PROPANE question

[ebola]

Hi,
what about propane as a main fuel for nitrous boosted engine? Some people states propane is not very predictible under high loads and temperatures, but I see there are powerfull propane wet systems with N2O...Can propane be used as main fuel for perfomance engine without or..with other fuel to support N2O? Does it exist any liquid propane controlers at market, or carburetors for gaseous propane only? Systems for carbs looks very very simple, What tempts to learn more about this fuel...One australian site had faq(I cant find it now), which stated that propane or LPG under high temperatures acts as low octane petrol, so its doubtly can be used as perfomance fuel.But today I see many sites with pictures of propane dragsters with quite a little info how systems are done.If youd have any links, would be great!
Regards
Andrius

 

[obanion]

Not sure, but I'm going to try it.

I started a discussion over at Supraforums about it. Thread located here:

http://www.supraforums.com/forum/showthread.php?s=&threadid=157638

____________________________

Here's the post, so you can respond to it here:

I should note up front, if it does become possible, will almost certainly require a AEM EMS to run it.

So the main question is, why? Some reasons:

1. 104 octane, need I say more?

2. Perfect atomization. Because propane exists as a vapor in the engine, it will always be fully vaporized. This has major benefits, or shall I say, doesn't have all the problems gasoline does.

Starting: Ever wonder why cars don't start so well when they are cold? Or why a gasoline engine requires a much richer AFR during starting and warm up? It's due to poor atomization. Gasoline doesn't burn, gasoline VAPOR does. The less atomization that occurs, the less gasoline is available to combine with oxygen. Heat encourages gasoline vaporization. Which is why at full operating temp, gasoline does pretty good. It's hitting hot valves, hot combustion chamber surfaces, etc, and the compression cylce is hotter which also promotes very good (but still not perfect) atomization by the time of ignition. On a cold engine, gasoline tends to stay in drops, which won't burn. Rather they get wasted and go out the tailpipe. This is why a 12:1 or so ratio is needed during warm-up, and cold cranking has a ratio of like 9:1 or so. You need all the extra fuel just to get enough vapor to start combustion. The extra fuel also hurts the combustion when it finally does occur, same reason cars lose power past 12:1, the extra fuel "gets in the way."

With propane, all these problems vanish. It will be a vapor down to -50F. No extra fuel should be needed for starting and warmup. You should be able to crank it over at 30F with the same stoich AFR as it idles at 180F coolant.

3. No potential for wash down. When starting a gasoline motor, or if for any reason the motor is run way too rich, the extra fuel collects on the cylinder walls and can cause "wash down," basically washing away lubrication and causing damage. This can't happen with propane, as it will always be a gas in the motor.

4. Cleaner engine, MUCH lower emmisions. Gasoline also requires (and at the pump it contains) a number of lubricants to protect the pump, injectors, and partially the cylinder walls. The burned lubricants are a main contributor to carbon deposits, and oil contamination, and lots of the stuff that shows up in a emmisions test. With propane, no burnt lubricants, no carbon deposits, and the emmisions will be MUCH lower. I'd be willing to guareentee any single turbo MKIV with NO cat should be able to pass a sniff test on propane. Oil should also stay looking clean for up to 10,000 miles.

5. Horsepower. Here I know people will step in with some information that propane doesn't make as much power. That is very misleading. By and large propane conversions have been, and continue to be, very primitive. The metering of fuel is very poor, leaving super rich AFRs under many conditions, which robs power. Similarly, ignition settings are never adjusted. Propane having different burn characteristics and octane than gas, requires different ignition settings. Staying with ignition curves made for gas results in more power loss. The system I'm working on will not have these factors hurting. AFR will be controlled precisely, and ignition will be optimized. On paper, propane should make more power with a given air mass. Here's why:

Propane 21,591 BTUs/lb
Gasoline 18,400 BTUs/lb

Propane, stoich 15.7:1 AFR
Gasoline, stoich 14.7:1 AFR

21591/15.7=1375.223 BTUs/lb of stoich propane air:fuel mix
18400/14.7=1251.701 BTUs/lb of stoich gasoline air:fuel mix

1375.223/1251.701=1.099 or about 10% more power with propane from the same mass air flow of air.

