2 cylinder vs 3 cylinder diesel

[squarebob]

OK - another question ( or two ) I need help with. I have been saving up to get the 2TN70 from Surplus Center. Should be the right size engine to do my project with. I have also located a Yanmar 3TN63, which is a 3 cylinder, 600cc engine compared to the 2TN70 which is a 570cc. It is rated at 15Hp @ 3200 vs 13.4Hp @ 3600 for the 2TN70.

a- Will the 3 cyl engine have any advantage over a 2 cyl engine?

b- Could I assume the fuel efficiency would be pretty close with the same load on the engine due to the cc's being so close.

Thanks

Bob

[LowGear]

I think a peek at squareness or stroke relationships might reveal some interesting theories.

LowGear

[Ronmar]

Hp = torque over time.  Nearly the same total displacement, but the tripple has 30% more power strokes for a given RPM.  For a given load, your fuel consumption should be similar.  The manufactures should have published BSFC numbers that will answer that question.  The tripple should naturally run smoother having more frequent power pulses.  It also makes more power at a lower RPM.  If you have planned on 13HP, you may be able to derate the tripple to make it even more comfortable to work around.  A 3600RPM diesel is not very pleasant to be around, and requires additional measures to quiet it for domestic sevice... 

Get them both, I am sure you will be able to sell the one you like the least:)

[Henry W]

I just fired the 2 cylinder Kubota Z482 for the first time and this is what I noticed. In order to have the engine smooth out it needs to run around 2400. Before I purchased the Z482 about 8 months ago I pretty much figured that the sweet spot to run it would bet 2500 to 2600 and it seems that these numbers are pretty close and this is where this engine will be running. Probably the same goes for the 2 cylinder Yanmar.

Henry

[squarebob]

My plan would to be to run the engine about 2200~2400 RPM or less. Primary load would be a 24V 150A alternator. Secondary load would be a ST gen head. Heat exchangers on cooling water and exhaust.

Bob

[Henry W]

The 2 cylinder is a good engine for the money. It looks like peak torque would be at around 2600 RPM's.

I would say 2400 to 2600 might be a good place to start.

Henry

[mobile_bob]

if your primary load is the 24volt alternator, @ 150amps, which will likely work out to around 120amps hot
and if you are charging batteries 28.8volts give or take, therefore 28.8 x 120 = 3456 watts

the alternator is likely around 50% efficient so the mechanical load will be about twice the generated power
or approx 7kwatts,  which is about all the two cylinder will do reliably.

now if you want to run the st head to power AC loads at the same time?  then you probably better figure
on the 3 cylinder and not drive the st head "until" the batteries charge rate drops off a bit.

if you plan on any other loads, such as an air compressor, you will likely want to invest in a balmar controller
reason being it has a terminal that when energized cuts the field to ~50% of rated output.

with a bit of added control you could switch in AC loads to the ST head, and at the same time trigger the 50% mode
on the balmar and in doing so free up some engine power to provide for driving the AC load.  this scheme will allow
about 3-3.5kwatts of AC power when the batteries are low because of the balmar cutting power from the 24volt alternator.

there is a variety of ways this could be accomplished, some quite simple, one that comes to mind is a current relay
which could be adjusted to trigger when the AC load exceeds a certain set point.

an electric clutch air compressor would be very easy to work with, because when the compressor clutch is energized the same
source could be used to power the balmar 50% terminal, so when the compressor clutch engages the balmar automatically
drops the alternator output to 50% of rated load.

in any event, going with the 3 cylinder might be easier to do all you want to do, the 2 cylinder will do it too but will require a bit
more control if you want to drive a couple differing driven components sharing a finite power source.

bob g

[squarebob]

bob g you are thinking along the same lines I am. Stagger the demand and keep the motor under load. I like the 50% feature of the Balmar. Makes things simpler to control. The more power strokes of the 3 cyl also seem make it a lot more user friendly.  I really want to head to TN and pick up that engine but not sure I can get it past the CFO!!!

Bob