How much "extra space" does alcohol actually need?

[Joe Mendelis]

I have talked with a few different people about running alcohol and they all say the port needs to be "bigger". This may very well be.
Everyone I've talked to so far say the extra volume of fuel in the intake port makes it need more area to accomodate the extra fuel.
This makes no sense to me the way people have explained it to me. I am basically being told the extra fuel "takes up space".I've done heads for Super Modified's, which are 470 inch alcohol injected BBC's. Those engines usually make around 850-900 hp. If the engine was running at 1.1 BSFC and 900 hp, making peak power at 7000, how much fuel would there be in the intake port per intake stroke?
I don't have a very accurate way to figure it out, but here's what I did:

900 hp/8 cylinders=112.5hp per cylinder

112 hp X 1.1 bsfc= 123 pounds per hour

123/60 minutes = 2 pounds per minute

two pounds divided by 3500 intake strokes per minute=.000571

.000571 pounds is how many cc?

[Guest]

It's fair game to add methanol takes 2.2 times as much to make the same btu's as gas. How much of that up to 3.2 sq. in. cross section is used for fuel? Kind of the same question. Any methanol guru's out there willing to comment?

[ozrace]

According to Allan Lockheed... author of "Engine Expert" software - around 10% bigger.

[Joe Mendelis]

According to Allan Lockheed... author of "Engine Expert" software - around 10% bigger.

I understand many people say alcohol needs a bigger port. I am in no way shape or form arguing that.

I am saying the actual volume of alcohol is less than a 1/3 of a cc per intake stroke. I just want to know why people (kinsler included) say the alcohol takes up "twice the space". I know it takes up twice the space of gas. You could cloth roll .3 cc out of a port by passing over every surface once.

In a 320 cc port or even 220 cc port I cant see how saying .3 cc of fuel warrants the extra volume to replace the volume the fuel displaces. Makes no sense.

Because of the physical properties of alcohol it may like a bigger port. I want to understand why. Kinsler gave me the "it takes up more volume in the port so the port needs to be bigger" answer. You have .15 cc more fuel so you need to make the port 15cc bigger? That's 100 times more volume of air than extra fuel. Obviously there is not 15cc of fuel in the port or the engine would go thru 25 tons of of fuel per hour.
Someone told me the air in a gasoline port moves to fast for the alcohol. This kind of makes sense to me but I would still like a logical answer I can understand.

[ozrace]

Joe
My post was an answer to the title of your thread "how much extra space does alcohol actually need".

These are Lockheed's comments which I haven't tried to analyse:-
"re: critical port size for alcohol engines. You need twice as much alcohol as gasoline in the fuel - air mixture, so there is less space for air AND alcohol cools the air and lowers it's sonic velocity.
Both factors call for a larger port critical area than set by Engine Expert's 690 ft/sec critical velocity. We recommend 8-10% more area (4 to 5 % width x height measurements) than for gasoline.

Hope this helps, or provides some food for thought/ discussion.

[Joe Mendelis]

You need twice as much alcohol as gasoline in the fuel - air mixture, so there is less space for air AND alcohol cools the air and lowers it's sonic velocity.
Both factors call for a larger port critical area than set by Engine Expert's 690 ft/sec critical velocity. We recommend 8-10% more area (4 to 5 % width x height measurements) than for gasoline.

Hope this helps, or provides some food for thought/ discussion.

Thanks for your input Oz, I didn't think about the fact that the alcohol will lower it's sonic velocity.

With all due respect, when you say there is twice as much alcohol and there is less space for air, wouldn't that be such an insignificant amount(under .25cc) in most engines that it wouldn't matter?
The thing in question here is the physical properties of the fuel, not the very small amount of extra fuel? Correct me if I am way off on my calculation for a 900 hp 7,000 rpm alcohol engine of .3cc of alcohol per intake stroke.Gas would still be .15, so you have alcohol taking up .05% of your port volume(if all the alcohol was in the intake port at once). Am I close on this? A 1/20th of a per cent doesn't seem like it would really matter.

