Ethanol as an Additive 6

[Haf]

While I was in grad school, I had a thermo professor that explained in detail why ethanol gasoline additives are harmful to typical IC engines. I can't remember his exact explanation, but I seem to remember that it was related to ethanol's higher auto-ignition temperature and higher adiabatic flame temperature.

My question is: what are the performance and engine wear implications of using gasoline with 10% ethanol? Should ethanol-containing gasolines be avoided? What are the thermodymic effects?

Thanks,

Haf

 

[Vapo]

in practice, 10% ethanol gasoline mixtures will give u a bit more power because the ethanol being a more volatile liquid, vaporises more easily and helps to cool the intake air/fuel charge. This increases volumetric efficiency and gives u more power. Dont expect too much difference, but a noticeable effect none the less. Because alcohols are toxic, especially if u use hydrated variants there will be increaed wear on the engines due to combustion residuals.

More than 10% will begin to affect driveability and fuel consumption will increase substantially...It really depends on the intended application, its not the recommended first option for more power, not for everyday use anyway, and obtainng good sources for use as additives is a problem.

 

[Haf]

Vapo,

Thanks for the response. It seems like many ethanol proponents hail it's environmental friendliness. I also have heard that power is slightly enhanced by ethanol. What I don't hear a lot about is it's potential to prematurely wear engines. When you say wear is increased, how significant is the increase? Will engine life be significantly decreased?

Also, is the increase in wear something that can be minimized by auto manufacturers by designing engines to account for ethanol additives (similar to how engines were redesigned in the early '70's to run on unleaded fuel)?

Haf

 

[patprimmer]

Some small corrections to Vapo's comments

Ethanol has a higher heat of vaporisation. That is why it cools the charge more, but it has les energy per gallon, so fuel useage goes up slightly. It also requires a different fuel air ratio, so the ability of your system to adjust is important

Wear has nothing to do with toxicity.

The extra wear associated with ethanol is twofold and of little consequence in modern engines.
1) fuels used to contain lead, but it was considered so toxic it is being banned. This toxic lead was also a lubricant, and a problem with introducing unleaded fuels, includeing alcohols, was the loss of the lead "lubricant"
2) ethanol absorbs water and is corrosive, especially with higher water content. It is especially corrosive of aluminium, but also steel.

Ethanol is quite high in it's octane rateing, and therefore burns slower than lower octane fuels. This is a problem in low compression engines, but not modern high compression engines, in fact the 10% will help to raise octane rateing back to that lost by removing the lead.

Overal, it shouldn't do any harm at 10%, except for slightly higher consumption rates

It is a renewable energy source, and recycles it's CO2.

Somewhere in another post in this forum there is reference to some sites which quote some real figures and research data Regards
pat

 

[patprimmer]

The thread is 71-41617, re tolune and xylene as octane boosters, and the particular posting is by Chumley.

The links are very useful Regards
pat

 

[KramRS2]

Hi,
Here in Brazil all gasoline uses 20-25% of ethanol. This is due to the lower price to product alcohol here and because ambient concerns. We have cars that run using only alcohol, and every gas station has pure alcohol to sell.
Between 1985 and 1990, 90% of all cars produced here were made to run alcohol. After a brake in production due to weather, the government obligated the use of alcohol in a mixture with gasoline for all autos sold here.
Alcohol is not good to operate in cold weather, but here we have a tropical one, and we can live easy with it.
There is no problem of toxicity with alcohol. At least less than gasoline. Really it has problem with corrosion and all imported cars need what we call “tropicalization” that consist in change the injectors for stainless steels ones and a remap in the ECU (more ignition advance and more fuel). If you want a car burning only alcohol you need to change the fuel pump to a stainless steel one also. And that is it. More powerful cars with a better $/km relation.

Regards
Mark

 

[Metalguy]

Haf,

The primary reason for the ~10% HP increase is NOT the charge coolng effect, but rather the fact that the alcohols contain a little oxygen. That's why you need more fuel (richer mixture). The other factors are secondary. You want a LOT of oxygen, try nitromethane!

I've seen the same "cooling of the charge" stuff wrt good ol' nitrous. Helps, but the real power comes from the ability to burn more fuel because of all that oxygen in the nitrous.

 

[Metalguy]

Haf,

Allow me to elaborate on my message above. The 10% I referred to is the usual HP increase when using straight methanol instead of gasoline. Straight ethanol seems not to be used much in the US, AFAIK.

Gasoline blended with 10% ethanol won't have much effect on HP, but the slight extra oxygen helps reduce CO emmisions. It also raises the octane rating.

Another factor is that alcohols attack some rubber compounds more than gasoline, and some car makers had a recall program to replace rubber fuel system parts with alky-resistant hoses, etc.

Hope this helps.

 

[drwebb]

1) Ethanol is present in many foodstuffs. If it is to be considered 'toxic', then I submit the term no longer has any useful meaning. Nevertheless, along with patprimmer I would be very interested (probably amused) to hear more about the connection between toxicity and wear.

2) Ethanol contains LESS chemical energy than hydrocarbon fuels, as consultation of the thermodynamics section of most freshman chemistry texts will confirm. Consequently, at constant engine tuning, substitution of ethanol for any portion of hydrocarbon fuel will increase fuel consumption and decrease engine volumetric efficiency with a significance directly proportional to the concentration.

