3 replies to this topic

[mariner]

I have to get my engine down to 3.5% CO to pass a test for on highway usage. As it runs a Holley 850 double pumper this is not easy. The engine test is run at idle and 3000 rpm off load to do the test so high power usage etc is not an issue. However getting it to run lean is difficult because I do not want to , nor am I skilled enough, to play around with the Holley internal jetting. My very limited understanding of air/fuel ratios and combustion chemistry is that high CO is a result of a mixture too rich for 100% combustion so leaving some CO as opposed to CO2.

Reading about alcohol engines I have noted that pure alcohol runs a 6.5 to 1.0 air fuel mix versus 14.7 etc for petrol/gasoline. So if E85 fuel is 85% alcohol I would THINK that it will give a leaner mixture if I run it through the standard carb. I would not use pure E85 , my idea is to mix some E85 and gasoline so as to reduce the richness under pure gasoline somewhat. I assume that in a fuel injected engine the E85 versions increase the injection duration to get the correct overall mixture base on reading the lambda sensor. As my carb can't read the mixture it will , I presume , just run leaner.

A wikepedia primer is here http://en.wikipedia.org/wiki/E85. The main useful points seem to be about fuel line chemical attack and potential vapouR explosion ( which does worry me!).

Three questions

1) Does my theory have any validity in terms of reducing CO ( within the limits of the test procedure)?

2) what ratio of E85 to striaght gasoline would make a difference to the CO level?

3) What practical problems/dangers may exist at the sort of E85 to gasoline ratios need at 2)?

[J. Edlund]

The stoichiometric air fuel ratio for E85 is about 9.8:1, pure ethanol is 9:1. 6.5:1 is methanol.

Blending in E85 in regular gas will make the engine run leaner which should reduce CO emissions. Lambda 1 or leaner is prefered for low CO emissions, I would try to go for lambda 1,1 if there's no limit on NOx. How much E85 is required in the gasoline will depend on how rich the engine is currently running.

Chemical attack on the fuel system is really only a problem if you plan to run the engine on ethanol blended gasoline (ethanol attacks steel, brass, aluminum, terne plating and other metals aswell as several polymers and cork), if you use it for a very limited time period there shouldn't be any problems.

Low concentrations of ethanol in gasline increase fuel evaporation.

[McGuire]

3.5% CO is not that hard to hit if the engine is running clean and sharp. In theory, stoich (14.7:1 A/F) is right about there without a cat. Ethanol absolutely will reduce CO as will any oxygenated fuel. CO is just CO2 that did not get enough oxygen when it was little. Also worth mentioning that any hardly noticeable exhaust leak between the manifolds and the tailpipe (where the sniffer probe is placed) that can pull in fresh air will reduce CO. Not suggesting one should ever cheat in that manner, just saying. You know.

You could shoot for E20 (20 percent ethanol, 80 percent gasoline) as that is what current, non-E85 carb and fuel system materials are designed to handle. If your carb is older it may be more sensitive, but the ethanol is not going to hurt anything expensive, just the accel pump and other synthetic bits. If the "rubber" parts in your carb are greenish-bluish/bluish-greenish, they are good up to E100.

I have no idea what part of the world you live in but depending... you might do better for these purposes blending up your own fuel from premium gasoline and straight, denatured anhydrous ethyl alcohol at about 18 percent. E85 at the pump can be E75, E80, or E85 depending on the time of year (reduced ethanol content for low temp starting), so it can be complicated figuring out just what ethanol content you have -- unless you can test it. You can (destructively) test ethanol content in gasoline by adding a precise portion of water (say 20%) to a precise amount of gasoline/ethanol blend in a graduated cylinder and shaking it. When the mixture settles and phases apart, the increase in apparent water percentage (the bottom phase) is the ethanol content, approximately.

[mariner]

As ever thanks guys for all the info.

It sounds feasible without too much risk of damage so I am going to check the Co % again on straight gasoline and then add E85 if the readings are close tot he 3.5% limit. I will use E85 which I can buy from a place about 80 miles away as using straight alcohol would risk violating the UK government road fuel tax regulations.