I 100% see what you are saying about the sonic velocity being lowered. That's 100% better answer than Kinsler gave me!

[panic]

I would also hazard that a lesser percentage of methanol may be vapor (vs. gas) as it traverses the port, which means its volume is an even lower percentage of the port volume, and much too small to require compensation.
If it cools the air the port should be smaller for the same mass at the same velocity.
The speed of a reversion pulse will be lower, but how does that affect X-sectional area?

I think what happened here is the classic confusion of co-incidence with causation.
Empirically, methanol appears to make good use of a larger port, and (not being satisfied with merely the results) they decided to attribute this to the phenomenon they believed present (viz. methanol volume vs. gas, relative temp, &c.). IDK what makes the larger port work, but it does not appear to be the result of these explanations.

Building a big motor does not necessarily mean that you knew what you were doing, or that your explanation of why it was successful is accurate...

[Joe Mendelis]

I would also hazard that a lesser percentage of methanol may be vapor (vs. gas) as it traverses the port, which means its volume is an even lower percentage of the port volume, and much too small to require compensation.
...

Thanks Panic, I see you understand what I mean about the alcohol displacing the air. Like you said, the end result leads people to believe after making the port bigger and it running better, they assumed it was from restoring all that space the alcohol takes up!! Post hoc ergo propter hoc.

[Racer7088]

You know what I will say Joe!

Alcohol has more wet flow problems than gasoline so that they want a slower short turn and airspeed on stuff like the 23 degrees especially. As has been said by panic that the alcohol stays more in areosol or liquid droplet form instead of vaporizing and expanding AND soaks up a lot more heat to finally vaporize so it's like a built in intercooler making the air denser and cooler which is a benefit but with the side effect of having more seperation at an extreme short turn since the droplets are still larger than the more easily vaporized gasoline droplets.

The problem is these small non easily vaporizing alcohol droplets will NOT turn the short turn as well as the smaller more readily vaporized gasoline droplets will and you end up with all the fuel piling on one side of the chamber with too much airspeed on alcohol as compared to the same head with gasoline.

Purpose built alcohol stuff with straighter ports and down nozzles is pretty small for what they flow usually it seems but with the down nozzle the wet flow problems are not there like on an alcohol carb at least. Blah Blah Blah...ramble ramble ramble! It's too damn late for me to be up Joe!

[Nwguy]

The main reason alky needs more "room" is as follows.

one pound of gasoline ( C8 H18 ) evaporated at STP occupies a volume of about 89 liters.

One pound of methanol ( C H3 OH ) evaporated at STP occupies a volume of 422.8 liters.

Since 2.2 times as much weight of alky is required for BTU equivalance, compared to gasoline, the fuel component of the incoming charge is almost 10 times greater with alky as compared to gasoline.

Dont believe me?? lookup the molecular weight of the respective fuels and take a gander at Avogadro's hypothesis.

Alky takes up a LOT more room in the ports than gas.

[ozrace]

A very logical explanation.
Thanks

[Racer7088]

The main reason alky needs more "room" is as follows.

one pound of gasoline ( C8 H18 ) evaporated at STP occupies a volume of about 89 liters.

One pound of methanol ( C H3 OH ) evaporated at STP occupies a volume of 422.8 liters.

Since 2.2 times as much weight of alky is required for BTU equivalance, compared to gasoline, the fuel component of the incoming charge is almost 10 times greater with alky as compared to gasoline.

Dont believe me?? lookup the molecular weight of the respective fuels and take a gander at Avogadro's hypothesis.

Alky takes up a LOT more room in the ports than gas.

Yes but how much of both actually evaporates in 10 milliseconds with the same amount of external heat present? It takes time and heat to evaporate both but WAY more heat to completely evaporate the acohol. We already know that even lighter gasolines introduced at very small droplets sizes never completely vaporizes while going down the runner. There isn't enough heat or time. Now you take acohol which takes even more heat to evaporate and it will NEVER even come close to evaporating during that short quick trip down the runner.

