thinking of a redesign of my proposed system

[LowGear]

Lithium ions are kind of pricey aren't they?  And then the charger?

Casey

[mobile_bob]

its been a while since i checked up on what is current in dual fuel diesel applications

here is something i find very interesting from catapiller

http://ringpower-systems.com/media/721216/rpc-bi-fuel-system-brochure.pdf

apparently with this system, there is no need to alter the engine internally, no timing changes, just bolt on and calibrate
the natural gas fumigation system.

apparently they have no loss in power if the nat gas is of sufficient quality.

no loss of oem engine warrantee

60% reduction in NOx emissions, smoke and particulate almost nil
this ought to meet tier 4 without issues, and something that the last time i talked to the epa
they were most interested in.

cat, cummins and detroit are onboard and approve the technology for use on their engine's

now granted the modern diesel engine's have lower compression ratio's than the changfa i am thinking of using
however their dynamic compression ratio is certainly as high or higher given they are turbocharged engines.

of course reading this got me to thinking,
why did cummins riogrand engine modify their engine's with lower compression pistons when they went to spark ignition conversions?
my bet is because they were to be used in well head gas applications in the field, where gas quality was so variable, with everything under the sun being mixed in, (things like condensate) which likely have a very low detonation limit and might well detonate with higher compression diesel engine configurations.

so i am thinking that if the engine does not detonate with utility grade natural gas in dual fuel mode, then the same engine fitted with a spark plug out not to exhibit detonation either.

surely would greatly simply this issue as it pertains to selling it to the epa for approval.

if this works, they all we need is approval for engines to be imported sans injector and injection pump, to be fitted here with spark ignition
governors, and nat gas delivery system.

no head changes, no internal modifications needed.

maybe, just maybe?

bob g

[BioHazard]

Sounds like you need to get on the phone with Changfa, Bob. 

[mobile_bob]

first a letter of approval from the epa, no small hurdle btw

then we can surely find someone to supply the engine's

changfa will not even talk to an american about non epa certified engines for export to the USA
unless they have a copy of an EPA exemption or approval.

bob g

[uber39]

Hi all,
       when last changing batts over, Trojan T105's cost $3,500 . Lithium ion cost $2,500 for 100A capacity new charger to suit cost $500. can charge or discharge at a C1 rate continues, for shorter term amps can go much higher. My little car saved over 400lb on the changeover and when the car only weighed 2000lb to start with it makes a big difference
http://solarbodge.blogspot.com/ this bloke has set up a home system using the same batts that I've got, only 4x the size, with auto start/stop on the inverters theres no reason you couldn't use a smaller batt bank, 100A X 48V = 4.8KWH for a energy efficient home gen might run twice a day, that might balance with hot water use also ??
       if I knew more,( alright anything) about electronics I think that is the way I'll be trying to go, without DHW and car charging we use approx 4KW/day.
       uber39
 

[BioHazard]

first a letter of approval from the epa, no small hurdle btw

I can't think of a better person to write such a letter to the EPA.  If we could get back to the "old days" of dime-a-dozen chinese engines I would sure be happy. I wonder if we could find a smaller MFG that would be interested in converting the engine to spark for us. I'm still leary of how the governor would work.

If that little mosquito fogger harbor freight 2 cycle generator is legal in california, it can't be that hard to get a spark engine to pass, especially on NG/LP.

[SteveU.]

Hey unber39!
Great post. Great pricing vs weight info.
Excellent real world user info on the fellows blog you put up.
Shows just haw difficult it is to set up stand-alone PV solar in an obvious maritime climate. Desert guys would have to be pre-occupied with cooking down and energy bleeding off.
And BOTH still could use/need "some" seasonal alternative energy system input like some kind of IC engine.
Stand-a-lone solutions are all just one layer away for any reason from "NO POWER!".
Best I think to have a hybrid balanced mixed of all season capable sources biased toward your needs and climate.

And yes. Aging shape changed now a bit, with always loaded pockets, I do actually were a belt and suspenders.