A simplified explanation follows: Combustion is the chemical reaction of a fuel with molecular oxygen. For example, full combustion of ethane (a hydrocarbon) produces CO2 and water. One could think of ethanol as the product of partial combustion of ethane. Thus because the ethane is already half 'burned' (combusted) if it goes into the cylinder as ethanol it can only be half burned even to completion inside, and the result is less energy output.

3) Ethanol is only a 'renewable' energy source if it is derived from biomass (i.e. crops). Ethanol may also be produced from petroleum feedstocks, and I understand it is more economical that way. If true then there is a cost/benefit side to the equation that most ethanol proponents leave out, and environmentally conscientious parties would be advised to verify the genesis of their ethanol.

Engine wear is mainly controlled by the lubricant selection, so I can't think of a mechanism whereby ethanol would adversely (or advantageously!) affect it.

 

[Metalguy]

>Ethanol contains LESS chemical energy than hydrocarbon fuels, as consultation of the thermodynamics section of most freshman chemistry texts will confirm. Consequently, at constant engine tuning, substitution of ethanol for any portion of hydrocarbon fuel will increase fuel consumption and decrease engine volumetric efficiency with a significance directly proportional to the concentration.<

Er, VE is airflow efficiency, and isn't affected by the fuel use to any significant degree.

 

[patprimmer]

In Australia it is currently a contencious issue as to the use of ethanol in fuel, with In MY OPINION ONLY, auto companies basicaly opposing it and the government basically, but binconsistently, endorsing it. I expect the auto co attitude is at least partly based on resisting the need to do some costly modifications to their cars, and possibly an interest in maintaining the status quo re oil company profits and mutual interest (wow, I didn't think I had a conspiracy theory complex).

The apparent government inconsistencies here possibly stem from the fact that the ruleing coilition government is composed of two parties, one with roots in big business and the other with roots in rural industries.

The ethanol used here is allegedly from sugar cane, as we have a glut, and the government is trying to prop up the sugar industry, while also, trying to score brownie points with the greens.

The extra power comes the fact, that even though the ethanol contains less energy per gallon (litre, pound or whatever), it also requires a richer mixture, which more than compensates, giving a net power increase.

The extra fuel hurts VE slightly, but the cooling effect helps VE. I am not sure of the net result.

At 10% only, these figures are significantly diminished, and masked by other additives in the fuel.

If ethanol is used as a substitute for other octane boosters, to maintain the same octane rateing, you cannot raise compression, however if it is used in addition to other octane boosters, you will get an increased octane rateing (depending on the final formulation) which will allow higher compression ratio, which will give better thermal efficiency, compared to the vsame formulation at lower compression.

Sorry if this all sounds verbose and complex, but there seems to be a lot of confusion out there. Regards
pat

 

[drwebb]

Alright, I swung by the library briefly and found SAE Transaction 810345, &quot;Ethanol Fuel- A single-Cylinder Engine Study of Efficiency and Emissions&quot;. A bit dated, but it compared a variable compression motor running gas at 7.5 compression ratio, (this was in '81 after all) and ethanol at various ratios from 7.5 to 18.0. It reports:

&quot;With ethanol at 7.5 CR, (thermal) efficiency was 3-4 percent greater than that with gasoline throughout the range of A/F ratios . . . Ethanol's advantage during combustion resulted from faster burning and higher peak pressures than those with gasoline. During expansion, ethanol's lower burned gas temperature provided reduced heat transfer to the cylinder walls. When CR was increased with ethanol from 7.5 to 12 and 18, efficiency increased about 10 and 18 percent, respectively . . . Although efficiency with ethanol was better than that with gasoline, fuel consumption was poorer with ethanol because of its low heating value. When compared at the same CR and A/F, ethanol fuel consumption was about 57 percent greater than that of gasoline. . . Increasing CR reduced fuel consumption; however, ethanol fuel consumption at 18 CR was still 30-36 percent greater than that with gasoline at 7.5 CR.&quot;

So I suppose the confusion is over thermal efficiency and it's relationship to fuel consumption; it would certainly appear that the considerably lower heat of combustion of ethanol (26.9 vs. 43.0 MJ/Kg) can be extracted 3-4% more fully by the engine than with gasoline, which I gather patprimmer is getting at. (Hey, I learn something new every day!)

I also found a fleet test SAE report from an Ohio state agency on mid-90's Tauruses running straight gasoline and others on 15-30% ethanol. Indeed, the gasahol cars showed higher maintenance costs, but it was attributed to requiring special low-ash motor oil. FOMOCO lifted this requirement midway through the 25K mile test, and the maintenance costs became equal. The gasahol cars were fitted with larger gas tanks, but the paper didn't elaborate whether there were any other modifications. The gasahol cars showed lower average fuel economy on a gallon basis but slightly better when corrected for the lower heating value of the fuel , which seems in agreement the above paper.

I have heard some of the dire warnings regarding the Australian situation and that in South America, yet haven't heard many reports of motors grinding to a halt on ethanol mixtures. I'm with patprimmer in suspecting other agendas at work.