Slow Speed Changfa Project

[veggie]

**** CHANGFA S195 SLOW SPEED MODIFICATION PROJECT ****

So....this forum is about experimentation, testing the limits of things, and trying new ideas. Right  ?
I have decided to drop the speed of my S195 even lower:
I realize that these engines are designed to run best between 1400 and 2200 rpm but I want to see if I can achieve smooth reliable operation in the 900 rpm range on a continuous basis (24/7 if necessary).

Reasons for this experiment:
1] reduce noise.
2] make only the amount of power that I need.
3] because I have this engine available and don't want to buy a smaller one  
4] for me, it's an interesting experiment which may also interest others on the forum.

GOAL:
The ultimate goal of this project is to drive a 50-70 amp, 12 volt alternator for battery bank charging using a slow speed, low noise, diesel engine fueled by diluted WVO. The engine will not incorporate a heating system for straight WVO, so fuel dilution is necessary.

Engine: The engine should run at ~900 rpm and develop 2+BHP

Load: The flywheel driven automotive alternator has a 3" serpentine pulley. The Flywheel is 16" diameter. (5.3:1 ratio)
        With an engine speed of 900, the alternator should turn at 4770 rpm. For the Delco 12SI this equates to approx. 86
        amps or 1032 watts (1.03kw). If we double the kw to achieve a HP rating, this results in a 2.06 BHP demand on the
        engine.


OBSTACLES:
For this section, I need input from the forum members.
Here's a few obtacles that come to mind...

1] Rotating mass. The S195 may need additional flywheel weight to run at lower speeds?

2] Vibration control. The counterbalance shafts in the Changfa may be designed for the current flywheel mass.
Changing the flywheel weight may upset the overall machine balance?

3] Dimensional Bore and stroke limitations?
   One thing of note is the similarity in bore/stroke ratios between slow speed engines like the Listers and the Changfa 195.
   
Let's look at the Bore/Stroke ratio:

                Bore   Stroke   Ratio
Changfa     3.75"     4.5"    .83:1
Lister 6/1   4.5"       5.5"    .81:1

It would seem that the bore and stroke of the Changfa are in line with other low speed engines.

4] Can the engine make 2HP at 900 rpm? no power curve exists for the Changfa, so this is not known at the moment.

5] Combustion. This is a DI engine. Does that pose a problem for slow speed blended WVO operation?

6] Other obstacles (from your contribution)

So, first I would like to focus on the obstacles and get a those summarized.
Then move on to attacking the obstacles one by one.
This is where I can see Bob, Henry and others helping a lot.

PS: Please let's not focus on why it can't or shouldn't be done, or why this is a stupid thing to do with a 12 hp engine, because I'm doing it anyway  
I do have the capability to make heavier flywheels or machine components if necessary, so let's get the suggestions rolling !

Hopefully this will turn out to be a cool project with an interesting outcome.
Veggie

[Henry W]

Hello Veggie,

From what I heard from venders selling S195's is that the engine should be brought up to operating rpm's as soon as possible.

Reasons:

• Shock load on gear train at low RPM's.

• Might not have enough oil pressure at 900 RPM's when oil is hot.
  

The shock load might be taken care of by increasing the flywheel mass. How much, I don't know.
Oil pressure can be checked running the engine at 900 RPM's while the oil is HOT.

Bob might be able to help out on output at lower engine speeds.

Henry

[veggie]

Hello Veggie,

From what I heard from venders selling S195's is that the engine should be brought up to operating rpm's as soon as possible.

Reasons:

• Shock load on gear train at low RPM's.

• Might not have enough oil pressure at 900 RPM's when oil is hot.
  

