NG fuel; compression and cam for low rpm high tourque

[NGgen]

We are using a modified Ford 460 to run a generator at 1800 rpm needing 148HP to make 100kW
Engine has 11:1 compression,stroker crank,and custome cam. Fuel-air ratio tuned through a venturi at 17:1. timing at 28. We are still experiencing short engine life, hot exhaust, detenation and hard to manage emissions. Looking for some experience with this type of design criteria.

 

[patprimmer]

11:1 and 17:1 I'm not surprised.

what fuel, why bother with a stroker and all the mods. What timing has the cam got.

If you need 11:1 to get the power at 1800 rpm, why not turn the engine a bit faster, use all stock specifications and use a reduction drive to the generator.

On modern fuel I would think 9.5:1 is enough compression and 15:1 is already a bit lean.

28 deg also sounds a lot for full load at 1800 rpm.

Regards

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[franzh]

NG stoich ratio is 16.8:1 (depend on whom is making the reference, but this is close enough). Pat is correct, this engine is being loaded to heavily at too low an rpm. No wonder the engine is detonating.

Some of these engines run lean burn at load to reduce exhaust temperatures and fuel consumption, plus many are turbocharged (the genset outside of my office is an Onan with a Ford 460 NG engine, with a turbo on top, pulling through an Impco 225. When it cycle-runs, the engine really sounds like it is laboring but it is throttled by pulling through the 225.

28 degrees may seem a bit high too, I would use an exhaust thermocouple and tune the timing for no detonation at load while trying to reach the lowest exhaust temps. You can also play around with fuel mixtures for the same end result.

You state you are having problems with emissions, which ones and what are they doing (real numbers please)?

Franz

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[turbocohen]

11:1 detonating on cng? yikes. Yep, about 17:1 is the a/f ratio.
100KW at 1800 rpm is way overloaded. Didnt think a 460 could make enough torque for that much hp on cng

 

[patprimmer]

Sorry, I missed the CNG bit. I was making my comments based on petrol.

Regards

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[NGgen]

Why bother with a stroker? Our new engine designer is adding a slight stroke adjustment to get the best size and cylinder environment for methane fuel.

Why not turn the engine a bit faster and gearing the rpm down to 1800? This is a consideration.
The generators are single bearing and use the fly wheel and rear main bearing as the second bearing (common in gen design). The down side of higher RPM is a redesign of the Genset plus higher rpm is additional wear and tear on the engine.
This system needs to run 24/7 360 days per year. We planned for annual rebuilds of the valve heads. The bottom end can be rebuilt as needed. We are using 8 gallons of oil recirculation through the pan at approx 220°f – 225°f.
The first engine was at 15:1 compression, with a serious miss design on the cam. This engine didn’t last long: Detonation, unburned fuel out the exhaust valve, stretched main bolts, pitted pistons, etc. a real mess. Needless to say the first engine builder is off the project.
We are trying a new approach with lower compression, small stroke, custom cam, custom valve head assembly with extra lubrication, guides, stelite, spring change.
Hopeful the new engine shop will have success, the builder has 45 yrs with speed and some time on low end high torque applications. No telling until we dyno the engine using methane to model the end fuel BTU. We use a NG venturi with electronic A/F regulator that uses O2 sensor and exhaust heat to manage fuel and emissions for California. A Continental Controls system

I should know by Wednesday and will report back. Emission are a result of the first engine design failures. I won’t bore you. I’ll let you know the results off the newest design.
This application is generation using oil field waste gas as fuel for rich burn IC engines. Making electricity to run electric motors on the oil wells. Tough environment. I don’t know if the ford can handle it. Lots of mixed reviews.

I’ll update every one interested later this week.

 

[turbocohen]

you might consider a john deere cng engine. best damn cng engine on earth in my not so humble opinion.

There is also a ready made generator that I have seen widely used in the field called Whisper Watt. a smart choice might be to take this model

http://www.mqpower.com/pages-products/ultrasilent/DCA-125USJ.html

and outfit it with a john deere 6.8 liter cng engine. Forget the Ford 460 for 24/7/365.

 

[franzh]

Oil field waste gas? Do you have ANY idea what the mean value is for the fuel? Just assuming that it is primarily methane is a gross misjudgement. You should assume some SO2, CO2, Propanes and Butanes, plus some water and nitrogen.

You should dyno the engine at the intended target rpm range with the fuel being used, not commercial pipeline gas. I agree with Turbo, the John Deere is one fine engine, designed for that rpm and load.

Franz

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[NGgen]

we have many gas composition samples over the last few years.
gas is 97% methane, 1.8-CO2,.4-O2, 1.8-N2. (978 btu)Pretty clean. using 100% methane to run dyno test.
I'll look into John Deere, I heard they don't support prime power generation with thier engines.
thank for the input keept it coming ideas will grow.
I would toss the ford, yet all the infrastructure for the generator is built to this engine spec. if this next attempt doesn't work we will go another rout. looking at chevywith higher RMP and reduction box also. too bad it all cost so much. but with $700k invested finding an engine is a must. Sorry we were talked into this by the vendor of the Genset. now it crisis management

 

[jc10000rpm]

not sure if this is still active post..........

first off no cam specs givin, WHAT ARE THEY??, what is vacume @ same rpm without load?

general rule of thumb, detenation= to much dynamic pressure for fuel used with mechanical combo.

Cure.....
start over with short duration cam and lower compression if not.......

less timing
colder plug
more duration on cam (helps bleed of pressure during overlap) with high static compression and low rpm heavy load
richer mix

or PLEASE start over with a typical RVcam.
As with any combo, @load check eng. vacume
advance timing 2deg. at a time while starting low (say about 12 or 15 deg.), once max vac at load is reached back timing off by 1.5 or 2 deg. for safety (and it reduces NOX gas)

happy Generating

 

[NGgen]

Thank for all the comments:
we have rebuilt the 460 block with a new cam, piston, rods, crank. On the first round of testing using methane(980btu)we got 478 ft# torque at 1800rpm at 17:1 f/a and 10:1 cmpression. we are tweaking the cam to get a few more # tourgue. the 100kw generator needs 420 ft# at 100% load. goal is the have a 20% torgue margin. unfortunatly I don't have the cam spec to share. MJOre as it happens,

 

[Fabrico]

Maybe a 500 cu in Cadillac engine could do it.

Heavy load at 1800 RPM is below the proper power range of any automobile engine. This type of engine would surely last longer at 2200-2400 RPM than 1800.

Most OEM gas truck engines have (had) some significant differences from automobile engines.

Nearly all the Diesel manufacturers offer CNG derivatives. Most of them run at fairly low speeds. Is there a size/weight restriction?