Best compression ratio for propane? 1

[vintageAP]

Hi all, new here - great site!

I'm investigating propane conversions for performance engines and understand that because of the higher octane with propane a higher mechanical compression ratio is desired for optimum performance.

Does anybody have this information handy or experience with this?

I'm sure that the same laws apply as with gasoline engines; too high and pre-ignition will come into play, but about where is that magic number? In gasoline engines there are factors that won't apply in a propane fuled engine such as quench area, puddling of liquid fuel, etc.. Am I still looking for the same aproimate A/F ratio - 14.7? Will cylinder temp affect flame travel and pre-ignition in the same way with propane? Any info and discussion is appreciated.

 

[GunMuse]

Sniff test yes.

By 60's style- Meaning - No smog pumps, no cat convertor. Stateing this didn't mean running a 40 year carb and low tolerance engine.

And you guys totally missed the point.

If you make a LAW that requires a cat convertor you are saying that there is ONLY one way to accomplish something.

The EPA in the USA has become an industry that gets a specific tweak into law to force the use of a specific patented item for mega bucks.

The point I was trying to make is that Goverment should set standards to achieve not laws on how to achieve them.

http://www.prnewsnow.com

 

[turbocohen]

Standards are required to allow commonality of fuel requirements. Cats are required, oxy sensors are a must for feedback, its good science bud.

 

[GunMuse]

Its good science TODAY. Its also restrictive thinking. And your argueing with me about standards when i agree they should be there.

If I invented an engine tomorrow that met or exceeded all requirements it would still be Illegal to sell it because it didn't have a cat or oxy sensors. See the problem? Society sets a goal and yet when you achieve that goal

Millions of dollars worth of state and federal testing are required to profit from doing so. Laws have to be rewritten, that means a couple of years go by while it goes into a research committee of lawyers who will pander for money to allow my idea to be an exception or part of new law.

My end all point that your not getting is by just meeting or exceeding the standard is not enough and it should be.

Anyone want to guess how many millions in legal fees chrysler just went through to put a 4 cylinder diesal in their new Jeeps. Not because meeting the standard was hard but because the law didn't have exceptions for 4 cylinder diesals, EPA laws that were written to PREVENT the sale of 4 cylinder diesals in the 80's(Remember the BMW imports that threatened jobs recovery in the US.)

EPA standards on propane will most like just increase the cost to the consumer to a point that its not profitable to research propane engines. Without profit there is no progress. Enviromentalists will sacrifice all profit without regard to "Good science"

http://www.prnewsnow.com

 

[franzh]

GunMuse:

Nope, wrong again. If you developed an engine tomorrow that would meet upcoming emissions standards and continue to meet them without degradation, you would NOT need an O2 sensor or catalyst. The catalyst is needed to convert the residuals after combustion that came from a fuel that is varying in quality across the country but still within standards, plus an engine that is constantly changing its performance profile, the O2 sensor is there to keep the catalyst happy.

There are NO laws preventing a 4 cylinder diesel, just to ensure that the resulting tailpipe standards are where they need to be. The EPA does NOT get a kickback from any company for doing so, just aint happening.

Legal fees? Hmm, anytime anything is developed and introduced, the legal eagles get involved. Thats just part of the progress. I agree that a diesel engine is needed and sorely missing from the US shores, but blame the public for their perceptions rather than the lack of good products worldwide. The reason more diesels are not for sale is not the manufacturers, its the lack of sales.

As for increasing the cost of fuel due to the EPA? If a finite fuel standard were to be introduced that everyone would use, I only see fuel sales increasing because the engines that use that fuel need a good reliable consistent fuel, more engines, more fuel, happier customers.

The price of fuel today is more governed by OPP (Other Peoples Problems) than the US regulations.

Lastly, we are WAY off topic for this thread, and no real place for a political discussion, I get enough of that at work! Care to redirect this thread back to an engineering discussion?

Franz

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[turbocohen]

skyooz me for hijacking Franz.. I am a supporter of advanced diesels however the EU typically has higher cetane levels on the order of 47-52 making it easier to meet lower smog numbers. The diesel here in the US is barely 40 cetane and seldom higher than 47. 07 fuel will change drastically to accomodate new diesels with lower sulphur and hopefully higher cetane.. in the lab new clean diesels can beat dang near all CNG and Propane emissions except CO2/hp/hr.
High compression DI LPG numbers aint better than 07 diesel. It is looking so good that I will bet diesel may make it into the indoor forklift market.

 

[vintageAP]

Hmmmm, about 12:1 then?............

 

[turbocohen]

For a reliable hot rod, 11. For a diesel conversion, 11 with supercharging up to 25psi.

Use an long life platinum plugs one or two heat ranges colder than suggested for gasoline and reduce plug gap .05-.08" otherwise coils and other lectronics let smoke out. By using Denso iridium plugs the ignition coils and high tension wire will last a long time because they require less voltage under load than old fuddy duddy plugs.

http://www.ngkspark.com.au/pages/bulletins/T92-1.htm

 

[marcdeluca]

I have built a few lp engines, and my experience has been that you shouldn't go above 10.5:1 on older iron head engines. I have a 454 in my old truck that has a vapor lp system, and when towing in the heat it will ping a little, and it is 10:1. With aluminum heads, you could go 11:1, and perhaps that high with vortec heads if it is a Chevy. Even though they claim it is 110 octane, it tests much lower than that.

 

[vintageAP]

Thanks Marc. Hmmm, now we're back down to what I can make a gasoline engine run at on the street, at 10.5:1. I know a lot depends on vehicle weight and load, and tuning. Full size pickup doing tow duty might be a little heavy for what I'm doing, but the info gives me a real-world paremeter.

 

[patprimmer]

A lot depends on quench, head temperature, spark timing, plug heat range, cylinder head material, cylinder head preparation, A/F ratio, quality of A/F mix, bore size, cam timing, rod to stroke ratio.

It will go a full ratio higher than any petrol you can afford to buy and is widely available.

If it pings at 10:1, something else is not optimised.

Regards

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[marcdeluca]

My 454 has a roller cam and rockers, so it breathes pretty good. It has the tamest cam I could get, because I wanted good torque. This engine will also ping a little with 93 octane gasoline. When it pings on either fuel, it is while towing in hills with fairly high ambient temps. Just driving by itself doesn't get the engine hot enough to ping. I'm sure you could get by with more compression in a lightly loaded car engine. Try natural gas, it likes 13:1. I have a Duramax with supplemental propane and natural gas, the cng is much more ping resistant than the lp.

 

[patprimmer]

I would suspect that your coolant temperature is higher with the LPG than petrol.

I would suspect your spark timing and plug heat range might be optimised for petrol rather than LPG.

To get the most from any fuel, an engine should be built with that one fuel only in mind.

A smaller bore alloy head engine will tolerate more compression than an iron head 454.

Regards

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