Noted:

Henry,
- What's the oil pressure of a warm S195 at normal speeds of 1400 to 2200 rpm ?
- The gear train only drives the countershafts? correct?

veggie

[mobile_bob]

just so i am clear on your objective(s)

is it to increase fuel efficiency? or rather reduce the amount of fuel consumed
to make a kw?

the crank gear turns the governor gear, the cam gear and the idler gears, and by extension
the oil pump.

it appears the crank gear is held in place by a snap ring, if so then the gear may not be pressed
on or shrink fitted? if it is a slip fit i would be very concerned with low rpm gear pounding the key to
death, loss of a key means bent valves i would suspect.

of course we don't know yet if that would be the case or not, till someone tries it.

are you sure the engine is DI and not IDI?

how new is this engine?

oil pressure at 2000rpm hot is around 125-150lbs i am told, but have not taken the time to measure that to confirm

i find it interesting that you can get it to run reliably at 900rpm, mine gets a bit irratic at 1000rpm, and is stable at 1200rpm
and up.

fwiw, i think you will find the fuel consumption in gr/kw/hr is going to be dreadful at 1 or 2 kwatt loading, at least it is so on mine
it really doesn't come into its own until i get over 6kwatt load on it, after that it will compete well with a listeroid, under 2kwatts
its laughable.

ymmv of course, so don't let me rain on your parade, perhaps your setup will do much better than what i have experienced here.

iirc the baseline fuel consumption for my changfa 195 idi engine, direct driving an st7.5 at 1800rpm with no electrical load
is right at 600gr/hr just to cover the windage, friction, and a bit of excitation of the st head and cover the losses associated with the
engine, so even if a good engine can produce a kwatt for 300 grams, added to the baseline makes the changfa come in at
about 900grams for the first kwatt.

thats not very good at all.

of course those numbers get better at lower rpm, but i don't recall how much better for sure, but iirc it would still likely be over 650 grams
for a kwatt out of one of the alternators at 1300rpm engine speed.

i haven't tried one of the little changfa's to see what its baseline consumption might be, who knows it might be even though they have
a higher consumption rate at rated load than a 195, they might end up burning less generating a single kwatt?

something we are sure to find out i would suspect

bob g

[Henry W]

The Crankshaft gear drives:
Governer Gear

Governer Gear drives:
Camshaft and injector pump, Oil pump and lower countershaft

Lower countershaft gear drives:
Hand crank/idler gear

Hand crank/idler gear drives:
upper countershaft

It might be different if the gears were helical cut. If they were I believe the geartrain would be:

• quieter

• Stronger that would be able to handle higher shock load.

Henry

[Henry W]

Sorry Bob you beat me to it.

Henry

[veggie]

Bob,

Bob wrote....
just so i am clear on your objective(s)
is it to increase fuel efficiency? or rather reduce the amount of fuel consumed
to make a kw?

Reply....
>>1] reduce noise
>>2] curiosity
>>3] Only need 1 kw but refuse to buy a smaller engine (which would run faster and louder)
>>4] Fuel consumption is not a concern ( yet   )
---------------------------------

The crank gear turns the governor gear, the cam gear and the idler gears, and by extension
the oil pump. It appears the crank gear is held in place by a snap ring, if so then the gear may not be pressed
on or shrink fitted? if it is a slip fit i would be very concerned with low rpm gear pounding the key to
death, loss of a key means bent valves i would suspect.

>>> Maybe, but we really don't know if the loads are destructive when the engine is loaded so lightly.

---------------------------------

are you sure the engine is DI and not IDI?
how new is this engine?

>>> Engine is 1 year old, brand new, right out of the crate.
>>> Designation is ZS195NM (Direct injection).
>>> Is that better or worse than a DI engine for low speed operation ?
----------------------------------

oil pressure at 2000rpm hot is around 125-150lbs i am told, but have not taken the time to measure that to confirm

>>> I will make a note to monitor the oil pressure at low speeds. What would be considered minimum?

----------------------------------

i find it interesting that you can get it to run reliably at 900rpm, mine gets a bit irratic at 1000rpm, and is stable at 1200rpm
and up.

>>>This could be a fuel rack/governor issue. Mine too is touchy below 950 rpm. (one more obstacle).