Regards
9-10 months wet 'n cloudy Washington State Steve Unruh

[Tom Reed]

A bank of these Li-FePo batteries would be interesting. I'm seriously giving these a thought to replace my FLA batteries in the basement when their day is done. Prices for these batteries have been dropping like a rock. Apparently they can use the same charge regime as the FLA batts too.

http://www.all-battery.com/3.2V100AhLiFePO4_LithiumIronPhosphate-30237.aspx

[Thob]

mobile_bob:

A little about engine theory here, if someone knows better please inform us!  What I know is mostly from reading old books and trying to figure out how things really work.  That said...

Diesel engines normally operate with the intake "wide open" - the cylinder gets a full charge of air every intake stroke.  It controls the engine speed by how much fuel is injected, and also controls the timing by when the fuel is injected.  Diesel engines always run very lean, around 100:1 at idle, and never as rich as the 13:1 magic number (stoichiometric).

Gas engines have a throttle plate that controls the amount of air entering the engine, and match the flow of fuel to the amount of air to attempt to get as close to 13:1 as possible.  They control the fuel with either a carburetor or fuel injection; the timing is controlled by when the spark fires.

So what happens if you take a spark ignited engine, with 13:1 air-fuel mix entering the combustion chamber, and raise its compression ratio?  It begins to ping and knock, it undergoes auto-ignition or pre-ignition, or, it diesels.  In other words, you loose control of the timing with the spark because in a hot engine, with high enough compression, it will ignite on its own.  This will destroy the engine in short order.

So why doesn't the diesel engine, with its high compression ratio, do this when you inject propane or natural gas in the intake?  Its because the mixture is too lean - too lean to ignite on its own.

So how can a diesel fire at all?  Isn't it too lean?  Actually, yes, if the fuel was completely mixed with the air.  What happens during an injection, however, is that once the injector squirts fuel into the injection chamber, there is a range of fuel mix ratios.  Near the injector, there is almost all fuel, way too rich.  Near the chamber walls, it is mostly air, way too lean.  Somewhere in between the air-fuel ratio is just right, it ignites, and starts burning.  Once it starts burning in one place, then the mixture can continue to mix and burn out from that point.  Including burning any gaseous fuel that was mixed in the intake.

So to get the high efficiency of a high compression ratio diesel engine, you need to mix the gas with incoming air and use a diesel "pilot" to time the combustion.  This means you need two types of fuel.

If you want to go with a spark ignited engine, you'll need stick to lower compression ratios.  But you only need one type of fuel.

I hope this helps -

[mobile_bob]

Thob

let me address your concerns as best i can

first let me preface the discussion with the following

1. i have over 37 years experience with diesel engines of various types, so i have a better than average understanding of their operation

2. if i were to setup the engine as a spark ignition unit, i would lower the compression, if for no other reason but to reduce stress and the possibility of detonation.. i would also use something like an impco carb and a governor of some sort, either an adaptation of the oem changfa
governor or an electronic unit. ,,(,currently  i am not proposing a spark conversion given the info from the Cat link.)

3. what i am proposing is a dual fuel engine, wherein i would admit natural gas into the intake stream, using pilot ignition (diesel fuel)

4. my system and general cogen philosophy holds that the prime mover should not run anytime at anything less than full rated load. this allows me not only to keep the unit at peak efficiency but also simplifies the natural gas control scheme.

now on to your concerns

"Diesel engines normally operate with the intake "wide open" - the cylinder gets a full charge of air every intake stroke.  It controls the engine speed by how much fuel is injected, and also controls the timing by when the fuel is injected.  Diesel engines always run very lean, around 100:1 at idle, and never as rich as the 13:1 magic number (stoichiometric)."

in both practice and theory i would agree.

"Gas engines have a throttle plate that controls the amount of air entering the engine, and match the flow of fuel to the amount of air to attempt to get as close to 13:1 as possible.  They control the fuel with either a carburetor or fuel injection; the timing is controlled by when the spark fires."

no argument here either

"So what happens if you take a spark ignited engine, with 13:1 air-fuel mix entering the combustion chamber, and raise its compression ratio?  It begins to ping and knock, it undergoes auto-ignition or pre-ignition, or, it diesels.  In other words, you loose control of the timing with the spark because in a hot engine, with high enough compression, it will ignite on its own.  This will destroy the engine in short order."

this is true only if you continue to use the same octane rating fuel at the higher compression ratio, if you use a higher octane fuel detonation can be eliminated. this is why propane engines typically have higher compression ratio's than their pump gasoline counterparts.  utility grade
natural gas has a high octane rating, apparently high enough to keep from detonating in modern diesel engine's running at ~18-20:1 dynamic compression ratio.  if the engine will not detonate with pilot injection, then the same engine will not detonate converted to spark ignition all else being the same.