Some of this power is offset by the fact that propane is already a gas occupying space in the incoming air, where gasoline does some of it's vaporization inside and some outside the cylinder. But the power potential is certainly higher with propane.

6. Electric consuption. In the case of the system I have planned, electrical power consumption for the whole system will be about 1-2amps. That's it. Compare to a upgraded fuel system, which uses about 20-30amps at full blast (injectors + two fuel pumps).

7. Flow. This would be a replacement for a fuel system. Flows of up to 1000RWHP shouldn't be a problem.

8. Usage Cost. This is a fuzzy subject. By the pound, propane certainly has more energy in it than gasoline. However, by the liquid gallon, propane has about 20% less BTUs/gal. With current prices, which have propane about the same price as 87 pump gas, and $.20 cheaper than 92, it works out to cost maybe 5% more/mile than premium gas. But compared to 104 pump gas, it's a LOT cheaper. Also keep in mind that we are at a very high price point for propane. For the previous 20 years, propane has nearly always been about 20% cheaper than regular pump gas. So expect the gas/propane price disparity to improve.

9. Purchase cost. Be a lot cheaper than a fuel system. I'd probably price it under $1000 for a complete conversion, able to support up to 1000RWHP.

10. Simplicity. One line, one valve, one injection point, one electrical connection. Compared to two feed lines, one return, rail, six injectors, six injection points, six electrical connections, etc.

11. Weight. If you are crazy about weight savings, you can drop your gasoline tank out and save about 30lbs, and another 5lbs or so by removing the lines, rail, injectors.

12. No more pump gas. If you do some reading, you will discover you aren't buying just gas at the pump. You are buying a mix of god knows what. Every station can have a different mix. Changes with state, city, and time of year. MTBE, ethanol, the list of things they already have in there is endless. MTBE for instance, will reduce the horsepower than can be made on that fuel. There can be up to 15% MTBE in some gas. The constant changes also effects the burn rate and combustion efficiency. The ideal ignition timing to make max power on one blend will differ with another.

Propane, since it's sold mostly to people with BBQs in use for food preparation, is sold very clean. You buy just propane when you buy propane. Tuning for max power won't be hurt by variances in the fuel.

 

[CRG]

“With propane, all these problems vanish. It will be a vapor down to -50F.” ??????


Problems to consider with a vapor delivery system:
It may be vapor when it is at -50degF; however, you will find it very difficult to get it out of the tank when it is close to that temperature. Propane is stored as a liquid under pressure. When fuel is required, it goes through a phase change from a liquid to gas. As such, when evaporating, it drops the temperature of the liquid propane. Unless some type of heater is provided for the storage tank, you may not be able to get enough gas to the engine at temperatures colder than minus 20 degF. Result will be car will idle however will not run down the road at cold temps. Not a problem if you live in a temperate area. Don’t neglect the potential for carb ice if gas is very cold.

Even with a liquid propane system, there may be problems vaporizing the fuel because of the temperature drop from vaporization at extreme temps. Also, consider the effects of “icing” problems at the inlet where fuel is injected if temperatures drop too much from the evaporation of the fuel.

 

[patdaly]

ebola, here is the home page of the Gentleman I mentioned on the other thread. He is about as knowledgeable as anyone I have ever known.

http://franzh.home.texas.net

 

[patprimmer]

I agree
franzh is the man on gas phase fuels.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[franzh]

Golly, I miss one afternoon and all of a sudden I am immortalized!

Gee, thanks guys!

What did I miss?

