Power Logging and Generator Hours

[ChrisOlson]

One of the things that was interesting about building the enclosure for the Honda was that I could NOT get pulse scavenging to work on the exhaust.  Leave it to Honda to think of something like this - but they got a forced air-cooled muffler on the damn thing:



The muffler is fully enclosed in a housing.  The engine cooling fan blows air over the cylinder barrel and head and the ductwork on the engine continues on to the muffler housing where it is forced to blow over the muffler and all the air exits that grille on the side.  There is a LOT of air coming out of there and it's so much that no matter what I did to try to get it to pulse scavenge the enclosure, it didn't work.  The best is to have the vent pipe right up to about 1/2" from the muffler like this:



I could put a scoop on the end of that vent pipe and have all the air blow into the scoop and out the vent pipe.  But I think that would remove so much heat that the enclosure would never get to 70 degrees in the winter time, even without the ventilation fan running.  The waste heat, as it is, is picked up by the airflow from the ventilation fan and carried right out the warm air exhaust vent, and the air flowing over the vent pipe actually seems to keep it a little cooler.  So I'll probably leave it like it is.

This is a photo of the unit when I was running the fuel consumption test on it:



--
Chris

[ChrisOlson]

Just sort of a report for folks on our new generator - I couldn't be happier with it.  After it was installed and operating correctly with the auto-start and auto-throttle, I filled it up with fuel and bought another 6 gallons of gas for it in a can.  The generator has run 22.4 hours since we bought it and I've only refueled it twice - just dumped the last of the 6 gallons in the can in it tonight and the gauge on the tank on the generator shows about 1/2 full.  So I need to buy another can of gas for it now.

According to my power logs it was Sept 9 when I filled the generator and bought that can of gas.  So we've only burned about 9.5 gallons in it in six weeks.  And the generator has run about 3.7 hours per week - all for load amps, and mostly for the range or clothes dryer - it has not done any battery charging yet.  However, it will get more hours on it per week in the dead of winter - usually 6-7 hours/week from mid-December to the end of February.

It is so much cheaper to run than the LP fueled Generac that the two generators are not even in the same class.  The Generac would've burned approximately 27 gallons of fuel to do the same job over the last six weeks.
--
Chris

[Frank S]

an average of .424 GPH or 63.1 ounces per hour! this is a lot less than your first hour run in sounds like the generator is a lot better than expected or your loads have not been nearly as high as the run in load. this would make sense to me since the start up or inductive loads would decrease as the appliances reached their operating temps. All in all it sounds great.
 I remember back in the day when LPG was 10% to 30% the cost of gasoline and gas prices were under a dollar everyone wanted to run LPG conversions on their vehicles. I did several conversions but couldn't see the justification for the expense even then. especially if the vehicle was older and had to have hardened valve seats and sodium filled valves installed in the heads just top compensate for the lower lubricity of the LPG it was bad enough when the Unleaded junk juice came on the market and replaced lead and Ethel reducing an engine's performance and MPG in some cases by over half.

[ChrisOlson]

Yes, it's like the convection oven in the range - my wife turns it on and it's an initial high amp draw.  But when it comes up to temperature, the power requirement drops as all it has to do is maintain the cooking temperature.  So the generator gets loaded and unloaded during the job.

This is what makes inverters with gen support so nice - you can run these big loads with a small generator.  If all you have is a pass-thru inverter then the generator has to be sized for the peak load and it wastes lots of fuel when the load is off peak.
--
Chris

[ChrisOlson]

an average of .424 GPH or 63.1 ounces per hour! this is a lot less than your first hour run in sounds like the generator is a lot better than expected or your loads have not been nearly as high as the run in load

Frank - one note on this - my initial fuel consumption test was a constant load to see what peak fuel/kWh efficiency would be under ideal loading conditions.  Real world is always different.  I did another test in real world with battery charging (which is more controlled conditions than load run) and got .44 gal/hr at an average 3.04 kVA output.  So the real world load run fuel consumption is still very close to what I got with battery charging during my one test.  The generator has not run for battery charging since that first test I did, so I'm confident that it will continue to be more efficient than the propane generator was by about 3%.

This is mainly due to the higher thermal efficiency of the gasoline fuel and the engine that burns it.  An LPG engine would have to run a compression ratio of around 12-13:1 to match it.  The Honda's iGX electronically controlled engine is obviously a masterpiece of engineering in small engines.  If you read about what Honda did with the thing, they made it so the engine's ECU communicates with the machine it's powering , whether it be a generator or a power trowel on a construction site.  On the generator application the CT (Current Transformer) sensor adjusts throttle opening and ignition timing before the load can affect engine rpm.  And it is VERY fast - there is no throttle linkage on it because the ECU is integral with the carburator.  So there is no "play" or "droop" that you would get even with conventional electronic governors.

Honda's system is strikingly similar for gasoline engines to what we developed for the Cummins N14 called the Celect Plus system.  On the Cummins Celect Plus engine management system the throttle pedal merely operates a potentiometer and injectors are directly controlled by the ECU with no mechanical linkages or interaction.  This allows very precise metering of fuel and injection timing - and the Honda's technologically advanced engine is doing the same thing with a gasoline unit.

I think this generator is more of a showcase of Honda's engineering prowess than anything else.  And believe me, when it comes to engineering, few companies on earth can match Honda.

When comparing LPG fuel to gasoline, you're going to burn at least 50% more fuel (gal/hr) with LPG than you will with gasoline just because the BTU content of LPG is so low compared to gasoline.  And then you look at volumetric efficiency, and the LPG gets worse.  Because of the low air/fuel ratio with LPG there's not as much room for oxygen molecules in the combustion chamber.

So the pumping losses in the four-stroke cycle are going to be higher with LPG, along with poor cylinder scavenging because of the volume of fuel that has to re-introduced to the cylinder on the intake stroke.  You can try to reduce the amount of raw fuel lost out the exhaust valve by reducing overlap on the valve timing events.  But then you trap some exhaust gas (poor cylinder scavenging) in the combustion chamber with the fresh charge - and once again you get reduced thermal efficiency because of a diluted charge.

There is basically no way to make a spark ignition engine as efficient on LPG as it can be made on gasoline because of the nature of the fuel, and the basic parameters that the four-stroke cycle uses to scavenge the cylinder and recharge it.  So people that put LPG conversions on gasoline engines are shooting themselves in the foot.
--
Chris