It's a question of total time and heat energy needed to completely vaporize them and people have big problems already with literally tons of liquid alcohol going down the runner. It's enough to significant dilute the oil on some engines since in fact it does not ever even come close to fully evaporating and neither does gasoline for the most part usually.

This still doesn't change the fact that you have to size the runners for tuning and velocity no matter what this other stuff works out as. Even if you really did end up with double the total space occupied by the same amount of total BTU's worth of AF mixture because of the fuel vapor occupying so much more space you couldn't make the runner twice as big and then think it would just all go into the cylinder now just because you wanted it to. The cylinder is a finite space and only so much will enter it depending on cam timing and tuning of the runner.

Hypothetically speaking, if it (an alcohol AF charge) really took up twice the TOTAL space as the gasoline (which we know it doesn't but just hypothetically speaking) then it would also half half the energy density and you would make around half the power. The resulting energy density of the AF mixture reaching the cylinder no matter what happens to it on the way there has a direct effect on power and this along with VE determines how much potential energy in fuel BTUs is actually trapped in an intake cylcle.

I think we all know that the amount of air going through an alcohol engine doesn't change a whole lot and also when the alcohol evaporates it also soaks up a lot of heat as is does this which reduces the temp and also reduces the space or volume that the previously hotter air occupied even as it increases the space that the fuel occupies.

[ozrace]

The Fuel device being used - i.e. Carb or Injector - along with the conditions between the fuel device and the cylinder, have to provide a large measure of fuel vaporisation for the fuel to burn. It certainly doesn't all happen after the Intake valve closes, and any droplets which are not of a "combustible" size will be passed out the exhaust un-used (or end up in the sump).

[maxracesoftware]

According to Allan Lockheed... author of "Engine Expert" software - around 10% bigger.---OZRACE

according to my Dyno and DragStrip tests, it looks like Allan Lockheed
is very close with his 10% prediction .

in very many Back-to-Back Dyno tests at 600 RPM/SEC
comparing Race Gas -VS- Methanol, theres on average
approx. a 10 % PerCent Loss in Ve%, with no other changes.
switching over to Methanol creates an immediate 8-12+ % Loss in Ve%

The problem is these small non easily vaporizing alcohol droplets will NOT turn the short turn as well as the smaller more readily vaporized gasoline droplets will and you end up with all the fuel piling on one side of the chamber with too much airspeed on alcohol as compared to the same head with gasoline.

Purpose built alcohol stuff with straighter ports and down nozzles is pretty small for what they flow usually it seems but with the down nozzle the wet flow problems are not there like on an alcohol carb at least---Racer7088

i use a 10 % PerCent "Rule-of-Thumb" (Allan Lockheed)

but you just don't make the Int Port 10% Larger,
you have to Pitot Probe the Ports to find potential Choke areas.


like Erik previously mentioned, you have to "Slow down"
Air Speed in Port areas when using Methanol -vs-Gasoline.
Example=> if the pushrod area is just perfect area/velocity FPS for Race Gas, then that same area will be a Choke when switching over to Methanol...you have to Slow-down the FPS...by making that area 10% larger

if you have a 260 CC Int Port (gasoline),..then its very possible that by the time you finish increasing the Port Areas to achieve the correct FPS to account for Methanol in Int Ports, then that same Int Port Volume will windup 10 % larger at approx = 286 CC's(Methanol)

the 10% Rule seems to work great with Craig Bourgeois 's A/ND Nostalgia front engine dragster
http://www.maxracesoftware.com/race_car_pictures.htm

another thing Erik mentioned is effects of Down-Nozzles,
however, its very possible that if Down-Nozzles point too much
spray towards the Short Turn, you will definetely loose some HP/TQ,
or at the least not show any real HP/TQ gains with Down-Nozzles -vs- Runner Nozzles.

[hotrod]

Could you extend this effect to other applications?

It would appear that the same sort of issue would crop up with turbocharged engines. As you improve the intercooling, (intake charge temp drops significantly) the ideal port size would need to be changed. Likewise folks running water injection or alcohol injection would by extension also need either more port size or perhaps slightly different cams to maximize the setup.

Does anyone have any observations on these related issues ?

Larry