----------------------------------

Bob, what about some additional flywheel weight?
I have not seen the crank bearing on the flywheel side, but do you think it could handle an additional 50+ lbs of weight ?

veggie

[Henry W]

The Crank Bearings are very Large:

Just over 2-3/4" dia.

Just over 1-1/4" wide with a 1/4" full circle groove in the center.

My 8 groove serpentine pulley on my S195 is almost 50 lbs and it seems it does not overload the bearing.
I don't think it will be a problem. Time will tell though.

Henry

[veggie]

The Crank Bearings are very Large:
Just over 2-3/4" dia.
Just over 1-1/4" wide with a 1/4" full circle groove in the center.
My 8 groove serpentine pulley on my S195 is almost 50 lbs and it seems it does not overload the bearing.
I don't think it will be a problem. Time will tell though.

Henry

Thanks Henry.
I think the stock flywheel is around 80 lbs.
I'm thinking of machining a secondary flywheel to bolt up to the sheave boss using the 3 available bolt holes.
Not sure how heavy it would need to be?

veggie

[veggie]

The engine is relatively quiet (80 db. @ 5 ft.) and runs very smooth.
I wonder if additional flywheel mass would reduce any concerning gear backlash that Henry and Bob brought up.?

The goal is only to reduce this speed by 100 rpm.! and add some features which make it happy at that speed.

Keep the ideas coming.....


veggie

[mobile_bob]

Veggie:

that is surprisingly smooth for a 195 at 1000rpm, perhaps the difference is it being a DI engine?

maybe we can talk Henry into running his down to 1000rpm and see how it compares

i have 3 of the DI engine's, but have never put one on the test stand, but plan to at some point
down the road, because i am looking for a pinch more efficiency they are supposed to be able to deliver
over that of the IDI engine's.

i guess dropping another 100rpm probably ain't gonna hurt?

very interesting venture you have there.

bob g

[veggie]

Bob, Henry....

Any suggestions on how much flywheel to add 

veggie

[Henry W]

I ran my S195 DI down that low and it runs the same.

The only thing I do not like is the geartrain sounds very harsh at speeds that low.

Bob mentioned about gear pounding and I see it as he does.

My engine has lots of extra inertia.

ST12 Genhead
Pulley for ST12 about 38 lbs.
Flywheel pulley about 50 Lbs.

I guess all this helps some.
I know if I shut it down at 1800 rpm's with no load it takes over 10 seconds to stop turning.

Henry

[mobile_bob]

i personally would not recommend more flywheel mass, especially if your engine is a plain brg model
and if you are targeting low rpm operation

there might not be sufficient load capacity in the main brg to carry appreciably more weight, unless
you plan on mounting the alternator up to so that the belt can help carry some/part/or all of the additional weight?

with the alternator up top, i would expect another 50 or so pounds would be just fine, perhaps as much as 75lbs

maybe a hell of a lot more!  

when you consider belt deflection when tight being maybe 20lbs, and then calculate the physics involved you end up
with perhaps 150-200lbs of actual pull on the belt.  so mounting the alternator up top like the one you have now should
allow you to add just about any amount of weight you would like.

within reason of course, because the next issue will be one of injection timing, you will need to slow the timing substantially
running a very heavy flywheel and low rpm  compared to the lighter wheel and 1800+ rpm, otherwise you may see
the big end brg start to fracture or delaminate in the high pressure region.

just as everything in life, compromises everywhere.

lots to consider when you re-engineer a product to do something it was not originally designed to do.

that doesn't mean it won't work, just means there are things to watch out for, and signs to keep tabs on
so that you can make adjustments before something is damaged.


bob g

[Henry W]

Bob, Henry....

Any suggestions on how much flywheel to add  

veggie

Well like my pulley setup because the boss on the pulley keeps it centered on the flywheel. I would not go much larger in dia because as we know there are only three mounting bolt holes on the flywheel and there might also be a harmonic ballance problem if you go too large.