Agree. I will find out some more about propane.

Rich Krause

 

Not really, I got that information from a reputable source, but they didn't have a source listed for further info. This is all I got:

http://www.geocities.com/rad87gn/tech/alcohol.html

 

Mike: don't the relative cooling effects follow the specific heats of vaporization? water>methanol>propane = 790>290>100cal/g. The much larger heat of vaporisation for water implies it's the best evaporative coolant. I agree that combustion effects are another thing to consider. I am not very knowledgable about them, but do know that there are number of reactions promoted by water which lead to more complete combustion of gasoline. They involve free radical formation. Here's the relevant paragraphs from the Gasoline FAQ "

"7.13 What does water injection achieve?.

Water injection, as a separate liquid or emulsion with gasoline, or as a vapour, has been thoroughly researched. If engines can calibrated to operate with small amounts of water, knock can be suppressed, hydrocarbon emissions will slightly increase, NOx emissions will decrease, CO does not change significantly, and fuel and energy consumption are increased [113].

Water injection was used in WWII aviation engine to provide a large increase in available power for very short periods. The injection of water does decrease the dew point of the exhaust gases. This has potential corrosion problems. The very high specific heat and heat of vaporisation of water means that the combustion temperature will decrease. It has been shown that
a 10% water addition to methanol reduces the power and efficiency by about 3%, and doubles the unburnt fuel emissions, but does reduce NOx by 25% [114].

A decrease in combustion temperature will reduce the theoretical maximum possible efficiency of an otto cycle engine that is operating correctly, but may improve efficiency in engines that are experiencing abnormal combustion on existing fuels.

Some aviation SI engines still use boost fluids. The water-methanol mixtures are used to provide increased power for short periods, up to 40% more - assuming adequate mechanical strength of the engine. The 40/60 or 45/55 water-methanol mixtures are used as boost fluids for aviation engines because
water would freeze. Methanol is just "preburnt" methane, consequently it only has about half the energy content of gasoline, but it does have a higher heat of vaporisation, which has a significant cooling effect on the charge. Water-methanol blends are more cost-effective than gasoline for combustion
cooling. The high Sensitivity of alcohol fuels has to be considered in the engine design and settings.

Boost fluids are used because they are far more economical than using the fuel. When a supercharged engine has to be operated at high boost, the mixture has to be enriched to keep the engine operating without knock. The extra fuel cools the cylinder walls and the charge, thus delaying the onset of knock which would otherwise occur at the associated higher temperatures.

The overall effect of boost fluid injection is to permit a considerable increase in knock-free engine power for the same combustion chamber temperature. The power increase is obtained from the higher allowable boost. In practice, the fuel mixture is usually weakened when using boost fluid injection, and the ratio of the two fuel fluids is approximately 100 parts
of avgas to 25 parts of boost fluid. With that ratio, the resulting
performance corresponds to an effective uprating of the fuel of about 25%, irrespective of its original value. Trying to increase power boosting above 40% is difficult, as the engine can drown because of excessive liquid [110].

Note that for water injection to provide useful power gains, the engine management and fuel systems must be able to monitor the knock and adjust both stoichiometry and ignition to obtain significant benefits. Aviation engines are designed to accommodate water injection, most automobile engines
are not. Returns on investment are usually harder to achieve on engines that do not normal extend their performance envelope into those regions. Water injection has been used by some engine manufacturers - usually as an expedient way to maintain acceptable power after regulatory emissions baggage was added to the engine, but usually the manufacturer quickly produces a modified engine that does not require water injection.

Rich Krause

 

Ya what he said....

It would be cool is someone got a dyno test of a boosted engine with straight water injection, straight methanol, meth/water mix and propane injection setups.....but thats a pipe dream.

I think that its easier to setup a propane system for long term use and get similar gains as an alky system, than havint to worry about corrosion of pumps, lines and injectors when running alcohol. But its a matter of preference I think, and I think the chemisty of it just needs some more research.

I just finished a rebuild of my Dodge Daytona's engine, and after inspection of the cylinder walls and piston skirts, I defiantly know that they were getting less oil than what they needed. Lots of scuffing and more wear than there should have been. I am gonna try and lower amount of water in the mixture to something like 75/25 alky/water, I was running 50/50 for about a year.
I will just have to see about it...I am upgrading the pump to something I pulled of a Caterpillar tractor, and the injector nozzles will be the new NOS Fogger2's. Ill tell ya how it works

Hunter

 

FWIW the term you are looking for is "Azeotrope" - water and methanol will form an azeotrope where the water and the vapor will have a eutectic (same) concentration/mole fraction. (Azeotrope are actually the maxima and minima on the phase diagram, but the term also applies to a mixture that exhibits the above characteristics).

Effectively the heat of vaporization, bp, etc. will be an average of the two, based on mole fraction (this would essentially be the case anyway, if flow is metered on a mass basis - even if they weren't azeotropes).

This really shouldn't make a big difference in this instance though - it would just prevent you from separating the liquids by factional distillation, etc.

Can't add any additional information, but I do have a couple of questions


1) Does the water injected have any real effect on the compression ratio in these volumes?

2) Do the free radicals limit combustion temps because of their tendency to cause pre-ignition situations (thus requiring less agressive fueling/timing), or is it some inherent characteristic?


