[Christ]

Diesels have injection throughout the powerstroke, the way I understand it, which is why they have so much more available torque. The "combustion" as it were, never occurs at one solid point in the piston's travel, only the ignition part of it.

In a properly tuned diesel, the AF ratio at almost any given moment (not counting moments before or after the one you're looking at) is lean. The overall combustion process, when measured on the exhaust stroke, shows "not-so-lean", but probably still not stoich.

IOW - Since the fuel is injected throughout the power stroke, from TDC to BDC (not really, but bare with me), and there is (let's say) 1L of air in the cylinder, considering stoich to be 15:1 (for easier figuring), there are now 1000mL of air, and to create a stoich mixture, you'd need 66.67mL of fuel.

So, now you take that 66.67mL of fuel, and inject it over the 90* of power stroke, and you end up with a mixture that starts out extremely lean, and as it burns up the air, it becomes less lean.

Assuming that fuel is injected from TDC to BDC (90*, but it's really not), that would be 66.7/90 = .75mL of fuel injected per degree of crankshaft rotation.

This results in the first degree of crankshaft rotation having a 750:1 AF ratio, and each subsequent degree being closer to stoich mixture, until the "total burn" AF ratio has become 15:1, as measured by the exhaust gasses.

Someone, please correct me if I'm wrong about this!