6/1 vs 20/2 fuel consumption......scale?

[admin]

Ronmar

it was on George's old forum that we went through the exercise

i am comfortable with your numbers they are more than accurate enough for the women i run with.

no real reason to get any more accurate unless one is deep into the weeds in R&D and trying to get a thorough understanding
of just what the efficiencies of all the related crap we use to generate power.

things like belt drives, differences in genheads, engines, temperature effects, and all sort of other crap.

the only other reason to get all wound up in high degree's of accuracy comes when one is trying to increase overall efficiencies of a genset
when a single percentage point becomes the benchmark.

as far as i am concerned your methods and numbers are good.

bob g

[Horsepoor]

Chris,

A couple of years ago, I extracted the trend line equation from the old forum 6/1 data. Very interesting, did it again yesterday. Incidentallu, since we both have the same GTC 20/2 enigine and down rated to 850 rpm for me and 750 rpm for you: Do you want to get together sometime and accurately measure the fuel burn in 1500 KW increments for 15 minute periods? Since reviewing the 6/1 data a few years ago on the other forum, I've often wondered about the actual fuel burn rate on our twins.

If you are willing to join me for this endevor, I was thinking about using a few of the extra electric hot water heating elements I have laying around. I have two 4500 watt elements (230V) and could pick up another two 1500 watt element to make: 1500, 3000, 4500, 6000, 7500, 9000, and 10,500 watt laods. We'll need to measure the actual power draw on each of the elements but it should be pretty close to the rated figure. These elements could be submerged in a bucket of water with a small cold water flow keeping it from boiling. Shouldnt take more than a couple hours one day or night.

[cujet]

I'm sure we could do it with a flow meter too. The flow rate, once stabilized on the load would be more than accurate enough for the listeroid world. I have a Floscan meter with digital display. I'd say an hour of running would do it to a high degree of accuracy. Really, you could probably do it in 5 or 10 minutes.

Could be fun! Since you have a single too, the data could confirm the existing data.

I stand by my initial "guess" though. The twins consume double, + or - a few percent. The belt drive has minimal losses so even a 50% increase in belt loading won't result in more than a percent change in fuel consumption. Same goes for the gen heads. The larger ST head certainly has higher parasitic losses. 

[Horsepoor]

Chris,

How will the flow meter be connected? I have marine hoses with snap fittings.

How accurate or what is the resolution of the meter? Under no to light loads, the folw will be very small.

Just thinking: I believe, we'll need a no load reading to measure the mechanical losses from the engine, ST generator head, electrict water pump, and to keep a standardized base line, I supose we should also engage one of the three electric cooling fans fulltime. This should eliminte the error from a fan running occasionally under light load and then running full time under heavy loads, which will occur later on during testing. I would like to get good, useable data, to allow a reasonable comparison to the 6/1 fuel data curve.

Back to creating a load bank. I mensioned the two 4,500 Watt hot water heating elements I currently have, plus I would need to buy a couple of 1500 Watt elements, then build fixtures to hold these elements in a bucket of water. Instead of doing all of this, I wonder if I should swing by the Faith Farm Thrift Store to see if they have any beat up, old, electric stoves / ranges. If I can get one for $20 or $30 dollars, this might make a nice load bank for testing. You thoughts?

Bruce

[DKMC]

I stand by my initial "guess" though. The twins consume double, + or - a few percent. The belt drive has minimal losses so even a 50% increase in belt loading won't result in more than a percent change in fuel consumption. Same goes for the gen heads. The larger ST head certainly has higher parasitic losses. 

You mean double for the same load?

As in a 10/1 uses 1 quart an hour for a 2000W load and a 20/2 uses 2 quarts an hour for a 2000W load??
How about the twin spreads the load over twice as many cylinders, plus a bit more fuel for added friction losses, plus a couple more percent due to light loading inefficiency?
But surely the twin is NOT half as efficient at the same load.....

[admin]

i will make a bold prediction

a 20/2 driving an st12 will come out to be just as efficient as a 6/1 driving an st5 under the following condition

make sure to test both at near full rated load

the little added frictional/pumping losses of the twin over the single will likely be offset by the slightly more efficient
st12 that it is spinning.

if both are running at 2000 watts the 6/1 should have the advantage because the load is really too light for a 20hp twin to efficiently
provide for, however it might not be too bad depending on ones needs.

there is always compromises to be made if you try to make one unit do everything, sort of a "jack of all trades, master of none".

if ultimate efficiency is the target, the use of two or more differing sizes of gensets, each tailored to the expected load will burn less fuel
than one larger or two smaller running in a tandem setup will end up using.

the compromise there is with money, size and everything related to multiple units, or

just buy a big one and compromise on the lower load end with consumption of more fuel?

depends on ones "real" needs i suppose

bob g

[DKMC]

lol....
At the RPM's and fuel burn ratios these engines operate at, I have a hard time imagining the difference is
measurable. BUT...make like I didn't write that.....I'm enjoying the debate and varying views presented here.

dk

[cujet]

I stand by my initial "guess" though. The twins consume double, + or - a few percent. The belt drive has minimal losses so even a 50% increase in belt loading won't result in more than a percent change in fuel consumption. Same goes for the gen heads. The larger ST head certainly has higher parasitic losses.  

You mean double for the same load?