Thanks,
Chris Bennight

 

And that's wonderful conjecture (no experience added), but I'm here to tell you that real world numbers show that if you're not running an alky/water spray with large FI numbers, then you're just not making power on 93. The fact is that I had my turbo car tuned by a marginal shop at 7.5 lbs with a percentage of knock, and now there is NO knock and at 9lbs with the SMC kit. The fact is that 93 won't support any REAL hp, and a spray that cools and adds octane is the ONLY way. Live it, love it, get your butt kicked by it!

SC-

 

sorry to be off topic but rich do you work at kennedys dyno tune?

and if you do, can you get discounts

 

I think I can adequatly answer this question on Rich's behalf.

No he doesn't, no he wont!

 

Kennedy's is my friend Bob's shop. I am there 2-3 evenings per week and usually one day on the weekend. I help out with various projects, keep the website updated, get involved in tuning, etc. Bob couldn't afford me, so I am not an employee!

Trust me when I tell you that the profit margin in a high performance shop is such that it's not reasonable to expect a discount. The shop labor rate is $71/h, Bob gets $125/h for tuning and a lot of $$$ goes through the shop in parts sales. A $550 water inejction kit has hundreds of $$$ in parts. Sounds like a lot of money, doesn't it? In spite of that, no one is getting rich. That's why I sometimes chime in when people ask things like "where's the cheapest place to get a cam installed" or something like that. If they are undercutting what a shop like Kennedy's charges they are cutting corners somewhere or it's a "casual" job done by someone at home after hours or something. If you can do work yourself, you will save a fortune. But don't assume it means your local high performance shop is ripping you off.

So, I can be a contact for you if you have questions, etc. But sorry, no discount

Rich Krause

 

I remember reading about water injection, It seems ''common'' on turbo cars. Please correct me if I am wrong but ihaving water in the combustion chamber would increase compression ratio since water(liquids) cannot be compressed.. But is there enough water in there to take it into account?

 

It's water vapor (steam) in the combustion chamber.

Rich Krause

 

those widebands are really expensive with really short life spans too

 

I do not believe there is a direct correlation between a hydrocarbon's octane rating and it's energy of oxidation.

Take for example n-heptane. It's a straight unbranched hydrocarbon that by definition has an octane of zero.

Now we can go to 2,3 dimethylpentane which has the same number of carbon's and hydrogens, so roughly the same energy of oxidation per mole, plus it is more dense so on a mass basis it will have more energy. It has an octane rating of 90.


Or again look at n-heptane - you get about 44.6 MJ/kg burned. Now let's look at 2-methylbutene-2 - this has 2 less carbons (only 5), but it has a higher octane 113/81 (R or M) vs. 0 for heptane, plus it gives you about 44.7 MJ/kg burned.


Octane rating is basically just an indication of how branched a hydrocarbon is - it has no direct correlation to energy content (or flame speed for that matter, which is another variable. Did you verify that the gasses used all had the same flame speed - if not this could easily account for the difference - and since flame speed is not related to octane value you can't assume anything).


Chris

 

Rich, could you give directions as to the source of this info? Some of this info appears to fly in the face of conclusions made based on testing several decades ago.

 

Arnie: I believe that the source of much of the original info were tests which were done by Sir Harry Ricardo. I have a copy of his book "The High-Speed Internal Combustion Engine" published in 1922. Great reading!

Here's a quote: "running throughout at a speed of 2,500 RPM and with a compression ratio of 7:1, the engine was run on an economical mixture, i.e. about 10% weak, and supercharge applied to the first incidence of detonation, which occurred when the BMEP had reached 168 pounds per square inch. The mixture strength was then increased, step by step, and more supercharge applied until the same intensity of detonation was recorded; this process was continued until a point was reached at which no further enrichment was effective. In fact, after about 60% excess fuel, not only did further enrichment have no effect but there was even some indication that it increased the tendency to detonate. A finely pulverized water spray was then delivered into the induction pipe which served to suppress detonation, in part by the inter-cooling it provided, and in part by the influence of steam as an anti-detonant, and so allow of further supercharging. This was continued progressively, admitting just sufficient water at each stage to ward off detonation until a BMEP of 290 pounds per square inch was reached, which was found to be the limit of the dynamometer. At the same time, it was noted that, with the addition of water, the influence of steam as an anti-knock allowed the fuel/air ratio being much reduced. From this curve as shown in the figure above it will be seen that under these operating conditions a limiting BMEP that could be reached with 87 octane petrol alone at an economical mixture strength was 168 psi. By enriching the mixture to the limit of usefulness, the BMEP could be stepped up to 237 psi. By the introduction of water, it could be further stepped up 290 psi and probably more; at the same time the fuel/air ratio could be reduced once again; in fact with gaseous intercooling, no appreciable advantage was found from the use of an overrich fuel/air mixture. It will be noted that the total specific consumption of liquid, i.e., fuel plus water, is not so very much greater than when running on a very rich mixture of fuel alone."

The text which I quoted originally is from the "Gasoline FAQ" which can be found at http://www.faqs.org/faqs/autos/gasoline-faq/part3/ The FAQ references the following sources, among others. "Alternative Fuels" by E.M.Goodger. MacMillan. ISBN 0-333-25813-4 (1980) and "Water Addition to Gasoline - Effect on Combustion, Emissions, Performance, and Knock" by J.A. Harrington. SAE Technical Paper 820314 (1982). I have not read these sources first hand.

What part is contradictory or do you not agree with?

Regards.

Rich Krause