"So why doesn't the diesel engine, with its high compression ratio, do this when you inject propane or natural gas in the intake?  Its because the mixture is too lean - too lean to ignite on its own."

yes and no, yes it will not detonate at no or very light loads because there is insufficient gas, too lean as you say, however
at full rated load there is certainly more than adequate amounts of gas in the chamber for it to detonate (mix now closer to 13:1) save for one thing, that being the higher octane rating of the nat gas fuel.

if you admit nat gas into the air stream of a diesel engine it will continue to run, using less and less diesel up until there is insufficient pilot fuel injected to initiate combustion. the engine will carry the load, not detonate and run just fine up to a point where it starts to run irratically
because there is intermittent ignition. some engines this takes place when the pilot fuel gets down to about 20% some will do fine down to about 5% before they start to miss and stumble.

"So how can a diesel fire at all?  Isn't it too lean?  Actually, yes, if the fuel was completely mixed with the air.  What happens during an injection, however, is that once the injector squirts fuel into the injection chamber, there is a range of fuel mix ratios.  Near the injector, there is almost all fuel, way too rich.  Near the chamber walls, it is mostly air, way too lean.  Somewhere in between the air-fuel ratio is just right, it ignites, and starts burning.  Once it starts burning in one place, then the mixture can continue to mix and burn out from that point.  Including burning any gaseous fuel that was mixed in the intake."

you are getting into flame fronts and flame propagation, yes the pilot fuel starts to burn and as it finds available oxygen it continues to burn
the mixed nat/gas meanwhile is also burning, but doing so in a more complete fashion.  no problems here.

"So to get the high efficiency of a high compression ratio diesel engine, you need to mix the gas with incoming air and use a diesel "pilot" to time the combustion.  This means you need two types of fuel."

YES exactly!  this seems the most appropriate for my end use, and the first step in testing before a spark conversion ought to take  place. the reason being i want to know how much load can the engine carry, what are the emissions, are there other issues that come up, etc?
if it proves out to be a good result, then i can convert to spark ignition, (carb, governor, spark, and maybe comp ratio) and see what those results might be?  then how the two methods compare?

i have enough engine's, enough parts to modify the 195 to dual fuel, and also to do a full on spark conversion, including dropping the compression ratio from 20:1 and from 17:1 down to ~12:1 or maybe a bit less.  i also have the test bed, equipment and all the related gear to do
very good and accurate BSFC at various output levels.  this allows me to do all sorts of testing without having to get permission from the EPA
because i need not import anything. proof of concept can be made, full testing done, with emissions first, then we have something to take to the EPA and show them.  otherwise we have what?  an idea? a theory?

"If you want to go with a spark ignited engine, you'll need stick to lower compression ratios.  But you only need one type of fuel."

generally speaking, maybe, maybe not. if an unmodified modern diesel engine can run at dynamic compression ratio's within the range of the changfa's static comp ratio, and do so using pilot injection, without detonation, then the same engine with the injector replaced by a spark plug ought not detonate either.

i hope this clears the air a bit?

thanks
bob g






3.

[Thob]

OK - Thanks Bob!

I see you already know more than I do!   I was thinking from your questions that you didn't realize the difference between taking in a fuel air mixture, and lighting it with a spark plug versus taking in just air, compressing it, and then injecting the fuel.  I see that you've already got that figured out, and much more.

Thanks for clarifying.

[mobile_bob]

not a problem, i appreciate questions!

while i have a pretty good understanding of things i am working on, i am always up for reality checks
and questions along the way.

i learn something every time! 

sometimes i need to rethink things based on a question someone puts forth.

that is the beauty of this and other good forums,  a place to bounce idea's off each other
ask questions, get some answers, and sometimes even get more questions.

its all  good in my opinion.

i just really appreciate being in the company of folks that use their heads for something other than a place to mount
a cap.

thanks
bob g