LPG ideas AGAIN...

[JustGav]

Just spotted this on supraforums.....

 

I know a lot of times this has been discused and dismissed, but given the rising cost of fuel....

 

Since I'm trying to do this, I'd figured I'd share with all of you. If the setup works, I'd also like to know how interested people would be in purchasing such a setup. Demand or no I plan to do it for my car, but it would be good to know up front if I should be prepared to make a kit out of it.

 

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.

 

Altho, I fear this may be a shortterm solution since the price of gas will go up as well eventually.....

 

However always worthwhile considering....

 

Gav

[tbourner]

Would be interested in any results.

[Burna]

Was discussing a gas conversion on the supra the weekend as a joke but a mate mentioned that he had heard that some skylines run on it with better performance.

 

No idea how true this so don't shoot me down, just putting the info out there.

[Ark]

Interesting stuff, but I am forced to wonder if it could work properly. For some reason I just can't picture a car running off a propane cylinder. Would be a smart idea though, since you can carry around spare cylinders, and pick up new ones at just about any garage.

[tbourner]

It'd confuse kwik-fit anyway.