Re: air - fuel ratio

BobJ wrote:
> What are the thoughts on the air-fuel ratio values using todays fuels.  
> How much does the (varied) alcohol content of todays fuels modify the 
> 'de facto' standard of 14:1 as the target mixture?
Virtually all newer vehicles use three-way catalyst exhaust 
after-treatment systems. For maximum catalyst efficiency the A/F target 
average is stoichiometric (or the chemically correct mixture ratio). For 
100% gasoline this is nominally 14.6:1. Most engine control systems 
purposefully dither on either side of stoich to maximize catalyst 
efficiency.

As alcohol(ethanol)is added, the feedback ECU controls will adjust the 
fuel system to keep the mixture at the mixture's stoichiometric value.
Here's a simple table to illustrate how stoich varies with %EtOH

%EtOH    Stoich A/F
0         14.6
5         14.16
10        13.74
15        13.35
20        12.98
85        9.55
100       9.00