As in a 10/1 uses 1 quart an hour for a 2000W load and a 20/2 uses 2 quarts an hour for a 2000W load??
How about the twin spreads the load over twice as many cylinders, plus a bit more fuel for added friction losses, plus a couple more percent due to light loading inefficiency?
But surely the twin is NOT half as efficient at the same load.....

No, I meant to simply take the published chart and double the figures. Not double the consumption at all. In fact, under mid loads, the consumption would be similar.

So, at zero load I'd expect .126GPH X 2 on a 12/2 twin running at the same RPM, or .25GPH. OK, so that's double at "no load", sure (but that's the only time you'll see that). As you travel up the chart,,, the single makes 1.5KW at .219GPH, so the twin would likely produce 3KW at 0.438 GPH. Clearly a little less efficient at that load (but not double)

My reasoning is that the diesel engine has a known efficiency by load. So a twin simply has 2 of the very same cylinders as the single, and the combustion efficiency is related to the individual load in the cylinder. So, double the load on a twin will result in the exact same cylinder load as a single.

Sure, there are small differences such as a center crank bearing and so on. However, I humbly submit that they are minimal in nature and won't result in much of a change. The major frictional component is piston ring swept area. And in the case of a twin, we simply have 2!

[cujet]

Chris,

How will the flow meter be connected? I have marine hoses with snap fittings.

How accurate or what is the resolution of the meter? Under no to light loads, the flow will be very small.


Bruce

The sensor uses 1/4 pipe threads on each end. It's quite small and is simply a counter of flow. It's very accurate as it counts volume per pulse. I'm not sure what the exact volume per pulse is, but since the sensor is small the volume per pulse is incredibly tiny. It's upper limit is about 30 gallons per hour. There is no lower limit. 1 pulse per hour is possible. (good enough for a model aircraft engine!)

It will count 1 pulse, or 10,000. The flow rate is, of course, how many pulses per unit time.

It's accurate enough to bet your life on. Many pilots do...

[WStayton]

Hi Guys;

  A look at a different perspective . . ..

  Admittedly this was with spark-ignition engines, not diesels, so the numbers are meaningless, but the trends are there . . . .

  When I worked at Ford, yea lo many years ago, wse looked at a v-8 engine management system that would have used four cylinders for idle/low-load, six cylinder for medium-loads and all eight for heavy loads.

  The first cut, since hardware to disable valves on the fly was expensive/complicated, was to just run several engines on the dyno with the push rods pulled out of the cylinder that you wanted to disable.

  Anyhow, the net result wa that we THOUGHT that if you could build the mechanism to disable the valve train components on-the-fly, we could gain about 10% om the EPA fuel economy test cycle. 

  The project was scrapped when they determined that it was going to be something like $400 to $500 per vehicle to build the necessary control/actuating hardware - which was huge for a vehicle where the total variable cost of manufacture was about $4,000 across the product line to which the technology was applicable - i.e. it didn't count four cylinder Pintos and in-line-six cylinder vehicles.

  GM has, since the advent of computer controls, used this sytem on some Cadillacs, and I presume it must be worth the cost, since EVERYTHING in the auto industry is driven by the bottom line!  <grin>

  A diesel is inherantly more fuel efficient than a spark ignition engine, so there is probably less to be gained by using fewer cylinders running at higher BMEP, but I would THINK that there must be 5% or so to be gained by running  cylinders at higher BMEP - the real question is, is this more than offset by the fact that the twin has one less main bearing, one (two?) less cam bearings, one less bearing in the injector pump, one less drive belt/shaft, etc etc.  My guess is that it would be about a wash, but that is a guess based on absolutely NO data!  <smile>

  Of course the numbers are going to depend on what BMEP, you measure at!

  My opinion which is worth EXACTLY what you paid for it!

Regardz,

Wayne Stayton
 

[cujet]

The sensor reads 29,590 pulses per gallon!

[Horsepoor]

Chris,

Good enough resolution for what we will be measuring for about 1 pulse for every 3 drops of fuel. Other considerations unique to my GTC 20/2 setup before we measure.

My 20/2 and 6/1 normally run on 4 to 6 year old waste jet fuel. For the test runs, I have some freshly purchased pump diesel. This should help reduce one source of error on the energy content. If others will be drawing comparisons to their twins, I wonder how some of my setup configurations will impact the test runs.

My 20/2 is down rated to run at 850 rpm with extra heavy flywheels and a very heavy gen head flywheel (about 80 lbs) on an ST 15 generator head. The gen head is connected to the engine with an 8 rib micro-v-belt. Now the ST 15 has much greater capacity than the maximum engine output at 850 rpm. During maximum load test runs, I have gotten sustained 11,200 watts output (15 minutes) but I consider 10,500 watts to be the upper limit. So I have a bigger gen head than most people will be using on a down rated 20/2 (850 rpm) with heavier flywheels than most people.

For the NO LOAD base line, do we want to include the electric water pump and the electric fan? I can isolate these loads from the generator head for just the bast line - no laod test run, which is probably best since it will provide more compatible data for others. Do you agree?

Lets talk via cell phone on how best (easily) to be able to switch the flow meter bewteen engine fuel supplies on my engines and yours.
.
Also, my Metro 6/1 is running at 800 rpm, 8 rib belt, ST 7.5 generator head (Overkill again), electric water pump and fans. I have a meticulousily tunned engine, 4,400 matts absolute maximum, 4,000 watts normal maximum load. Add sea level and 80 degree F