my take on this is that a stoichmetric mixture is one where all the components are burnt entirely, ie a perfect mix of fuel and oxygen to ensure its all spent.

When driving along, if in fifth at about 3200 rpm, slight incline holding a steady speed, I see my lambdalink will sit bang on the middle amber light and hold it there all day long (well, at least till the load/conditions change).

does this mean I am acheiving stoich? and hence a very efficient car?

Andy

 

"The lambda sensor, or O2 sensor, measures the oxygen in the exhaust of your engine. It then sends a signal to the ECU to regulate the fuel mixture to an "ideal" stoichmetric 14.7:1 ratio to be delivered to your engine. When it isn't properly working, you may experience bad gas mileage, a rough idle, or the engine dying when stopped. If it is in closed loop, the O2 sensor usually lies between 0 and 1 volt with a higher voltage suggesting a rich mixture (little oxygen in the exhaust) and a lower voltage, a lean mixture. It should oscillate between 0.1v and 0.9v 1-2 times per second at idle and 4-5 times per second while revving or driving. This cycling occurs because the sensor is sending different pulse widths to the ECU adjusting the air fuel ratio, allowing the cat to reduce the emissions blowing out your tailpipe. A cat is around 60-90% efficient meaning it cuts emissions by 60-90%. Too rich a mixture can damage your cat."

Stoichmetric refers to an Air/Fuel Ratio of 14.7:1 which is given to be the ideal ration of air to fuel for a clean burn. This ratio AFAIK is mainly achieved in lean burn engines and is only targeted in other engines. I would think the Subaru would mostly have a propensity to achieve a little richer than stoich on light throttle with extra rich on more throttle due to the extra fuelling protection this engine needs.
When you are at full throttle Subaru operates on Open Loop which means that Lamda is not read by the ECU. Stoich can only be achieved whilst the engine is run in closed loop i.e. with feedback from the Lamda.

 

but at light cruise its closed loop operation, also, I dont have a subaru ecu

 

Yes light cruise is closed loop if you are using Lamda as feedback. If you dont have a Subaru ECU then it probably depends on the mapper how it is set up.

The point is that stoich is air/fuel ratio of 14.7:1. What you are achieving is the most efficient fuel consumption for your set up, which may or may not be stoich.

 

... and only applicable to petrol ... different fuels have different stoich' ratios ... cars will always err on the richer side of the mixture - I don't think you'll get a road car that is set up to actually run at the actual point.

 

try telling honda that

http://world.honda.com/news/2003/4031127.html

 

that's cheating - they're including the recycled exhasut gas within that figure!