Franz

 

[ebola]

Gaseous propane systems are very common in my country.Id say 50% petrol based cars uses LPG.Most stations sells propane.And it costs more that twice as less than petrol.Good friend of mine produces mixers for various german and japanese cars.So its nothing exotic for us, but...propane has always been treated here as economy fuel with out any advantages for racing/perfomance use.Now I find many artcles on the net, stating propane is used for perfomance.As a nitrous wetter, and even as drag race fuel.
Thats why Im trying to get more info about propane behavior at higher than ordinary loads, temperatures.To set gaseous(not liquid) propane system costs nothing for me, systems are cheap, market is overfilled with high quality italian and duch brands, but I dont think that gaseous carbureted systems can do much for race.Liquid propane injection - maybe, but I think proper control system would cost hell a lot.I was thinking maybe very staight big diameter liquid tract from tank to efi controled port injectors would work, but I cant find any info what injectors could work in this kind of application.Constant pressure I could keep with tank warmer and relays...I dont know, but handling liquid propane feels to be compilcated....
Thanks for info everybody.

 

[franzh]

Ebola:
Reverting to your original post about using LPG and NOS, then reading your last post about using LPG systems is a bit confusing.

Using liquid propane injection is possible but the control strategy is unique. Since the liquid is 270 times as dense as propane in vapor phase, the injectors must be 1/270th the size (greatly simplified). Now, add in the rest of the equation.

Vapor phase injectors typically use about 60 psig (about 4 BAR). Liquid phase injectors use saturation phase (the temperature/pressure constant) plus about 3.5 BAR to keep the propane in liquid state.

This is the rationale. (All temps in Fahrenheit.)

Lets assume that the ambient temperature is 70°F, and that the fuel tank is US grade HD-5, about 95% propane. The tank pressure will be approximately 120 psig. If you use strictly tank pressure to supply the engine with fuel, there would be no particular problem. However, the under body and under hood (under bonnet) temps are vastly higher, especially during heat soak saturation. The fuel pressure must be approximately 3.5-4 BAR above the soak temperatures to keep the propane in liquid state. We now need an in-tank fuel pump to supply the additional pressure. One solution is to pump the injectors with surplus fuel to purge the rails of propane liquid and vapor slurry. The surplus would return to the tank, where the absorbed heat will be transferred to the tank and hopefully dissipated.

The down side is that it is possible to have increasing tank pressures as a result of heat absorption from the engine compartment. I have seen several cases where the tank pressure is considerably higher than the fuel storage tank and unable to be refilled, even when a pump is used.

Several strategies have evolved. Lower the temperature on the fuel tank by artificial refrigeration (has the bonus of lowering the pressures and increasing the density of the fuel), and to use the natural evaporation of liquid propane to control temperatures (first and second law of thermo in conflict here).

On the positive side, liquid phase injection can indeed provide increased power over vapor phase due to the increased air charge principal by the vaporizing fuel in the intake manifold. Emissions are good too since the intake air charge is cooled, the formation of Nox is also reduced.

The control strategy is difficult and the physical components are complicated too. A special fuel tank must be used, special injectors, capable of flowing a precise and minute amount of fuel at pressures in the 400 psig range. This is NOT a project for the do-it-yourselfer. You are working with a fuel that is temperature sensitive, and whatever you do, do NOT use petrol/gasoline injectors! They will not work at the pressures, I have seen them blow apart!

In other parts of the world (I am in the southern US) butane is a greater part of the chemical makeup of LPG, and pressures are considerably lower, but the control strategy remains the same.

Help any?

Franz

 

[fueldoc]

Using LP to boost hp and reduce burn temp has been done in the past, but only with a carb/mixer combo. A company called Quantum has injectors which can be Y coupled in a special fitting with a gasoline injector and a gaseous LP injector (their product) using a simple pressure regulator. Have a look at their site

http://www.qtww.com.

FD

 

[rdd48856]

Like I already wrotte on another post there are a few manufacturers of liquid LPG injection kits. But they are expensive (4000€)and custom made. You have to ship your inlet manifold so they can fix the injectors in. If you speak french you should visit

http://www.borel.fr

or

http://www.vialle.nl