I can't answer your question about air/diesel fuel mixture directly, if at all, but will attempt to share some intel on the subject. By the way, I've been driving semis for 27 years and have never heard anyone be concerned about this question, or figure; though I am a driver and not a mechanic. Not exactly sure where you are going with it. The 14.7 figure sounds about like a compression ratio for a diesel to me. The "How Stuff Works" site gives a basic overview of how a diesel engine functions but doesn't really get into many specifics.
Most diesel engines are turbocharged. This functions something like a supercharger, but less efficient, less responsive, but also less parasitic on the power. The turbo operates off of a fan spun by the exhaust gas. The exhaust gas does not return into the engine (untill 10/02 EGR engines anyway)
http://www.cat.com/products/shared/t...cert/index.htm
but is kept seperate. So, the faster the rpm, the more air is forced into the cylinder. There is somewhat of a lag time on the turbo operating, more fuel, faster rpm; faster rpm more air from the turbo: more air from the turbo, more fuel: more fuel, faster rpm. and so on........again, I can't give you an ideal air/fuel mixture number, if one even exists. Please remember that I am NOT a diesel mechanic. If there is one on here, please feel free to correct me as needed. (maybe all of it!
Diesel engines are direct injected, by at least two different methods. Some engines (Cummins, maybe not all) have the injectors in the heads with a fuel line through the head sort of past each injector. The injector is opened with linkage from the valve train. There is constant pressure in the fuel line and when the injector "opens" fuel is sprayed into the cylinder. The pressure in the line (rail pressure) can be increased by turning up the pump. Certain limits exist where you would need to change the turbo and some other parts if you went crazy with turning up the rail pressure. Most of the newer, electronic controlled engines have the capability to make some horsepower changes through the engine computer and a laptop with the correct software. Detroit Diesel was sort of the pioneer in this technology.
Other diesel engines (Caterpiller, IH, John Deere, and others) have the injectors in the side of the head and have a fuel line to each individual cylinder. This fuel pump is much more complicated and precise than the previously mentioned style. The pump itself determines exactly when to send fuel through each line and how much. You will notice if you look at this type of engine that the cylinders closest to the pump have fuel lines that sort of go all over the place instead of running in a straight line. This is so that each line is exactly the same length. All lines are the same length as the one going to the farthest cylinder from the pump. This way the same amount and pressure of fuel is sent to each cylinder.
As the rpms increase the turbo spins faster forcing more air in the cylinder. At the same time more fuel would be injected into the cylinder to increase the rpm even further. I don't have any idea if this ratio is the same, at say idle and full throttle. I guess my thought would be that it would be a lot larger percentage of fuel at full throttle than at idle, but don't know for sure since you are also jamming a lot more air into the cylinder with the turbo.
(No brainer?)
You might have noticed some trucks belching out huge amounts of black smoke, especially starting out or pulling a big hill. That is mostly unburned fuel,
either due to the pump turned up and providing more fuel than can burn in the power stroke, possibly bad injector(s) spraying a poor pattern, blown turbo, or any other number of things not right. The idea is that you get a little more fuel into the cylinder than you burn, that way you know you have as much as you possibly can burn. I don't know if you can be "too rich" and actually lose power or not. I guess you could, taken to an extreme it probably wouldn't run at all. I do know that usually when they are blowing black smoke they are running very good, or terrible; at least till they blow up. With the price of fuel these days, and states like California that have opacity regulations, you don't see the trucks having much visible exhaust anymore. Can't afford to have that much fun any longer if you want to survive. California used to give you one freebee, but the next fine was in the thousands of dollars so you didn't want to do that real regular like.
I know I didn't answer your main question but hope this helps somehow/what. Again, feel free to correct my misguided thinking as needed. I'm jsut a sipmle trcuk drvier; and sometimes that is debatable.
Happy Hauling,
Doug