Ideas wanted for low speed propane engine

[Henry W]

I would not recommend it. I believe idle speed is around 1200 rpm. i would keep it within recommended operating speed. I believe the lowest recommended speed is 1800 rpm. Recommended max net BHP is just under 7 hp. It seems like it might work.

Log in and look at the charts below.
If you want a slower speed Briggs v-twin than I would try to look for a 14 hp vanguard v-twin. It has more hp than the 16 hp v-twin until they get to 2600 rpm's. Than the 16 hp v-twin starts pulling away from the 14. My understanding is that the only differance between the two engines is carburetors. The peak torque curve on the 14 is at 2000 rpm. The 16 is at 2600 rpm. But I've heard from the Briggs application engineer that I spoke to that the 16hp peak torque curve is closer to 2400 rpm.

It is surprising how quiet these engines are at 2600 rpm's.

[Henry W]

Second picture

[Henry W]

Here is one similar to the one that I will be building.

http://www.generatorsales.com/order/Slow-Turning-Propane-Generator.asp?page=S6500

Instead of using a two pole head I will be using a four pole. I will experiment running it at 2600 and 3000 rpm's.

[pressurepro]

Odd they are specing 15w40 in it...wonder if they have cleared it with briggs .....one more thing...i may be wrong but im not sure any of the big manufacturers (briggs,kohler,honda)have certified and will warranty there engines to run on lp/ng ....obviously these guys are doin it but may be taking the warranty/risk on themselves instead....gonna do some investigating...

[Henry W]

I was wondering about the oil also. Briggs says only use a 30, 10-30 or 5-30 grade oil. They are also recommending synthetic 5-30 from the start if customers want to use it. I am not sure about LP or natural gas. You could be right that they are taking all the risks.

[pressurepro]

Somebody is...doesnt look like briggs is or wants too....
http://www.briggsandstratton.com/us/en/support/faqs/alternate-lp-ng-propane-fuel-conversion

[glort]

Why not use a small Car engine?
Would easily do the HP and torque you want at the revs you are after and LPG kits are available as bolt on's for any engine.  You could probably get one cheap at a wreckers and the longevity even on a good used engine would outlast modern stationary engine brands. Would be quiet being water cooled and easy to get any parts for.

[Henry W]

Glort,
We are discussing about an engine that will put out around 6hp at lower rpm's. An auto engine would have too much friction loss from the extra resipicating parts and in turn it would not be very fuel efficient. There are some small three cylinder engines available that I would consider for applications near 7kW.

There is a small single cylinder modern stationary engine that Briggs manufactured back in the late 80's. It was a 272 cc, single-cylinder, four- cycle, liquid-cooled engine rated 7.5 hp. The engine ran from 1200 to 3600 rpm. The engine features a 4000-hour service interval and a 40,000-hour life.

[BruceM]

Thanks for the continued good thoughts and helping with my engine education! 

Air cooled does create a design issue in dumping that heat from the engine shed without leaking sound as well.  I've read one author that suggested a pair of squirrel cage blowers to address that since the blower housing acts as a sound baffle.   The loss for the blowers just needs to be figured in the total power and overall efficiency, and I don't think it's a show stopper at all. 

[Henry W]

Here is a design for making a sound resistant generator shed. My Vanguard project will be on a trailer. I will be using the same design principles in the drawing below.

Henry

[mike90045]

Here is a design for making a sound resistant generator shed.....

I'd like to see that exhaust take another 45 deg down and away from the eves.   The sound traps are very reminiscent of light traps for a darkroom.

[Henry W]

Having the exhaust angled down is a good idea. I like it.

[pressurepro]

http://www.marathonengine.com/

[buickanddeere]

  For a senior probably an off the shelf generator that can be bought and serviced anywhere maybe a consideration.
  Variable speed inverter generators in particular need to be over sized if starting motor loads while on eco variable mode.

[Henry W]

Pressurepro, you beat me to it.
Thanks,