling out the diesel injection system (nozzles, pump, etc.) and
> * replacing it with spark ignition system (plugs, distributor, etc.), 
> adding a governor & adjusting the compression ratio.
> Diesel-type engines apparently are preferred for Natural Gas service
(& 
> presumably biogas since both are methane fuels) for their high
compression 
> ratios or ratios that can be lowered to suit Natural Gas (or biogas.)
>
> Since governors, gas pressure & flow controllers can be purchased off
the 
> shelf and installing spark ignition systems is a doable project, what
are 
> the ideal compression ratios needed when fueling with biogas?
>
> Thanks in advance for any info or continued discussions on this topic.
>
> Gerry Baron
> Philippines
>
>
>
> ----- Original Message ----
> From: "Zietsman, Rex" <Rex at Process.co.za>
> To: digestion at listserv.repp.org
> Cc: Shelby <shelby at biogaspower.co.za>
> Sent: Friday, May 9, 2008 7:59:11 AM
> Subject: Re: [Digestion] Digestion Digest, Vol 23, Issue 3
>
> Mike,
>
> Realistically, you can get down to about 70% to 80% replacement but
with
> a whole lot of challenges. With bleeding into the air intake, you can
> safely replace 50% of the diesel with low risk of mechanical problems
-
> over fueling, etc. If you are running at a nice steady load, you can
> increase the replacement but, to get to the really high replacement
> values, you need to control both the gas and the diesel. This is less
> straight forward than simply bleeding in the biogas.
>
> For your information, there are engines out there that have pilot
diesel
> injectors in addition to the main injectors. They start with diesel on
> the main injectors, introduce gas cutting back on the diesel until
only
> the pilot injectors are running. This cuts back the diesel to as low
as
> 1%, just enough to fire the gas mixture. So, when answering your
> question, it is a bit of "how long is a piece of string?".
>
> I cannot answer the explosivity question but would imagine that the
risk
> is no more at a slightly hotter temperature than at a lower
temperature.
> The gas density is less but the risk of leaks is just as good at
ambient
> temperatures. Just make sure that the engine room is well ventilated
to
> allow leaks to dissipate.
>
> All the best
> Rex
>
>
> Thanks Rex, and to all who have responded!
>
> I have taken a look at the website and it seems reasonably easy. Are
> there no explosion concerns about bleeding it into the air intake
area?
> I am thinking if the engine room or air intake gets real hot as it can
> here in Jamaica.
>
> I am wondering how much percent diesel usage I could possibly replace
by
> this arrangement?
>
> Mike
> JAMAICA
>
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