diesel smell?

What causes different engines to have different smells? I had a ford truck from around 2000 pass me the other day, and the exhaust didn't even really smell like diesel, it smelled more like a kerosene heater. Is it the fuel used, the compression of the engine? I have noticed that internationals never smell good, older GMC don't either, almost all cummins do smell good and fords are nearly split half and half. I can't figure out the correlation. What makes them smell different?

Dirty air filter, missing catalytic converter, dino diesel, chicken bio, soy bio, walnut bio,old worn out injectors, leaking rings, dirty fuel filter and strainer, injection pump timing, overfueled chips. All are factors in the stink. On the more modern diesels it starts with the catalytic converter which changes the smell and if it is bad or missing you get a stinky vehicle. My converter works sort of sometimes but usually my car is stinky. My tractor shoots its exhaust up and out of my face so I do not smell it that much. I can't really tell how stinky it is but when I ran chicken biodiesel in it I had a smile on my face as I could smell that burning.